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Classifications

Harrison's Part

Lysosomal Storage

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Mappings

MONDO

MONDO:0009290 glycogen storage disease II DisMech

MONDO:0018485 is a child of MONDO:0009290. The umbrella Pompe disease entity is curated separately as kb/disorders/Pompe_Disease.yaml; this broadMatch records the parent relationship without claiming equivalence, and deliberately does not retire MONDO:0009290 from the curation queue.

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Definitions

1

GeneReviews onset/cardiomyopathy case definition

GeneReviews partitions Pompe disease by age of onset together with the presence or absence of cardiomyopathy. LOPD is defined as onset after age 12 months, or onset before 12 months without cardiomyopathy. The cardiomyopathy criterion, not age alone, is what separates the two forms at the boundary.

CASE_DEFINITION

Show evidence (1 reference)

PMID:20301438 SUPPORT Other

"late-onset Pompe disease (LOPD) (i.e., individuals with onset before age 12 months without cardiomyopathy, and all individuals with onset after age 12 months)"

States the GeneReviews case definition of LOPD used by this entry.

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Inheritance

1

Autosomal recessive HP:0000007

LOPD is autosomal recessive. The characteristic LOPD genotype is compound heterozygosity for the leaky c.-32-13T>G intron-1 splice variant on one allele and a fully deleterious GAA variant on the other, so that the leaky allele sets the residual enzyme activity and therefore the phenotype.

Autosomal recessive inheritance

Show evidence (3 references)

PMID:36299500 SUPPORT Human Clinical

"Of the definite LOPD participants, 8 (89%) were Caucasian and were heterozygous for the common leaky (IVS1) splice site mutation in the GAA gene (c -32-13T>G), with a second mutation that was previously confirmed to be pathogenic."

Documents the compound-heterozygous leaky-allele-plus-null genotype that characterizes LOPD.

PMID:20301438 SUPPORT Other

"each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier"

GeneReviews states the sibling recurrence risks that follow from biallelic GAA inheritance. This is the counselling figure the block exists to record, and it is quantitative in a way the IPaNeMA genotype observation is not, so both are kept.

PMID:20301438 SUPPORT Other

"Once the GAA pathogenic variants have been identified in an affected family member, molecular genetic carrier testing for at-risk relatives and prenatal/preimplantation genetic testing are possible."

Establishes that identifying the proband's biallelic GAA variants is what makes carrier and prenatal testing available to the family.

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Discussions and Knowledge Gaps

2

When should enzyme replacement therapy be started in a person with a confirmed LOPD genotype who has no symptoms, as is now routine after newborn screening or family cascade testing?

KNOWLEDGE GAP OPEN lopd_presymptomatic_ert_initiation

Attached to

pathophysiology#Incomplete Response to Enzyme Replacement Therapy

Newborn screening and family screening increasingly identify LOPD before any clinical sign. Because LOPD is defined by a decades-long latency, the conventional trigger for treatment - symptom onset - may come after irreversible myofiber loss, but treating a pre-symptomatic patient commits them to lifelong infusions with cost, infusion-reaction risk, and immunogenicity. Guidance is not settled: European recommendations favour monitoring asymptomatic cases with minimal muscle MRI findings, while other guidance would start therapy once any muscle involvement (for example paraspinal) is detectable. Siblings sharing a genotype can differ markedly in age at presentation and MRI burden, so genotype alone does not resolve the question.

Show evidence (3 references)

PMID:36833288 SUPPORT Human Clinical

"The dilemma is when to start Enzyme Replacement Therapy (ERT) in patients without any clinical sign of the disease, considering its important benefits in terms of loss of muscle but also its very high cost, risk of side effects, and long-term immunogenicity."

States the pre-symptomatic treatment-initiation gap that this discussion records.

PMID:36833288 SUPPORT Human Clinical

"European guidelines suggest monitoring in asymptomatic LOPD cases with minimal MRI findings, although other guidelines consider starting ERT in apparently asymptomatic cases with initial muscle involvement (e.g., paraspinal muscles)."

Documents the disagreement between guidelines that makes this an open question rather than settled practice.

PMID:24383498 SUPPORT Human Clinical

"The best outcome of ERT both clinically and morphologically was observed in the NBS patients."

Argues for earlier initiation, since newborn-screening-detected patients had the best clinical and histological response - but this is an uncontrolled comparison across onset groups, so it informs rather than settles the question.

Does autophagic mistargeting of endocytosed recombinant GAA, demonstrated in single fibers of the GAA knockout mouse, account for the therapeutic ceiling observed in treated human LOPD skeletal muscle?

HUMAN MODEL MISMATCH OPEN lopd_autophagic_mistargeting_model_fidelity

Attached to

pathophysiology#Autophagic Mistargeting of Endocytosed Recombinant Enzyme

The mistargeting mechanism is directly imaged in live single muscle fibers of GAA knockout mice, which model complete rather than partial enzyme deficiency. LOPD muscle retains residual enzyme and accumulates storage over decades, so the extent of autophagic buildup - and therefore how much of the human treatment ceiling it explains - is not established from the mouse data alone. The human counterpart evidence in this entry is indirect: fat fraction continues to rise and some patients still progress to ventilation on therapy, which is consistent with the mechanism but does not measure enzyme trafficking in human muscle.

Proposed experiments

Trafficking of labelled rhGAA in LOPD patient muscle biopsy fibers

lopd_rhgaa_trafficking_in_patient_myofibers

Assess whether endocytosed recombinant GAA reaches lysosomes or is retained in autophagic compartments in myofibers from genotyped LOPD patients, stratified by residual enzyme activity and by duration of enzyme replacement therapy.

Show evidence (1 reference)

PMID:17008131 SUPPORT Model Organism

"These findings may explain why ERT often falls short of reversing the disease process and point toward new avenues for the development of pharmacological intervention."

The authors present the mechanism as an explanation that "may" account for the therapeutic shortfall, which is the translational uncertainty recorded here.

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Pathophysiology

10

Leaky GAA Splicing and Partial Residual Enzyme Activity

Mechanism confidence: Established

The LOPD-defining lesion is partial rather than complete loss of acid alpha-glucosidase. The commonest LOPD allele, c.-32-13T>G (IVS1), sits in intron 1 and weakens the splice acceptor of GAA exon 2. Most transcripts from that allele are aberrantly spliced (partial or complete exon 2 skipping), but a low level of correctly spliced, fully functional transcript escapes. That residual activity - conventionally quoted as roughly 1-30% of normal, though see the caveat in the biochemical section and in notes - is what shifts the phenotype from infantile to late onset. In the great majority of LOPD patients the leaky allele is carried in trans with a second, more deleterious pathogenic variant, so the leaky allele is the one setting how much enzyme the patient makes.

GAA hgnc:4065 ↓ DECREASED

Genetic context GAA hgnc:4065 allele_type: SNV variant_origin: GERMLINE zygosity: COMPOUND_HETEROZYGOUS functional_impact_category: PARTIAL_LOSS_OF_FUNCTION

Compound heterozygosity for the leaky c.-32-13T>G intron-1 splice variant and a second, more deleterious pathogenic GAA variant.

GAA pre-mRNA splicing at the exon 2 acceptor GO:0000398 ↓ DECREASED

acid alpha-glucosidase activity GO:0004558 ↓ DECREASED

Downstream

Attenuated Lysosomal Glycogen Accumulation in Skeletal and Respiratory Muscle Residual GAA activity slows, but does not prevent, lysosomal glycogen accumulation, producing a decades-long rather than months-long storage course.

Relative Cardiac Sparing Residual enzyme activity is sufficient to keep cardiomyocyte glycogen turnover below the threshold that produces infantile hypertrophic cardiomyopathy. The quantitative threshold itself has not been measured in human myocardium, so the link is recorded with unknown intermediates.

Lysosomal Glycogen Accumulation in Vascular and Visceral Smooth Muscle The same partial enzyme deficit is exhausted in smooth muscle as well as in skeletal muscle, opening the extra-muscular arm of the disease.

Show evidence (2 references)

PMID:28624228 SUPPORT In Vitro

"which weakens the splice acceptor of GAA exon 2 and induces partial and complete exon 2 skipping. It also allows a low level of leaky wild-type splicing, leading to a childhood/adult phenotype."

Establishes the leaky-splicing mechanism by which c.-32-13T>G yields residual enzyme and a late-onset phenotype.

PMID:33972680 SUPPORT Human Clinical

"The presence of at least one splice site variant (c.546 G > C/p.T182 = , c.1076-22 T > G, c.2646 + 2 T > A, and the classic c.-32-13T > G variant) was associated with LOPD, while the presence of non-splice site variants on both alleles was associated with IOPD."

Human genotype-phenotype data tying retention of a leaky splice allele to the late-onset phenotype.

Attenuated Lysosomal Glycogen Accumulation in Skeletal and Respiratory Muscle

Mechanism confidence: Established

Partial GAA activity permits slow lysosomal glycogen accumulation that is concentrated in skeletal muscle, including the respiratory muscles, rather than the generalized multisystem storage of infantile disease. The tissue selectivity reflects the very high glycogen flux of muscle relative to its residual degradative capacity, so muscle is the first compartment in which the reduced enzyme reserve is exhausted.

Skeletal muscle fiber CL:0008002

Lysosomal glycogen catabolism GO:0005980 ↓ DECREASED

lysosome GO:0005764

skeletal muscle tissue UBERON:0001134

Downstream

Autophagic Mistargeting of Endocytosed Recombinant Enzyme Glycogen-engorged lysosomes disturb autophagic flux in myofibers.

Pre-Vacuolar Metabolic Reprogramming of Myonuclei Storage perturbs myonuclear metabolic gene expression before any vacuole is visible on histology.

Progressive Limb-Girdle and Axial Myofiber Degeneration Cumulative storage and autophagic damage destroy contractile architecture in proximal lower-limb and paraspinal muscle.

Phrenic Motor Unit Failure Storage in the diaphragm undermines the principal muscle of inspiration.

Show evidence (1 reference)

PMID:33214927 SUPPORT Human Clinical

"Late-onset Pompe disease (LOPD) is a rare autosomal recessive glycogen storage disease that results in accumulation of glycogen in muscle cells causing muscular weakness."

Anchors muscle-cell glycogen accumulation as the storage lesion that produces LOPD weakness.

Relative Cardiac Sparing

Mechanism confidence: Established

Absence of hypertrophic cardiomyopathy is a defining feature of LOPD and part of its formal case definition, not merely a statistical tendency. Residual GAA activity is sufficient to keep cardiomyocyte glycogen storage subclinical, so the cardiorespiratory collapse that kills untreated infants does not occur; the respiratory system, not the heart, becomes the life-limiting organ. This node is curated as a mechanistic contrast rather than as a claim that the myocardium is entirely normal - adult arteriopathy and rare conduction findings are described in the umbrella Pompe disease entry.

Cardiac muscle cell CL:0000746

Show evidence (1 reference)

PMID:20301438 SUPPORT Other

"late-onset Pompe disease (LOPD) (i.e., individuals with onset before age 12 months without cardiomyopathy, and all individuals with onset after age 12 months)"

GeneReviews makes absence of cardiomyopathy definitional for LOPD.

Autophagic Mistargeting of Endocytosed Recombinant Enzyme

Mechanism confidence: Established

Skeletal myofibers in Pompe disease develop large autophagic areas alongside glycogen-filled lysosomes. These areas trap endocytosed recombinant human GAA in a partially processed form so that it never reaches the lysosome, which is a mechanistic explanation for why enzyme replacement therapy is far more effective in cardiac than in skeletal muscle and why it slows rather than arrests the LOPD myopathy. Because LOPD is a decades-long disease treated for decades, this therapeutic ceiling is a defining clinical problem of the late-onset form.

Skeletal muscle fiber CL:0008002

autophagy GO:0006914 ↑ INCREASED endosomal transport of endocytosed enzyme GO:0016197 ↓ DECREASED

Downstream

Incomplete Response to Enzyme Replacement Therapy Enzyme that never reaches the lysosome cannot clear stored glycogen.

Show evidence (6 references)

PMID:17008131 SUPPORT Model Organism

"Confocal microscopy of live single muscle fibers exposed to fluorescently labeled rhGAA indicates that a significant portion of the endocytosed enzyme in the KO was trapped as a partially processed form in the autophagic areas instead of reaching its target--the lysosomes."

Demonstrates autophagic mistargeting of therapeutic enzyme in skeletal muscle fibers.

PMID:17008131 SUPPORT Model Organism

"The therapy, which relies on receptor-mediated endocytosis of recombinant human GAA (rhGAA), appears to be effective in cardiac muscle, but less so in skeletal muscle."

States the cardiac-versus-skeletal-muscle discrepancy in ERT response that this node explains.

PMID:24383498 SUPPORT Human Clinical

"numerous lysosomes and autolysosomes loaded with lipofuscin appear to be a hallmark of LOPD skeletal muscle"

Human LOPD muscle biopsies confirm an autophagic-lysosomal lesion in the late-onset form itself, not only in the knockout mouse.

+ 3 more references

Pre-Vacuolar Metabolic Reprogramming of Myonuclei

Mechanism confidence: Provisional

Single-nucleus RNA sequencing combined with spatial transcriptomics of LOPD muscle biopsies shows that myofibers are transcriptionally abnormal before they are histologically abnormal. Fibers that are not yet vacuolated already show reduced glycolytic gene expression with increased lipid and amino-acid metabolism, upregulated autophagy genes, and downregulated ribosomal and mitochondrial programmes producing defective oxidative phosphorylation. Inflammation, apoptosis, and regeneration signatures appear only once vacuolation is established. This staging matters for LOPD specifically, because it identifies an early, possibly still-tractable metabolic derangement that precedes the structural damage enzyme replacement therapy cannot undo. The study reports only a "tendency" for therapy to restore the dysregulated metabolism, so reversibility is a hypothesis this node raises rather than a result it records.

Skeletal muscle fiber CL:0008002 Slow (type I) muscle fiber CL:0000189 Muscle-infiltrating macrophage CL:0000235

glycolytic process GO:0006096 ↓ DECREASED lipid metabolic process GO:0006629 ↑ INCREASED oxidative phosphorylation GO:0006119 ↓ DECREASED

Downstream

Progressive Limb-Girdle and Axial Myofiber Degeneration Metabolically compromised fibers progress to vacuolation, inflammation, apoptosis, and replacement by fat.

Show evidence (5 references)

PMID:39045638 SUPPORT Human Clinical

"The expression of the genes involved in glycolysis was reduced, whereas the expression of the genes involved in the metabolism of lipids and amino acids was increased in non-vacuolated fibres, indicating early metabolic abnormalities."

Demonstrates metabolic reprogramming in histologically unaffected LOPD myofibers, before vacuolation.

PMID:39045638 SUPPORT Human Clinical

"Upregulation of genes associated with inflammation, apoptosis and muscle regeneration was observed only in vacuolated fibres."

Separates the later inflammatory/degenerative programme from the earlier metabolic one, which is the staging claim of this node.

PMID:39045638 SUPPORT Human Clinical

"Notably, enzyme replacement therapy (the only available therapy for the disease) showed a tendency to restore dysregulated metabolism, particularly within slow fibres."

Bounds the reversibility claim - the authors report a tendency, not a demonstrated restoration, which is why this node is PROVISIONAL.

+ 2 more references

Progressive Limb-Girdle and Axial Myofiber Degeneration

Mechanism confidence: Established

Chronic storage and autophagic injury destroy myofibers, which are replaced by fat. The distribution is characteristically limb-girdle and axial, with early involvement of the psoas and paraspinal muscles; quantitative fat fraction on lumbar MRI correlates with strength, walking distance, stair climbing and supine spirometry, and continues to rise during enzyme replacement therapy.

Skeletal muscle fiber CL:0008002

skeletal muscle tissue UBERON:0001134

Downstream

Progressive proximal muscle weakness Loss of contractile tissue in limb-girdle and axial muscle produces the characteristic LOPD weakness pattern.

Show evidence (1 reference)

PMID:29315315 SUPPORT Human Clinical

"A significant increase in the MR-derived fat fraction of the psoas muscle was found between baseline and follow-up 1 (P = 0.016), as was a significant decrease in the performance on the 6-minute walk test (P = 0.006) and 4-step stair climb test (P = 0.034)"

Shows progressive fatty replacement of proximal/axial muscle with concurrent functional decline during ERT.

Phrenic Motor Unit Failure

Mechanism confidence: Provisional

Diaphragm weakness in LOPD is disproportionate to limb weakness and is the proximate cause of nocturnal hypoventilation and ultimately of ventilatory failure. Neurophysiological study of treated LOPD patients found that those with respiratory failure had absent or severely reduced phrenic nerve compound muscle action potentials and diaphragm EMG showing neurogenic as well as myopathic changes, implicating spinal phrenic motor neuron dysfunction alongside myofiber disease. Because intravenous recombinant enzyme does not cross the blood-brain barrier, a motor neuron contribution would explain residual respiratory decline on enzyme replacement therapy. The motor neuron arm is curated as PROVISIONAL: the supporting series is small (eight patients) and calls for confirmation.

Skeletal muscle fiber CL:0008002 Phrenic motor neuron CL:0000100

diaphragm UBERON:0001103

Downstream

Nocturnal hypoventilation and sleep-disordered breathing Inspiratory muscle failure is expressed first during sleep, when accessory muscle recruitment falls and ventilation depends on the diaphragm.

Respiratory insufficiency due to muscle weakness Progressive diaphragm failure produces daytime hypercapnic respiratory failure, the leading cause of death in untreated LOPD.

Show evidence (3 references)

PMID:38653115 SUPPORT Human Clinical

"Diaphragm needle EMG revealed both myopathic and neurogenic changes in 3 (60%) and myopathic potentials in 1 patient."

Provides the electrophysiological observation of combined neurogenic and myopathic diaphragm involvement.

PMID:38653115 SUPPORT Human Clinical

"Our study provide new insights regarding respiratory mechanisms in LOPD, suggesting a contribution of spinal phrenic motor neuron dysfunction for diaphragm weakness."

The authors themselves frame the phrenic motor neuron contribution as a suggestion requiring confirmation, which is why this node is PROVISIONAL.

PMID:42074341 SUPPORT Other

"limited penetration across the blood-brain barrier (BBB), resulting in persistent central nervous system involvement, and immune responses against the infused enzyme"

Supports the pharmacological half of this node's argument - intravenous recombinant enzyme does not reach the central nervous system, so a phrenic motor neuron contribution would not be corrected by enzyme replacement therapy.

Incomplete Response to Enzyme Replacement Therapy

Mechanism confidence: Established

Enzyme replacement therapy changes the trajectory of LOPD but does not normalize it. Walking distance and forced vital capacity improve modestly relative to placebo in the short term, yet muscle fat fraction continues to increase, some patients still progress to ventilatory support, and the effect on sleep-disordered breathing is undocumented. This residual disease burden is a mechanistic consequence of the autophagic mistargeting node and, possibly, of the motor neuron arm of diaphragm weakness, which intravenous enzyme cannot reach.

Show evidence (3 references)

PMID:38653115 SUPPORT Human Clinical

"Late-onset Pompe disease (LOPD) patients may still need ventilation support at some point of their disease course, despite regular recombinant human alglucosidase alfa treatment."

Documents residual progression to ventilatory support despite ongoing enzyme replacement therapy.

PMID:33214927 SUPPORT Human Clinical

"Whilst disease-modifying enzyme replacement therapy (ERT) delays progression of locomotor dysfunction and prolongs life, its effect on respiratory function and SDB remains unclear."

States that the respiratory benefit of ERT in LOPD is not established, bounding the claim of therapeutic benefit.

PMID:33799647 SUPPORT Human Clinical

"178 proteins were changed in abundance in LOPD patients, 47 of them recovered normal level after ERT. Defects in oxidative metabolism, muscle contractile protein regulation, cytoskeletal rearrangement, and membrane reorganization persisted."

Quantifies the molecular residue of disease in LOPD muscle after a year of enzyme replacement therapy - roughly a quarter of the altered proteome normalizes.

Lysosomal Glycogen Accumulation in Vascular and Visceral Smooth Muscle

Mechanism confidence: Established

Residual GAA activity is exhausted in smooth muscle as well as in skeletal muscle. Autopsy of a woman with LOPD demonstrated lysosomal glycogen inside vascular smooth muscle cells by transmission electron microscopy, alongside involvement of the bladder, intestine, and esophagus. This is a distinct cellular compartment from the skeletal and respiratory myofiber storage that dominates the LOPD clinical picture, and it is the substrate for the disease's two extra-muscular arms: the dilative arteriopathy of large arteries, and the gastrointestinal and genitourinary symptoms that patients report independently of limb weakness. Smooth-muscle storage is the reason LOPD is a systemic lysosomal disease rather than a pure myopathy.

vascular smooth muscle cell CL:0000359 smooth muscle cell of bladder CL:0002597 smooth muscle cell of the esophagus CL:0002599 intestinal smooth muscle cell CL:0002504

lysosomal glycogen degradation in smooth muscle GO:0005980 ↓ DECREASED

glycogen-distended lysosome GO:0005764

Animal models

Gaa-/- global knockout mouse (smooth muscle characterization) Mouse recapitulates Quantitative glycogen assay, PAS histology and LAMP1/LC3 immunoblotting all show the storage-plus-vacuolar-accumulation lesion in the same smooth-muscle beds implicated by human autopsy.

Downstream

Dilative Arteriopathy of the Aorta and Intracranial Arteries Glycogen-laden smooth muscle cells in the tunica media are the proposed structural cause of progressive arterial wall remodeling and dilatation.

Gastroesophageal reflux Storage in esophageal and gastric smooth muscle is the proposed basis of the reflux LOPD patients report; the contractile deficit linking the two has not been measured in human tissue.

Constipation Storage in intestinal smooth muscle is the proposed basis of the chronic constipation LOPD patients report; as with reflux, the contractile deficit linking the two has not been measured in human tissue.

Urinary incontinence Bladder smooth muscle storage is the proposed basis of urinary incontinence in LOPD.

Show evidence (3 references)

PMID:22664150 SUPPORT Human Clinical

"Transmission electron microscopy disclosed lysosomal glycogen accumulation within skeletal, cardiac, and vascular smooth muscle cells"

Direct human ultrastructural demonstration that lysosomal glycogen accumulates in vascular smooth muscle cells in late-onset Pompe disease, which is what makes this a curated node rather than a proposed one.

PMID:22664150 SUPPORT Human Clinical

"Organs containing smooth muscle cells (the bladder, intestine, and esophagus) were also affected"

Extends the same storage lesion from vascular to visceral smooth muscle, supporting the visceral half of this node.

PMID:33883348 SUPPORT Model Organism

"Increased levels of glycogen were present in smooth muscle cells of the aorta, trachea, esophagus, stomach, and bladder of Gaa-/- mice, compared to wild type mice."

Independent quantitative confirmation in a GAA-deficient mouse that the storage lesion is present across vascular, airway, gastrointestinal and genitourinary smooth muscle.

Dilative Arteriopathy of the Aorta and Intracranial Arteries

Mechanism confidence: Provisional

Progressive dilatation, ectasia and aneurysm formation affecting the ascending thoracic aorta and the intracranial arteries, with the vertebrobasilar system most often involved, together with a small-vessel component that shows up as white matter hyperintensity and cerebellar and brainstem microbleeds. It is the second organ system LOPD damages after muscle, and it is largely uncoupled from myopathy severity: patients are identified on surveillance imaging rather than by limb weakness, and enzyme replacement therapy did not change vessel calibre over a year of follow-up in the one series that looked. The node is recorded as PROVISIONAL rather than ESTABLISHED because the causal step from smooth-muscle glycogen to wall weakness is inferred rather than demonstrated - one aortic specimen showed connective-tissue changes resembling a fibrillinopathy rather than a storage lesion, and the Gaa-/- mouse accumulates little aortic glycogen, which led that study's authors to decline to attribute aortic wall weakness to glycogen accumulation (see animal_models).

medial vascular smooth muscle cell CL:0000359

ascending thoracic aorta UBERON:0001496 basilar artery UBERON:0001633 arterial tunica media UBERON:0002522

Animal models

Gaa-/- global knockout mouse (smooth muscle characterization) Mouse fails to recapitulate The aorta accumulated the least glycogen of any smooth-muscle tissue measured and did not accumulate more between 6 and 15 months, and the authors state that this does not support the glycogen-to-wall-weakness hypothesis. The only aortic change seen was tunica media remodeling at 15 months. Note the study assayed glycogen and wall histology; it did not report vessel-calibre measurements, so what is recorded here is failure to reproduce the storage-driven wall lesion rather than a measured absence of dilatation.

Downstream

Dilatation of the ascending thoracic aorta

Vertebrobasilar dolichoectasia

Dilatation of the intracranial arteries

Stroke Dilative and stenotic arteriopathy predisposes to both infarction and hemorrhage, but the proportion of LOPD strokes attributable to the arteriopathy rather than to conventional risk factors has not been established.

Cerebral white matter hyperintensities Small-vessel involvement accompanies the large-artery disease; white matter change is its parenchymal correlate.

Show evidence (4 references)

PMID:21605996 SUPPORT Human Clinical

"We report evidence of dilated arteriopathy involving primarily the ascending thoracic aorta in 5 females with late-onset Pompe disease."

The case series that established thoracic aortic dilatation as an LOPD complication rather than an incidental finding.

PMID:39010129 SUPPORT Human Clinical

"Intracranial vasculopathy involving both large arteries and small vessels is an important organ damage in LOPD patients."

A 30-patient imaging cohort establishing intracranial arteriopathy as a systematic organ manifestation of LOPD.

PMID:22945242 SUPPORT INDIRECT Human Clinical

"the histological work-up of resected aortic tissue revealed changes mimicking those observed in patients with classic connective tissue diseases"

Supports the arteriopathy while complicating the mechanism - the resected wall looked like a connective-tissue disease rather than a storage lesion, which is part of why this node is PROVISIONAL.

+ 1 more reference

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Histopathology

1

Lipofuscin-loaded autolysosomes in skeletal muscle

Muscle biopsies from adult-onset, juvenile-onset, and newborn-screening-detected LOPD patients on enzyme replacement therapy contain areas of autophagic buildup filled with large autofluorescent inclusions identified as lipofuscin. These lipofuscin-loaded lysosomes and autolysosomes are the dominant pathology that persists in myofibers after enzyme replacement therapy, and are proposed to aggravate the lysosomal and autophagic abnormalities that caused them.

Show evidence (2 references)

PMID:24383498 SUPPORT Human Clinical

"The areas of autophagic buildup found in patients' biopsies of all three groups, contained large autofluorescent inclusions which we show are made of lipofuscin, an indigestible intralysosomal material typically associated with ageing."

Identifies the lipofuscin content of the autophagic areas in LOPD muscle biopsies.

PMID:24383498 SUPPORT Human Clinical

"Late-onset Pompe disease (LOPD) is a debilitating progressive muscle disorder that can occur anytime from early childhood to late adulthood. ... In this study, we examined the clinical status and muscle pathology of 22 LOPD patients and one atypical infantile patient on ERT to understand the..."

Identifies the LOPD study, retains its atypical infantile comparator and age/diagnosis groups, and connects persistent inclusions to lipofuscin-loaded lysosomes/autolysosomes. The final possible feedback mechanism retains the source's may qualification.

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Pathograph

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Phenotypes

18

Cardiovascular 4

Dilatation of the ascending thoracic aorta Thoracic aortic aneurysm HP:0012727

Show evidence (2 references)

PMID:20301438 SUPPORT Other

"Some adults have developed arteriopathy, including dilatation of the ascending thoracic aorta."

GeneReviews names ascending thoracic aortic dilatation as an adult (late-onset) manifestation of Pompe disease.

PMID:20301438 SUPPORT Other

"echocardiography (to include assessment for aortic dilatation in those with LOPD)"

The surveillance recommendation is LOPD-specific, which is why this phenotype is curated on the late-onset entry rather than left to the umbrella entry.

Vertebrobasilar dolichoectasia FREQUENT HP:0020038

Course: PROGRESSIVE

Show evidence (3 references)

PMID:39010129 SUPPORT Human Clinical

"Dilative arteriopathy was found in 19 patients (19/30), with vertebrobasilar dolichoectasia found in 17 patients and dilatation of the anterior circulation arteries found in 8 patients."

17 of 30 imaged LOPD adults, which is 57 percent and maps to the FREQUENT band (30-79 percent).

PMID:39010129 SUPPORT Human Clinical

"The maximum diameter of the basilar artery was correlated with disease duration"

Supports the PROGRESSIVE clinical course annotation on this phenotype.

PMID:20559845 SUPPORT Human Clinical

"Four out of six patients had brain vascular anomalies including dolichoectasia of the basilar artery and ectasia of internal carotids."

Independent replication in a separate European cohort, which is why this is curated as a recurrent phenotype rather than a single-cohort observation.

Dilatation of the intracranial arteries Dilatation of the cerebral artery HP:0004944

Show evidence (3 references)

PMID:39010129 SUPPORT Human Clinical

"In addition, aneurysms (7/30) and fenestrations (3/30) were discovered."

Documents intracranial aneurysm formation as part of the LOPD arteriopathy.

PMID:21605996 SUPPORT Human Clinical

"Another patient with juvenile onset disease had both thoracic and basilar artery aneurysms."

Shows the aortic and intracranial arms of the arteriopathy occurring in the same patient, supporting them as one systemic vascular process.

PMID:20559845 SUPPORT Human Clinical

"At 1 year follow-up, enzyme replacement therapy did not modify the size of cerebral vessels"

Supports the statement that this manifestation did not respond to enzyme replacement therapy over the observed interval.

Stroke OCCASIONAL HP:0001297

Show evidence (2 references)

PMID:39010129 SUPPORT Human Clinical

"Seven patients (7/30) had acute cerebral infarction or hemorrhage."

7 of 30 imaged LOPD adults, which is 23 percent and maps to the OCCASIONAL band (5-29 percent).

PMID:20559845 SUPPORT Human Clinical

"Two patients had clinical signs related to the arteriopathy, including partial paralysis of the third cranial nerve and transient ischemic attacks."

Independent documentation of symptomatic cerebrovascular events attributable to the arteriopathy.

Digestive 3

Dysphagia HP:0002015

Show evidence (2 references)

PMID:33214927 SUPPORT Human Clinical

"They may also report weight loss, due to difficulty swallowing"

Records difficulty swallowing among the presenting symptoms of LOPD.

PMID:33214927 SUPPORT Human Clinical

"Case reports also suggest LOPD can cause bulbar dysfunction"

Identifies bulbar dysfunction as the mechanism, and bounds it - the supporting literature is case reports, so no frequency band is assigned here.

Gastroesophageal reflux HP:0002020

Show evidence (2 references)

PMID:20559845 SUPPORT Human Clinical

"These patients also complained of gastrointestinal symptoms (chronic constipation and gastrointestinal reflux)."

Documents reflux as a reported symptom in this LOPD cohort.

PMID:20559845 SUPPORT Human Clinical

"patients reported a marked improvement of intestinal symptoms"

Supports the statement that the gastrointestinal symptoms, unlike the vascular findings, improved on enzyme replacement therapy.

Constipation HP:0002019

Temporal: CHRONIC

Show evidence (1 reference)

PMID:20559845 SUPPORT Human Clinical

"These patients also complained of gastrointestinal symptoms (chronic constipation and gastrointestinal reflux)."

Documents chronic constipation as a reported symptom, supporting both the phenotype and its CHRONIC temporality annotation.

Metabolism 1

Elevated creatine kinase Elevated circulating creatine kinase activity HP:0003236

Show evidence (1 reference)

PMID:36299500 SUPPORT Human Clinical

"All successive patients presenting with proximal muscle weakness or isolated hyperCKemia and/or neck muscle weakness to these 13 centers were invited to participate in the study."

Isolated hyperCKemia is used as a case-finding criterion for LOPD in neuromuscular practice.

Musculoskeletal 5

Progressive proximal muscle weakness VERY_FREQUENT HP:0003701

Course: PROGRESSIVE

Show evidence (3 references)

PMID:20301438 SUPPORT Other

"LOPD can manifest from the first decade to as late as the seventh decade of life with progressive proximal muscle weakness primarily affecting the lower limbs, which may require use of a wheelchair."

GeneReviews identifies progressive lower-limb-predominant proximal weakness as the defining LOPD motor phenotype.

PMID:33214927 SUPPORT Human Clinical

"It causes a progressive proximal myopathy, accompanied by respiratory muscle weakness, which can lead to ventilatory failure."

Confirms progressive proximal myopathy as the core LOPD phenotype.

PMID:33214927 SUPPORT Human Clinical

"Most patients will present with a lower limb girdle and truncal muscle weakness pattern"

Frequency evidence - "most patients" maps to the VERY_FREQUENT band (80-100%).

Respiratory insufficiency due to muscle weakness FREQUENT HP:0002747

Course: PROGRESSIVE

Show evidence (4 references)

PMID:33214927 SUPPORT Human Clinical

"It causes a progressive proximal myopathy, accompanied by respiratory muscle weakness, which can lead to ventilatory failure. In untreated LOPD, the most common cause of death is respiratory failure."

Establishes respiratory muscle weakness progressing to ventilatory failure as the dominant cause of death in untreated LOPD.

PMID:20301438 SUPPORT Other

"Respiratory insufficiency progressing to respiratory failure is a significant cause of morbidity and mortality."

GeneReviews confirms respiratory insufficiency as a major source of LOPD morbidity and mortality.

PMID:33214927 SUPPORT Human Clinical

"Approximately half will suffer respiratory involvement during the course of their illness"

Frequency evidence - "approximately half" falls in the FREQUENT band (30-79%).

+ 1 more reference

Axial and paraspinal muscle weakness Axial muscle weakness HP:0003327

Course: PROGRESSIVE

Show evidence (2 references)

PMID:33214927 SUPPORT Human Clinical

"Most patients will present with a lower limb girdle and truncal muscle weakness pattern"

Records truncal (axial) weakness as part of the presenting LOPD weakness pattern.

PMID:33799647 SUPPORT Human Clinical

"Late-onset Pompe disease (LOPD) is characterized by progressive proximal and axial muscle weakness and atrophy, causing respiratory failure."

Independently characterizes axial weakness, alongside proximal weakness, as a defining feature of LOPD.

Scoliosis FREQUENT HP:0002650

Show evidence (3 references)

PMID:37759679 SUPPORT Other

"For example, degeneration of bones and joints as a consequence of muscle weakness is a frequent finding, as scoliosis, kyphosis, and hyperlordosis are usually linked to abdominal and hip extensor weakness"

Frequency evidence - an LOPD review calls the skeletal consequence of muscle weakness a frequent finding and names scoliosis as one of them, which is the basis for the FREQUENT band. It also states the mechanism this phenotype's description asserts, namely that the deformity follows trunk and hip extensor weakness.

PMID:37265469 SUPPORT Other

"Subsequent secondary musculoskeletal complications include contractures, limb and spinal deformities (winging scapula, scoliosis, lumbar hyperlordosis, and rigid spine syndrome), and osteopenia/osteoporosis"

The neurology expert consensus independently lists scoliosis among the expected secondary musculoskeletal complications of LOPD.

PMID:20301438 SUPPORT Other

"assess for scoliosis; monitor for evidence of aspiration and respiratory insufficiency"

Scoliosis is under active surveillance at every visit, supporting it as a recurrent rather than incidental manifestation.

Reduced bone mineral density Osteoporosis HP:0000939

Show evidence (3 references)

PMID:20301438 SUPPORT Other

"Standard treatment for arteriopathy, muscle weakness, scoliosis, osteoporosis, and hearing loss."

GeneReviews lists osteoporosis among the Pompe disease manifestations requiring management, establishing it as a curatable phenotype rather than an incidental comorbidity.

PMID:20301438 SUPPORT Other

"At least annually, bone mineral density screening (DXA) in those with LOPD"

The annual DXA recommendation is written specifically for the late-onset group, which is why reduced bone density is curated here.

PMID:37265469 SUPPORT Other

"Subsequent secondary musculoskeletal complications include contractures, limb and spinal deformities (winging scapula, scoliosis, lumbar hyperlordosis, and rigid spine syndrome), and osteopenia/osteoporosis"

Places osteopenia/osteoporosis among the expected secondary musculoskeletal complications of LOPD, and identifies it as secondary to the myopathy rather than a primary bone defect.

Nervous System 1

Cerebral white matter hyperintensities FREQUENT Hyperintensity of cerebral white matter on MRI HP:0030890

Cerebellar and brainstem microbleeds accompany the white matter change in this cohort, but they are not curated as a separate phenotype here: HPO has no cerebral microhemorrhage or microbleed term, and Cerebral hemorrhage (HP:0001342) names a clinical event rather than a susceptibility-weighted imaging finding, so binding it would overstate what was observed. The microbleed evidence is recorded on the Dilative Arteriopathy of the Aorta and Intracranial Arteries node instead, where it supports the small-vessel claim without needing a phenotype binding.

Show evidence (1 reference)

PMID:39010129 SUPPORT Human Clinical

"White matter hyperintensities were present in 13 patients (13/28)."

13 of 28 imaged patients, which is 46 percent and maps to the FREQUENT band (30-79 percent).

Respiratory 1

Nocturnal hypoventilation and sleep-disordered breathing HP:0002877

Show evidence (2 references)

PMID:33214927 SUPPORT Human Clinical

"Diaphragm weakness leads to nocturnal hypoventilation, which can result in sleep disruption."

Directly links diaphragm weakness to nocturnal hypoventilation in LOPD.

PMID:33214927 SUPPORT Human Clinical

"Patients suffering from respiratory compromise may present with symptoms of sleep-disordered breathing (SDB) before overt signs of respiratory failure."

Supports sleep-disordered breathing as an early, pre-failure respiratory manifestation.

Constitutional 3

Exercise intolerance HP:0003546

Show evidence (2 references)

PMID:37265469 SUPPORT Other

"restrictive respiratory insufficiency with hyperCKemia and/or exercise intolerance as the red flag symptoms/signs that raise the index of suspicion for LOPD diagnosis"

The neurology expert consensus names exercise intolerance as a red-flag sign for LOPD, which is both the phenotype claim and its diagnostic significance.

PMID:33214927 SUPPORT Human Clinical

"Patients will initially report complaints suggestive of progressively reducing muscle strength, such as a difficulty with physical exercise, difficulty climbing stairs or standing from a chair."

Places reduced exercise capacity as the initial functional complaint in LOPD.

Myalgia and fatigue HP:0003326

Show evidence (1 reference)

PMID:33214927 SUPPORT Human Clinical

"This is likely to be associated with muscle aches and tiredness."

Records myalgia (muscle aches) and fatigue (tiredness) as accompaniments of the early LOPD weakness. Fatigue is described in the same sentence and is captured in this entry's description rather than as a separate poorly specific phenotype.

Urinary incontinence HP:0000020

Show evidence (1 reference)

PMID:22664150 SUPPORT Human Clinical

"explaining reports of symptoms such as urinary incontinence and dysphagia"

The autopsy study links bladder smooth-muscle involvement to reported urinary incontinence in LOPD.

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Genetic Associations

1

GAA leaky splice-site variants (Causative)

Gene: GAA hgnc:4065 gene page relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (4 references)

PMID:33972680 SUPPORT Human Clinical

"To extend the findings of prior studies, we found that multiple types of splice site variants beyond the classic c.-32-13T > G variant are often associated with a milder phenotype."

Shows the late-onset phenotype tracks with splice-site (leaky) alleles generally, not only c.-32-13T>G.

PMID:36299500 SUPPORT Human Clinical

"Of the definite LOPD participants, 8 (89%) were Caucasian and were heterozygous for the common leaky (IVS1) splice site mutation in the GAA gene (c -32-13T>G), with a second mutation that was previously confirmed to be pathogenic."

Quantifies the dominance of the leaky IVS1 allele among LOPD patients in a North American neuromuscular cohort.

PMID:39273088 SUPPORT Human Clinical

"Our study concluded that Italian patients exhibited a characteristic genetic profile similar to that of the broader European population, with the c.-32-13T>G variant being the most prevalent."

A second, independent European cohort confirms c.-32-13T>G as the most prevalent allele, so the leaky-allele finding is not specific to the North American series.

+ 1 more reference

Variants (1)

c.-32-13T>G (IVS1) Pathogenic

mLOE

Intron-1 variant 13 nucleotides upstream of GAA exon 2. It weakens the exon 2 splice acceptor, causing partial and complete exon 2 skipping, while permitting a low level of correctly spliced wild-type transcript - the "leaky" behaviour that yields residual enzyme and late-onset disease.

Show evidence (1 reference)

PMID:28624228 SUPPORT In Vitro

"which weakens the splice acceptor of GAA exon 2 and induces partial and complete exon 2 skipping. It also allows a low level of leaky wild-type splicing, leading to a childhood/adult phenotype."

Characterizes the splicing consequence and residual-activity behaviour of the IVS1 variant.

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Medical Actions

4

Enzyme replacement therapy for late-onset disease

Action: enzyme replacement therapy Ontology label: Protein Replacement Therapy NCIT:C16221

Agent: alglucosidase alfa NCIT:C65221 avalglucosidase alfa NCIT:C169795 cipaglucosidase alfa NCIT:C175059 miglustat CHEBI:50381

Platform: Protein replacement

Intravenous recombinant human GAA is the standard disease-modifying treatment. Alglucosidase alfa is approved for LOPD; avalglucosidase alfa is approved for individuals with LOPD older than one year; and cipaglucosidase alfa with miglustat is approved for adults with LOPD weighing at least 40 kg who are not improving on their current regimen. Benefit in LOPD is real but partial, and is limited by autophagic mistargeting of enzyme in skeletal muscle.

Mechanism Target:

MODULATES Attenuated Lysosomal Glycogen Accumulation in Skeletal and Respiratory Muscle — Recombinant enzyme supplies the deficient lysosomal hydrolase and reduces the stored glycogen burden in muscle.

Show evidence (1 reference)

PMID:20393176 SUPPORT Human Clinical

"At 78 weeks, the estimated mean changes from baseline in the primary end points favored alglucosidase alfa (an increase of 28.1+/-13.1 m on the 6-minute walk test and an absolute increase of 3.4+/-1.2 percentage points in FVC; P=0.03 and P=0.006, respectively)."

The pivotal LOPD randomized trial shows enzyme replacement modifies walking distance and vital capacity relative to placebo.

Target Phenotypes: Proximal muscle weakness HP:0003701 Respiratory insufficiency due to muscle weakness HP:0002747

Show evidence (4 references)

PMID:20393176 SUPPORT Human Clinical

"At 78 weeks, the estimated mean changes from baseline in the primary end points favored alglucosidase alfa (an increase of 28.1+/-13.1 m on the 6-minute walk test and an absolute increase of 3.4+/-1.2 percentage points in FVC; P=0.03 and P=0.006, respectively)."

Randomized, placebo-controlled evidence of benefit for alglucosidase alfa in late-onset Pompe disease.

PMID:34800399 SUPPORT Human Clinical

"We consider that this study provides evidence of clinically meaningful improvement with avalglucosidase alfa therapy over alglucosidase alfa in respiratory function, ambulation, and functional endurance, with no new safety signals reported."

Head-to-head phase 3 evidence supporting avalglucosidase alfa in late-onset disease.

PMID:38057636 SUPPORT Human Clinical

"Overall, cipa + mig was well tolerated with a safety profile like alglucosidase alfa. ATB200-02 results show the potential benefits of cipa + mig as a long-term treatment option for Pompe disease."

Supplies the long-term (48-month) safety and efficacy evidence for the third approved LOPD regimen, cipaglucosidase alfa with miglustat.

+ 1 more reference

Non-invasive ventilation

Action: mechanical ventilation Ontology label: Mechanical Ventilation NCIT:C70909

Platform: Device

Non-invasive ventilation is the mainstay of treatment for sleep-disordered breathing and ventilatory failure in LOPD, targeting adequate ventilation during sleep and prevention of acute hypercapnic decompensation. It addresses the diaphragmatic failure node directly and is required regardless of enzyme replacement therapy in many patients.

Mechanism Target:

MODULATES Phrenic Motor Unit Failure — Positive-pressure ventilation substitutes for failing inspiratory muscle work rather than correcting the underlying storage lesion.

Show evidence (1 reference)

PMID:33214927 SUPPORT Human Clinical

"The mainstay of treatment for SDB and respiratory failure in LOPD is non-invasive ventilation (NIV), which aims to ensure adequate ventilation, particularly during sleep, and prevent acute hypercapnic failure."

Identifies non-invasive ventilation as the primary intervention for the respiratory failure node.

Target Phenotypes: Nocturnal hypoventilation HP:0002877 Respiratory insufficiency due to muscle weakness HP:0002747

Show evidence (1 reference)

PMID:33214927 SUPPORT Human Clinical

"The mainstay of treatment for SDB and respiratory failure in LOPD is non-invasive ventilation (NIV), which aims to ensure adequate ventilation, particularly during sleep, and prevent acute hypercapnic failure."

Establishes non-invasive ventilation as standard management of respiratory failure in LOPD.

Structured multidisciplinary surveillance

Action: multidisciplinary disease surveillance Ontology label: Disease Screening NCIT:C15419

Platform: Other

LOPD is managed as a multisystem disease on a fixed schedule rather than symptomatically. GeneReviews specifies, at least annually, DXA bone mineral density (a recommendation written specifically for the late-onset group), pulmonary function tests, echocardiography including assessment for aortic dilatation, EKG, audiology, and BNP where cardiomyopathy is a concern; MR cerebral angiography at least every five years for progressive cerebral vessel dilation; and, as clinically indicated, whole-body MRI, polysomnography, and videofluoroscopic swallow study. This is the surveillance counterpart of the aortic dilatation, reduced bone density, dysphagia, and sleep-disordered breathing phenotypes curated above.

Show evidence (3 references)

PMID:20301438 SUPPORT Other

"At least annually, bone mineral density screening (DXA) in those with LOPD (in those with IOPD, DXA scan every two to three years until puberty, then every one to two years); pulmonary function tests; echocardiography (to include assessment for aortic dilatation in those with LOPD); EKG;..."

GeneReviews sets out the annual surveillance panel, with the DXA and aortic assessment items written specifically for late-onset patients.

PMID:20301438 SUPPORT Other

"At least every five years, MR cerebral angiography to evaluate for progressive dilation of cerebral vasculature."

Records the cerebral vascular surveillance interval, the intracranial counterpart of the aortic arteriopathy curated as a phenotype.

PMID:39482698 SUPPORT Other

"Polysomnography and/or oxycapnography should be performed every 12 months."

The European pathway independently sets an annual sleep-study interval, which is the surveillance that detects the nocturnal hypoventilation phenotype before daytime failure.

Anaesthetic and cardiovascular agent precautions

Action: avoidance of high-risk agents and circumstances Ontology label: Supportive Care NCIT:C15747

Platform: Other

This is a negative recommendation rather than an intervention. Anaesthesia carries disproportionate risk in LOPD because reduced cardiovascular return combines with the underlying respiratory insufficiency, and GeneReviews advises using it only when absolutely necessary. Positioning matters for the same reason: because vital capacity falls on lying flat, LOPD patients should not be laid completely supine. Digoxin, inotropes, diuretics, and afterload-reducing agents can worsen left ventricular outflow obstruction; that caution is inherited from Pompe disease generally and is less applicable to the typically cardiac-spared LOPD patient, so it is recorded here as context rather than as an LOPD-specific claim.

Show evidence (3 references)

PMID:20301438 SUPPORT Other

"Anesthesia should be used only when absolutely necessary because reduced cardiovascular return and underlying respiratory insufficiency pose significant risks."

GeneReviews states the anaesthetic caution and the two physiological reasons for it.

PMID:39482698 SUPPORT Other

"It should be noted that most patients have lower FVC in supine position due to poor diaphragmatic function; therefore, they should not lay totally flat, but be positioned in a (slightly) upright position."

Gives the positioning precaution that follows from the same diaphragmatic weakness, applicable during respiratory decompensation and around procedures.

PMID:20301438 SUPPORT Other

"The use of digoxin, ionotropes, diuretics, and afterload-reducing agents may worsen left ventricular outflow obstruction, although they may be indicated in later stages of the disease"

Bounds the cardiac drug caution - it is written for Pompe disease as a whole, and the outflow obstruction it guards against is a feature of the infantile-onset cardiomyopathy rather than of typically cardiac-spared LOPD.

🔬

Biochemical Markers

1

Reduced but not absent acid alpha-glucosidase activity (DECREASED)

Context: LOPD is biochemically defined by partial rather than absent GAA activity, conventionally cited as roughly 1-30% of normal. Enzyme activity alone, however, does not reliably separate LOPD from IOPD - genotype carries more predictive information - so a low-but-not-absent value should be interpreted alongside GAA sequencing.

Show evidence (2 references)

PMID:33972680 SUPPORT Human Clinical

"Enzyme activity levels in isolation were not sufficient to predict disease subtype or other major clinical features."

Bounds the diagnostic claim - residual enzyme activity alone does not classify a patient as LOPD versus IOPD.

PMID:36299500 SUPPORT Human Clinical

"Whole blood was tested for acid alpha-glucosidase (GAA) assay through the fluorometric method, and all cases with enzyme levels of ≤10 pmoL/punch/h were reflexed to molecular testing for mutations in the GAA gene."

Documents the reflex-testing workflow in which a reduced GAA activity result is confirmed by GAA genotyping.

🔬

Diagnosis

9

Recognition of the LOPD red-flag presentation

Because LOPD presents insidiously with non-specific complaints, the rate-limiting step is clinical suspicion rather than any assay. Unexplained proximal or axial weakness, restrictive respiratory insufficiency, hyperCKemia, and exercise intolerance are the agreed red flags that should trigger GAA testing; reduced pulmonary function specifically in the supine position is the LOPD-typical modifier. Normal CK, EMG, or muscle biopsy do not exclude the diagnosis.

LOPD red-flag case finding NCIT:C15419

Results: Any of these red flags in an adult or older child without a better explanation should prompt a dried blood spot GAA assay rather than further undirected neuromuscular workup.

Show evidence (3 references)

PMID:37265469 SUPPORT Other

"the presence of unexplained proximal/axial weakness (with or without respiratory symptoms) or restrictive respiratory insufficiency with hyperCKemia (up to 15-fold) and/or exercise intolerance should be considered as the red flag symptoms/signs that raise suspicion for LOPD diagnosis"

The neurology expert consensus enumerates the red flags that open the LOPD diagnostic algorithm.

PMID:39482698 SUPPORT Other

"proximal limb girdle weakness and/or axial muscle weakness with or without reduced pulmonary function, in particular when in supine position should be considered as red flags for LOPD patients"

The MetabERN European clinical pathway independently defines the same red-flag set and adds the supine-position qualifier that is characteristic of LOPD.

PMID:37265469 SUPPORT Other

"it should be noted that normal CK values or the normal findings on EMG or muscle biopsy do not exclude the LOPD diagnosis"

Bounds the negative predictive value of the supporting tests - a normal CK, EMG, or biopsy must not be used to close the diagnostic question.

Dried blood spot GAA activity as first-line screen

A GAA enzyme assay on a dried blood spot is the first-line test: cheap, minimally invasive, and fast. It is explicitly a screening test and is never sufficient for a definitive diagnosis. Modern assays include acarbose to competitively inhibit maltase-glucoamylase, which otherwise confounds activity measured at acidic pH; poor spotting, humidity, and heat during shipping are recognized preanalytical causes of spurious results.

dried blood spot acid alpha-glucosidase assay NCIT:C15419

Results: Reduced GAA activity on dried blood spot is a positive screen that must be referred on for confirmation; a normal result in a patient with strong red flags does not close the question.

Show evidence (3 references)

PMID:39482698 SUPPORT Other

"A GAA enzyme assay in dried blood spot assay can be used as a first line test. However, this test is not sufficient for a definitive diagnosis."

States both the first-line role of the dried blood spot assay and its explicit insufficiency for diagnosis.

PMID:37759679 SUPPORT Other

"It is frequently a first-line test because it has the advantages of being easy to perform, inexpensive, minimally invasive, and able to provide rapid results"

Gives the reasons the dried blood spot assay occupies the screening position.

PMID:37759679 SUPPORT Other

"incorrect blood spotting and the combination of humidity and heat caused by insufficient drying or inappropriate shipping can interfere with enzyme stability and, consequently, the assessment of GAA levels"

Documents the preanalytical failure modes that make a single dried blood spot result unreliable on its own.

Confirmatory enzyme and molecular genetic testing

A positive screen is confirmed either by GAA enzyme assay in a second tissue (peripheral leukocytes or lymphocytes, cultured skin fibroblasts, or muscle) or by identifying biallelic pathogenic GAA variants. Molecular confirmation is the more informative of the two in LOPD, because residual enzyme activity alone does not separate late-onset from infantile-onset disease whereas the genotype - in practice the presence of the leaky c.-32-13T>G allele - largely does.

GAA molecular genetic testing NCIT:C15709

Results: Deficient GAA activity in a confirmatory tissue and/or two pathogenic GAA variants in trans establish the diagnosis.

Show evidence (3 references)

PMID:20301438 SUPPORT Other

"The diagnosis of Pompe disease is established in a proband who has deficiency of acid alpha-glucosidase (GAA) enzyme activity in isolated lymphocytes or mixed leukocytes and/or by identification of biallelic pathogenic (or likely pathogenic) variants in GAA by molecular genetic testing"

GeneReviews states the two accepted routes to a confirmed diagnosis.

PMID:39482698 SUPPORT Other

"The diagnosis of Pompe disease should be confirmed by GAA enzyme assay in at least one of the following: peripheral leukocytes/lymphocytes, cultured fibroblasts from skin biopsy, muscle biopsy."

Names the acceptable confirmatory tissues for the enzyme route.

PMID:33972680 SUPPORT Human Clinical

"Enzyme activity levels in isolation were not sufficient to predict disease subtype or other major clinical features."

Supports preferring genotype over residual activity when the question is whether a confirmed patient has late-onset rather than infantile-onset disease.

Pseudodeficiency alleles as a false-positive trap

A reduced GAA activity result with no pathogenic genotype may reflect a pseudodeficiency allele rather than disease. The best-characterized example is GAA c.271G>A (p.Asp91Asn), which depresses measured enzyme activity but has been formally reviewed as benign for Pompe disease. This is the specific reason molecular confirmation - and, when the genotype does not explain the phenotype, broader genetic analysis - is required rather than optional.

GAA variant classification NCIT:C15709

Results: Low measured GAA activity without two pathogenic variants should raise a pseudodeficiency allele and prompt variant curation against ACMG-AMP criteria, not a diagnosis of Pompe disease.

The preprint additionally reports a patient homozygous for c.271G>A whose symptoms were ultimately explained by a PABPN1 variant, which is the clinical shape of the error this entry is guarding against.

Show evidence (2 references)

PMID:37759679 SUPPORT Other

"Rarely, positive DBS with no pathogenic variant may also be related to pseudodeficiency alleles"

Establishes pseudodeficiency as a recognized cause of a positive screen without disease.

DOI:10.1101/2024.10.03.24314698 Preprint · not peer-reviewed SUPPORT Other

"We demonstrated that GAA :c.271G>A meets the criterion of being classified as benign for Pompe."

Identifies the specific pseudodeficiency allele and its expert-panel-reviewed benign classification. This source is a preprint, so it is cited for the variant classification only and the general trap is carried by the peer-reviewed citation above.

Sitting and supine forced vital capacity

Spirometry performed in both the sitting and the supine position is the routine diaphragm-specific measurement in LOPD. Because the diaphragm is disproportionately affected, vital capacity falls on lying flat, so a supine drop identifies diaphragm weakness that a seated measurement alone can miss. It is recommended at least annually.

sitting and supine spirometry NCIT:C38081

Results: A fall in forced vital capacity from sitting to supine indicates diaphragmatic weakness; an FVC below 40% predicted should prompt referral to a home ventilation team.

Show evidence (3 references)

PMID:39482698 SUPPORT Other

"Due to the involvement of diaphragm, pulmonary function in supine position may be more affected than in upright position."

States the physiological basis for measuring vital capacity in both positions.

PMID:39482698 SUPPORT Other

"Pulmonary function (FVC sitting, supine) should be evaluated in both sitting and supine position at least once a year or more frequently depending on patients' conditions."

Gives the recommended frequency and the two-position protocol.

PMID:39482698 SUPPORT Other

"Patients with an FVC < 40% should be brought to the attention of a home ventilation team"

Provides the actionable threshold that makes this measurement a management decision point.

Electrodiagnostic study with paraspinal needle EMG

Needle electromyography with nerve conduction studies is the step that separates LOPD from other neuromuscular causes of the same presentation. Electrophysiological myotonia without clinical myotonia, particularly in the paraspinal muscles, is considered highly suggestive of LOPD. It is a supportive, not a confirmatory, investigation.

needle electromyography NCIT:C38056

Results: Paraspinal electrophysiological myotonia in the absence of clinical myotonia strengthens the case for GAA testing; a normal study does not exclude LOPD.

Show evidence (2 references)

PMID:37265469 SUPPORT Other

"The presence of electrophysiological myotonia in the absence of clinical myotonia and permanent weakness, particularly in paraspinal muscles, are highly suggestive of LOPD diagnosis"

Identifies the characteristic electrodiagnostic finding and its paraspinal localization.

PMID:39482698 SUPPORT Other

"EMG and peripheral nerve conduction studies are optional and may be considered at diagnosis as a supportive element."

Bounds the claim - the European pathway rates electrodiagnosis as optional and supportive, so it is curated here as an adjunct rather than a required step.

Skeletal muscle MRI for disease burden

Skeletal muscle MRI documents muscle trophism and fatty degeneration and is used to map disease burden rather than to make the diagnosis. Whole-body protocols cover muscle groups a targeted study would miss, and quantitative muscle MRI is offered to late-onset patients as an addition to annual assessment. The supine position required for imaging is itself a hazard in patients with diaphragm weakness.

skeletal muscle magnetic resonance imaging NCIT:C16809

Results: A characteristic pattern of fatty replacement in paraspinal, pelvic, and thigh muscle supports the diagnosis and quantifies burden for follow-up.

MetabERN cautions that the supine position needed for MRI may aggravate respiratory failure, which is a real constraint in exactly the LOPD patients whose burden most needs mapping.

Show evidence (2 references)

PMID:39482698 SUPPORT Other

"Whole-body MRI protocols are more inclusive than standard MRI protocols focusing on specific anatomical regions (e.g., paraspinal muscles, tongues, pelvis, thigh), enabling evaluation of relevant muscle groups beyond the pelvis and proximal lower extremities"

Supports whole-body over targeted protocols for mapping LOPD muscle involvement.

PMID:39482698 SUPPORT Other

"Quantitative muscle MRI can be performed in late-onset patients in addition to annual investigations."

Bounds the role - quantitative muscle MRI is an addition to, not a component of, the core annual LOPD assessment.

Newborn screening and the pre-symptomatic LOPD patient

Newborn screening measures GAA activity in dried blood spots and is designed to catch infantile-onset disease early enough for enzyme replacement therapy to work. Its consequence for LOPD is a distinct and growing group: children identified pre-symptomatically who cannot be told when, or whether, they will become symptomatic. Current screening cannot separate infantile-onset from late-onset disease, so these are patients in waiting requiring long-term monitoring.

newborn screening for Pompe disease NCIT:C81178

Results: An out-of-range newborn screen requires confirmatory enzyme and molecular testing; a confirmed child without infantile-onset features enters long-term surveillance rather than immediate treatment.

Show evidence (2 references)

PMID:39482698 SUPPORT Other

"Newborn screening (NBS) for Pompe disease is possible by measuring GAA activity in dried blood spots with different methods (tandem-mass spectrometry, fluorometry, microfluidics)"

Establishes the assay basis of newborn screening.

PMID:39482698 SUPPORT Other

"the NBS screening in its current form cannot discern IOPD from LOPD. LOPD patients are thereby patients in waiting requiring long term follow-up and monitoring which may create uncertainty and a psychological burden for families"

States the LOPD-specific consequence of newborn screening, which is the pre-symptomatic, screening-detected patient group this entry needs to represent.

Urinary glucose tetrasaccharide as a second-tier and monitoring marker

Urinary glucose tetrasaccharide (Glc4/Hex4) is used as a second-tier test after a positive dried blood spot and as a follow-up marker. It is not specific to Pompe disease - urinary infection, acute pancreatitis, muscle trauma, and some cancers also raise it - and early-phase patients may excrete normal amounts, so it supports rather than establishes a diagnosis.

urinary glucose tetrasaccharide measurement NCIT:C15419

Results: An elevated Glc4 supports the diagnosis after a positive screen and tracks response on therapy; a normal Glc4 does not exclude early LOPD.

Show evidence (3 references)

PMID:37759679 SUPPORT Other

"Urinary glucose tetrasaccharide (Glc4) could be used as a second-tier test after positive DBS, and its concentration seems to correlate with age of symptom onset, with more elevated levels in IOPD patients"

Places Glc4 as a second-tier test and notes its correlation with onset age.

PMID:37759679 SUPPORT Other

"elevated urinary tetrasaccharide glucose levels are not specific to PD and may also be related to urinary infections, acute pancreatitis, muscular trauma, and some cancers"

Bounds the specificity of the marker, which is why it is curated as second-tier rather than diagnostic.

PMID:20301438 SUPPORT Other

"obtain electrolytes, BUN, creatinine, liver function tests, CK level, and urine total glucotetrasaccharide (Hex4) level"

GeneReviews includes urinary Hex4 in routine follow-up laboratory monitoring.

📈

Progression

2

Clinically manifest disease

Age: Onset from the first to the seventh decade; median age at diagnosis 38 years, median age at death 56 years in untreated natural-history series

LOPD is insidious and lifelong. The wide onset range is the clinical expression of the residual-activity gradient set by the patient's leaky allele, and there is no spontaneous remission.

Show evidence (2 references)

PMID:33214927 SUPPORT Human Clinical

"Median age at diagnosis is 38 years, while median age at death is 56 years"

Provides the natural-history timing of diagnosis and death in late-onset disease.

PMID:20301438 SUPPORT Other

"LOPD can manifest from the first decade to as late as the seventh decade of life"

GeneReviews states the age-of-onset range that defines the late-onset form.

Ventilator-dependent phase

A substantial minority progress to requiring ventilatory support, usually non-invasive and initially nocturnal.

Show evidence (1 reference)

PMID:33214927 SUPPORT Human Clinical

"of which the majority will receive non-invasive ventilation (NIV)"

Documents that ventilatory support in LOPD is predominantly non-invasive.

📊

Prevalence

2

Global live births

Birth Prevalence 2.4 per 100,000 (1.8–3.0) 1–9 per 100,000 (births)

Pooled global birth prevalence of the late-onset form specifically, from a 2024 systematic review and meta-analysis (2.4 per 100,000 live births, 95% CI 1.8-3.0), higher than the infantile-onset estimate of 1.0 per 100,000.

Show evidence (1 reference)

PMID:39424261 SUPPORT Human Clinical

"Global birth prevalence of late-onset Pompe disease was 2.4 cases (95% CI: 1.8-3.0) per 100,000 live births."

Provides the pooled birth-prevalence estimate specific to late-onset Pompe disease.

Adults presenting to 13 North American academic neuromuscular clinics with proximal weakness, neck weakness, or isolated hyperCKemia (diagnostic yield, not a population rate)

Unknown Unknown

The IPaNeMA study reports a 1% diagnostic yield of LOPD among 906 screened neuromuscular-clinic patients. This is a selected referral cohort, so the figure is a case-finding yield and is deliberately not converted to a population rate.

Show evidence (1 reference)

PMID:36299500 SUPPORT Human Clinical

"GAA enzyme assay results were available on 906 of the 921 participants who consented for the study. LOPD was confirmed in 9 participants (1% prevalence)."

Quantifies the LOPD yield of enzyme screening in a selected neuromuscular referral population.

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Related Datasets

2

Deferoxamine mesylate improves splicing and GAA activity of the common c.-32-13T>G allele in late-onset Pompe disease patient fibroblasts geo:GSE155637

RNA-seq of primary fibroblasts from late-onset Pompe disease patients carrying the c.-32-13T>G allele, treated with deferoxamine or vehicle, testing pharmacological correction of the leaky-splicing defect that defines LOPD.

human BULK RNA SEQ n=6

PMID:33426149

Discovered via `just discover-datasets Late-Onset_Pompe_Disease` as a DIRECT match (the disease and the c.-32-13T>G allele are both named in the dataset title) and manually triaged as on-topic for the leaky-splicing node of this entry. Verified with `just verify-datasets`. Retrieved 2026-08-18.

GAA deficiency in Pompe disease is alleviated by exon inclusion in iPS cell-derived skeletal muscle cells geo:GSE75713

Microarray profiling of iPSC-derived skeletal muscle cells from Pompe disease patients in which GAA deficiency is corrected by splice modulation promoting exon inclusion - the in vitro counterpart of the leaky-splicing mechanism curated here.

human MICROARRAY n=6

Discovered via `just discover-datasets` as a GENE_ONLY candidate and retained after manual relevance triage: the GEO title and summary describe splice-based exon-inclusion correction of GAA deficiency in a patient iPSC skeletal-muscle model, which is the LOPD splicing mechanism. The GEO record carries no linked publication, so no `publication:` is asserted. Verified with `just verify-datasets`. Retrieved 2026-08-18.

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Clinical Trials

4

NCT00158600 PHASE_III COMPLETED

The Late-Onset Treatment Study (LOTS): randomized, double-blind, placebo-controlled trial of alglucosidase alfa in late-onset Pompe disease, the pivotal trial that established enzyme replacement therapy for this form.

Target Phenotypes: Proximal muscle weakness HP:0003701 Respiratory insufficiency due to muscle weakness HP:0002747

Show evidence (1 reference)

clinicaltrials:NCT00158600 SUPPORT Human Clinical

"The overall objective is to evaluate the safety, efficacy, and pharmacokinetics (PK) of alglucosidase alfa treatment in patients with late-onset Pompe disease as compared to placebo."

Registration record for the placebo-controlled trial underpinning enzyme replacement therapy in late-onset disease.

NCT02782741 PHASE_III COMPLETED

COMET: head-to-head phase 3 trial of avalglucosidase alfa versus alglucosidase alfa in treatment-naive late-onset Pompe disease, with upright percent-predicted forced vital capacity as the primary respiratory endpoint.

Target Phenotypes: Respiratory insufficiency due to muscle weakness HP:0002747

Show evidence (1 reference)

clinicaltrials:NCT02782741 SUPPORT Human Clinical

"To determine the effect of avalglucosidase alfa treatment on respiratory muscle strength measured by percent (%) predicted forced vital capacity (FVC) in the upright position, as compared to alglucosidase alfa."

Documents that the head-to-head trial was powered on a respiratory-muscle endpoint, matching the diaphragmatic failure node of this entry.

NCT03729362 PHASE_III COMPLETED

PROPEL: phase 3 trial of cipaglucosidase alfa (ATB200) with the enzyme stabilizer miglustat (AT2221) versus alglucosidase alfa plus placebo in adults with late-onset Pompe disease.

Target Phenotypes: Proximal muscle weakness HP:0003701

Show evidence (1 reference)

clinicaltrials:NCT03729362 SUPPORT Human Clinical

"This is a phase 3 double-blind randomized study to study the efficacy and safety of intravenous ATB200 Co-administered with oral AT2221 in adult subjects with Late Onset Pompe Disease compared with Alglucosidase Alfa/placebo."

Registration record for the trial supporting the cipaglucosidase alfa plus miglustat regimen approved specifically for adults with late-onset disease.

NCT04093349 PHASE_I ACTIVE_NOT_RECRUITING

RESOLUTE: phase 1/2 dose-escalation study of a single intravenous infusion of the AAV gene therapy SPK-3006 in adults with clinically moderate late-onset Pompe disease already receiving enzyme replacement therapy. It targets the therapeutic ceiling of infused enzyme by aiming for sustained endogenous GAA secretion.

Target Phenotypes: Proximal muscle weakness HP:0003701

Show evidence (1 reference)

clinicaltrials:NCT04093349 SUPPORT Human Clinical

"The purpose of this study is to evaluate the safety, tolerability, and efficacy of a single intravenous infusion of SPK-3006 in adults with clinically moderate, late-onset Pompe disease receiving enzyme replacement therapy (ERT)."

Registration record for the gene-therapy trial addressing the incomplete-response node in late-onset disease.

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Animal Models

1

Gaa-/- global knockout mouse (smooth muscle characterization)

The most widely used Pompe mouse, a global Gaa knockout that survives into adulthood without treatment. This entry curates the study that characterized its smooth muscle rather than its skeletal muscle, because that is what bears on the extra-muscular arms of LOPD. Glycogen, lysosomes and autophagosomes accumulate across aortic, tracheal, esophageal, gastric and bladder smooth muscle, with the gastrointestinal and genitourinary tissues most affected. The model's central limitation for late-onset disease is genetic: a global null has essentially no residual enzyme, whereas LOPD is defined by partial activity from a leaky splice allele, so the mouse is genotypically closer to infantile-onset disease and its tempo cannot be read across.

Species

Mouse

Genotype

Gaa-/- (targeted disruption of exon 6), homozygous null

Background

B6;129

Genes

GAA hgnc:4065

Publication

PMID:33883348

Pathograph links

Lysosomal Glycogen Accumulation in Vascular and Visceral Smooth Muscle recapitulates fidelity: moderate Quantitative glycogen assay, PAS histology and LAMP1/LC3 immunoblotting all show the storage-plus-vacuolar-accumulation lesion in the same smooth-muscle beds implicated by human autopsy.

Limitations: A global null has no residual GAA, whereas LOPD is defined by partial activity from a leaky splice allele, so the model reproduces the lesion but not the late-onset tempo or threshold. Aortic glycogen was the lowest of the tissues measured and did not increase between 6 and 15 months, so the vascular half of this node is the weakest part of the match.

Readouts

Tissue glycogen content in smooth-muscle organs

Enzymatic glycogen quantification of aorta, trachea, esophagus, stomach and bladder in 6-month-old Gaa-/- versus wild-type mice, normalized to protein.

Direction: INCREASED

Interpretation: Direct measurement of the storage lesion this node asserts, in the smooth muscle beds relevant to the vascular and visceral arms of LOPD.

Show evidence (1 reference)

PMID:33883348 SUPPORT Model Organism

"Increased levels of glycogen were present in smooth muscle cells of the aorta, trachea, esophagus, stomach, and bladder of Gaa-/- mice, compared to wild type mice."

Reports the glycogen measurement behind this readout.

LAMP1 abundance in smooth-muscle organs

Western blot quantification of the lysosomal membrane protein LAMP1, normalized to loading control, as a proxy for lysosomal expansion.

Direction: INCREASED

Interpretation: Lysosomal expansion is the cellular consequence of the glycogen load and grounds the glycogen-distended lysosome annotation on this node.

Show evidence (1 reference)

PMID:33883348 SUPPORT Model Organism

"In the aorta, esophagus, stomach, and bladder, significantly higher levels of LAMP1 are present in Gaa-/- mice, compared to WT."

Reports the LAMP1 immunoblot measurement behind this readout.

Show evidence (1 reference)

PMID:33883348 SUPPORT Model Organism

"we show that GAA deficiency results in subsequent pathology in smooth muscle cells, which may lead to life-threatening complications if not properly treated"

Supports treating this model as informative for the smooth-muscle storage node, which is the claim this link makes.

Dilative Arteriopathy of the Aorta and Intracranial Arteries fails to recapitulate fidelity: low The aorta accumulated the least glycogen of any smooth-muscle tissue measured and did not accumulate more between 6 and 15 months, and the authors state that this does not support the glycogen-to-wall-weakness hypothesis. The only aortic change seen was tunica media remodeling at 15 months. Note the study assayed glycogen and wall histology; it did not report vessel-calibre measurements, so what is recorded here is failure to reproduce the storage-driven wall lesion rather than a measured absence of dilatation.

Limitations: This is a negative result about the aorta specifically, in a model whose lifespan (6-9 months untreated, examined to 15 months) is far shorter than the decades over which human aortic dilatation develops, so failure to recapitulate may reflect insufficient time rather than a wrong mechanism. It is recorded because it is the main reason the human arteriopathy node is marked PROVISIONAL, not as a refutation of the mechanism.

Readouts

Aortic PAS-positive glycogen deposits at 6 and 15 months

Periodic acid-Schiff histology of aortic sections in Gaa-/- mice at two ages, scored for glycogen deposit number and size.

Direction: UNCHANGED

Interpretation: Aortic glycogen did not increase with age, which is why the authors declined to attribute aortic wall weakness to glycogen accumulation in this model.

Show evidence (1 reference)

PMID:33883348 SUPPORT Model Organism

"there is not an increase in either the number or size of glycogen deposits in the aorta at this age"

Reports the negative aortic histology result at 15 months that grounds this readout.

Show evidence (1 reference)

PMID:33883348 SUPPORT Model Organism

"the limited PAS+ present at both 6 and 15 months in the aorta of Gaa-/- mice does not corroborate our hypothesis that glycogen accumulation is responsible for aortic wall weakness"

The authors' own statement that the aortic findings in this model do not support glycogen accumulation as the cause of aortic wall weakness. It supports the claim this link makes - that the model fails to recapitulate the human arteriopathy.

Show evidence (1 reference)

PMID:33883348 SUPPORT Model Organism

"In conclusion, GAA deficiency results in significant glycogen accumulation in the airway, vascular, GI and GU smooth muscle."

Establishes this model as informative for the smooth-muscle compartment of GAA deficiency, which is the arm of LOPD it is cited for here.

{ }

Source YAML

click to show

name: Late-Onset Pompe Disease
creation_date: '2026-08-18T00:00:00Z'
category: Mendelian
description: >
  Late-onset Pompe disease (LOPD; glycogen storage disease due to acid maltase
  deficiency, late-onset) is the attenuated end of the acid alpha-glucosidase
  (GAA) deficiency spectrum. It is defined clinically as Pompe disease presenting
  after age 12 months, or before 12 months in the absence of cardiomyopathy, and
  can declare itself anywhere from the first to the seventh decade of life. The
  mechanistic distinction from infantile-onset disease is quantitative rather than
  categorical: LOPD genotypes retain partial GAA activity, most commonly through
  the "leaky" intron-1 splice variant c.-32-13T>G, which weakens the exon 2 splice
  acceptor but still permits a low level of correctly spliced transcript. Residual
  enzyme keeps lysosomal glycogen turnover above the threshold at which
  cardiomyocytes decompensate, so the heart is largely spared, while slowly
  progressive storage in skeletal and respiratory muscle produces a limb-girdle
  myopathy with disproportionate diaphragmatic involvement. Respiratory failure,
  not cardiac failure, is the dominant cause of death in untreated LOPD. Enzyme
  replacement therapy slows but does not arrest the myopathy, in part because
  autophagic buildup in skeletal myofibers mistargets endocytosed recombinant
  enzyme away from the lysosome. Newborn screening now identifies pre-symptomatic
  LOPD, creating a management problem the infantile form does not have.
disease_term:
  preferred_term: Late-onset Pompe disease
  term:
    id: MONDO:0018485
    label: glycogen storage disease due to acid maltase deficiency, late-onset
synonyms:
- LOPD
- Pompe disease, late-onset
- Glycogen storage disease type II, late-onset
- Acid maltase deficiency, late-onset
- Adult-onset acid maltase deficiency
parents:
- Pompe Disease
- Glycogen Storage Disease
- Lysosomal Storage Disease
classifications:
  harrisons_chapter:
  - classification_value: ENDOCRINOLOGY_METABOLISM
    evidence:
    - reference: PMID:33214927
      reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Late-onset Pompe disease (LOPD) is a rare autosomal recessive glycogen storage disease that results in accumulation of glycogen in muscle cells causing muscular weakness."
      explanation: Places LOPD among inherited metabolic (glycogen storage) disorders for chapter assignment.
  lysosomal_storage_category:
    classification_value: disorder of glycogen metabolism
    evidence:
    - reference: PMID:33214927
      reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Late-onset Pompe disease (LOPD) is a rare autosomal recessive glycogen storage disease that results in accumulation of glycogen in muscle cells causing muscular weakness."
      explanation: Supports classifying LOPD as a lysosomal disorder of glycogen metabolism.
definitions:
- name: GeneReviews onset/cardiomyopathy case definition
  definition_type: CASE_DEFINITION
  derivation_basis: ESTABLISHED_CRITERIA
  description: >
    GeneReviews partitions Pompe disease by age of onset together with the presence
    or absence of cardiomyopathy. LOPD is defined as onset after age 12 months, or
    onset before 12 months without cardiomyopathy. The cardiomyopathy criterion, not
    age alone, is what separates the two forms at the boundary.
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "late-onset Pompe disease (LOPD) (i.e., individuals with onset before age 12 months without cardiomyopathy, and all individuals with onset after age 12 months)"
    explanation: States the GeneReviews case definition of LOPD used by this entry.
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0009290
      label: glycogen storage disease II
    mapping_predicate: skos:broadMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0018485 is a child of MONDO:0009290. The umbrella Pompe disease
      entity is curated separately as kb/disorders/Pompe_Disease.yaml; this
      broadMatch records the parent relationship without claiming equivalence,
      and deliberately does not retire MONDO:0009290 from the curation queue.
inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >
    LOPD is autosomal recessive. The characteristic LOPD genotype is compound
    heterozygosity for the leaky c.-32-13T>G intron-1 splice variant on one allele
    and a fully deleterious GAA variant on the other, so that the leaky allele sets
    the residual enzyme activity and therefore the phenotype.
  evidence:
  - reference: PMID:36299500
    reference_title: "Investigating Late-Onset Pompe Prevalence in Neuromuscular Medicine Academic Practices: The IPaNeMA Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Of the definite LOPD participants, 8 (89%) were Caucasian and were heterozygous for the common leaky (IVS1) splice site mutation in the GAA gene (c -32-13T>G), with a second mutation that was previously confirmed to be pathogenic."
    explanation: Documents the compound-heterozygous leaky-allele-plus-null genotype that characterizes LOPD.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier"
    explanation: >-
      GeneReviews states the sibling recurrence risks that follow from biallelic GAA
      inheritance. This is the counselling figure the block exists to record, and it is
      quantitative in a way the IPaNeMA genotype observation is not, so both are kept.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Once the GAA pathogenic variants have been identified in an affected family member, molecular genetic carrier testing for at-risk relatives and prenatal/preimplantation genetic testing are possible."
    explanation: >-
      Establishes that identifying the proband's biallelic GAA variants is what makes
      carrier and prenatal testing available to the family.
prevalence:
- population: Global live births
  measure_type: BIRTH_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 2.4
  rate_low: 1.8
  rate_high: 3.0
  notes: >-
    Pooled global birth prevalence of the late-onset form specifically, from a
    2024 systematic review and meta-analysis (2.4 per 100,000 live births, 95% CI
    1.8-3.0), higher than the infantile-onset estimate of 1.0 per 100,000.
  evidence:
  - reference: PMID:39424261
    reference_title: "Global birth prevalence of Pompe disease: A systematic review and meta-analysis"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Global birth prevalence of late-onset Pompe disease was 2.4 cases (95% CI: 1.8-3.0) per 100,000 live births."
    explanation: Provides the pooled birth-prevalence estimate specific to late-onset Pompe disease.
- population: >-
    Adults presenting to 13 North American academic neuromuscular clinics with
    proximal weakness, neck weakness, or isolated hyperCKemia (diagnostic yield,
    not a population rate)
  measure_type: UNKNOWN
  prevalence_class: UNKNOWN
  notes: >-
    The IPaNeMA study reports a 1% diagnostic yield of LOPD among 906 screened
    neuromuscular-clinic patients. This is a selected referral cohort, so the
    figure is a case-finding yield and is deliberately not converted to a
    population rate.
  evidence:
  - reference: PMID:36299500
    reference_title: "Investigating Late-Onset Pompe Prevalence in Neuromuscular Medicine Academic Practices: The IPaNeMA Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "GAA enzyme assay results were available on 906 of the 921 participants who consented for the study. LOPD was confirmed in 9 participants (1% prevalence)."
    explanation: Quantifies the LOPD yield of enzyme screening in a selected neuromuscular referral population.
progression:
- phase: Clinically manifest disease
  age_range: >-
    Onset from the first to the seventh decade; median age at diagnosis 38 years,
    median age at death 56 years in untreated natural-history series
  notes: >-
    LOPD is insidious and lifelong. The wide onset range is the clinical expression
    of the residual-activity gradient set by the patient's leaky allele, and there
    is no spontaneous remission.
  evidence:
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Median age at diagnosis is 38 years, while median age at death is 56 years"
    explanation: Provides the natural-history timing of diagnosis and death in late-onset disease.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "LOPD can manifest from the first decade to as late as the seventh decade of life"
    explanation: GeneReviews states the age-of-onset range that defines the late-onset form.
- phase: Ventilator-dependent phase
  notes: >-
    A substantial minority progress to requiring ventilatory support, usually
    non-invasive and initially nocturnal.
  evidence:
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "of which the majority will receive non-invasive ventilation (NIV)"
    explanation: Documents that ventilatory support in LOPD is predominantly non-invasive.
pathophysiology:
- name: Leaky GAA Splicing and Partial Residual Enzyme Activity
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >
    The LOPD-defining lesion is partial rather than complete loss of acid
    alpha-glucosidase. The commonest LOPD allele, c.-32-13T>G (IVS1), sits in
    intron 1 and weakens the splice acceptor of GAA exon 2. Most transcripts from
    that allele are aberrantly spliced (partial or complete exon 2 skipping), but a
    low level of correctly spliced, fully functional transcript escapes. That
    residual activity - conventionally quoted as roughly 1-30% of normal, though see
    the caveat in the biochemical section and in notes - is what shifts the phenotype
    from infantile to late onset. In the great majority of LOPD patients the leaky
    allele is carried in trans with a second, more deleterious pathogenic variant, so
    the leaky allele is the one setting how much enzyme the patient makes.
  gene:
    preferred_term: GAA
    description: >-
      Acid alpha-glucosidase, the lysosomal enzyme that hydrolyzes alpha-1,4 and
      alpha-1,6 glycosidic bonds of glycogen.
    modifier: DECREASED
    term:
      id: hgnc:4065
      label: GAA
  molecular_functions:
  - preferred_term: acid alpha-glucosidase activity
    modifier: DECREASED
    term:
      id: GO:0004558
      label: alpha-1,4-glucosidase activity
  biological_processes:
  - preferred_term: GAA pre-mRNA splicing at the exon 2 acceptor
    modifier: DECREASED
    term:
      id: GO:0000398
      label: mRNA splicing, via spliceosome
  genetic_context:
    gene:
      preferred_term: GAA
      term:
        id: hgnc:4065
        label: GAA
    allele_type: SNV
    variant_origin: GERMLINE
    zygosity: COMPOUND_HETEROZYGOUS
    functional_impact_category: PARTIAL_LOSS_OF_FUNCTION
    description: >-
      Compound heterozygosity for the leaky c.-32-13T>G intron-1 splice variant and
      a second, more deleterious pathogenic GAA variant.
  evidence:
  - reference: PMID:28624228
    reference_title: "Antisense Oligonucleotides Promote Exon Inclusion and Correct the Common c.-32-13T>G GAA Splicing Variant in Pompe Disease."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "which weakens the splice acceptor of GAA exon 2 and induces partial and complete exon 2 skipping. It also allows a low level of leaky wild-type splicing, leading to a childhood/adult phenotype."
    explanation: Establishes the leaky-splicing mechanism by which c.-32-13T>G yields residual enzyme and a late-onset phenotype.
  - reference: PMID:33972680
    reference_title: "Phenotypic implications of pathogenic variant types in Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presence of at least one splice site variant (c.546 G > C/p.T182 = , c.1076-22 T > G, c.2646 + 2 T > A, and the classic c.-32-13T > G variant) was associated with LOPD, while the presence of non-splice site variants on both alleles was associated with IOPD."
    explanation: Human genotype-phenotype data tying retention of a leaky splice allele to the late-onset phenotype.
  downstream:
  - target: Attenuated Lysosomal Glycogen Accumulation in Skeletal and Respiratory Muscle
    causal_link_type: DIRECT
    description: >-
      Residual GAA activity slows, but does not prevent, lysosomal glycogen
      accumulation, producing a decades-long rather than months-long storage course.
    evidence:
    - reference: PMID:28624228
      reference_title: "Antisense Oligonucleotides Promote Exon Inclusion and Correct the Common c.-32-13T>G GAA Splicing Variant in Pompe Disease."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "It also allows a low level of leaky wild-type splicing, leading to a childhood/adult phenotype."
      explanation: Links the residual enzyme produced by leaky splicing to the attenuated childhood/adult disease course.
  - target: Relative Cardiac Sparing
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Residual enzyme activity is sufficient to keep cardiomyocyte glycogen turnover
      below the threshold that produces infantile hypertrophic cardiomyopathy. The
      quantitative threshold itself has not been measured in human myocardium, so
      the link is recorded with unknown intermediates.
    evidence:
    - reference: PMID:33214927
      reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Late-onset Pompe disease (LOPD), caused by reduced rather than absent GAA, presents with a milder form, any time from 1 year to adulthood."
      explanation: Attributes the milder late-onset phenotype specifically to reduced rather than absent enzyme.
  - target: Lysosomal Glycogen Accumulation in Vascular and Visceral Smooth Muscle
    causal_link_type: DIRECT
    description: >-
      The same partial enzyme deficit is exhausted in smooth muscle as well as in
      skeletal muscle, opening the extra-muscular arm of the disease.
    evidence:
    - reference: PMID:21605996
      reference_title: "Expanding the clinical spectrum of late-onset Pompe disease: dilated arteriopathy involving the thoracic aorta, a novel vascular phenotype uncovered."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Evidence of increased aortic stiffness in some patients and smooth muscle involvement in LOPD raises the possibility of aortic involvement."
      explanation: >-
        States that smooth muscle is involved in LOPD, which is the step from the
        enzyme deficit to the smooth-muscle storage node.
- name: Attenuated Lysosomal Glycogen Accumulation in Skeletal and Respiratory Muscle
  biological_scale: CELLULAR
  conforms_to: "lysosomal_substrate_accumulation#Lysosomal Substrate Accumulation"
  mechanism_confidence: ESTABLISHED
  description: >
    Partial GAA activity permits slow lysosomal glycogen accumulation that is
    concentrated in skeletal muscle, including the respiratory muscles, rather than
    the generalized multisystem storage of infantile disease. The tissue selectivity
    reflects the very high glycogen flux of muscle relative to its residual
    degradative capacity, so muscle is the first compartment in which the reduced
    enzyme reserve is exhausted.
  cell_types:
  - preferred_term: Skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: Lysosomal glycogen catabolism
    modifier: DECREASED
    term:
      id: GO:0005980
      label: glycogen catabolic process
  cellular_components:
  - preferred_term: lysosome
    term:
      id: GO:0005764
      label: lysosome
  chemical_entities:
  - preferred_term: glycogen
    modifier: INCREASED
    term:
      id: CHEBI:28087
      label: glycogen
  locations:
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  evidence:
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Late-onset Pompe disease (LOPD) is a rare autosomal recessive glycogen storage disease that results in accumulation of glycogen in muscle cells causing muscular weakness."
    explanation: Anchors muscle-cell glycogen accumulation as the storage lesion that produces LOPD weakness.
  downstream:
  - target: Autophagic Mistargeting of Endocytosed Recombinant Enzyme
    causal_link_type: DIRECT
    description: >-
      Glycogen-engorged lysosomes disturb autophagic flux in myofibers.
    evidence:
    - reference: PMID:17008131
      reference_title: "Autophagy and mistargeting of therapeutic enzyme in skeletal muscle in Pompe disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Our findings here demonstrate a progressive age-dependent autophagic buildup in addition to enlargement of glycogen-filled lysosomes in multiple muscle groups in the KO."
      explanation: Shows autophagic buildup accompanying glycogen-filled lysosomes in multiple muscle groups.
  - target: Pre-Vacuolar Metabolic Reprogramming of Myonuclei
    causal_link_type: DIRECT
    description: >-
      Storage perturbs myonuclear metabolic gene expression before any vacuole is
      visible on histology.
    evidence:
    - reference: PMID:39045638
      reference_title: "Decoding the muscle transcriptome of patients with late-onset Pompe disease reveals markers of disease progression."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Additionally, we detected upregulation of autophagy genes and downregulation of the genes involved in ribosomal and mitochondrial function leading to defective oxidative phosphorylation."
      explanation: Links the storage lesion to the transcriptional metabolic derangement of LOPD myonuclei.
  - target: Progressive Limb-Girdle and Axial Myofiber Degeneration
    causal_link_type: DIRECT
    description: >-
      Cumulative storage and autophagic damage destroy contractile architecture in
      proximal lower-limb and paraspinal muscle.
    evidence:
    - reference: PMID:33214927
      reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "It causes a progressive proximal myopathy, accompanied by respiratory muscle weakness, which can lead to ventilatory failure."
      explanation: Connects muscle-cell glycogen accumulation to the progressive proximal myopathy of LOPD.
  - target: Phrenic Motor Unit Failure
    causal_link_type: DIRECT
    description: >-
      Storage in the diaphragm undermines the principal muscle of inspiration.
    evidence:
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Respiratory insufficiency progressing to respiratory failure is a significant cause of morbidity and mortality."
      explanation: GeneReviews records respiratory muscle involvement as a principal consequence of late-onset storage disease.
- name: Relative Cardiac Sparing
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  description: >
    Absence of hypertrophic cardiomyopathy is a defining feature of LOPD and part of
    its formal case definition, not merely a statistical tendency. Residual GAA
    activity is sufficient to keep cardiomyocyte glycogen storage subclinical, so
    the cardiorespiratory collapse that kills untreated infants does not occur; the
    respiratory system, not the heart, becomes the life-limiting organ. This node is
    curated as a mechanistic contrast rather than as a claim that the myocardium is
    entirely normal - adult arteriopathy and rare conduction findings are described
    in the umbrella Pompe disease entry.
  cell_types:
  - preferred_term: Cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "late-onset Pompe disease (LOPD) (i.e., individuals with onset before age 12 months without cardiomyopathy, and all individuals with onset after age 12 months)"
    explanation: GeneReviews makes absence of cardiomyopathy definitional for LOPD.
- name: Autophagic Mistargeting of Endocytosed Recombinant Enzyme
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >
    Skeletal myofibers in Pompe disease develop large autophagic areas alongside
    glycogen-filled lysosomes. These areas trap endocytosed recombinant human GAA in
    a partially processed form so that it never reaches the lysosome, which is a
    mechanistic explanation for why enzyme replacement therapy is far more effective
    in cardiac than in skeletal muscle and why it slows rather than arrests the LOPD
    myopathy. Because LOPD is a decades-long disease treated for decades, this
    therapeutic ceiling is a defining clinical problem of the late-onset form.
  cell_types:
  - preferred_term: Skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: autophagy
    modifier: INCREASED
    term:
      id: GO:0006914
      label: autophagy
  - preferred_term: endosomal transport of endocytosed enzyme
    modifier: DECREASED
    term:
      id: GO:0016197
      label: endosomal transport
  evidence:
  - reference: PMID:17008131
    reference_title: "Autophagy and mistargeting of therapeutic enzyme in skeletal muscle in Pompe disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Confocal microscopy of live single muscle fibers exposed to fluorescently labeled rhGAA indicates that a significant portion of the endocytosed enzyme in the KO was trapped as a partially processed form in the autophagic areas instead of reaching its target--the lysosomes."
    explanation: Demonstrates autophagic mistargeting of therapeutic enzyme in skeletal muscle fibers.
  - reference: PMID:17008131
    reference_title: "Autophagy and mistargeting of therapeutic enzyme in skeletal muscle in Pompe disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The therapy, which relies on receptor-mediated endocytosis of recombinant human GAA (rhGAA), appears to be effective in cardiac muscle, but less so in skeletal muscle."
    explanation: States the cardiac-versus-skeletal-muscle discrepancy in ERT response that this node explains.
  - reference: PMID:24383498
    reference_title: "The value of muscle biopsies in Pompe disease: identifying lipofuscin inclusions in juvenile- and adult-onset patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "numerous lysosomes and autolysosomes loaded with lipofuscin appear to be a hallmark of LOPD skeletal muscle"
    explanation: Human LOPD muscle biopsies confirm an autophagic-lysosomal lesion in the late-onset form itself, not only in the knockout mouse.
  - reference: PMID:38785980
    reference_title: Failure of Autophagy in Pompe Disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "As in mouse models, autophagic buildup, filled with potentially toxic ubiquitinated protein aggregates, glycogen particles, autophagy substrate p62/SQSTM1, and lipofuscin (an indicator of oxidative damage and mitochondrial dysfunction), is a prominent feature in muscle from patients with the disease; in some fibers, particularly from biopsies of adult patients, the enlarged lysosomes in the surrounding buildup-free areas look like innocent bystanders compared to the autophagic pathology"
    explanation: >-
      States that the autophagic buildup, not the enlarged lysosome, is the dominant
      lesion in patient muscle, and specifically in biopsies from adult patients - which
      is the late-onset population this entry covers. It also names the p62/SQSTM1 and
      lipofuscin content of the buildup.
  - reference: PMID:38785980
    reference_title: Failure of Autophagy in Pompe Disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "However, a major mechanism underlying autophagic buildup is an impairment of autophagosomal–lysosomal fusion, a condition known as autophagic block."
    explanation: >-
      Supplies the mechanism by which the buildup forms and therefore why endocytosed
      enzyme delivered into that compartment does not reach a functional lysosome.
  - reference: PMID:35682977
    reference_title: "Isogenic GAA-KO Murine Muscle Cell Lines Mimicking Severe Pompe Mutations as Preclinical Models for the Screening of Potential Gene Therapy Strategies."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "All of the generated GAA-KO cells lacked GAA activity and presented an increased autophagy and increased glycogen content by means of myotube differentiation as well as the downregulation of mannose 6-phosphate receptors (CI-MPRs)"
    explanation: >-
      Isogenic GAA-null myotubes reproduce both the increased autophagy of this node and
      downregulation of the CI-MPR receptor that recombinant enzyme depends on for uptake,
      a second route by which delivered enzyme fails to reach the lysosome.
  downstream:
  - target: Incomplete Response to Enzyme Replacement Therapy
    causal_link_type: DIRECT
    description: >-
      Enzyme that never reaches the lysosome cannot clear stored glycogen.
    evidence:
    - reference: PMID:17008131
      reference_title: "Autophagy and mistargeting of therapeutic enzyme in skeletal muscle in Pompe disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "These findings may explain why ERT often falls short of reversing the disease process and point toward new avenues for the development of pharmacological intervention."
      explanation: The authors propose autophagic mistargeting as the explanation for the incomplete response to enzyme replacement therapy.
- name: Pre-Vacuolar Metabolic Reprogramming of Myonuclei
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  description: >
    Single-nucleus RNA sequencing combined with spatial transcriptomics of LOPD
    muscle biopsies shows that myofibers are transcriptionally abnormal before they
    are histologically abnormal. Fibers that are not yet vacuolated already show
    reduced glycolytic gene expression with increased lipid and amino-acid
    metabolism, upregulated autophagy genes, and downregulated ribosomal and
    mitochondrial programmes producing defective oxidative phosphorylation.
    Inflammation, apoptosis, and regeneration signatures appear only once
    vacuolation is established. This staging matters for LOPD specifically, because
    it identifies an early, possibly still-tractable metabolic derangement that
    precedes the structural damage enzyme replacement therapy cannot undo. The
    study reports only a "tendency" for therapy to restore the dysregulated
    metabolism, so reversibility is a hypothesis this node raises rather than a
    result it records.
  cell_types:
  - preferred_term: Skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  - preferred_term: Slow (type I) muscle fiber
    term:
      id: CL:0000189
      label: slow muscle cell
  - preferred_term: Muscle-infiltrating macrophage
    term:
      id: CL:0000235
      label: macrophage
  biological_processes:
  - preferred_term: glycolytic process
    modifier: DECREASED
    term:
      id: GO:0006096
      label: glycolytic process
  - preferred_term: lipid metabolic process
    modifier: INCREASED
    term:
      id: GO:0006629
      label: lipid metabolic process
  - preferred_term: oxidative phosphorylation
    modifier: DECREASED
    term:
      id: GO:0006119
      label: oxidative phosphorylation
  evidence:
  - reference: PMID:39045638
    reference_title: "Decoding the muscle transcriptome of patients with late-onset Pompe disease reveals markers of disease progression."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The expression of the genes involved in glycolysis was reduced, whereas the expression of the genes involved in the metabolism of lipids and amino acids was increased in non-vacuolated fibres, indicating early metabolic abnormalities."
    explanation: Demonstrates metabolic reprogramming in histologically unaffected LOPD myofibers, before vacuolation.
  - reference: PMID:39045638
    reference_title: "Decoding the muscle transcriptome of patients with late-onset Pompe disease reveals markers of disease progression."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Upregulation of genes associated with inflammation, apoptosis and muscle regeneration was observed only in vacuolated fibres."
    explanation: Separates the later inflammatory/degenerative programme from the earlier metabolic one, which is the staging claim of this node.
  - reference: PMID:39045638
    reference_title: "Decoding the muscle transcriptome of patients with late-onset Pompe disease reveals markers of disease progression."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, enzyme replacement therapy (the only available therapy for the disease) showed a tendency to restore dysregulated metabolism, particularly within slow fibres."
    explanation: Bounds the reversibility claim - the authors report a tendency, not a demonstrated restoration, which is why this node is PROVISIONAL.
  - reference: PMID:33799647
    reference_title: "Muscle Proteomic Profile before and after Enzyme Replacement Therapy in Late-Onset Pompe Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Defects in oxidative metabolism, muscle contractile protein regulation, cytoskeletal rearrangement, and membrane reorganization persisted."
    explanation: >-
      Independent corroboration by a different modality - muscle proteomics rather than
      single-nucleus transcriptomics - that the oxidative-metabolism defect of this node
      is real and survives a year of enzyme replacement therapy.
  - reference: PMID:33799647
    reference_title: "Muscle Proteomic Profile before and after Enzyme Replacement Therapy in Late-Onset Pompe Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Metabolic changes, ER stress and UPR (unfolded protein response) contribute to muscle proteostasis dysregulation with active membrane remodeling (high levels of LC3BII/LC3BI) and accumulation of p62, suggesting imbalance in the autophagic process."
    explanation: >-
      Supplies the p62 and LC3 protein-level readout of the autophagic imbalance that the
      transcriptomic study infers from autophagy gene upregulation.
  downstream:
  - target: Progressive Limb-Girdle and Axial Myofiber Degeneration
    causal_link_type: DIRECT
    description: >-
      Metabolically compromised fibers progress to vacuolation, inflammation,
      apoptosis, and replacement by fat.
    evidence:
    - reference: PMID:39045638
      reference_title: "Decoding the muscle transcriptome of patients with late-onset Pompe disease reveals markers of disease progression."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We observed an increase in the proportion of slow and regenerative muscle fibres and macrophages in LOPD muscles."
      explanation: Documents the shift toward regenerative fibers and macrophage infiltration that accompanies progression to overt degeneration.
- name: Progressive Limb-Girdle and Axial Myofiber Degeneration
  biological_scale: TISSUE
  mechanism_confidence: ESTABLISHED
  description: >
    Chronic storage and autophagic injury destroy myofibers, which are replaced by
    fat. The distribution is characteristically limb-girdle and axial, with early
    involvement of the psoas and paraspinal muscles; quantitative fat fraction on
    lumbar MRI correlates with strength, walking distance, stair climbing and supine
    spirometry, and continues to rise during enzyme replacement therapy.
  cell_types:
  - preferred_term: Skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  locations:
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  evidence:
  - reference: PMID:29315315
    reference_title: "Quantification of intramuscular fat in patients with late-onset Pompe disease by conventional magnetic resonance imaging for the long-term follow-up of enzyme replacement therapy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A significant increase in the MR-derived fat fraction of the psoas muscle was found between baseline and follow-up 1 (P = 0.016), as was a significant decrease in the performance on the 6-minute walk test (P = 0.006) and 4-step stair climb test (P = 0.034)"
    explanation: Shows progressive fatty replacement of proximal/axial muscle with concurrent functional decline during ERT.
  downstream:
  - target: Progressive proximal muscle weakness
    causal_link_type: DIRECT
    description: >-
      Loss of contractile tissue in limb-girdle and axial muscle produces the
      characteristic LOPD weakness pattern.
    evidence:
    - reference: PMID:29315315
      reference_title: "Quantification of intramuscular fat in patients with late-onset Pompe disease by conventional magnetic resonance imaging for the long-term follow-up of enzyme replacement therapy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Measurements derived from the quantitative method correlated well with Medical Research Council scores of muscle strength, with moderate correlations found for the 6-minute walk test, the 4-step stair climb test, and spirometry in the supine position."
      explanation: Fatty replacement of proximal and paraspinal muscle correlates with measured strength and function, linking the tissue lesion to the weakness phenotype.
- name: Phrenic Motor Unit Failure
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  description: >
    Diaphragm weakness in LOPD is disproportionate to limb weakness and is the
    proximate cause of nocturnal hypoventilation and ultimately of ventilatory
    failure. Neurophysiological study of treated LOPD patients found that those with
    respiratory failure had absent or severely reduced phrenic nerve compound muscle
    action potentials and diaphragm EMG showing neurogenic as well as myopathic
    changes, implicating spinal phrenic motor neuron dysfunction alongside myofiber
    disease. Because intravenous recombinant enzyme does not cross the blood-brain
    barrier, a motor neuron contribution would explain residual respiratory decline
    on enzyme replacement therapy. The motor neuron arm is curated as PROVISIONAL:
    the supporting series is small (eight patients) and calls for confirmation.
  cell_types:
  - preferred_term: Skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  - preferred_term: Phrenic motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  locations:
  - preferred_term: diaphragm
    term:
      id: UBERON:0001103
      label: diaphragm
  evidence:
  - reference: PMID:38653115
    reference_title: "Diaphragm weakness in late-onset Pompe disease: A complex interplay between lower motor neuron and muscle fibre degeneration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Diaphragm needle EMG revealed both myopathic and neurogenic changes in 3 (60%) and myopathic potentials in 1 patient."
    explanation: Provides the electrophysiological observation of combined neurogenic and myopathic diaphragm involvement.
  - reference: PMID:38653115
    reference_title: "Diaphragm weakness in late-onset Pompe disease: A complex interplay between lower motor neuron and muscle fibre degeneration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our study provide new insights regarding respiratory mechanisms in LOPD, suggesting a contribution of spinal phrenic motor neuron dysfunction for diaphragm weakness."
    explanation: The authors themselves frame the phrenic motor neuron contribution as a suggestion requiring confirmation, which is why this node is PROVISIONAL.
  - reference: PMID:42074341
    reference_title: "Pompe Disease: Pathogenesis, Molecular Mechanisms, Neurological Aspects, Diagnostics and Modern Therapeutic Approaches."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "limited penetration across the blood-brain barrier (BBB), resulting in persistent central nervous system involvement, and immune responses against the infused enzyme"
    explanation: >-
      Supports the pharmacological half of this node's argument - intravenous recombinant
      enzyme does not reach the central nervous system, so a phrenic motor neuron
      contribution would not be corrected by enzyme replacement therapy.
  downstream:
  - target: Nocturnal hypoventilation and sleep-disordered breathing
    causal_link_type: DIRECT
    description: >-
      Inspiratory muscle failure is expressed first during sleep, when accessory
      muscle recruitment falls and ventilation depends on the diaphragm.
    evidence:
    - reference: PMID:33214927
      reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Diaphragm weakness leads to nocturnal hypoventilation, which can result in sleep disruption."
      explanation: States the diaphragm-to-nocturnal-hypoventilation causal step directly.
  - target: Respiratory insufficiency due to muscle weakness
    causal_link_type: DIRECT
    description: >-
      Progressive diaphragm failure produces daytime hypercapnic respiratory failure,
      the leading cause of death in untreated LOPD.
    evidence:
    - reference: PMID:33214927
      reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In untreated LOPD, the most common cause of death is respiratory failure."
      explanation: Establishes ventilatory failure as the terminal consequence of respiratory muscle weakness in untreated LOPD.
- name: Incomplete Response to Enzyme Replacement Therapy
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  description: >
    Enzyme replacement therapy changes the trajectory of LOPD but does not normalize
    it. Walking distance and forced vital capacity improve modestly relative to
    placebo in the short term, yet muscle fat fraction continues to increase, some
    patients still progress to ventilatory support, and the effect on
    sleep-disordered breathing is undocumented. This residual disease burden is a
    mechanistic consequence of the autophagic mistargeting node and, possibly, of the
    motor neuron arm of diaphragm weakness, which intravenous enzyme cannot reach.
  evidence:
  - reference: PMID:38653115
    reference_title: "Diaphragm weakness in late-onset Pompe disease: A complex interplay between lower motor neuron and muscle fibre degeneration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Late-onset Pompe disease (LOPD) patients may still need ventilation support at some point of their disease course, despite regular recombinant human alglucosidase alfa treatment."
    explanation: Documents residual progression to ventilatory support despite ongoing enzyme replacement therapy.
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Whilst disease-modifying enzyme replacement therapy (ERT) delays progression of locomotor dysfunction and prolongs life, its effect on respiratory function and SDB remains unclear."
    explanation: States that the respiratory benefit of ERT in LOPD is not established, bounding the claim of therapeutic benefit.
  - reference: PMID:33799647
    reference_title: "Muscle Proteomic Profile before and after Enzyme Replacement Therapy in Late-Onset Pompe Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "178 proteins were changed in abundance in LOPD patients, 47 of them recovered normal level after ERT. Defects in oxidative metabolism, muscle contractile protein regulation, cytoskeletal rearrangement, and membrane reorganization persisted."
    explanation: Quantifies the molecular residue of disease in LOPD muscle after a year of enzyme replacement therapy - roughly a quarter of the altered proteome normalizes.
- name: Lysosomal Glycogen Accumulation in Vascular and Visceral Smooth Muscle
  biological_scale: CELLULAR
  conforms_to: "lysosomal_substrate_accumulation#Lysosomal Substrate Accumulation"
  mechanism_confidence: ESTABLISHED
  description: >
    Residual GAA activity is exhausted in smooth muscle as well as in skeletal
    muscle. Autopsy of a woman with LOPD demonstrated lysosomal glycogen inside
    vascular smooth muscle cells by transmission electron microscopy, alongside
    involvement of the bladder, intestine, and esophagus. This is a distinct
    cellular compartment from the skeletal and respiratory myofiber storage that
    dominates the LOPD clinical picture, and it is the substrate for the disease's
    two extra-muscular arms: the dilative arteriopathy of large arteries, and the
    gastrointestinal and genitourinary symptoms that patients report independently
    of limb weakness. Smooth-muscle storage is the reason LOPD is a systemic
    lysosomal disease rather than a pure myopathy.
  cell_types:
  - preferred_term: vascular smooth muscle cell
    term:
      id: CL:0000359
      label: vascular associated smooth muscle cell
  - preferred_term: smooth muscle cell of bladder
    term:
      id: CL:0002597
      label: smooth muscle cell of bladder
  - preferred_term: smooth muscle cell of the esophagus
    term:
      id: CL:0002599
      label: smooth muscle cell of the esophagus
  - preferred_term: intestinal smooth muscle cell
    description: >-
      The segment-agnostic term is chosen over its small- and large-intestine
      children because the cited autopsy names "intestine" without specifying
      segment.
    term:
      id: CL:0002504
      label: enteric smooth muscle cell
  biological_processes:
  - preferred_term: lysosomal glycogen degradation in smooth muscle
    modifier: DECREASED
    term:
      id: GO:0005980
      label: glycogen catabolic process
  cellular_components:
  - preferred_term: glycogen-distended lysosome
    modifier: INCREASED
    term:
      id: GO:0005764
      label: lysosome
  evidence:
  - reference: PMID:22664150
    reference_title: "Autopsy findings in late-onset Pompe disease: a case report and systematic review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Transmission electron microscopy disclosed lysosomal glycogen accumulation within skeletal, cardiac, and vascular smooth muscle cells"
    explanation: >-
      Direct human ultrastructural demonstration that lysosomal glycogen accumulates
      in vascular smooth muscle cells in late-onset Pompe disease, which is what
      makes this a curated node rather than a proposed one.
  - reference: PMID:22664150
    reference_title: "Autopsy findings in late-onset Pompe disease: a case report and systematic review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Organs containing smooth muscle cells (the bladder, intestine, and esophagus) were also affected"
    explanation: >-
      Extends the same storage lesion from vascular to visceral smooth muscle,
      supporting the visceral half of this node.
  - reference: PMID:33883348
    reference_title: "Glycogen accumulation in smooth muscle of a Pompe disease mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Increased levels of glycogen were present in smooth muscle cells of the aorta, trachea, esophagus, stomach, and bladder of Gaa-/- mice, compared to wild type mice."
    explanation: >-
      Independent quantitative confirmation in a GAA-deficient mouse that the storage
      lesion is present across vascular, airway, gastrointestinal and genitourinary
      smooth muscle.
  downstream:
  - target: Dilative Arteriopathy of the Aorta and Intracranial Arteries
    causal_link_type: DIRECT
    description: >-
      Glycogen-laden smooth muscle cells in the tunica media are the proposed
      structural cause of progressive arterial wall remodeling and dilatation.
    evidence:
    - reference: PMID:33386209
      reference_title: "Cardiovascular disease in non-classic Pompe disease: A systematic review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Vascular abnormalities, such as aneurysms and arterial dolichoectasia, likely caused by glycogen accumulation in arterial walls, have been reported in non-classic Pompe patients."
      explanation: >-
        A systematic review attributing the vascular abnormalities of non-classic
        Pompe disease to glycogen accumulation in the arterial wall, which is the
        causal step this edge asserts.
  - target: Gastroesophageal reflux
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Storage in esophageal and gastric smooth muscle is the proposed basis of the
      reflux LOPD patients report; the contractile deficit linking the two has not
      been measured in human tissue.
    evidence:
    - reference: PMID:33883348
      reference_title: "Glycogen accumulation in smooth muscle of a Pompe disease mouse model."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "Many of the symptoms associated with glycogen storage in the GI and GU tracts such as gastroesophageal reflux, abdominal pain, feeding difficulties, and urinary incontinence are often noted as poor quality of life measures"
      explanation: >-
        Draws the causal link from gastrointestinal smooth-muscle glycogen storage to
        reflux. Marked INDIRECT because the storage measurement is in mouse tissue and
        the symptom attribution is an inference to human patients.
    - reference: PMID:20559845
      reference_title: "Abnormalities of cerebral arteries are frequent in patients with late-onset Pompe disease."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: "At 1 year follow-up, enzyme replacement therapy did not modify the size of cerebral vessels, but patients reported a marked improvement of intestinal symptoms."
      explanation: >-
        Human therapeutic-response support for this edge: supplying the missing enzyme
        reversed the intestinal symptoms, which the paper defines earlier as chronic
        constipation and reflux, and which argues they arise from the GAA-deficient
        smooth muscle. INDIRECT because the inference runs through
        treatment response rather than a measurement of the tissue. The same sentence
        shows the vessels did not respond, which is why the arteriopathy arm is not
        curated with this argument.
  - target: Constipation
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Storage in intestinal smooth muscle is the proposed basis of the chronic
      constipation LOPD patients report; as with reflux, the contractile deficit
      linking the two has not been measured in human tissue.
    evidence:
    - reference: PMID:20559845
      reference_title: "Abnormalities of cerebral arteries are frequent in patients with late-onset Pompe disease."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: "At 1 year follow-up, enzyme replacement therapy did not modify the size of cerebral vessels, but patients reported a marked improvement of intestinal symptoms."
      explanation: >-
        Human therapeutic-response support for this edge. The intestinal symptoms the
        paper reports as improving are the chronic constipation and reflux it names
        earlier, so their reversal on enzyme replacement argues they arise from the
        GAA-deficient smooth muscle. INDIRECT because the inference runs through
        treatment response rather than a measurement of the tissue.
  - target: Urinary incontinence
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Bladder smooth muscle storage is the proposed basis of urinary incontinence in
      LOPD.
    evidence:
    - reference: PMID:22664150
      reference_title: "Autopsy findings in late-onset Pompe disease: a case report and systematic review of the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "explaining reports of symptoms such as urinary incontinence and dysphagia"
      explanation: >-
        The autopsy study draws this specific inference from smooth-muscle organ
        involvement to the incontinence symptom.
- name: Dilative Arteriopathy of the Aorta and Intracranial Arteries
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  description: >
    Progressive dilatation, ectasia and aneurysm formation affecting the ascending
    thoracic aorta and the intracranial arteries, with the vertebrobasilar system
    most often involved, together with a small-vessel component that shows up as
    white matter hyperintensity and cerebellar and brainstem microbleeds. It is the
    second organ system LOPD damages after muscle,
    and it is largely uncoupled from myopathy severity: patients are identified on
    surveillance imaging rather than by limb weakness, and enzyme replacement
    therapy did not change vessel calibre over a year of follow-up in the one series
    that looked. The node is recorded as PROVISIONAL rather than ESTABLISHED because
    the causal step from smooth-muscle glycogen to wall weakness is inferred rather
    than demonstrated - one aortic specimen showed connective-tissue changes
    resembling a fibrillinopathy rather than a storage lesion, and the Gaa-/- mouse
    accumulates little aortic glycogen, which led that study's authors to decline to
    attribute aortic wall weakness to glycogen accumulation (see animal_models).
  locations:
  - preferred_term: ascending thoracic aorta
    term:
      id: UBERON:0001496
      label: ascending aorta
  - preferred_term: basilar artery
    term:
      id: UBERON:0001633
      label: basilar artery
  - preferred_term: arterial tunica media
    term:
      id: UBERON:0002522
      label: tunica media
  cell_types:
  - preferred_term: medial vascular smooth muscle cell
    term:
      id: CL:0000359
      label: vascular associated smooth muscle cell
  evidence:
  - reference: PMID:21605996
    reference_title: "Expanding the clinical spectrum of late-onset Pompe disease: dilated arteriopathy involving the thoracic aorta, a novel vascular phenotype uncovered."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report evidence of dilated arteriopathy involving primarily the ascending thoracic aorta in 5 females with late-onset Pompe disease."
    explanation: >-
      The case series that established thoracic aortic dilatation as an LOPD
      complication rather than an incidental finding.
  - reference: PMID:39010129
    reference_title: "Intracranial vasculopathy: an important organ damage in young adult patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Intracranial vasculopathy involving both large arteries and small vessels is an important organ damage in LOPD patients."
    explanation: >-
      A 30-patient imaging cohort establishing intracranial arteriopathy as a
      systematic organ manifestation of LOPD.
  - reference: PMID:22945242
    reference_title: "Huge aneurysm of the ascending aorta in a patient with adult-type Pompe's disease: histological findings mimicking fibrillinopathy."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "the histological work-up of resected aortic tissue revealed changes mimicking those observed in patients with classic connective tissue diseases"
    explanation: >-
      Supports the arteriopathy while complicating the mechanism - the resected wall
      looked like a connective-tissue disease rather than a storage lesion, which is
      part of why this node is PROVISIONAL.
  - reference: PMID:39010129
    reference_title: "Intracranial vasculopathy: an important organ damage in young adult patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Microbleeds, predominantly located in the cerebellum and brainstem, were detected in 7 patients (7/22) via susceptibility-weighted imaging."
    explanation: >-
      Supports the small-vessel half of this node. Recorded here rather than as a
      phenotype because HPO has no cerebral microbleed term.
  downstream:
  - target: Dilatation of the ascending thoracic aorta
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:21605996
      reference_title: "Expanding the clinical spectrum of late-onset Pompe disease: dilated arteriopathy involving the thoracic aorta, a novel vascular phenotype uncovered."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Aneurysmal dilatation of the thoracic aorta is an underreported vascular complication of LOPD"
      explanation: Names aortic dilatation as the clinical expression of the LOPD arteriopathy.
  - target: Vertebrobasilar dolichoectasia
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20559845
      reference_title: "Abnormalities of cerebral arteries are frequent in patients with late-onset Pompe disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Four out of six patients had brain vascular anomalies including dolichoectasia of the basilar artery and ectasia of internal carotids."
      explanation: Ties the arteriopathy directly to the vertebrobasilar dolichoectasia phenotype.
  - target: Dilatation of the intracranial arteries
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:39010129
      reference_title: "Intracranial vasculopathy: an important organ damage in young adult patients with late-onset Pompe disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Brain magnetic resonance angiography (MRA) or computed tomography angiography (CTA) revealed artery abnormalities in 23 patients (23/30)."
      explanation: >-
        Establishes intracranial arterial abnormality as the imaging expression of the
        arteriopathy in the majority of an LOPD cohort.
  - target: Stroke
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Dilative and stenotic arteriopathy predisposes to both infarction and
      hemorrhage, but the proportion of LOPD strokes attributable to the arteriopathy
      rather than to conventional risk factors has not been established.
    evidence:
    - reference: PMID:39010129
      reference_title: "Intracranial vasculopathy: an important organ damage in young adult patients with late-onset Pompe disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "LOPD should be considered a key differential diagnosis in young adults with cryptogenic stroke"
      explanation: >-
        The authors' own inference from the imaging findings to stroke risk in this
        population.
  - target: Cerebral white matter hyperintensities
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Small-vessel involvement accompanies the large-artery disease; white matter
      change is its parenchymal correlate.
    evidence:
    - reference: PMID:39010129
      reference_title: "Intracranial vasculopathy: an important organ damage in young adult patients with late-onset Pompe disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Intracranial vasculopathy involving both large arteries and small vessels is an important organ damage in LOPD patients."
      explanation: >-
        The authors report large-artery and small-vessel disease as one process, which
        is the causal claim this edge makes.
phenotypes:
- category: Musculoskeletal
  name: Progressive proximal muscle weakness
  description: >
    Slowly progressive limb-girdle weakness with lower-limb predominance is the
    cardinal motor manifestation of LOPD, and may progress to wheelchair use.
  phenotype_term:
    preferred_term: Proximal muscle weakness
    term:
      id: HP:0003701
      label: Proximal muscle weakness
    clinical_course: PROGRESSIVE
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "LOPD can manifest from the first decade to as late as the seventh decade of life with progressive proximal muscle weakness primarily affecting the lower limbs, which may require use of a wheelchair."
    explanation: GeneReviews identifies progressive lower-limb-predominant proximal weakness as the defining LOPD motor phenotype.
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It causes a progressive proximal myopathy, accompanied by respiratory muscle weakness, which can lead to ventilatory failure."
    explanation: Confirms progressive proximal myopathy as the core LOPD phenotype.
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Most patients will present with a lower limb girdle and truncal muscle weakness pattern"
    explanation: Frequency evidence - "most patients" maps to the VERY_FREQUENT band (80-100%).
- category: Respiratory
  name: Respiratory insufficiency due to muscle weakness
  description: >
    Respiratory muscle weakness, principally of the diaphragm, progresses to
    ventilatory failure and is the leading cause of death in untreated LOPD. In
    roughly a third of patients respiratory symptoms are the presenting complaint,
    ahead of limb weakness.
  phenotype_term:
    preferred_term: Respiratory insufficiency due to muscle weakness
    term:
      id: HP:0002747
      label: Respiratory insufficiency due to muscle weakness
    clinical_course: PROGRESSIVE
  frequency: FREQUENT
  evidence:
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It causes a progressive proximal myopathy, accompanied by respiratory muscle weakness, which can lead to ventilatory failure. In untreated LOPD, the most common cause of death is respiratory failure."
    explanation: Establishes respiratory muscle weakness progressing to ventilatory failure as the dominant cause of death in untreated LOPD.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Respiratory insufficiency progressing to respiratory failure is a significant cause of morbidity and mortality."
    explanation: GeneReviews confirms respiratory insufficiency as a major source of LOPD morbidity and mortality.
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Approximately half will suffer respiratory involvement during the course of their illness"
    explanation: Frequency evidence - "approximately half" falls in the FREQUENT band (30-79%).
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "One-third of patients present with respiratory symptoms as their first manifestation of the illness"
    explanation: Supports the description's claim that respiratory symptoms are the presenting complaint in about a third of patients.
- category: Respiratory
  name: Nocturnal hypoventilation and sleep-disordered breathing
  description: >
    Diaphragm weakness is expressed earliest during sleep, so sleep-disordered
    breathing and nocturnal hypoventilation typically precede overt daytime
    respiratory failure and are accompanied by sleep disruption, excessive daytime
    sleepiness, and reduced health-related quality of life.
  phenotype_term:
    preferred_term: Nocturnal hypoventilation
    term:
      id: HP:0002877
      label: Nocturnal hypoventilation
  evidence:
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Diaphragm weakness leads to nocturnal hypoventilation, which can result in sleep disruption."
    explanation: Directly links diaphragm weakness to nocturnal hypoventilation in LOPD.
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients suffering from respiratory compromise may present with symptoms of sleep-disordered breathing (SDB) before overt signs of respiratory failure."
    explanation: Supports sleep-disordered breathing as an early, pre-failure respiratory manifestation.
- category: Musculoskeletal
  name: Axial and paraspinal muscle weakness
  description: >
    Weakness of the paraspinal and other axial muscles is a characteristic feature of
    the LOPD weakness pattern, running alongside the limb-girdle involvement rather
    than following it, and it is the substrate for the scoliosis and lumbar
    hyperlordosis seen on examination.
  phenotype_term:
    preferred_term: Axial and paraspinal muscle weakness
    term:
      id: HP:0003327
      label: Axial muscle weakness
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Most patients will present with a lower limb girdle and truncal muscle weakness pattern"
    explanation: Records truncal (axial) weakness as part of the presenting LOPD weakness pattern.
  - reference: PMID:33799647
    reference_title: "Muscle Proteomic Profile before and after Enzyme Replacement Therapy in Late-Onset Pompe Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Late-onset Pompe disease (LOPD) is characterized by progressive proximal and axial muscle weakness and atrophy, causing respiratory failure."
    explanation: >-
      Independently characterizes axial weakness, alongside proximal weakness, as a
      defining feature of LOPD.
- category: Musculoskeletal
  name: Scoliosis
  description: >
    Axial and paraspinal muscle involvement produces scoliosis, which is frequent in
    late-onset disease and is one of the manifestations GeneReviews places under
    routine assessment at every visit.
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
  frequency: FREQUENT
  evidence:
  - reference: PMID:37759679
    reference_title: A Comprehensive Update on Late-Onset Pompe Disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "For example, degeneration of bones and joints as a consequence of muscle weakness is a frequent finding, as scoliosis, kyphosis, and hyperlordosis are usually linked to abdominal and hip extensor weakness"
    explanation: >-
      Frequency evidence - an LOPD review calls the skeletal consequence of muscle
      weakness a frequent finding and names scoliosis as one of them, which is the basis
      for the FREQUENT band. It also states the mechanism this phenotype's description
      asserts, namely that the deformity follows trunk and hip extensor weakness.
  - reference: PMID:37265469
    reference_title: "Expert opinion on the diagnostic odyssey and management of late-onset Pompe disease: a neurologist's perspective."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Subsequent secondary musculoskeletal complications include contractures, limb and spinal deformities (winging scapula, scoliosis, lumbar hyperlordosis, and rigid spine syndrome), and osteopenia/osteoporosis"
    explanation: >-
      The neurology expert consensus independently lists scoliosis among the expected
      secondary musculoskeletal complications of LOPD.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "assess for scoliosis; monitor for evidence of aspiration and respiratory insufficiency"
    explanation: >-
      Scoliosis is under active surveillance at every visit, supporting it as a
      recurrent rather than incidental manifestation.
- category: Cardiovascular
  name: Dilatation of the ascending thoracic aorta
  description: >
    A minority of adults with LOPD develop an arteriopathy whose best-characterized
    expression is dilatation of the ascending thoracic aorta. It is distinct from the
    hypertrophic cardiomyopathy of infantile-onset disease - the LOPD myocardium is
    typically spared - and it is specific enough to LOPD that GeneReviews adds aortic
    assessment to the annual echocardiogram for this group. Its mechanism is now
    curated on this entry: it is the aortic expression of the dilative arteriopathy
    node, downstream of lysosomal glycogen storage in vascular smooth muscle. That
    causal step is recorded as PROVISIONAL rather than established - see the
    arteriopathy node and the Gaa-/- mouse link for the evidence that qualifies it.
  phenotype_term:
    preferred_term: Dilatation of the ascending thoracic aorta
    term:
      id: HP:0012727
      label: Thoracic aortic aneurysm
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Some adults have developed arteriopathy, including dilatation of the ascending thoracic aorta."
    explanation: >-
      GeneReviews names ascending thoracic aortic dilatation as an adult (late-onset)
      manifestation of Pompe disease.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "echocardiography (to include assessment for aortic dilatation in those with LOPD)"
    explanation: >-
      The surveillance recommendation is LOPD-specific, which is why this phenotype is
      curated on the late-onset entry rather than left to the umbrella entry.
- category: Gastrointestinal
  name: Dysphagia
  description: >
    Bulbar and tongue involvement produces difficulty swallowing, which patients may
    report indirectly as weight loss. It is the reason a videofluoroscopic swallow
    study and monitoring for aspiration form part of LOPD follow-up.
  phenotype_term:
    preferred_term: Dysphagia
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "They may also report weight loss, due to difficulty swallowing"
    explanation: Records difficulty swallowing among the presenting symptoms of LOPD.
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Case reports also suggest LOPD can cause bulbar dysfunction"
    explanation: >-
      Identifies bulbar dysfunction as the mechanism, and bounds it - the supporting
      literature is case reports, so no frequency band is assigned here.
- category: Musculoskeletal
  name: Reduced bone mineral density
  description: >
    Low bone density and osteoporosis are recognized LOPD complications, driven by
    reduced mechanical loading from the myopathy, and are managed with standard
    osteoporosis treatment. Annual DXA screening is recommended specifically in the
    late-onset group.
  phenotype_term:
    preferred_term: Osteoporosis
    term:
      id: HP:0000939
      label: Osteoporosis
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Standard treatment for arteriopathy, muscle weakness, scoliosis, osteoporosis, and hearing loss."
    explanation: >-
      GeneReviews lists osteoporosis among the Pompe disease manifestations requiring
      management, establishing it as a curatable phenotype rather than an incidental
      comorbidity.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "At least annually, bone mineral density screening (DXA) in those with LOPD"
    explanation: >-
      The annual DXA recommendation is written specifically for the late-onset group,
      which is why reduced bone density is curated here.
  - reference: PMID:37265469
    reference_title: "Expert opinion on the diagnostic odyssey and management of late-onset Pompe disease: a neurologist's perspective."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Subsequent secondary musculoskeletal complications include contractures, limb and spinal deformities (winging scapula, scoliosis, lumbar hyperlordosis, and rigid spine syndrome), and osteopenia/osteoporosis"
    explanation: >-
      Places osteopenia/osteoporosis among the expected secondary musculoskeletal
      complications of LOPD, and identifies it as secondary to the myopathy rather than
      a primary bone defect.
- category: Musculoskeletal
  name: Exercise intolerance
  description: >
    Reduced exercise tolerance, often reported as difficulty climbing stairs or rising
    from a chair, is typically the earliest functional complaint in LOPD and - with
    hyperCKemia - is one of the red flags that should trigger GAA testing.
  phenotype_term:
    preferred_term: Exercise intolerance
    term:
      id: HP:0003546
      label: Exercise intolerance
  evidence:
  - reference: PMID:37265469
    reference_title: "Expert opinion on the diagnostic odyssey and management of late-onset Pompe disease: a neurologist's perspective."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "restrictive respiratory insufficiency with hyperCKemia and/or exercise intolerance as the red flag symptoms/signs that raise the index of suspicion for LOPD diagnosis"
    explanation: >-
      The neurology expert consensus names exercise intolerance as a red-flag sign for
      LOPD, which is both the phenotype claim and its diagnostic significance.
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients will initially report complaints suggestive of progressively reducing muscle strength, such as a difficulty with physical exercise, difficulty climbing stairs or standing from a chair."
    explanation: Places reduced exercise capacity as the initial functional complaint in LOPD.
- category: Constitutional
  name: Myalgia and fatigue
  description: >
    Muscle aches and tiredness accompany the early weakness and are part of why LOPD
    is commonly mistaken for a non-specific or functional complaint before enzyme
    testing is considered.
  phenotype_term:
    preferred_term: Myalgia
    term:
      id: HP:0003326
      label: Myalgia
  evidence:
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is likely to be associated with muscle aches and tiredness."
    explanation: >-
      Records myalgia (muscle aches) and fatigue (tiredness) as accompaniments of the
      early LOPD weakness. Fatigue is described in the same sentence and is captured in
      this entry's description rather than as a separate poorly specific phenotype.
- category: Laboratory
  name: Elevated creatine kinase
  description: >
    Serum creatine kinase is commonly raised and may be the only abnormality that
    brings a patient to neuromuscular attention; isolated hyperCKemia is one of the
    accepted triggers for GAA enzyme screening.
  phenotype_term:
    preferred_term: Elevated circulating creatine kinase activity
    term:
      id: HP:0003236
      label: Elevated circulating creatine kinase activity
  diagnostic: true
  evidence:
  - reference: PMID:36299500
    reference_title: "Investigating Late-Onset Pompe Prevalence in Neuromuscular Medicine Academic Practices: The IPaNeMA Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All successive patients presenting with proximal muscle weakness or isolated hyperCKemia and/or neck muscle weakness to these 13 centers were invited to participate in the study."
    explanation: Isolated hyperCKemia is used as a case-finding criterion for LOPD in neuromuscular practice.
- category: Neurologic
  name: Vertebrobasilar dolichoectasia
  description: >
    Elongation and dilatation of the vertebrobasilar arteries is the single most
    common vascular abnormality in LOPD and is usually asymptomatic until it is
    looked for. Basilar artery diameter correlates with disease duration, so it
    behaves as a progressive manifestation rather than a static malformation.
  phenotype_term:
    preferred_term: Vertebrobasilar dolichoectasia
    term:
      id: HP:0020038
      label: Vertebrobasilar dolichoectasia
    clinical_course: PROGRESSIVE
  frequency: FREQUENT
  evidence:
  - reference: PMID:39010129
    reference_title: "Intracranial vasculopathy: an important organ damage in young adult patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Dilative arteriopathy was found in 19 patients (19/30), with vertebrobasilar dolichoectasia found in 17 patients and dilatation of the anterior circulation arteries found in 8 patients."
    explanation: >-
      17 of 30 imaged LOPD adults, which is 57 percent and maps to the FREQUENT band
      (30-79 percent).
  - reference: PMID:39010129
    reference_title: "Intracranial vasculopathy: an important organ damage in young adult patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The maximum diameter of the basilar artery was correlated with disease duration"
    explanation: Supports the PROGRESSIVE clinical course annotation on this phenotype.
  - reference: PMID:20559845
    reference_title: "Abnormalities of cerebral arteries are frequent in patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Four out of six patients had brain vascular anomalies including dolichoectasia of the basilar artery and ectasia of internal carotids."
    explanation: >-
      Independent replication in a separate European cohort, which is why this is
      curated as a recurrent phenotype rather than a single-cohort observation.
- category: Neurologic
  name: Dilatation of the intracranial arteries
  description: >
    Beyond the vertebrobasilar system, LOPD arteriopathy affects the anterior
    circulation, produces saccular and fusiform aneurysms, and coexists with
    arterial stenosis in a third of patients. Enzyme replacement therapy did not
    reduce vessel calibre over a year of follow-up, so this arm of the disease is
    not currently treatment-responsive.
  phenotype_term:
    preferred_term: Dilatation of the intracranial arteries
    term:
      id: HP:0004944
      label: Dilatation of the cerebral artery
  evidence:
  - reference: PMID:39010129
    reference_title: "Intracranial vasculopathy: an important organ damage in young adult patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition, aneurysms (7/30) and fenestrations (3/30) were discovered."
    explanation: Documents intracranial aneurysm formation as part of the LOPD arteriopathy.
  - reference: PMID:21605996
    reference_title: "Expanding the clinical spectrum of late-onset Pompe disease: dilated arteriopathy involving the thoracic aorta, a novel vascular phenotype uncovered."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Another patient with juvenile onset disease had both thoracic and basilar artery aneurysms."
    explanation: >-
      Shows the aortic and intracranial arms of the arteriopathy occurring in the same
      patient, supporting them as one systemic vascular process.
  - reference: PMID:20559845
    reference_title: "Abnormalities of cerebral arteries are frequent in patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At 1 year follow-up, enzyme replacement therapy did not modify the size of cerebral vessels"
    explanation: >-
      Supports the statement that this manifestation did not respond to enzyme
      replacement therapy over the observed interval.
- category: Neurologic
  name: Stroke
  description: >
    Acute cerebral infarction or intracranial hemorrhage occurs in a minority of
    LOPD adults and may be the presenting event. It is the clinically consequential
    endpoint of the intracranial arteriopathy and the reason vascular imaging is
    proposed as routine workup in this group.
  phenotype_term:
    preferred_term: Stroke
    term:
      id: HP:0001297
      label: Stroke
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:39010129
    reference_title: "Intracranial vasculopathy: an important organ damage in young adult patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seven patients (7/30) had acute cerebral infarction or hemorrhage."
    explanation: >-
      7 of 30 imaged LOPD adults, which is 23 percent and maps to the OCCASIONAL band
      (5-29 percent).
  - reference: PMID:20559845
    reference_title: "Abnormalities of cerebral arteries are frequent in patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two patients had clinical signs related to the arteriopathy, including partial paralysis of the third cranial nerve and transient ischemic attacks."
    explanation: >-
      Independent documentation of symptomatic cerebrovascular events attributable to
      the arteriopathy.
- category: Neurologic
  name: Cerebral white matter hyperintensities
  description: >
    T2/FLAIR white matter hyperintensity accompanies the large-artery disease in
    roughly half of imaged LOPD adults, with cerebellar and brainstem microbleeds in
    a smaller subset. Together these constitute the small-vessel arm of LOPD
    cerebrovascular involvement.
  phenotype_term:
    preferred_term: Hyperintensity of cerebral white matter on MRI
    term:
      id: HP:0030890
      label: Hyperintensity of cerebral white matter on MRI
  frequency: FREQUENT
  evidence:
  - reference: PMID:39010129
    reference_title: "Intracranial vasculopathy: an important organ damage in young adult patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "White matter hyperintensities were present in 13 patients (13/28)."
    explanation: >-
      13 of 28 imaged patients, which is 46 percent and maps to the FREQUENT band
      (30-79 percent).
  notes: >-
    Cerebellar and brainstem microbleeds accompany the white matter change in this
    cohort, but they are not curated as a separate phenotype here: HPO has no
    cerebral microhemorrhage or microbleed term, and Cerebral hemorrhage
    (HP:0001342) names a clinical event rather than a susceptibility-weighted
    imaging finding, so binding it would overstate what was observed. The
    microbleed evidence is recorded on the Dilative Arteriopathy of the Aorta and
    Intracranial Arteries node instead, where it supports the small-vessel claim
    without needing a phenotype binding.
- category: Gastrointestinal
  name: Gastroesophageal reflux
  description: >
    Reflux is reported by LOPD patients alongside constipation and is attributed to
    glycogen storage in gastrointestinal smooth muscle rather than to the limb
    myopathy. It improved markedly on enzyme replacement therapy in the one series
    that followed it, which distinguishes it from the vascular arm of smooth-muscle
    disease.
  phenotype_term:
    preferred_term: Gastroesophageal reflux
    term:
      id: HP:0002020
      label: Gastroesophageal reflux
  evidence:
  - reference: PMID:20559845
    reference_title: "Abnormalities of cerebral arteries are frequent in patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These patients also complained of gastrointestinal symptoms (chronic constipation and gastrointestinal reflux)."
    explanation: Documents reflux as a reported symptom in this LOPD cohort.
  - reference: PMID:20559845
    reference_title: "Abnormalities of cerebral arteries are frequent in patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "patients reported a marked improvement of intestinal symptoms"
    explanation: >-
      Supports the statement that the gastrointestinal symptoms, unlike the vascular
      findings, improved on enzyme replacement therapy.
- category: Gastrointestinal
  name: Constipation
  description: >
    Chronic constipation is reported by LOPD patients and is attributed to the same
    intestinal smooth-muscle storage lesion as reflux.
  phenotype_term:
    preferred_term: Constipation
    term:
      id: HP:0002019
      label: Constipation
    temporality: CHRONIC
  evidence:
  - reference: PMID:20559845
    reference_title: "Abnormalities of cerebral arteries are frequent in patients with late-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These patients also complained of gastrointestinal symptoms (chronic constipation and gastrointestinal reflux)."
    explanation: >-
      Documents chronic constipation as a reported symptom, supporting both the
      phenotype and its CHRONIC temporality annotation.
- category: Genitourinary
  name: Urinary incontinence
  description: >
    Urinary incontinence in LOPD is attributed to lysosomal glycogen storage in
    bladder smooth muscle demonstrated at autopsy, rather than to pelvic floor
    weakness secondary to the limb-girdle myopathy.
  phenotype_term:
    preferred_term: Urinary incontinence
    term:
      id: HP:0000020
      label: Urinary incontinence
  evidence:
  - reference: PMID:22664150
    reference_title: "Autopsy findings in late-onset Pompe disease: a case report and systematic review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "explaining reports of symptoms such as urinary incontinence and dysphagia"
    explanation: >-
      The autopsy study links bladder smooth-muscle involvement to reported urinary
      incontinence in LOPD.
biochemical:
- name: Reduced but not absent acid alpha-glucosidase activity
  presence: DECREASED
  context: >
    LOPD is biochemically defined by partial rather than absent GAA activity,
    conventionally cited as roughly 1-30% of normal. Enzyme activity alone,
    however, does not reliably separate LOPD from IOPD - genotype carries more
    predictive information - so a low-but-not-absent value should be interpreted
    alongside GAA sequencing.
  evidence:
  - reference: PMID:33972680
    reference_title: "Phenotypic implications of pathogenic variant types in Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Enzyme activity levels in isolation were not sufficient to predict disease subtype or other major clinical features."
    explanation: Bounds the diagnostic claim - residual enzyme activity alone does not classify a patient as LOPD versus IOPD.
  - reference: PMID:36299500
    reference_title: "Investigating Late-Onset Pompe Prevalence in Neuromuscular Medicine Academic Practices: The IPaNeMA Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Whole blood was tested for acid alpha-glucosidase (GAA) assay through the fluorometric method, and all cases with enzyme levels of ≤10 pmoL/punch/h were reflexed to molecular testing for mutations in the GAA gene."
    explanation: Documents the reflex-testing workflow in which a reduced GAA activity result is confirmed by GAA genotyping.
histopathology:
- name: Lipofuscin-loaded autolysosomes in skeletal muscle
  description: >
    Muscle biopsies from adult-onset, juvenile-onset, and newborn-screening-detected
    LOPD patients on enzyme replacement therapy contain areas of autophagic buildup
    filled with large autofluorescent inclusions identified as lipofuscin. These
    lipofuscin-loaded lysosomes and autolysosomes are the dominant pathology that
    persists in myofibers after enzyme replacement therapy, and are proposed to
    aggravate the lysosomal and autophagic abnormalities that caused them.
  diagnostic: false
  evidence:
  - reference: PMID:24383498
    reference_title: "The value of muscle biopsies in Pompe disease: identifying lipofuscin inclusions in juvenile- and adult-onset patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The areas of autophagic buildup found in patients' biopsies of all three groups, contained large autofluorescent inclusions which we show are made of lipofuscin, an indigestible intralysosomal material typically associated with ageing."
    explanation: Identifies the lipofuscin content of the autophagic areas in LOPD muscle biopsies.
  - reference: PMID:24383498
    reference_title: "The value of muscle biopsies in Pompe disease: identifying lipofuscin inclusions in juvenile- and adult-onset patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Late-onset Pompe disease (LOPD) is a debilitating progressive muscle disorder that can occur
      anytime from early childhood to late adulthood. ... In this study, we examined the clinical
      status and muscle pathology of 22 LOPD patients and one atypical infantile patient on ERT to
      understand the reasons for muscle resistance to ERT. ... The patients were divided into three
      groups for analysis, based on the age of onset and diagnosis: adult-onset patients,
      juvenile-onset patients, and those identified through newborn screening (NBS). The areas of
      autophagic buildup found in patients' biopsies of all three groups, contained large
      autofluorescent inclusions which we show are made of lipofuscin, an indigestible
      intralysosomal material typically associated with ageing. These inclusions, analysed by
      staining, spectral analysis, time-resolved Fluorescence Lifetime Imaging (FLIM), and Second
      Harmonic Generation (SHG) imaging, were the major pathology remaining in many fibers after
      ERT. ... The muscle biopsy, in spite of its shortcomings, allowed us to recognize an
      underreported, ERT-resistant pathology in LOPD; numerous lysosomes and autolysosomes loaded
      with lipofuscin appear to be a hallmark of LOPD skeletal muscle. Lipofuscin accumulation - a
      result of inefficient lysosomal degradation - may in turn exacerbate both lysosomal and
      autophagic abnormalities.
    explanation: >-
      Identifies the LOPD study, retains its atypical infantile comparator and age/diagnosis groups,
      and connects persistent inclusions to lipofuscin-loaded lysosomes/autolysosomes. The final
      possible feedback mechanism retains the source's may qualification.
genetic:
- name: GAA leaky splice-site variants
  gene_term:
    preferred_term: GAA
    term:
      id: hgnc:4065
      label: GAA
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  notes: >
    The LOPD genotype is defined by retention of at least one allele that still
    produces some functional enzyme. c.-32-13T>G is by far the commonest such
    allele in populations of European ancestry, but it is not the only one: several
    other splice-site variants are similarly associated with the late-onset
    phenotype, whereas two non-splice-site (typically null) alleles produce
    infantile disease.
  evidence:
  - reference: PMID:33972680
    reference_title: "Phenotypic implications of pathogenic variant types in Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To extend the findings of prior studies, we found that multiple types of splice site variants beyond the classic c.-32-13T > G variant are often associated with a milder phenotype."
    explanation: Shows the late-onset phenotype tracks with splice-site (leaky) alleles generally, not only c.-32-13T>G.
  - reference: PMID:36299500
    reference_title: "Investigating Late-Onset Pompe Prevalence in Neuromuscular Medicine Academic Practices: The IPaNeMA Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Of the definite LOPD participants, 8 (89%) were Caucasian and were heterozygous for the common leaky (IVS1) splice site mutation in the GAA gene (c -32-13T>G), with a second mutation that was previously confirmed to be pathogenic."
    explanation: Quantifies the dominance of the leaky IVS1 allele among LOPD patients in a North American neuromuscular cohort.
  - reference: PMID:39273088
    reference_title: "Mutation Spectrum of GAA Gene in Pompe Disease: Current Knowledge and Results of an Italian Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our study concluded that Italian patients exhibited a characteristic genetic profile similar to that of the broader European population, with the c.-32-13T>G variant being the most prevalent."
    explanation: >-
      A second, independent European cohort confirms c.-32-13T>G as the most prevalent
      allele, so the leaky-allele finding is not specific to the North American series.
  - reference: PMID:39273088
    reference_title: "Mutation Spectrum of GAA Gene in Pompe Disease: Current Knowledge and Results of an Italian Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In the whole cohort of patients analyzed with reduced or borderline activity, genetic testing was done, and we found 39 patients with two causative mutations in GAA gene connected to PD, and 22 subjects with GVUS variants."
    explanation: >-
      Bounds the genotype-first framing - in a screened cohort, a substantial minority
      carried variants of uncertain significance rather than a resolvable genotype, which
      is the practical limit on classifying a patient by GAA sequence.
  variants:
  - name: c.-32-13T>G (IVS1)
    description: >
      Intron-1 variant 13 nucleotides upstream of GAA exon 2. It weakens the exon 2
      splice acceptor, causing partial and complete exon 2 skipping, while permitting
      a low level of correctly spliced wild-type transcript - the "leaky" behaviour
      that yields residual enzyme and late-onset disease.
    clinical_significance: PATHOGENIC
    regulatory_category: mLOE
    evidence:
    - reference: PMID:28624228
      reference_title: "Antisense Oligonucleotides Promote Exon Inclusion and Correct the Common c.-32-13T>G GAA Splicing Variant in Pompe Disease."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "which weakens the splice acceptor of GAA exon 2 and induces partial and complete exon 2 skipping. It also allows a low level of leaky wild-type splicing, leading to a childhood/adult phenotype."
      explanation: Characterizes the splicing consequence and residual-activity behaviour of the IVS1 variant.
treatments:
- name: Enzyme replacement therapy for late-onset disease
  description: >
    Intravenous recombinant human GAA is the standard disease-modifying treatment.
    Alglucosidase alfa is approved for LOPD; avalglucosidase alfa is approved for
    individuals with LOPD older than one year; and cipaglucosidase alfa with
    miglustat is approved for adults with LOPD weighing at least 40 kg who are not
    improving on their current regimen. Benefit in LOPD is real but partial, and is
    limited by autophagic mistargeting of enzyme in skeletal muscle.
  therapeutic_modality: PROTEIN_REPLACEMENT
  treatment_term:
    preferred_term: enzyme replacement therapy
    term:
      id: NCIT:C16221
      label: Protein Replacement Therapy
    therapeutic_agent:
    - preferred_term: alglucosidase alfa
      term:
        id: NCIT:C65221
        label: Alglucosidase Alfa
    - preferred_term: avalglucosidase alfa
      term:
        id: NCIT:C169795
        label: Avalglucosidase Alfa
    - preferred_term: cipaglucosidase alfa
      term:
        id: NCIT:C175059
        label: Cipaglucosidase Alfa
    - preferred_term: miglustat
      term:
        id: CHEBI:50381
        label: miglustat
  target_phenotypes:
  - preferred_term: Proximal muscle weakness
    term:
      id: HP:0003701
      label: Proximal muscle weakness
  - preferred_term: Respiratory insufficiency due to muscle weakness
    term:
      id: HP:0002747
      label: Respiratory insufficiency due to muscle weakness
  target_mechanisms:
  - target: Attenuated Lysosomal Glycogen Accumulation in Skeletal and Respiratory Muscle
    treatment_effect: MODULATES
    description: >-
      Recombinant enzyme supplies the deficient lysosomal hydrolase and reduces the
      stored glycogen burden in muscle.
    evidence:
    - reference: PMID:20393176
      reference_title: "A randomized study of alglucosidase alfa in late-onset Pompe's disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "At 78 weeks, the estimated mean changes from baseline in the primary end points favored alglucosidase alfa (an increase of 28.1+/-13.1 m on the 6-minute walk test and an absolute increase of 3.4+/-1.2 percentage points in FVC; P=0.03 and P=0.006, respectively)."
      explanation: The pivotal LOPD randomized trial shows enzyme replacement modifies walking distance and vital capacity relative to placebo.
  evidence:
  - reference: PMID:20393176
    reference_title: "A randomized study of alglucosidase alfa in late-onset Pompe's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At 78 weeks, the estimated mean changes from baseline in the primary end points favored alglucosidase alfa (an increase of 28.1+/-13.1 m on the 6-minute walk test and an absolute increase of 3.4+/-1.2 percentage points in FVC; P=0.03 and P=0.006, respectively)."
    explanation: Randomized, placebo-controlled evidence of benefit for alglucosidase alfa in late-onset Pompe disease.
  - reference: PMID:34800399
    reference_title: "Safety and efficacy of avalglucosidase alfa versus alglucosidase alfa in patients with late-onset Pompe disease (COMET): a phase 3, randomised, multicentre trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We consider that this study provides evidence of clinically meaningful improvement with avalglucosidase alfa therapy over alglucosidase alfa in respiratory function, ambulation, and functional endurance, with no new safety signals reported."
    explanation: Head-to-head phase 3 evidence supporting avalglucosidase alfa in late-onset disease.
  - reference: PMID:38057636
    reference_title: "Long-term safety and efficacy of cipaglucosidase alfa plus miglustat in individuals living with Pompe disease: an open-label phase I/II study (ATB200-02)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Overall, cipa + mig was well tolerated with a safety profile like alglucosidase alfa. ATB200-02 results show the potential benefits of cipa + mig as a long-term treatment option for Pompe disease."
    explanation: >-
      Supplies the long-term (48-month) safety and efficacy evidence for the third
      approved LOPD regimen, cipaglucosidase alfa with miglustat.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "ERT options include alglucosidase alfa for both IOPD and LOPD; avalglucosidase for individuals with LOPD who are older than age one year; and cipaglucosidase alfa with miglustat for adults with LOPD who weigh at least 40 kg and are not improving on their current ERT regimen."
    explanation: GeneReviews sets out the approved enzyme replacement options specific to late-onset disease.
- name: Non-invasive ventilation
  description: >
    Non-invasive ventilation is the mainstay of treatment for sleep-disordered
    breathing and ventilatory failure in LOPD, targeting adequate ventilation during
    sleep and prevention of acute hypercapnic decompensation. It addresses the
    diaphragmatic failure node directly and is required regardless of enzyme
    replacement therapy in many patients.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: mechanical ventilation
    term:
      id: NCIT:C70909
      label: Mechanical Ventilation
  target_phenotypes:
  - preferred_term: Nocturnal hypoventilation
    term:
      id: HP:0002877
      label: Nocturnal hypoventilation
  - preferred_term: Respiratory insufficiency due to muscle weakness
    term:
      id: HP:0002747
      label: Respiratory insufficiency due to muscle weakness
  target_mechanisms:
  - target: Phrenic Motor Unit Failure
    treatment_effect: MODULATES
    description: >-
      Positive-pressure ventilation substitutes for failing inspiratory muscle work
      rather than correcting the underlying storage lesion.
    evidence:
    - reference: PMID:33214927
      reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The mainstay of treatment for SDB and respiratory failure in LOPD is non-invasive ventilation (NIV), which aims to ensure adequate ventilation, particularly during sleep, and prevent acute hypercapnic failure."
      explanation: Identifies non-invasive ventilation as the primary intervention for the respiratory failure node.
  evidence:
  - reference: PMID:33214927
    reference_title: "Respiratory failure and sleep-disordered breathing in late-onset Pompe disease: a narrative review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mainstay of treatment for SDB and respiratory failure in LOPD is non-invasive ventilation (NIV), which aims to ensure adequate ventilation, particularly during sleep, and prevent acute hypercapnic failure."
    explanation: Establishes non-invasive ventilation as standard management of respiratory failure in LOPD.
- name: Structured multidisciplinary surveillance
  description: >
    LOPD is managed as a multisystem disease on a fixed schedule rather than
    symptomatically. GeneReviews specifies, at least annually, DXA bone mineral
    density (a recommendation written specifically for the late-onset group),
    pulmonary function tests, echocardiography including assessment for aortic
    dilatation, EKG, audiology, and BNP where cardiomyopathy is a concern; MR cerebral
    angiography at least every five years for progressive cerebral vessel dilation;
    and, as clinically indicated, whole-body MRI, polysomnography, and
    videofluoroscopic swallow study. This is the surveillance counterpart of the
    aortic dilatation, reduced bone density, dysphagia, and sleep-disordered breathing
    phenotypes curated above.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: multidisciplinary disease surveillance
    term:
      id: NCIT:C15419
      label: Disease Screening
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "At least annually, bone mineral density screening (DXA) in those with LOPD (in those with IOPD, DXA scan every two to three years until puberty, then every one to two years); pulmonary function tests; echocardiography (to include assessment for aortic dilatation in those with LOPD); EKG; audiology evaluation; BNP level (if there are concerns for evolving cardiomyopathy)."
    explanation: >-
      GeneReviews sets out the annual surveillance panel, with the DXA and aortic
      assessment items written specifically for late-onset patients.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "At least every five years, MR cerebral angiography to evaluate for progressive dilation of cerebral vasculature."
    explanation: >-
      Records the cerebral vascular surveillance interval, the intracranial counterpart
      of the aortic arteriopathy curated as a phenotype.
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Polysomnography and/or oxycapnography should be performed every 12 months."
    explanation: >-
      The European pathway independently sets an annual sleep-study interval, which is
      the surveillance that detects the nocturnal hypoventilation phenotype before
      daytime failure.
- name: Anaesthetic and cardiovascular agent precautions
  description: >
    This is a negative recommendation rather than an intervention. Anaesthesia carries
    disproportionate risk in LOPD because reduced cardiovascular return combines with
    the underlying respiratory insufficiency, and GeneReviews advises using it only
    when absolutely necessary. Positioning matters for the same reason: because vital
    capacity falls on lying flat, LOPD patients should not be laid completely supine.
    Digoxin, inotropes, diuretics, and afterload-reducing agents can worsen left
    ventricular outflow obstruction; that caution is inherited from Pompe disease
    generally and is less applicable to the typically cardiac-spared LOPD patient, so
    it is recorded here as context rather than as an LOPD-specific claim.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: avoidance of high-risk agents and circumstances
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Anesthesia should be used only when absolutely necessary because reduced cardiovascular return and underlying respiratory insufficiency pose significant risks."
    explanation: GeneReviews states the anaesthetic caution and the two physiological reasons for it.
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "It should be noted that most patients have lower FVC in supine position due to poor diaphragmatic function; therefore, they should not lay totally flat, but be positioned in a (slightly) upright position."
    explanation: >-
      Gives the positioning precaution that follows from the same diaphragmatic weakness,
      applicable during respiratory decompensation and around procedures.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The use of digoxin, ionotropes, diuretics, and afterload-reducing agents may worsen left ventricular outflow obstruction, although they may be indicated in later stages of the disease"
    explanation: >-
      Bounds the cardiac drug caution - it is written for Pompe disease as a whole, and
      the outflow obstruction it guards against is a feature of the infantile-onset
      cardiomyopathy rather than of typically cardiac-spared LOPD.
diagnosis:
- name: Recognition of the LOPD red-flag presentation
  description: >
    Because LOPD presents insidiously with non-specific complaints, the rate-limiting
    step is clinical suspicion rather than any assay. Unexplained proximal or axial
    weakness, restrictive respiratory insufficiency, hyperCKemia, and exercise
    intolerance are the agreed red flags that should trigger GAA testing; reduced
    pulmonary function specifically in the supine position is the LOPD-typical
    modifier. Normal CK, EMG, or muscle biopsy do not exclude the diagnosis.
  diagnosis_term:
    preferred_term: LOPD red-flag case finding
    term:
      id: NCIT:C15419
      label: Disease Screening
  results: >-
    Any of these red flags in an adult or older child without a better explanation
    should prompt a dried blood spot GAA assay rather than further undirected
    neuromuscular workup.
  evidence:
  - reference: PMID:37265469
    reference_title: "Expert opinion on the diagnostic odyssey and management of late-onset Pompe disease: a neurologist's perspective."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "the presence of unexplained proximal/axial weakness (with or without respiratory symptoms) or restrictive respiratory insufficiency with hyperCKemia (up to 15-fold) and/or exercise intolerance should be considered as the red flag symptoms/signs that raise suspicion for LOPD diagnosis"
    explanation: The neurology expert consensus enumerates the red flags that open the LOPD diagnostic algorithm.
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "proximal limb girdle weakness and/or axial muscle weakness with or without reduced pulmonary function, in particular when in supine position should be considered as red flags for LOPD patients"
    explanation: >-
      The MetabERN European clinical pathway independently defines the same red-flag
      set and adds the supine-position qualifier that is characteristic of LOPD.
  - reference: PMID:37265469
    reference_title: "Expert opinion on the diagnostic odyssey and management of late-onset Pompe disease: a neurologist's perspective."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "it should be noted that normal CK values or the normal findings on EMG or muscle biopsy do not exclude the LOPD diagnosis"
    explanation: >-
      Bounds the negative predictive value of the supporting tests - a normal CK, EMG,
      or biopsy must not be used to close the diagnostic question.
- name: Dried blood spot GAA activity as first-line screen
  description: >
    A GAA enzyme assay on a dried blood spot is the first-line test: cheap, minimally
    invasive, and fast. It is explicitly a screening test and is never sufficient for
    a definitive diagnosis. Modern assays include acarbose to competitively inhibit
    maltase-glucoamylase, which otherwise confounds activity measured at acidic pH;
    poor spotting, humidity, and heat during shipping are recognized preanalytical
    causes of spurious results.
  diagnosis_term:
    preferred_term: dried blood spot acid alpha-glucosidase assay
    term:
      id: NCIT:C15419
      label: Disease Screening
  results: >-
    Reduced GAA activity on dried blood spot is a positive screen that must be
    referred on for confirmation; a normal result in a patient with strong red flags
    does not close the question.
  evidence:
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "A GAA enzyme assay in dried blood spot assay can be used as a first line test. However, this test is not sufficient for a definitive diagnosis."
    explanation: States both the first-line role of the dried blood spot assay and its explicit insufficiency for diagnosis.
  - reference: PMID:37759679
    reference_title: A Comprehensive Update on Late-Onset Pompe Disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "It is frequently a first-line test because it has the advantages of being easy to perform, inexpensive, minimally invasive, and able to provide rapid results"
    explanation: Gives the reasons the dried blood spot assay occupies the screening position.
  - reference: PMID:37759679
    reference_title: A Comprehensive Update on Late-Onset Pompe Disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "incorrect blood spotting and the combination of humidity and heat caused by insufficient drying or inappropriate shipping can interfere with enzyme stability and, consequently, the assessment of GAA levels"
    explanation: Documents the preanalytical failure modes that make a single dried blood spot result unreliable on its own.
- name: Confirmatory enzyme and molecular genetic testing
  description: >
    A positive screen is confirmed either by GAA enzyme assay in a second tissue
    (peripheral leukocytes or lymphocytes, cultured skin fibroblasts, or muscle) or by
    identifying biallelic pathogenic GAA variants. Molecular confirmation is the more
    informative of the two in LOPD, because residual enzyme activity alone does not
    separate late-onset from infantile-onset disease whereas the genotype - in
    practice the presence of the leaky c.-32-13T>G allele - largely does.
  diagnosis_term:
    preferred_term: GAA molecular genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  results: >-
    Deficient GAA activity in a confirmatory tissue and/or two pathogenic GAA variants
    in trans establish the diagnosis.
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The diagnosis of Pompe disease is established in a proband who has deficiency of acid alpha-glucosidase (GAA) enzyme activity in isolated lymphocytes or mixed leukocytes and/or by identification of biallelic pathogenic (or likely pathogenic) variants in GAA by molecular genetic testing"
    explanation: GeneReviews states the two accepted routes to a confirmed diagnosis.
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The diagnosis of Pompe disease should be confirmed by GAA enzyme assay in at least one of the following: peripheral leukocytes/lymphocytes, cultured fibroblasts from skin biopsy, muscle biopsy."
    explanation: Names the acceptable confirmatory tissues for the enzyme route.
  - reference: PMID:33972680
    reference_title: "Phenotypic implications of pathogenic variant types in Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Enzyme activity levels in isolation were not sufficient to predict disease subtype or other major clinical features."
    explanation: >-
      Supports preferring genotype over residual activity when the question is whether
      a confirmed patient has late-onset rather than infantile-onset disease.
- name: Pseudodeficiency alleles as a false-positive trap
  description: >
    A reduced GAA activity result with no pathogenic genotype may reflect a
    pseudodeficiency allele rather than disease. The best-characterized example is
    GAA c.271G>A (p.Asp91Asn), which depresses measured enzyme activity but has been
    formally reviewed as benign for Pompe disease. This is the specific reason
    molecular confirmation - and, when the genotype does not explain the phenotype,
    broader genetic analysis - is required rather than optional.
  diagnosis_term:
    preferred_term: GAA variant classification
    term:
      id: NCIT:C15709
      label: Genetic Testing
  results: >-
    Low measured GAA activity without two pathogenic variants should raise a
    pseudodeficiency allele and prompt variant curation against ACMG-AMP criteria, not
    a diagnosis of Pompe disease.
  evidence:
  - reference: PMID:37759679
    reference_title: A Comprehensive Update on Late-Onset Pompe Disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Rarely, positive DBS with no pathogenic variant may also be related to pseudodeficiency alleles"
    explanation: Establishes pseudodeficiency as a recognized cause of a positive screen without disease.
  - reference: DOI:10.1101/2024.10.03.24314698
    reference_title: "From Past to Present: Pompe Disease, Pseudodeficiency Alleles, and Diagnostic Challenges"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "We demonstrated that GAA :c.271G>A meets the criterion of being classified as benign for Pompe."
    explanation: >-
      Identifies the specific pseudodeficiency allele and its expert-panel-reviewed
      benign classification. This source is a preprint, so it is cited for the variant
      classification only and the general trap is carried by the peer-reviewed citation
      above.
  notes: >-
    The preprint additionally reports a patient homozygous for c.271G>A whose symptoms
    were ultimately explained by a PABPN1 variant, which is the clinical shape of the
    error this entry is guarding against.
- name: Sitting and supine forced vital capacity
  description: >
    Spirometry performed in both the sitting and the supine position is the routine
    diaphragm-specific measurement in LOPD. Because the diaphragm is
    disproportionately affected, vital capacity falls on lying flat, so a supine drop
    identifies diaphragm weakness that a seated measurement alone can miss. It is
    recommended at least annually.
  diagnosis_term:
    preferred_term: sitting and supine spirometry
    term:
      id: NCIT:C38081
      label: Pulmonary Function Test
  results: >-
    A fall in forced vital capacity from sitting to supine indicates diaphragmatic
    weakness; an FVC below 40% predicted should prompt referral to a home ventilation
    team.
  evidence:
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Due to the involvement of diaphragm, pulmonary function in supine position may be more affected than in upright position."
    explanation: States the physiological basis for measuring vital capacity in both positions.
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Pulmonary function (FVC sitting, supine) should be evaluated in both sitting and supine position at least once a year or more frequently depending on patients' conditions."
    explanation: Gives the recommended frequency and the two-position protocol.
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Patients with an FVC < 40% should be brought to the attention of a home ventilation team"
    explanation: Provides the actionable threshold that makes this measurement a management decision point.
- name: Electrodiagnostic study with paraspinal needle EMG
  description: >
    Needle electromyography with nerve conduction studies is the step that separates
    LOPD from other neuromuscular causes of the same presentation. Electrophysiological
    myotonia without clinical myotonia, particularly in the paraspinal muscles, is
    considered highly suggestive of LOPD. It is a supportive, not a confirmatory,
    investigation.
  diagnosis_term:
    preferred_term: needle electromyography
    term:
      id: NCIT:C38056
      label: Electromyography
  results: >-
    Paraspinal electrophysiological myotonia in the absence of clinical myotonia
    strengthens the case for GAA testing; a normal study does not exclude LOPD.
  evidence:
  - reference: PMID:37265469
    reference_title: "Expert opinion on the diagnostic odyssey and management of late-onset Pompe disease: a neurologist's perspective."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The presence of electrophysiological myotonia in the absence of clinical myotonia and permanent weakness, particularly in paraspinal muscles, are highly suggestive of LOPD diagnosis"
    explanation: Identifies the characteristic electrodiagnostic finding and its paraspinal localization.
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "EMG and peripheral nerve conduction studies are optional and may be considered at diagnosis as a supportive element."
    explanation: >-
      Bounds the claim - the European pathway rates electrodiagnosis as optional and
      supportive, so it is curated here as an adjunct rather than a required step.
- name: Skeletal muscle MRI for disease burden
  description: >
    Skeletal muscle MRI documents muscle trophism and fatty degeneration and is used to
    map disease burden rather than to make the diagnosis. Whole-body protocols cover
    muscle groups a targeted study would miss, and quantitative muscle MRI is offered
    to late-onset patients as an addition to annual assessment. The supine position
    required for imaging is itself a hazard in patients with diaphragm weakness.
  diagnosis_term:
    preferred_term: skeletal muscle magnetic resonance imaging
    term:
      id: NCIT:C16809
      label: Magnetic Resonance Imaging
  results: >-
    A characteristic pattern of fatty replacement in paraspinal, pelvic, and thigh
    muscle supports the diagnosis and quantifies burden for follow-up.
  evidence:
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Whole-body MRI protocols are more inclusive than standard MRI protocols focusing on specific anatomical regions (e.g., paraspinal muscles, tongues, pelvis, thigh), enabling evaluation of relevant muscle groups beyond the pelvis and proximal lower extremities"
    explanation: Supports whole-body over targeted protocols for mapping LOPD muscle involvement.
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Quantitative muscle MRI can be performed in late-onset patients in addition to annual investigations."
    explanation: >-
      Bounds the role - quantitative muscle MRI is an addition to, not a component of,
      the core annual LOPD assessment.
  notes: >-
    MetabERN cautions that the supine position needed for MRI may aggravate respiratory
    failure, which is a real constraint in exactly the LOPD patients whose burden most
    needs mapping.
- name: Newborn screening and the pre-symptomatic LOPD patient
  description: >
    Newborn screening measures GAA activity in dried blood spots and is designed to
    catch infantile-onset disease early enough for enzyme replacement therapy to work.
    Its consequence for LOPD is a distinct and growing group: children identified
    pre-symptomatically who cannot be told when, or whether, they will become
    symptomatic. Current screening cannot separate infantile-onset from late-onset
    disease, so these are patients in waiting requiring long-term monitoring.
  diagnosis_term:
    preferred_term: newborn screening for Pompe disease
    term:
      id: NCIT:C81178
      label: Newborn Screening
  results: >-
    An out-of-range newborn screen requires confirmatory enzyme and molecular testing;
    a confirmed child without infantile-onset features enters long-term surveillance
    rather than immediate treatment.
  evidence:
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Newborn screening (NBS) for Pompe disease is possible by measuring GAA activity in dried blood spots with different methods (tandem-mass spectrometry, fluorometry, microfluidics)"
    explanation: Establishes the assay basis of newborn screening.
  - reference: PMID:39482698
    reference_title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "the NBS screening in its current form cannot discern IOPD from LOPD. LOPD patients are thereby patients in waiting requiring long term follow-up and monitoring which may create uncertainty and a psychological burden for families"
    explanation: >-
      States the LOPD-specific consequence of newborn screening, which is the
      pre-symptomatic, screening-detected patient group this entry needs to represent.
- name: Urinary glucose tetrasaccharide as a second-tier and monitoring marker
  description: >
    Urinary glucose tetrasaccharide (Glc4/Hex4) is used as a second-tier test after a
    positive dried blood spot and as a follow-up marker. It is not specific to Pompe
    disease - urinary infection, acute pancreatitis, muscle trauma, and some cancers
    also raise it - and early-phase patients may excrete normal amounts, so it
    supports rather than establishes a diagnosis.
  diagnosis_term:
    preferred_term: urinary glucose tetrasaccharide measurement
    term:
      id: NCIT:C15419
      label: Disease Screening
  results: >-
    An elevated Glc4 supports the diagnosis after a positive screen and tracks response
    on therapy; a normal Glc4 does not exclude early LOPD.
  evidence:
  - reference: PMID:37759679
    reference_title: A Comprehensive Update on Late-Onset Pompe Disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Urinary glucose tetrasaccharide (Glc4) could be used as a second-tier test after positive DBS, and its concentration seems to correlate with age of symptom onset, with more elevated levels in IOPD patients"
    explanation: Places Glc4 as a second-tier test and notes its correlation with onset age.
  - reference: PMID:37759679
    reference_title: A Comprehensive Update on Late-Onset Pompe Disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "elevated urinary tetrasaccharide glucose levels are not specific to PD and may also be related to urinary infections, acute pancreatitis, muscular trauma, and some cancers"
    explanation: Bounds the specificity of the marker, which is why it is curated as second-tier rather than diagnostic.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "obtain electrolytes, BUN, creatinine, liver function tests, CK level, and urine total glucotetrasaccharide (Hex4) level"
    explanation: GeneReviews includes urinary Hex4 in routine follow-up laboratory monitoring.
clinical_trials:
- name: NCT00158600
  phase: PHASE_III
  status: COMPLETED
  description: >
    The Late-Onset Treatment Study (LOTS): randomized, double-blind,
    placebo-controlled trial of alglucosidase alfa in late-onset Pompe disease,
    the pivotal trial that established enzyme replacement therapy for this form.
  target_phenotypes:
  - preferred_term: Proximal muscle weakness
    term:
      id: HP:0003701
      label: Proximal muscle weakness
  - preferred_term: Respiratory insufficiency due to muscle weakness
    term:
      id: HP:0002747
      label: Respiratory insufficiency due to muscle weakness
  evidence:
  - reference: clinicaltrials:NCT00158600
    reference_title: "Randomized, Double-Blind, Placebo-Controlled Study of the Safety, Efficacy and Pharmacokinetics of Myozyme in Patients With Late-Onset Pompe Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The overall objective is to evaluate the safety, efficacy, and pharmacokinetics (PK) of alglucosidase alfa treatment in patients with late-onset Pompe disease as compared to placebo."
    explanation: Registration record for the placebo-controlled trial underpinning enzyme replacement therapy in late-onset disease.
- name: NCT02782741
  phase: PHASE_III
  status: COMPLETED
  description: >
    COMET: head-to-head phase 3 trial of avalglucosidase alfa versus alglucosidase
    alfa in treatment-naive late-onset Pompe disease, with upright percent-predicted
    forced vital capacity as the primary respiratory endpoint.
  target_phenotypes:
  - preferred_term: Respiratory insufficiency due to muscle weakness
    term:
      id: HP:0002747
      label: Respiratory insufficiency due to muscle weakness
  evidence:
  - reference: clinicaltrials:NCT02782741
    reference_title: "A Phase 3 Randomized, Multicenter, Multinational, Double-blinded Study Comparing the Efficacy and Safety of Repeated Biweekly Infusions of Avalglucosidase Alfa (neoGAA, GZ402666) and Alglucosidase Alfa in Treatment naïve Patients With Late-onset Pompe Disease"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To determine the effect of avalglucosidase alfa treatment on respiratory muscle strength measured by percent (%) predicted forced vital capacity (FVC) in the upright position, as compared to alglucosidase alfa."
    explanation: Documents that the head-to-head trial was powered on a respiratory-muscle endpoint, matching the diaphragmatic failure node of this entry.
- name: NCT03729362
  phase: PHASE_III
  status: COMPLETED
  description: >
    PROPEL: phase 3 trial of cipaglucosidase alfa (ATB200) with the enzyme
    stabilizer miglustat (AT2221) versus alglucosidase alfa plus placebo in adults
    with late-onset Pompe disease.
  target_phenotypes:
  - preferred_term: Proximal muscle weakness
    term:
      id: HP:0003701
      label: Proximal muscle weakness
  evidence:
  - reference: clinicaltrials:NCT03729362
    reference_title: "A Phase 3 Double-blind Randomized Study to Assess the Efficacy and Safety of Intravenous ATB200 Co-administered With Oral AT2221 in Adult Subjects With Late-onset Pompe Disease Compared With Alglucosidase Alfa/Placebo"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is a phase 3 double-blind randomized study to study the efficacy and safety of intravenous ATB200 Co-administered with oral AT2221 in adult subjects with Late Onset Pompe Disease compared with Alglucosidase Alfa/placebo."
    explanation: Registration record for the trial supporting the cipaglucosidase alfa plus miglustat regimen approved specifically for adults with late-onset disease.
- name: NCT04093349
  phase: PHASE_I
  status: ACTIVE_NOT_RECRUITING
  description: >
    RESOLUTE: phase 1/2 dose-escalation study of a single intravenous infusion of
    the AAV gene therapy SPK-3006 in adults with clinically moderate late-onset
    Pompe disease already receiving enzyme replacement therapy. It targets the
    therapeutic ceiling of infused enzyme by aiming for sustained endogenous GAA
    secretion.
  target_phenotypes:
  - preferred_term: Proximal muscle weakness
    term:
      id: HP:0003701
      label: Proximal muscle weakness
  evidence:
  - reference: clinicaltrials:NCT04093349
    reference_title: "Phase 1/2, Dose-escalation Study to Evaluate the Safety, Tolerability and Efficacy of a Single Intravenous Infusion of SPK-3006 in Adults With Late-onset Pompe Disease"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The purpose of this study is to evaluate the safety, tolerability, and efficacy of a single intravenous infusion of SPK-3006 in adults with clinically moderate, late-onset Pompe disease receiving enzyme replacement therapy (ERT)."
    explanation: Registration record for the gene-therapy trial addressing the incomplete-response node in late-onset disease.
discussions:
- discussion_id: lopd_presymptomatic_ert_initiation
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Incomplete Response to Enzyme Replacement Therapy
  prompt: >-
    When should enzyme replacement therapy be started in a person with a confirmed
    LOPD genotype who has no symptoms, as is now routine after newborn screening or
    family cascade testing?
  rationale: >
    Newborn screening and family screening increasingly identify LOPD before any
    clinical sign. Because LOPD is defined by a decades-long latency, the
    conventional trigger for treatment - symptom onset - may come after irreversible
    myofiber loss, but treating a pre-symptomatic patient commits them to lifelong
    infusions with cost, infusion-reaction risk, and immunogenicity. Guidance is not
    settled: European recommendations favour monitoring asymptomatic cases with
    minimal muscle MRI findings, while other guidance would start therapy once any
    muscle involvement (for example paraspinal) is detectable. Siblings sharing a
    genotype can differ markedly in age at presentation and MRI burden, so genotype
    alone does not resolve the question.
  evidence:
  - reference: PMID:36833288
    reference_title: "Treatment Dilemma in Children with Late-Onset Pompe Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The dilemma is when to start Enzyme Replacement Therapy (ERT) in patients without any clinical sign of the disease, considering its important benefits in terms of loss of muscle but also its very high cost, risk of side effects, and long-term immunogenicity."
    explanation: States the pre-symptomatic treatment-initiation gap that this discussion records.
  - reference: PMID:36833288
    reference_title: "Treatment Dilemma in Children with Late-Onset Pompe Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "European guidelines suggest monitoring in asymptomatic LOPD cases with minimal MRI findings, although other guidelines consider starting ERT in apparently asymptomatic cases with initial muscle involvement (e.g., paraspinal muscles)."
    explanation: Documents the disagreement between guidelines that makes this an open question rather than settled practice.
  - reference: PMID:24383498
    reference_title: "The value of muscle biopsies in Pompe disease: identifying lipofuscin inclusions in juvenile- and adult-onset patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The best outcome of ERT both clinically and morphologically was observed in the NBS patients."
    explanation: Argues for earlier initiation, since newborn-screening-detected patients had the best clinical and histological response - but this is an uncontrolled comparison across onset groups, so it informs rather than settles the question.
- discussion_id: lopd_autophagic_mistargeting_model_fidelity
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Autophagic Mistargeting of Endocytosed Recombinant Enzyme
  prompt: >-
    Does autophagic mistargeting of endocytosed recombinant GAA, demonstrated in
    single fibers of the GAA knockout mouse, account for the therapeutic ceiling
    observed in treated human LOPD skeletal muscle?
  rationale: >
    The mistargeting mechanism is directly imaged in live single muscle fibers of
    GAA knockout mice, which model complete rather than partial enzyme deficiency.
    LOPD muscle retains residual enzyme and accumulates storage over decades, so the
    extent of autophagic buildup - and therefore how much of the human treatment
    ceiling it explains - is not established from the mouse data alone. The human
    counterpart evidence in this entry is indirect: fat fraction continues to rise
    and some patients still progress to ventilation on therapy, which is consistent
    with the mechanism but does not measure enzyme trafficking in human muscle.
  proposed_experiments:
  - experiment_id: lopd_rhgaa_trafficking_in_patient_myofibers
    name: Trafficking of labelled rhGAA in LOPD patient muscle biopsy fibers
    description: >-
      Assess whether endocytosed recombinant GAA reaches lysosomes or is retained in
      autophagic compartments in myofibers from genotyped LOPD patients, stratified
      by residual enzyme activity and by duration of enzyme replacement therapy.
  evidence:
  - reference: PMID:17008131
    reference_title: "Autophagy and mistargeting of therapeutic enzyme in skeletal muscle in Pompe disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These findings may explain why ERT often falls short of reversing the disease process and point toward new avenues for the development of pharmacological intervention."
    explanation: The authors present the mechanism as an explanation that "may" account for the therapeutic shortfall, which is the translational uncertainty recorded here.
notes: >
  Scope. This entry curates the late-onset arm of the acid alpha-glucosidase
  deficiency spectrum (MONDO:0018485) as a distinct entity from the umbrella Pompe
  disease entry (MONDO:0009290, kb/disorders/Pompe_Disease.yaml). It deliberately
  does not restate the umbrella entry's generic GAA/glycogen biology, its
  infantile-onset content, or its full treatment catalogue. What is curated here is
  the mechanism that makes late onset late: partial rather than absent enzyme
  activity arising from leaky splicing, the resulting cardiac sparing and
  muscle-restricted storage, the diaphragm-predominant respiratory arm including
  its possible phrenic motor neuron component, and the autophagic ceiling on
  enzyme replacement therapy.

  Smooth muscle and the vascular arm. The entry also curates the extra-muscular
  compartment that distinguishes LOPD from a pure myopathy: lysosomal glycogen in
  vascular and visceral smooth muscle, demonstrated by transmission electron
  microscopy at autopsy, and the dilative arteriopathy of the ascending aorta and
  the intracranial arteries that follows from it. The arteriopathy node is marked
  PROVISIONAL rather than ESTABLISHED on purpose. The storage lesion is not in
  doubt, but the step from it to arterial wall weakness is inferred: one resected
  aneurysmal aorta showed connective-tissue changes rather than a storage lesion,
  and the Gaa-/- mouse accumulates little aortic glycogen, which led that study's
  authors to decline to attribute aortic wall weakness to it. That negative model
  result is curated as a FAILS_TO_RECAPITULATE link rather than left out, since it
  is the main reason the human node is qualified. Frequencies for the cerebrovascular phenotypes come from a single
  30-patient Chinese imaging cohort and should be read as that cohort's numbers,
  not as pooled estimates.

  A residual-activity range of roughly 1-30% of normal is widely cited for LOPD and
  is recorded in the umbrella entry's subtype description; it is stated here as
  context in the biochemical entry rather than as an evidence-bearing claim, because
  the cited genotype-phenotype study explicitly found enzyme activity alone
  insufficient to classify disease subtype.
animal_models:
- name: Gaa-/- global knockout mouse (smooth muscle characterization)
  species: Mouse
  genotype: Gaa-/- (targeted disruption of exon 6), homozygous null
  background: B6;129
  publication: PMID:33883348
  genes:
  - preferred_term: GAA
    term:
      id: hgnc:4065
      label: GAA
  description: >
    The most widely used Pompe mouse, a global Gaa knockout that survives into
    adulthood without treatment. This entry curates the study that characterized its
    smooth muscle rather than its skeletal muscle, because that is what bears on the
    extra-muscular arms of LOPD. Glycogen, lysosomes and autophagosomes accumulate
    across aortic, tracheal, esophageal, gastric and bladder smooth muscle, with the
    gastrointestinal and genitourinary tissues most affected. The model's central
    limitation for late-onset disease is genetic: a global null has essentially no
    residual enzyme, whereas LOPD is defined by partial activity from a leaky splice
    allele, so the mouse is genotypically closer to infantile-onset disease and its
    tempo cannot be read across.
  evidence:
  - reference: PMID:33883348
    reference_title: "Glycogen accumulation in smooth muscle of a Pompe disease mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In conclusion, GAA deficiency results in significant glycogen accumulation in the airway, vascular, GI and GU smooth muscle."
    explanation: >-
      Establishes this model as informative for the smooth-muscle compartment of GAA
      deficiency, which is the arm of LOPD it is cited for here.
  modeled_mechanisms:
  - target: Lysosomal Glycogen Accumulation in Vascular and Visceral Smooth Muscle
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Quantitative glycogen assay, PAS histology and LAMP1/LC3 immunoblotting all show
      the storage-plus-vacuolar-accumulation lesion in the same smooth-muscle beds
      implicated by human autopsy.
    limitations: >-
      A global null has no residual GAA, whereas LOPD is defined by partial activity
      from a leaky splice allele, so the model reproduces the lesion but not the
      late-onset tempo or threshold. Aortic glycogen was the lowest of the tissues
      measured and did not increase between 6 and 15 months, so the vascular half of
      this node is the weakest part of the match.
    evidence:
    - reference: PMID:33883348
      reference_title: "Glycogen accumulation in smooth muscle of a Pompe disease mouse model."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "we show that GAA deficiency results in subsequent pathology in smooth muscle cells, which may lead to life-threatening complications if not properly treated"
      explanation: >-
        Supports treating this model as informative for the smooth-muscle storage node,
        which is the claim this link makes.
    readouts:
    - name: Tissue glycogen content in smooth-muscle organs
      target: Lysosomal Glycogen Accumulation in Vascular and Visceral Smooth Muscle
      description: >-
        Enzymatic glycogen quantification of aorta, trachea, esophagus, stomach and
        bladder in 6-month-old Gaa-/- versus wild-type mice, normalized to protein.
      direction: INCREASED
      interpretation: >-
        Direct measurement of the storage lesion this node asserts, in the smooth
        muscle beds relevant to the vascular and visceral arms of LOPD.
      evidence:
      - reference: PMID:33883348
        reference_title: "Glycogen accumulation in smooth muscle of a Pompe disease mouse model."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Increased levels of glycogen were present in smooth muscle cells of the aorta, trachea, esophagus, stomach, and bladder of Gaa-/- mice, compared to wild type mice."
        explanation: Reports the glycogen measurement behind this readout.
    - name: LAMP1 abundance in smooth-muscle organs
      target: Lysosomal Glycogen Accumulation in Vascular and Visceral Smooth Muscle
      description: >-
        Western blot quantification of the lysosomal membrane protein LAMP1,
        normalized to loading control, as a proxy for lysosomal expansion.
      direction: INCREASED
      interpretation: >-
        Lysosomal expansion is the cellular consequence of the glycogen load and
        grounds the glycogen-distended lysosome annotation on this node.
      evidence:
      - reference: PMID:33883348
        reference_title: "Glycogen accumulation in smooth muscle of a Pompe disease mouse model."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "In the aorta, esophagus, stomach, and bladder, significantly higher levels of LAMP1 are present in Gaa-/- mice, compared to WT."
        explanation: Reports the LAMP1 immunoblot measurement behind this readout.
  - target: Dilative Arteriopathy of the Aorta and Intracranial Arteries
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    description: >-
      The aorta accumulated the least glycogen of any smooth-muscle tissue measured
      and did not accumulate more between 6 and 15 months, and the authors state that
      this does not support the glycogen-to-wall-weakness hypothesis. The only aortic
      change seen was tunica media remodeling at 15 months. Note the study assayed
      glycogen and wall histology; it did not report vessel-calibre measurements, so
      what is recorded here is failure to reproduce the storage-driven wall lesion
      rather than a measured absence of dilatation.
    limitations: >-
      This is a negative result about the aorta specifically, in a model whose lifespan
      (6-9 months untreated, examined to 15 months) is far shorter than the decades
      over which human aortic dilatation develops, so failure to recapitulate may
      reflect insufficient time rather than a wrong mechanism. It is recorded because
      it is the main reason the human arteriopathy node is marked PROVISIONAL, not as
      a refutation of the mechanism.
    readouts:
    - name: Aortic PAS-positive glycogen deposits at 6 and 15 months
      target: Dilative Arteriopathy of the Aorta and Intracranial Arteries
      description: >-
        Periodic acid-Schiff histology of aortic sections in Gaa-/- mice at two ages,
        scored for glycogen deposit number and size.
      direction: UNCHANGED
      interpretation: >-
        Aortic glycogen did not increase with age, which is why the authors declined to
        attribute aortic wall weakness to glycogen accumulation in this model.
      evidence:
      - reference: PMID:33883348
        reference_title: "Glycogen accumulation in smooth muscle of a Pompe disease mouse model."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "there is not an increase in either the number or size of glycogen deposits in the aorta at this age"
        explanation: >-
          Reports the negative aortic histology result at 15 months that grounds this
          readout.
    evidence:
    - reference: PMID:33883348
      reference_title: "Glycogen accumulation in smooth muscle of a Pompe disease mouse model."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "the limited PAS+ present at both 6 and 15 months in the aorta of Gaa-/- mice does not corroborate our hypothesis that glycogen accumulation is responsible for aortic wall weakness"
      explanation: >-
        The authors' own statement that the aortic findings in this model do not support
        glycogen accumulation as the cause of aortic wall weakness. It supports the claim
        this link makes - that the model fails to recapitulate the human arteriopathy.
datasets:
- accession: geo:GSE155637
  title: >-
    Deferoxamine mesylate improves splicing and GAA activity of the common
    c.-32-13T>G allele in late-onset Pompe disease patient fibroblasts
  description: >-
    RNA-seq of primary fibroblasts from late-onset Pompe disease patients carrying
    the c.-32-13T>G allele, treated with deferoxamine or vehicle, testing
    pharmacological correction of the leaky-splicing defect that defines LOPD.
  data_type: BULK_RNA_SEQ
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  sample_count: 6
  genes:
  - preferred_term: GAA
    term:
      id: hgnc:4065
      label: GAA
  publication: PMID:33426149
  notes: >-
    Discovered via `just discover-datasets Late-Onset_Pompe_Disease` as a DIRECT
    match (the disease and the c.-32-13T>G allele are both named in the dataset
    title) and manually triaged as on-topic for the leaky-splicing node of this
    entry. Verified with `just verify-datasets`. Retrieved 2026-08-18.
- accession: geo:GSE75713
  title: >-
    GAA deficiency in Pompe disease is alleviated by exon inclusion in iPS
    cell-derived skeletal muscle cells
  description: >-
    Microarray profiling of iPSC-derived skeletal muscle cells from Pompe disease
    patients in which GAA deficiency is corrected by splice modulation promoting
    exon inclusion - the in vitro counterpart of the leaky-splicing mechanism
    curated here.
  data_type: MICROARRAY
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  sample_count: 6
  genes:
  - preferred_term: GAA
    term:
      id: hgnc:4065
      label: GAA
  notes: >-
    Discovered via `just discover-datasets` as a GENE_ONLY candidate and retained
    after manual relevance triage: the GEO title and summary describe splice-based
    exon-inclusion correction of GAA deficiency in a patient iPSC skeletal-muscle
    model, which is the LOPD splicing mechanism. The GEO record carries no linked
    publication, so no `publication:` is asserted. Verified with
    `just verify-datasets`. Retrieved 2026-08-18.
references:
- reference: PMID:20301438
  title: "Pompe Disease."
  tags:
  - GeneReviews

📚

References & Deep Research

References

1

PMID:20301438

Pompe Disease.

No top-level findings curated for this source.

Deep Research

3

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (2)

Augment Late-Onset Pompe Disease with the smooth-muscle and vascular arm · 2026-09-01T11:07:07Z · View source

Augmented the existing MONDO:0018485 entry rather than creating a duplicate: the requested disorder name is the MONDO label already curated as kb/disorders/Late-Onset_Pompe_Disease.yaml (issue #8759, PR #8878). Deep research: two runs. The requested provider (falcon) failed authentication (403, empty EDISON_API_KEY), so the run was made with --fallback and completed as openscientist; research/Late-Onset_Pompe_Disease-deep-research-openscientist.md carries fell_back: true, requested_provider: falcon and the provider_attempts trail, with 52/52 references resolved. That report has no smooth-muscle or vascular content, so it corroborates the existing entry rather than this augmentation. A second run with claude_code (no API key needed) produced research/Late-Onset_Pompe_Disease-deep-research-claude_code.md (231s, 17 web searches, 70 citations, 47/47 references resolved), and it is the one that bears on this work: it independently identified the same vasculopathy literature found by direct PubMed search, which is the triangulation this augmentation rests on. Its reference_validation carries needs_review: true for one unsupported quote (PMC:PMC11638199, 'unexplained limb-girdle weakness'), which was not used here. The openscientist report is also needs_review, for one mislabelled term (HP:0001638 read as 'Minor/mild cardiac involvement'; HP calls it Cardiomyopathy), which was not used. The claude_code term_validation flagged six mislabelled CURIEs; notably it offered CL:0000192 for *vascular* smooth muscle, which CL calls plain 'smooth muscle cell'. That binding was not taken - CL:0000359 (vascular associated smooth muscle cell) was verified independently with OAK and used instead. The pre-existing falcon report from the original curation was left in place. What was added. The prior curation recorded, on the 'Dilatation of the ascending thoracic aorta' phenotype, that glycogen storage in vascular smooth muscle was 'the proposed substrate, but the mechanism is not established here and is deliberately not asserted'. That gap is now closed with human evidence and the phenotype description updated accordingly. Two pathophysiology nodes: 'Lysosomal Glycogen Accumulation in Vascular and Visceral Smooth Muscle' (CELLULAR, ESTABLISHED, conforms to lysosomal_substrate_accumulation) on the strength of LOPD autopsy transmission electron microscopy (PMID:22664150) plus Gaa-/- mouse quantification (PMID:33883348); and 'Dilative Arteriopathy of the Aorta and Intracranial Arteries' (TISSUE, PROVISIONAL) from PMID:21605996, PMID:39010129, PMID:33386209 and PMID:22945242. The arteriopathy node is deliberately PROVISIONAL rather than ESTABLISHED: the step from smooth-muscle glycogen to arterial wall weakness is inferred, one resected aneurysmal aorta showed connective-tissue rather than storage changes, and the mouse does not develop the lesion. Seven phenotypes: vertebrobasilar dolichoectasia (HP:0020038, FREQUENT, 17/30), dilatation of the intracranial arteries (HP:0004944), stroke (HP:0001297, OCCASIONAL, 7/30), cerebral white matter hyperintensities (HP:0030890, FREQUENT, 13/28), gastroesophageal reflux (HP:0002020), constipation (HP:0002019), urinary incontinence (HP:0000020). Every frequency band is backed by a quoted denominator; all four cerebrovascular frequencies come from one 30-patient Chinese imaging cohort and the notes say so rather than presenting them as pooled estimates. New animal_models section: the Gaa-/- B6;129 global knockout (PMID:33883348), carrying two links. It RECAPITULATES the smooth-muscle storage node (MODERATE, two readouts: tissue glycogen INCREASED, LAMP1 INCREASED) and FAILS_TO_RECAPITULATE the arteriopathy node (LOW), with the authors' own statement that their aortic findings do not corroborate the glycogen-to-wall-weakness hypothesis, plus an UNCHANGED aortic PAS readout. The negative result is curated rather than dropped because it is the reason the human node is qualified. Both links record the model's central limitation for late-onset disease: a global null has no residual enzyme, whereas LOPD is defined by partial activity from a leaky splice allele. Validation. just validate passed (schema, terms, references). just validate-disorders (the batched CI gate) passed: schema OK, terms OK, 156/157 snippets verified. just count-verified-snippets --unskip-prefix DOI reports 157/157, so the one DOI-keyed item CI skips was checked by hand and verifies. check-entity-refs, check-causal-targets, check-duplicate-keys, check-enum-values, check-qualifier-terms, check-folded-hyphens, check-snippet-length, check-title-snippets and check-snippet-grading all clean with no new baseline entries. Compliance rose from 98.5 percent (256/260) to 98.8 percent (331/335); the four remaining gaps are pre-existing (two datasets lacking evidence, one proposed experiment). Two literature cache files (PMID_34800399, PMID_39424261) were rewritten as formatting-only churn by the research runs' validator and were reverted, since they carry no content change and are unrelated to this curation. Separately, the --fallback run renamed the falcon output directory on its way to openscientist, which deleted the previously committed falcon report, its citations sidecar and its artifact, and left a duplicate of that artifact inside the openscientist artifact directory. The falcon files were restored from git and the stray duplicate removed, so the only research additions here are the two new reports. Review round (PR #10363). The automated reviewer approved with no blocking findings and five advisory notes; three were actionable and are addressed. First, the microbleed evidence item sat on the white-matter-hyperintensity phenotype, where it supported the description but not HP:0030890. The reviewer proposed a sibling phenotype on an HPO cerebral-microhemorrhage term, but no such term exists: OAK returns nothing for microbleed or microhemorrhage, and Cerebral hemorrhage (HP:0001342) names a clinical event rather than a susceptibility-weighted imaging finding, so binding it would overstate the observation. The evidence item was moved to the arteriopathy node, where it supports the small-vessel claim without needing a phenotype binding, and the phenotype carries a notes entry recording why the suggested fix was not taken. Second, the visceral smooth-muscle cell type was bound at the generic CL:0000192; the reviewer asked for an OAK check, and CL does carry organ-specific terms, so bladder is now CL:0002597 and esophagus CL:0002599. The intestinal component stays at CL:0000192 because CL offers only small- and large-intestine terms below that point while the cited autopsy says "intestine" without specifying segment. Third, the gastroesophageal-reflux edge was carried only by a mouse paper's background prose about human symptoms; a human therapeutic-response item was added from PMID:20559845, where enzyme replacement reversed the gastrointestinal symptoms while leaving cerebral vessel calibre unchanged - INDIRECT support that those symptoms arise from GAA- deficient smooth muscle, and the same sentence marks the contrast with the vascular arm. The fourth note, that the PR body misattributed the autopsy evidence to PMID:21605996 instead of PMID:22664150, was already corrected before the review posted; the YAML was never wrong. The fifth was informational about diff size. After these changes all gates were re-run: validate, validate-terms, entity-refs, causal-targets, duplicate-keys, enum-values and qualifier-terms are clean, and count-verified-snippets --unskip-prefix DOI reports 158/158. Second review round (PR #10363). The re-review requested changes on two findings, both correct and both mine. First, the note added in the previous round claimed CL offers only small- and large-intestine smooth-muscle terms; it does not. CL:0002504 "enteric smooth muscle cell" is defined as "A smooth muscle cell of the intestine", carries "intestinal smooth muscle cell" as an exact synonym, is already in cache/cl/terms.csv and the celltypeterm enum cache, and is already used in four other entries. The earlier OAK search missed it because the label contains no form of the word "intestine". The binding is now CL:0002504 and the false claim is replaced by a note that the segment-agnostic term was chosen over its children because the autopsy does not specify segment. Second, the Constipation phenotype asserted in its description that it shares the intestinal smooth-muscle mechanism but had no incoming pathograph edge, so it rendered as a floating node while its two siblings were wired up; nothing gates an unconnected phenotype, so no check caught it. An INDIRECT_UNKNOWN_INTERMEDIATES edge mirroring the reflux one was added, carrying the same PMID:20559845 enzyme-replacement-response sentence. Two advisory notes were also taken: the reflux edge explanation said "gastrointestinal symptoms" where the quote says "intestinal symptoms", now corrected to track the quote and to say that the paper defines those symptoms earlier as constipation and reflux; and the arteriopathy node description, which described only the aorta and intracranial arteries, now acknowledges the small-vessel component that the white-matter-hyperintensity and microbleed evidence covers. After these changes: validate, validate-terms, entity-refs, causal-targets, duplicate-keys, enum-values and qualifier-terms clean, count-verified-snippets --unskip-prefix DOI 159/159, and compliance-connectivity for this entry rises from 10/18 to 11/18 phenotypes connected, with all seven remaining unconnected phenotypes pre-existing and out of scope.

Create: Late-Onset Pompe Disease (MONDO:0018485) · 2026-08-19T04:24:35Z · View source

Standalone entry for the late-onset arm of acid alpha-glucosidase deficiency (MONDO:0018485; OMIM:621314; Orphanet:420429). SCOPE DECISION. kb/disorders/Pompe_Disease.yaml (MONDO:0009290) already carried an LOPD subtype with a display_name and description but no bound term. Chose a standalone entry over binding-only, because the late-onset form has substantive mechanism that is not derivable from the umbrella entry and that the umbrella deliberately does not model: (a) partial rather than absent enzyme, produced by leaky intron-1 splicing at c.-32-13T>G; (b) the resulting relative cardiac sparing, which is part of the formal case definition rather than a statistical tendency; (c) diaphragm-predominant respiratory failure with a possible spinal phrenic motor neuron component; (d) an autophagic/lipofuscin ceiling on enzyme replacement therapy that only matters because LOPD is treated for decades; (e) pre-vacuolar metabolic reprogramming of myonuclei; and (f) the newborn-screening pre-symptomatic treatment-initiation dilemma. The umbrella entry is otherwise left untouched except for one surgical edit: the LOPD subtype block now carries subtype_term MONDO:0018485 and a pointer to this file. The IOPD subtype block was deliberately not touched, because a sibling agent is concurrently curating MONDO:0017694 (issue 8758). CONTENT. 8 pathophysiology nodes wired into a single chain from leaky splicing to incomplete ERT response, conforming at lysosomal_substrate_accumulation#Lysosomal Substrate Accumulation. 5 phenotypes, 2 progression phases, 1 biochemical marker, 1 histopathology finding (lipofuscin-loaded autolysosomes), 1 genetic entry with the c.-32-13T>G variant, 2 treatments with target_mechanisms, 4 clinical trials (LOTS, COMET, PROPEL, RESOLUTE), 2 datasets, and 2 discussions (a KNOWLEDGE_GAP on pre-symptomatic ERT initiation and a HUMAN_MODEL_MISMATCH on whether GAA-knockout-mouse enzyme mistargeting explains the human treatment ceiling). DEEP RESEARCH. falcon (Edison), research/Late-Onset_Pompe_Disease-deep-research-falcon.md. Report reference_validation: 12/12 references resolved, confabulation_rate 0.0, 0 off topic. `just preflight-dr` against MONDO:0018485 returned SKIP because MONDO records no RO:0004003 causal gene for this subtype term; the manual fallback was run and passes - GAA dominates the report's gene mentions (GAA=23, next highest 2), and the OMIM difference (report cites 232300, MONDO xrefs 621314) is the expected umbrella-vs-subtype split rather than a Named Entity Confusion signal, since OMIM:621314 is a recent LOPD-specific entry that the literature does not yet use. Only two claims were taken from the report and both were independently re-verified against freshly fetched abstracts: the single-nucleus RNA-seq staging study (PMID:39045638) and the post-ERT muscle proteomics study (PMID:33799647). VALIDATION. `just validate` (schema + terms + full reference validation) passed; `just validate-disorders` (the batched --no-full-text sweep CI runs) passed; `just count-verified-snippets` reports 67/67 snippets verified against cached references; `just verify-datasets` resolved 2/2 accessions; `just check-duplicate-keys` clean over 2334 files. Compliance 95%. No references_cache or cache CSV file was hand-written - all were produced by `just fetch-reference` and `just validate-terms`.

Claude Code ▸

Late-Onset Pompe Disease (LOPD): Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 70 citations 2026-09-01T10:48:01.515064

Late-Onset Pompe Disease (LOPD): Comprehensive Research Report

1. Disease Information

Overview. Late-onset Pompe disease (LOPD) is a progressive, treatable metabolic (lysosomal storage) myopathy caused by partial deficiency of acid α-glucosidase (GAA, acid maltase), the enzyme that hydrolyzes lysosomal glycogen to glucose. It is a subtype of Pompe disease (glycogen storage disease type II, acid maltase deficiency), distinguished from infantile-onset Pompe disease (IOPD) by residual enzyme activity (typically 3–30% of normal, vs. <3% in IOPD) and by later, more slowly progressive presentation. Convention defines LOPD as onset after 12 months of age, or onset under 12 months without cardiomyopathy (PMC10526932; MDPI 13:1279). Clinically it presents as a progressive limb-girdle and axial myopathy with respiratory muscle involvement, often mimicking other neuromuscular disorders, which historically delayed diagnosis by years (NeurologyLive).

Key identifiers: - OMIM: Pompe disease (GSD II) #232300; Late-onset Pompe disease specifically has its own OMIM phenotype entry, #621314 "POMPE DISEASE, LATE-ONSET; LOPD" (OMIM:621314) - Gene: GAA, OMIM *606800, chromosome 17q25.3 - Orphanet: ORPHA:365667 (Late-onset Pompe disease), part of ORPHA:365 (Glycogen storage disease due to acid maltase deficiency) - Synonyms: Acid maltase deficiency (AMD), glycogenosis type II, GSD II, adult/childhood/juvenile-onset acid maltase deficiency, alpha-1,4-glucosidase deficiency - Evidence base is largely aggregated (registries — the Pompe Registry, French National Pompe Registry, ADVANCE study cohort) supplemented by individual case reports/series and single-center retrospective cohorts (e.g., 68-patient single-center Chinese cohort, Frontiers 2026).

2. Etiology

Causal factor: LOPD is monogenic and autosomal recessive, caused by biallelic pathogenic variants in GAA. Over 400–800+ pathogenic/likely pathogenic variants have been catalogued; a large international retrospective study of >30,000 samples from 57 countries identified 723 confirmed cases with 283 distinct GAA alterations, 98 of them novel (PMC10526932).

Genetic risk factors: - The dominant LOPD-associated allele is the intronic splice variant c.-32-13T>G, located 13 nucleotides upstream of the intron 1 acceptor site of GAA. It is a "leaky" splice mutation — it permits a reduced amount of correctly spliced (normal) mRNA alongside aberrantly spliced transcripts lacking exon 2, yielding residual enzyme activity sufficient to avoid the infantile phenotype. It is present on at least one allele in ~90% of LOPD patients and accounts for roughly two-thirds of LOPD alleles overall (PubMed:36401034; ATM Peruzzo). - Population-specific alleles: c.2560C>T (p.Arg854Ter) is the most common pathogenic variant in individuals of African/African-American ancestry, with a documented founder effect traced to North/Central Africa via the transatlantic slave trade (MAF ≈0.0019 in African/African-American gnomAD subpopulation) (Rare Disease Advisor). - Genotype-phenotype correlation: clinical severity correlates broadly with residual GAA activity — <3% normal activity → classic infantile phenotype; 3–30% → late-onset phenotype (PMC7467391; PMC8228169). - Pseudodeficiency alleles (e.g., common in Asian populations) reduce measured GAA enzymatic activity on screening assays without causing disease, complicating newborn screening and dried-blood-spot (DBS) interpretation and requiring confirmatory genetic testing (Neurology Genetics).

Environmental/other risk factors: No environmental, infectious, or lifestyle causal factors are established; LOPD is purely a monogenic disorder. Age and cumulative disease duration are the principal modifiers of severity/functional decline rather than external exposures.

Protective factors: No specific protective genetic or environmental factors have been robustly established; higher residual enzyme activity (a function of genotype) is the primary attenuating factor.

3. Phenotypes

The hallmark phenotype is a slowly progressive limb-girdle and axial myopathy with disproportionate respiratory muscle weakness (PMC6642938).

Phenotype	Frequency/Notes	Suggested HPO term
Proximal/limb-girdle muscle weakness	Core, near-universal finding; pelvic girdle > shoulder girdle	HP:0003325 (Limb-girdle muscle weakness)
Axial (paraspinal/abdominal) weakness → lumbar hyperlordosis, rigid spine	Common, often early	HP:0003713 (Axial muscle weakness); HP:0002943 (Lumbar hyperlordosis)
Exercise intolerance / exertional dyspnea	Common presenting symptom	HP:0003546 (Exercise intolerance)
Respiratory muscle weakness / diaphragmatic weakness → chronic respiratory insufficiency	Major driver of morbidity/mortality; occurs disproportionately relative to limb weakness in a subset	HP:0002093 (Respiratory insufficiency); HP:0009027 (Diaphragmatic weakness)
Scapular winging	~1/3 of patients	HP:0003691 (Scapular winging)
Ptosis (often asymmetric/unilateral)	~1/4 of patients	HP:0000508 (Ptosis)
Bulbar weakness — dysphagia, dysarthria, tongue weakness	Present in a minority, tongue weakness may be early	HP:0002015 (Dysphagia); HP:0001260 (Dysarthria)
HyperCKemia	Very common lab finding	HP:0003236 (Elevated CK)
Wheelchair dependence	~50% by long-term follow-up (mean 16 years)	HP:0002996 (Wheelchair dependence, if modeled)
Ventilator dependence	~19% at long-term follow-up	HP:0040270 (or descriptive)
Cerebral/intracranial arteriopathy (dolichoectasia, aneurysm, stenosis)	~77% (23/30) had abnormal MRA/CTA in one Chinese cohort; 7/30 had stroke/hemorrhage	HP:0002617 (Aneurysm); vascular dolichoectasia terms
Cardiac conduction abnormalities (WPW, short PR)	Present in both IOPD and LOPD, more common in IOPD but reported in LOPD	HP:0001680 (WPW pattern)
Left ventricular hypertrophy	Uncommon/mild in LOPD (~11.5% in one series), unlike IOPD	HP:0001712 (LVH)

Sources: PMC6642938, ATM 27142, PMC5085764, Orphanet J Rare Dis 2024 intracranial vasculopathy.

Onset/progression: Onset ranges from early childhood through late adulthood; median age at diagnosis in one large cohort was 38 years. Progression is typically slow, starting with trunk/lower-limb weakness and progressing to respiratory decline; course is progressive rather than episodic, though rate is variable across patients (PMC3135500).

Quality of life: LOPD substantially impairs mobility, occupational function, and psychosocial well-being; qualitative interviews and EQ-5D-based utility studies (UK) document meaningful QoL decrements tied to mobility loss and respiratory support dependence (PMC9985911).

4. Genetic/Molecular Information

Causal gene: GAA (HGNC:4065; OMIM *606800), chromosome 17q25.3; encodes a 110-kDa precursor polypeptide undergoing extensive ER/Golgi post-translational proteolytic processing to mature lysosomal forms (76 and 70 kDa) (PMC10526932).
Variant classification: ClinGen's Lysosomal Diseases Variant Curation Expert Panel has published ACMG/AMP specifications for GAA variant classification (PMC10872922).
Predominant LOPD allele: c.-32-13T>G (IVS1, leaky splice site variant), typically compound heterozygous with a second, more severe (often null/frameshift/nonsense) allele.
Variant types: missense, nonsense (e.g., c.2560C>T/p.Arg854Ter), frameshift, splice-site (c.-32-13T>G being the classic example), and structural variants.
Allele frequency: Population carrier frequency data derived from gnomAD/general population databases have been used to estimate genetic prevalence, generally exceeding clinically ascertained prevalence, implying underdiagnosis (ScienceDirect S2214426921000288).
Somatic vs. germline: Exclusively germline (autosomal recessive Mendelian disease); no somatic mosaicism disease mechanism reported.
Functional consequence: Loss-of-function (partial) — reduced but non-zero residual GAA enzymatic activity in LOPD, contrasted with near-complete loss in IOPD.
Modifier genes: No robust modifier genes are established, though variability in phenotype among patients with identical genotypes (including twins) suggests undefined modifiers/epigenetic or stochastic factors.
Epigenetics: Not a primary described disease mechanism in LOPD; no major DiseaseMeth/ENCODE-cataloged epigenetic driver identified in the literature reviewed.
Chromosomal abnormalities: Not applicable — LOPD is not associated with aneuploidy or large chromosomal rearrangements; it is a single-gene point-mutation/small-indel disorder.

5. Environmental Information

LOPD has no established environmental, infectious, or toxin-related causal or risk factors — it is a purely genetic (Mendelian) disease. Environmental interaction is largely limited to disease-modifying activity: physical exertion can unmask/exacerbate exercise intolerance, and intercurrent respiratory infections can precipitate acute decompensation given underlying respiratory muscle weakness, but neither modifies underlying genetic risk (Gene-environment interaction: not established in the literature searched).

6. Mechanism / Pathophysiology

Ordered causal chain:

Biallelic pathogenic GAA variants (e.g., c.-32-13T>G + a severe null allele) → leads to reduced synthesis/processing of functional lysosomal acid α-glucosidase enzyme, yielding residual activity of ~3–30% of normal (as opposed to <3% in IOPD).
Reduced GAA activity → results in impaired lysosomal hydrolysis of glycogen, causing progressive lysosomal glycogen accumulation predominantly in skeletal (and to a lesser extent cardiac and smooth) muscle (PMC10419125).
Glycogen-laden, enlarged lysosomes → leads to lysosomal membrane rupture/leakage and mechanical/structural disruption of myofibrillar architecture, contributing directly to muscle fiber damage.
Concurrently, lysosomal acidification defects and dysregulated AMPK–TSC2 signaling suppress mTORC1 activity at the lysosome (mTORC1 is normally lysosome-recruited and activated by Rheb-GTP) → results in failure to inhibit autophagy initiation (loss of mTORC1-mediated ULK1/TFEB suppression) while simultaneously impairing autophagosome–lysosome fusion ("autophagic block") → leads to massive accumulation of autophagic debris (autophagic buildup), which independently displaces contractile elements and worsens fiber damage. This is inferred largely from mouse/cell models but corroborated by human muscle biopsy pathology (EMBO Mol Med; PMC11118179).
In parallel, disrupted lysosomal glucose/glycogen handling triggers cytoplasmic (extralysosomal) glycogen metabolism dysregulation — upregulation of glycogenin (GYG1), glycogen synthase (GYS1), GLUT4, GBE1, and UGP2 — leading to additional cytoplasmic glycogen accumulation that further disrupts myofibrillar structural organization (demonstrated in Pompe mouse muscle and human LOPD biopsies) (PMC10092494).
Chronic ER stress and unfolded protein response activation from proteostasis dysregulation → contributes to ongoing muscle proteostasis failure, active membrane remodeling, and p62/SQSTM1 accumulation, indicating imbalance in autophagic clearance (predominantly in mid-to-late disease stages, while glycogenin elevation is an earlier marker) (PMC10419125).
Cumulative myofiber structural disruption, autophagic buildup, and secondary inflammation → leads to progressive muscle fiber atrophy/necrosis and replacement fibrosis, clinically manifesting as limb-girdle and axial muscle weakness.
Independently, glycogen accumulation in diaphragmatic and other respiratory muscle fibers, and in motor neurons/phrenic nerve pathways, contributes to progressive respiratory insufficiency, a partly independent (branching) pathway from limb weakness, with etiology described as multifactorial (muscle + possible motor neuron pathology) (PMC5085764).
Separately, glycogen accumulation in vascular smooth muscle cells of cerebral arteries, arterioles, and capillaries (demonstrated at autopsy) → leads to progressive arterial wall remodeling and dilative arteriopathy (dolichoectasia, fusiform dilation, aneurysm formation) → can result in cerebral infarction or hemorrhage in a subset of LOPD patients, and separately thoracic aortic dilation, representing a distinct vascular branch of the pathophysiology largely independent of skeletal myopathy severity (Orphanet J Rare Dis 2024; J Neurol 2010).

Molecular pathways: mTORC1/AMPK/TSC2 nutrient-sensing signaling axis (dysregulated); autophagy-lysosome pathway (ULK1, TFEB/TFE3); UPR/ER stress pathway.

Cellular processes: autophagy (defective flux/fusion), lysosomal dysfunction, cytoplasmic glycogen metabolism dysregulation, myofiber atrophy, chronic low-grade inflammation.

Suggested GO terms: GO:0005980 (glycogen catabolic process), GO:0006914 (autophagy), GO:0016236 (macroautophagy), GO:0007041 (lysosomal transport), GO:0034976 (response to endoplasmic reticulum stress), GO:0004339 (glycogen debranching enzyme activity — comparator pathway), GO:0004558 (alpha-1,4-glucosidase activity).

Suggested CL terms: CL:0000188 (skeletal muscle cell/myofiber), CL:0000746 (cardiac muscle cell), CL:0000192 (smooth muscle cell — vascular), CL:0000540 (neuron — motor neuron/phrenic pathway involvement).

Molecular profiling: A muscle proteomic study comparing pre- and post-ERT tissue in LOPD patients found treatment-associated shifts in proteins related to glycolysis, oxidative stress, and cytoskeletal organization (PMC8001152). iPSC-derived skeletal muscle models have been used to model infantile-onset disease and study proteostasis (PMC5647434).

7. Anatomical Structures Affected

Primary organs: skeletal muscle (proximal limb-girdle, axial/paraspinal, diaphragm/respiratory muscles), with cardiac muscle involvement typically mild/absent in LOPD (contrasting sharply with IOPD's severe hypertrophic cardiomyopathy).
Secondary/complication-level involvement: cerebral and thoracic aortic vasculature (dilative arteriopathy, aneurysm, stroke); peripheral/central motor neuron pathways potentially contributing to respiratory muscle dysfunction.
Body systems: musculoskeletal, respiratory, cardiovascular (conduction system and vasculature), and to a lesser degree nervous system (motor pathways, cerebrovascular).
Tissue/cell level: skeletal myofibers (type I/II), diaphragmatic muscle fibers, vascular smooth muscle cells of cerebral/aortic arteries, cardiac conduction tissue (accessory pathways implicated in WPW).
Subcellular level: lysosomes (primary site of glycogen accumulation and dysfunction; GO Cellular Component GO:0005764), autophagosomes, sarcoplasm/myofibrillar apparatus, endoplasmic reticulum (UPR activation).
Anatomical terms (UBERON): UBERON:0001134 (skeletal muscle tissue), UBERON:0001086 (diaphragm), UBERON:0000948 (heart), UBERON:0001981 (blood vessel — cerebral/aortic).
Laterality: Predominantly bilateral/symmetric muscle weakness, though ptosis is frequently asymmetric/unilateral.

8. Temporal Development

Onset: LOPD spans onset from early childhood through late adulthood by definition (after 12 months of age, or infantile-onset without cardiomyopathy); onset pattern is typically insidious/subacute rather than acute.
Progression: Chronic, generally slowly progressive; longitudinal follow-up (mean 16 years) in Dutch cohorts showed pulmonary function decline of ~1.6%/year and gradual proximal weakness progression (PubMed:15659425; referenced in PMC3135500).
Course pattern: Progressive (not relapsing-remitting or episodic); rate is variable between individuals even with similar genotypes.
Disease duration: Chronic, lifelong.
Remission: No spontaneous remission; enzyme replacement therapy (ERT) can stabilize or slow — but generally not reverse — established damage; presymptomatic treatment (newborn-screening-identified) is being explored as a critical window to prevent irreversible myopathy (ScienceDirect S0035378725006083).
Critical period: Early (presymptomatic) initiation of ERT — enabled by newborn screening — is increasingly recognized as a critical intervention window before irreversible muscle damage accrues.

9. Inheritance and Population

Epidemiology: - Global birth prevalence of Pompe disease overall: ~2.0 per 100,000 live births (95% CI 1.5–2.4); infantile-onset ~1.0/100,000; late-onset ~2.4/100,000 (95% CI 1.8–3.0) (PMC12057045). - Newborn screening birth-prevalence estimates for LOPD vary geographically: 1 in 82,914 in Taiwan vs. 1 in 17,133 in Pennsylvania, reflecting both true population variation and pseudodeficiency-allele confounding (PMC7712483; Neurology Genetics). - French National Pompe Registry: diagnosis rate rose from 2.6/year (pre-2001) to 12.8/year (2011–2015), reflecting improved diagnostic awareness/DBS testing rather than true incidence change.

Inheritance pattern: Autosomal recessive. Penetrance: Complete for biallelic pathogenic (non-pseudodeficiency) genotypes, though expressivity (age of onset, rate of progression) is highly variable. Expressivity: Markedly variable, even among patients sharing the c.-32-13T>G/severe-allele genotype. Genetic anticipation: Not described as a feature of LOPD (no repeat-expansion mechanism). Founder effects: c.2560C>T (p.Arg854Ter) — African/African-American founder allele traced to North/Central Africa; other population-specific founder variants reported in isolated populations (e.g., French Guiana Maroon population for infantile disease, PubMed:29637184). Carrier frequency: Estimated from population genomic databases (gnomAD-based); genetic-prevalence modeling suggests carrier frequency and "genetic prevalence" figures often exceed clinically ascertained prevalence, implying underdiagnosis (ScienceDirect S2214426921000288). Population demographics: Higher LOPD prevalence reported in populations of African descent; higher frequency of pseudodeficiency alleles in Asian populations affecting screening specificity. No strong sex-ratio skew is characteristically reported for LOPD (autosomal disease).

10. Diagnostics

First-line test: GAA enzyme activity assay on dried blood spot (DBS), using lysosomal enzyme testing at pH 3.8 with/without specific inhibition (Nature EJHG). Sensitivity limitations exist: in one cohort, reduced DBS activity was found in 7.6% of patients with elevated CK/limb-girdle weakness, but LOPD was molecularly confirmed in only 2.4%, indicating DBS alone can be inconclusive (PubMed:29742245).
Confirmatory testing: Molecular/genetic sequencing of all GAA coding exons and flanking intronic regions (to detect c.-32-13T>G and other variants) is required to confirm diagnosis and exclude pseudodeficiency.
Biomarkers: Urinary/plasma glucose tetrasaccharide (Hex4/Glc4) and creatine kinase (CK) are used as disease-activity/treatment-response biomarkers (elevated pre-treatment, decline with effective ERT) (PMC10834735).
Electromyography: Myopathic changes with characteristic (though not universal) fibrillations/myotonic-like discharges especially in paraspinal muscles.
Muscle biopsy/histopathology: Vacuolar myopathy with PAS-positive glycogen accumulation, though biopsy can be falsely normal in some LOPD patients given patchy involvement — a key diagnostic pitfall.
Pulmonary function testing: Upright and supine forced vital capacity (FVC) — a critical functional biomarker for respiratory muscle involvement and treatment response, used as a primary endpoint in ERT trials.
Genetic testing overview: Single-gene GAA sequencing plus deletion/duplication analysis is generally sufficient (only one causal gene); broader neuromuscular gene panels or WES are used when GAA testing is negative but suspicion remains, and have identified previously unexplained LOPD cases among cohorts referred for "unexplained limb-girdle weakness" (e.g., 606-patient WES cohort, Orphanet J Rare Dis; global NGS cohort, PMC11638199).
Differential diagnosis: limb-girdle muscular dystrophies, Becker muscular dystrophy, facioscapulohumeral muscular dystrophy, scapuloperoneal syndromes, rigid spine syndrome, myasthenia gravis, spinal muscular atrophy, polymyositis, other glycogen storage diseases (III, IV, V, VII), Danon disease, mitochondrial myopathies (PMC7467391).
Screening: Newborn screening for Pompe disease (via DBS GAA activity, now implemented in many US states — Pennsylvania, Illinois, California, and internationally including Taiwan) identifies both IOPD and (presymptomatically) LOPD cases, raising management questions about when to initiate treatment in asymptomatic screen-positive infants/children (PMC7422979; PMC7422983).
Imaging: Muscle MRI shows characteristic patterns of fatty infiltration/edema in paraspinal, gluteal, and thigh musculature, useful for diagnosis and monitoring, though not detailed further in the sources reviewed here.

11. Outcome/Prognosis

Survival (natural history, pre-ERT): In a cohort of 268 untreated adults, median survival after diagnosis was 27 years, with median age at diagnosis 38 years. Median age at death was ~56 years, with respiratory failure accounting for >70% of deaths (PMC3135500).
Functional decline: In a 16-year longitudinal follow-up of 16 LOPD patients, 50% became wheelchair-bound and 19% became ventilator-dependent; pulmonary function (FVC) declined ~1.6%/year at the group level.
Prognostic stratification: 5-year survival was 95% in patients without wheelchair/respiratory support at baseline vs. 74% in those who were wheelchair-bound and on respiratory support — mobility/respiratory status is a major prognostic factor.
Complications: chronic respiratory insufficiency/failure (leading cause of death), cerebrovascular events (aneurysm rupture, stroke), scoliosis/rigid spine, dysphagia-related aspiration risk, and cardiac conduction abnormalities in a minority.
Quality of life: Substantially reduced with disease progression, correlating strongly with mobility and respiratory-support dependence (PMC9985911; PMC4015278 discusses limitations of current LOPD outcome measures).

12. Treatment

Pharmacotherapy — Enzyme Replacement Therapy (ERT), the mainstay of treatment:

Agent	Brand	Mechanism/notes	Suggested NCIT term
Alglucosidase alfa	Myozyme/Lumizyme	First-generation recombinant human GAA (rhGAA); FDA-approved 2006	NCIT:C15986 (Pharmacotherapy) + therapeutic_agent
Avalglucosidase alfa	Nexviazyme/Nexviadyme (Sanofi)	Second-generation; engineered with enhanced bis-mannose-6-phosphate glycan content for improved cellular/M6P-receptor-mediated uptake; superior to alglucosidase alfa on upright FVC% and 6-minute walk test in the Phase 3 COMET trial (treatment-naïve LOPD adults, 49–97 weeks) (PubMed:37036722; PMC10087094)	NCIT:C15986
Cipaglucosidase alfa + miglustat	Pombiliti + Opfolda (Amicus)	Cipaglucosidase alfa uses naturally enriched bis-phosphorylated high-mannose glycans for uptake; miglustat is a small-molecule stabilizer preventing enzyme degradation in circulation; approved combination regimen (Frontiers 2024)	NCIT:C15986

Real-world switch studies (alglucosidase alfa → avalglucosidase alfa) show statistically significant improvement in CK, Hex4, and AST biomarkers post-switch (PMC10834735). Network meta-analyses comparing avalglucosidase alfa vs. cipaglucosidase+miglustat (no head-to-head RCT exists) have been published to guide relative positioning (Becaris CER-2024-0045).

Immunogenicity management: ERT is limited by anti-drug antibody (ADA) development, more prominent and clinically consequential in CRIM-negative infantile patients but also observed in LOPD (antibody titers typically peak within first ~1000 days of ERT then decline with long-term exposure, generally without major efficacy loss). Immune tolerance induction (ITI) regimens — including bortezomib/rituximab/methotrexate/IVIG-based protocols — are used for patients with high-sustained anti-rhGAA titers (Frontiers 2024; PMC10526476).

Advanced/experimental therapeutics — Gene therapy: - ACTUS-101 (AAV2/8-LSPhGAA) (AskBio) — liver-directed gene therapy establishing a hepatic GAA-secretion depot to potentially replace chronic ERT; Phase 1/2 trial in LOPD showed all participants met ERT-withdrawal criteria at week 24 and remained off ERT through week 104 (AskBio; PMC10494494). - SPK-3006 (Roche/Spark, AAVRh74-based liver-directed GAA gene therapy, RESOLUTE trial NCT04093349) — program discontinued by Roche (CGTlive). - Muscle-directed AAV approaches (e.g., AAVMYO3-Gaa) remain preclinical, showing normalized glycogen pathology, restored strength/mass, and normalized survival in mouse models (2024 study) (ScienceDirect S2212877824000309). - As of February 2025, approximately 41 active/recruiting Pompe disease clinical trials span ERT, gene therapy, and substrate-reduction approaches (Rare Disease Advisor).

RNA-based/experimental splice-correction therapy: - Antisense oligonucleotides (splice-modulating phosphorodiamidate morpholino oligomers) designed to enhance GAA exon 2 inclusion in patients heterozygous for c.-32-13T>G, restoring some acid α-glucosidase activity in patient-derived cells — an approach specific to the dominant LOPD splice variant (PubMed:36401034; PMC7174337).

Supportive/rehabilitative care: Non-invasive/invasive ventilatory support for respiratory insufficiency, physical/occupational therapy for mobility preservation, dietary/nutritional management, and mobility aids (wheelchairs) as disease progresses — NCIT:C15302 (Physical Therapy), NCIT:C15747 (Supportive Care).

Treatment strategy: Early diagnosis and presymptomatic/early initiation of ERT (facilitated by newborn screening) is emphasized as key to preserving muscle mass/function before irreversible fibrotic replacement occurs; case reports document improved muscle strength/respiratory function with early ERT initiation (J Med Case Reports 2024).

13. Prevention

Primary prevention: Not applicable in the traditional sense (monogenic recessive disease) — carrier screening and genetic counseling for at-risk families/populations (e.g., known founder-variant communities) is the main preventive lever, alongside prenatal/preimplantation genetic diagnosis for known-carrier couples.
Secondary prevention (screening/early detection): Newborn screening for GAA activity via DBS is implemented in numerous jurisdictions (Pennsylvania, Illinois, California, Taiwan, and others), enabling presymptomatic identification of both IOPD and LOPD cases and earlier treatment initiation (PMC7712483; PMC7422988). Five-year outcomes of NBS-identified Pennsylvania patients have been reported (PMC11943203).
Tertiary prevention: Regular pulmonary function monitoring, cardiac/vascular surveillance (given cerebral/aortic arteriopathy risk), and proactive rehabilitative care to prevent/delay complications (contractures, aspiration, respiratory failure) in diagnosed patients.
Genetic counseling: Recommended for families of affected individuals, particularly relevant given autosomal recessive inheritance and documented founder-effect populations.
Disparities: Documented gaps exist in following up NBS-identified LOPD patients, particularly across sociodemographic groups, highlighting a public-health/pediatric-practice challenge in translating screening into timely care (ScienceDirect S1096719223002639).

14. Other Species / Natural Disease

No naturally occurring veterinary/companion-animal Pompe disease (spontaneous GAA-deficiency) was identified in this search; available information concerns engineered laboratory models (see Section 15). No OMIA entries or veterinary case series for spontaneous canine/feline GSD II were surfaced by the queries run.

15. Model Organisms

Model	Type	Notes
Gaa knockout mouse (B6;129-Gaatm1Rabn/J, Jackson Labs)	Genetic knockout	Full deletion of exon 6 (lacks human ortholog exon); classic Pompe mouse model widely used in preclinical ERT/gene therapy studies
Gaa c.1826dupA transgenic mouse	Patient-derived pathogenic variant knock-in, preserving endogenous Gaa gene structure	Orthologous to human IOPD variant; recapitulates cardiac, myopathic, and biochemical phenotypes longitudinally (Dis Model Mech)
Gaa c.1935C>A (p.D645E) CRISPR knock-in mouse	CRISPR-Cas9 HDR knock-in	Recapitulates multiple features of human infantile-onset Pompe disease (PMC9751086; Sci Rep)
Novel early-onset mouse model with spinal cord/respiratory defects	Genetic	Used to demonstrate rescue via secreted-GAA gene therapy (eBioMedicine)
Rat model (muscle-directed AAV studies)	Genetic/induced	Used for infantile-onset Pompe muscle-directed AAV gene therapy testing (ScienceDirect S2212877824000309)
Zebrafish, quail	Genetic models (referenced)	Noted as additional animal models used in the field, though detail was not retrieved in this search
Patient-derived iPSC skeletal muscle model	Cellular/in vitro	Modeling infantile-onset Pompe disease with patient-specific iPS cells, capturing proteostasis and structural phenotypes (PMC5647434)

Model limitations: Most published genetic mouse models best recapitulate the infantile-onset phenotype (severe/near-null activity); models specifically calibrated to reproduce the partial (leaky) residual-activity genotype characteristic of LOPD are less well represented in the literature surveyed, and cardiac hypertrophy (prominent in IOPD mouse models) is not a major LOPD feature, limiting direct translational relevance for the LOPD cardiac question. The exon-6-deletion knockout allele in the standard Jackson Labs model lacks a direct human orthologous mutation, which is a noted limitation for variant-specific modeling.

Applications: These models have been central to development and validation of ERT (alglucosidase/avalglucosidase alfa), muscle- and liver-directed AAV gene therapy (ACTUS-101 precursor studies, AAVMYO3-Gaa), and mechanistic studies of autophagy/mTORC1 dysregulation and cytoplasmic glycogen metabolism.

Summary of Suggested Ontology Bindings for KB Curation

Gene: hgnc:4065 (GAA)
Disease terms: MONDO (LOPD-specific term, if available) with OMIM #621314 (specific), #232300 (parent GSD II); ORPHA:365667
Key HP terms: HP:0003325 (Limb-girdle muscle weakness), HP:0003713 (Axial muscle weakness), HP:0002093 (Respiratory insufficiency), HP:0003691 (Scapular winging), HP:0000508 (Ptosis), HP:0002015 (Dysphagia), HP:0003236 (Elevated CK), HP:0002617 (Aneurysm)
Key GO terms: GO:0005980 (glycogen catabolic process), GO:0006914 (autophagy), GO:0004558 (alpha-1,4-glucosidase activity)
Key CL terms: CL:0000188 (skeletal muscle myofiber), CL:0000192 (vascular smooth muscle cell)
Key UBERON terms: UBERON:0001134 (skeletal muscle tissue), UBERON:0001086 (diaphragm)
Treatment NCIT terms: NCIT:C15986 (Pharmacotherapy) + therapeutic_agent bindings for alglucosidase alfa / avalglucosidase alfa / cipaglucosidase alfa; therapeutic_modality: PROTEIN_REPLACEMENT (ERT) or GENE_THERAPY (ACTUS-101/AAV programs)

Sources

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	47
Resolved	47
Unresolved (possible confabulation)	0
Unverifiable	0
Quoted claims checked	1
Quoted claims found in source	0
Quoted claims not found in source	1
Quoted claims with nothing to check against	1
References weighed for topical relevance	47
On topic	38
Off topic	0

Quotes not found in the cited source

Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:

Every one of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.

PMC:PMC11638199 (abstract only): "unexplained limb-girdle weakness"
Text part not found as substring: 'unexplained limb-girdle weakness' (note: only abstract available for PMID:39678382, full text may contain this excerpt)

Quotes that could not be checked

There was no text to compare these against, so they are neither confirmed nor contradicted:

DOI:10.1186/s13023-017-0722-1: "unexplained limb-girdle weakness"
Reference resolved but exposes no abstract or full text to search

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome	Count
Terms checked	44
Resolved	34
Unresolved (possible confabulation)	0
Obsolete	1
Unverifiable	9
Terms whose name was checked	30
Terms named correctly	18
Terms named as a different term	6
Terms whose name is worth a second look	6

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

HP:0002996 (1 mention) - the report calls it "Wheelchair dependence, if modeled"; HP calls it Limited elbow movement
HP:0001680 (1 mention) - the report calls it "WPW pattern"; HP calls it Coarctation of aorta
HP:0001712 (1 mention) - the report calls it "LVH"; HP calls it Left ventricular hypertrophy
GO:0004339 (1 mention) - the report calls it "glycogen debranching enzyme activity — comparator pathway"; GO calls it glucan 1,4-alpha-glucosidase activity
CL:0000540 (1 mention) - the report calls it "neuron — motor neuron/phrenic pathway involvement"; CL calls it neuron
UBERON:0001086 (2 mentions) - the report calls it "diaphragm"; UBERON calls it obsolete articular cartilage

Obsolete terms

These terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:

UBERON:0001086 (obsolete articular cartilage) (2 mentions)

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

HP:0003713 (2 mentions) - the report calls it "Axial muscle weakness"; HP calls it Muscle fiber necrosis
HP:0003236 (2 mentions) - the report calls it "Elevated CK"; HP calls it Elevated circulating creatine kinase activity, and lists "Elevated serum CPK" among its other names
HP:0002617 (2 mentions) - the report calls it "Aneurysm"; HP calls it Vascular dilatation, and lists "Aneurysm" among its other names
CL:0000188 (2 mentions) - the report calls it "skeletal muscle cell/myofiber", "skeletal muscle myofiber"; CL calls it cell of skeletal muscle, and lists "skeletal muscle cell" among its other names
CL:0000192 (2 mentions) - the report calls it "smooth muscle cell — vascular", "vascular smooth muscle cell"; CL calls it smooth muscle cell
UBERON:0001981 (1 mention) - the report calls it "blood vessel — cerebral/aortic"; UBERON calls it blood vessel

Terms named inconsistently

The report gives these identifiers more than one name of its own:

CL:0000188 - called "skeletal muscle cell/myofiber", "skeletal muscle myofiber"
CL:0000192 - called "smooth muscle cell — vascular", "vascular smooth muscle cell"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: OMIM, ORPHA, PubMed.

Falcon ▸

Late-Onset Pompe Disease: Comprehensive Disease-Characteristics Report

Edison Scientific Literature 49 citations 2026-08-18T21:14:57.753330

Late-Onset Pompe Disease: Comprehensive Disease-Characteristics Report

Executive summary

Late-onset Pompe disease (LOPD) is a rare, chronic, autosomal-recessive lysosomal glycogen-storage myopathy caused by biallelic pathogenic variants in GAA. Partial deficiency of lysosomal acid α-glucosidase causes glycogen accumulation, lysosomal expansion, blocked autophagic flux, metabolic stress, and progressive injury of skeletal and respiratory muscle. Unlike classic infantile Pompe disease, LOPD usually lacks severe hypertrophic cardiomyopathy. Its defining clinical problems are slowly progressive proximal/axial weakness and diaphragmatic respiratory insufficiency, which can occur independently of limb weakness. Diagnosis relies on low GAA activity—usually screened by dried blood spot—and confirmation by molecular testing and/or a second-tissue enzyme assay. Disease-modifying treatment is lifelong enzyme replacement therapy (ERT), supplemented by respiratory, rehabilitative, nutritional, orthopedic, and psychosocial care.

The most authoritative recent clinical source located was the November 2024 MetabERN pathway, developed using systematic review, AGREE II, and GRADE methods DOI/URL. Its central expert position is that Pompe care should be standardized, multidisciplinary, and initiated before irreversible muscle damage develops. (parenti2024theeuropeanreference pages 11-13, parenti2024theeuropeanreference pages 6-8, parenti2024theeuropeanreference pages 13-14)

Domain	Key facts	Suggested ontology terms
Disease identity / identifiers	Late-onset Pompe disease (LOPD) is the attenuated, non-classic form of Pompe disease/glycogen storage disease type II caused by deficient lysosomal acid alpha-glucosidase; typically presents after infancy with progressive skeletal and respiratory muscle involvement and little/no hypertrophic cardiomyopathy (labella2023acomprehensiveupdate pages 8-10, ozdamar2023expertopinionon pages 1-2)	MONDO: Late-onset Pompe disease (exact ID not confirmed here); OMIM: Pompe disease 232300; MeSH: Pompe Disease (ID not confirmed here)
Synonyms	Acid maltase deficiency; glycogen storage disease type II; late-onset acid alpha-glucosidase deficiency; non-classic Pompe disease (parenti2024theeuropeanreference pages 11-13, labella2023acomprehensiveupdate pages 8-10)	MONDO exact synonyms (curate locally)
Data provenance	Information is disease-level, aggregated from guidelines, reviews, cohorts, clinical trials, and registries rather than individual EHR-only evidence (ozdamar2023expertopinionon pages 4-6, parenti2024theeuropeanreference pages 11-13, labella2023acomprehensiveupdate pages 8-10)	Evidence model: aggregated disease knowledge
Causal gene / inheritance	Caused by biallelic pathogenic variants in GAA; autosomal recessive inheritance. Residual GAA activity is higher in LOPD than infantile disease and correlates with attenuated severity (parenti2024theeuropeanreference pages 6-8, labella2023acomprehensiveupdate pages 8-10)	HGNC: GAA; GO: glycogen catabolic process; inheritance term: autosomal recessive inheritance
Common pathogenic / notable variants	The splice variant c.-32-13T>G is the most common in many Caucasian cohorts; substantial allelic heterogeneity exists with hundreds of disease-associated variants. Pseudodeficiency alleles can complicate diagnosis and should not be overcalled as pathogenic (alandydy2019variableclinicalfeatures pages 1-2, moschetti2024mutationspectrumof pages 1-2, giliberto2024frompastto pages 12-15)	Sequence ontology classes: splice-region variant, missense variant, frameshift variant, nonsense variant; ClinVar/ACMG classification terms
Hallmark phenotype: proximal/axial weakness	Core phenotype is progressive proximal limb-girdle and axial/paraspinal weakness, often with exercise intolerance, fatigue, and difficulty climbing stairs/rising from chairs (ozdamar2023expertopinionon pages 3-4, ozdamar2023expertopinionon pages 2-3)	HPO: Proximal muscle weakness (HP:0003701); Limb-girdle muscle weakness (HP:0003325); Axial muscle weakness (HP:0003327); Exercise intolerance (HP:0003546); Fatigue (HP:0012378)
Hallmark phenotype: respiratory involvement	Diaphragmatic/intercostal weakness may precede marked limb weakness; restrictive ventilatory insufficiency, sleep-disordered breathing, morning headache, impaired cough, and respiratory failure drive major morbidity/mortality (ozdamar2023expertopinionon pages 3-4, labella2023acomprehensiveupdate pages 8-10, ozdamar2023expertopinionon pages 1-2)	HPO: Respiratory insufficiency (HP:0002093); Restrictive ventilatory defect (HP:0002091); Sleep apnea (HP:0010535); Dyspnea (HP:0002094)
Additional manifestations	HyperCKemia may be present but can be normal; myalgia, scoliosis/spinal deformity, winged scapula, osteopenia/osteoporosis, dysphagia, and reported cerebrovascular abnormalities such as aneurysms/vertebrobasilar dolichoectasia (ozdamar2023expertopinionon pages 3-4, parenti2024theeuropeanreference pages 11-13, labella2023acomprehensiveupdate pages 8-10, ozdamar2023expertopinionon pages 2-3)	HPO: Elevated creatine kinase (HP:0003236); Myalgia (HP:0003326); Scoliosis (HP:0002650); Dysphagia (HP:0002015); Osteoporosis (HP:0000939); Intracranial aneurysm (HP:0004942)
Anatomy affected	Primary organs/tissues: skeletal muscle and respiratory muscles, especially paraspinal, abdominal, hip extensor, and diaphragm-related musculature; secondary systems include bone, GI/swallowing, and cerebrovascular structures (parenti2024theeuropeanreference pages 11-13, labella2023acomprehensiveupdate pages 8-10, ozdamar2023expertopinionon pages 2-3)	UBERON: skeletal muscle tissue; diaphragm; respiratory system; CL: skeletal muscle cell/myofiber (exact CL ID not confirmed here); macrophage
Temporal course / natural history	Onset is juvenile-to-adult and often insidious. Diagnostic delay may span 5-30 years; untreated disease shows progressive decline in respiratory function and ambulation, with FVC deterioration detectable within ~2 years and 6MWT decline within ~9 years in natural-history observations summarized by experts (ozdamar2023expertopinionon pages 3-4, ozdamar2023expertopinionon pages 4-6)	HPO onset modifiers: juvenile onset, adult onset; course: progressive
Core mechanism	Loss of lysosomal GAA prevents normal glycogen hydrolysis, causing lysosomal glycogen accumulation, swollen lysosomes, and progressive myofiber dysfunction; skeletal muscle pathology is strongly linked to autophagic buildup and impaired lysosome-autophagosome fusion (monceau2024decodingthemuscle pages 1-2, do2024failureofautophagy pages 7-8, do2024failureofautophagy pages 4-5)	GO: glycogen catabolic process; lysosome organization; autophagy; macroautophagy; GO-CC: lysosome; autophagosome
Downstream molecular pathology	Human and model data show autophagy gene upregulation, reduced mTORC1 activity, AMPK activation, impaired oxidative phosphorylation, mitochondrial/ribosomal dysfunction, oxidative stress, ubiquitinated aggregates, and p62/SQSTM1 accumulation (monceau2024decodingthemuscle pages 1-2, monceau2024decodingthemuscle pages 2-3, moriggi2021muscleproteomicprofile pages 1-2, do2024failureofautophagy pages 5-7)	GO: regulation of mTOR signaling; AMPK signaling (pathway label; exact GO term curate locally); mitochondrial ATP synthesis coupled electron transport; response to oxidative stress; protein ubiquitination
Cell types implicated	Main affected cells are skeletal myofibers; 2024 single-nucleus/spatial transcriptomics also found increased regenerative/slow fibers and macrophages in LOPD muscle (monceau2024decodingthemuscle pages 1-2)	CL: skeletal muscle cell (exact ID not confirmed here); slow-twitch skeletal muscle fiber (term curate locally); myoblast/regenerating myonucleus (term curate locally); macrophage (CL:0000235)
Omics findings	Single-nucleus RNA-seq plus spatial transcriptomics in 8 LOPD biopsies and 4 controls identified early reduced glycolysis, increased lipid/amino-acid metabolism, autophagy activation, and vacuole-specific inflammation/apoptosis/regeneration signals; proteomics found 178 altered proteins, with only 47 normalized after 1 year of ERT (monceau2024decodingthemuscle pages 1-2, moriggi2021muscleproteomicprofile pages 1-2)	GO: glycolytic process; lipid catabolic/metabolic process; amino acid metabolic process; apoptotic process; muscle regeneration (curate exact GO term)
Diagnostic approach	First-line screening is dried blood spot GAA enzyme activity followed by confirmatory GAA testing in leukocytes/fibroblasts/muscle and/or molecular testing. Normal CK, EMG, or biopsy does not exclude LOPD (ozdamar2023expertopinionon pages 3-4, ozdamar2023expertopinionon pages 1-2)	NCIT-style diagnostics: dried blood spot assay; enzyme activity assay; molecular genetic testing
Diagnostic tests / findings	EMG may show myopathic changes with myotonic discharges, especially in paraspinal muscles; muscle MRI often shows paravertebral/abdominal/hip extensor involvement; biopsy shows vacuolar myopathy with glycogen storage (ozdamar2023expertopinionon pages 3-4, labella2023acomprehensiveupdate pages 8-10)	HPO: Myopathic EMG abnormalities (HP:0003457) (confirm locally); pathology term: vacuolar myopathy; imaging term: muscle MRI abnormality
Biomarkers / monitoring	CK may be mildly elevated or normal; AST/ALT may rise; urinary glucose tetrasaccharide/Glc4 (Hex4), BNP/pro-BNP, vacuolated PAS-positive lymphocytes, dystromirs (miR-1-3p, miR-133a-3p, miR-206), and neurofilament light chain are reported monitoring biomarkers (parenti2024theeuropeanreference pages 6-8, labella2023acomprehensiveupdate pages 8-10, labella2023acomprehensiveupdate pages 21-22, byrne2024longtermsafetyand pages 1-2)	CHEBI: glucose tetrasaccharide (exact CHEBI ID not confirmed here); biomarker labels: CK, BNP, pro-BNP, miR-1-3p, miR-133a-3p, miR-206, NfL
Functional monitoring	Recommended serial assessments include seated/supine FVC, polysomnography where indicated, MRC/manual muscle testing, 6-minute walk test, timed tests, hand-held dynamometry, ECG/echocardiography, and periodic brain/cerebrovascular imaging in selected patients (ozdamar2023expertopinionon pages 4-6, parenti2024theeuropeanreference pages 11-13, parenti2024theeuropeanreference pages 6-8, labella2023acomprehensiveupdate pages 8-10)	NCIT-style procedures: spirometry; polysomnography; 6-minute walk test; electromyography; echocardiography; magnetic resonance imaging
Differential diagnosis	Limb-girdle muscular dystrophies, inflammatory myopathies, mitochondrial disorders, other glycogenoses, and oculopharyngeal muscular dystrophy should be considered; pseudodeficiency alleles can mimic low enzyme activity (parenti2024theeuropeanreference pages 11-13, ozdamar2023expertopinionon pages 1-2, giliberto2024frompastto pages 12-15)	Differential set terms: limb-girdle muscular dystrophy; inflammatory myopathy; mitochondrial myopathy; oculopharyngeal muscular dystrophy
Epidemiology / population	Rare disease; often cited prevalence/incidence is roughly 1 in 40,000-57,000, with under-recognition likely. Geographic/population carrier frequencies and predicted prevalence vary substantially, including higher predicted prevalence in some East Asian datasets (alandydy2019variableclinicalfeatures pages 1-2, sharshakova2026pompediseasepathogenesis pages 1-2, aguilargonzalez2022isogenicgaakomurine pages 1-2)	ORDO/epidemiology labels: rare disease; prevalence estimate
Prognosis / burden	Chronic lifelong disorder with reduced survival in adult/non-classic Pompe disease and substantial HRQoL impact. Respiratory insufficiency remains a major cause of morbidity and mortality despite ERT (ozdamar2023expertopinionon pages 1-2, byrne2024longtermsafetyand pages 1-2)	HPO: Reduced life expectancy (HP:0003676) (use cautiously); patient-reported outcome domains: physical function, fatigue, mobility, self-care
Approved disease-modifying therapy: alglucosidase alfa	First-generation recombinant human GAA; licensed dose 20 mg/kg every 2 weeks IV. Improves/stabilizes 6MWT and FVC, but benefit often plateaus after ~2-3 years with later decline in many patients (labella2023acomprehensiveupdate pages 11-12, parenti2024theeuropeanreference pages 13-14)	NCIT-style intervention: Enzyme Replacement Therapy; drug label: alglucosidase alfa
Approved disease-modifying therapy: avalglucosidase alfa	Next-generation rhGAA with enhanced mannose-6-phosphate targeting; approved FDA 2021 / EMA 2022. In expert-summary data, FVC gain at week 49 was 2.89% vs 0.46% for alglucosidase comparator (ozdamar2023expertopinionon pages 4-6, parenti2024theeuropeanreference pages 13-14)	NCIT-style intervention: Enzyme Replacement Therapy; drug label: avalglucosidase alfa
Approved disease-modifying therapy: cipaglucosidase alfa + miglustat	Two-component therapy approved in adults with LOPD (EMA 2023 noted in guideline evidence). Long-term studies show maintained/stable respiratory and walking outcomes with biomarker improvement; phase I/II used 20 mg/kg IV biweekly cipaglucosidase alfa + 260 mg oral miglustat (byrne2024longtermsafetyand pages 1-2, parenti2024theeuropeanreference pages 13-14)	NCIT-style interventions: Enzyme Replacement Therapy + Pharmacological Chaperone Therapy/Enzyme Stabilizer; drug labels: cipaglucosidase alfa, miglustat
Supportive care	Multidisciplinary management includes pulmonary support/ventilation, airway clearance, physical therapy, swallowing/nutrition assessment, orthopedic/bone health management, psychological care, pregnancy planning, and QoL monitoring (parenti2024theeuropeanreference pages 11-13, labella2023acomprehensiveupdate pages 8-10, ozdamar2023expertopinionon pages 2-3)	NCIT-style interventions: noninvasive ventilation; physical therapy; occupational therapy; nutritional support; speech/swallow therapy
Experimental / active trials	RESOLUTE (NCT04093349): AAV gene transfer (SPK-3006), phase 1/2, active-not-recruiting, adults on prior ERT; additional interventional studies include S-606001 add-on therapy (NCT07123155) and extension (NCT07750990) (NCT04093349 chunk 1, NCT07123155 chunk 1, NCT07750990 chunk 1)	NCIT-style intervention: Gene Therapy; AAV vector gene transfer; small-molecule add-on therapy
Prevention / screening	No primary environmental prevention. Secondary prevention centers on newborn screening where available, early recognition of asymptomatic/presymptomatic cases, carrier testing, cascade family testing, reproductive counseling, and early treatment before fixed muscle damage (ozdamar2023expertopinionon pages 4-6, labella2023acomprehensiveupdate pages 8-10)	NCIT-style interventions: newborn screening; carrier screening; genetic counseling; cascade screening
Environmental / infectious factors	No established infectious cause. No convincing environmental toxin/lifestyle cause for disease occurrence; non-genetic factors mainly influence complications and management rather than primary causation (labella2023acomprehensiveupdate pages 8-10, ozdamar2023expertopinionon pages 1-2)	Not applicable / no established environmental etiologic ontology term
Model organisms / natural disease	Key preclinical systems include Gaa knockout mouse, murine GAA-KO muscle cell lines, and naturally occurring animal models including Japanese quail; models recapitulate lysosomal glycogen storage and autophagic pathology and are used for ERT/gene-therapy development (aguilargonzalez2022isogenicgaakomurine pages 1-2, do2024failureofautophagy pages 7-8)	NCBI Taxon: Mus musculus; Coturnix japonica; model types: knockout mouse, muscle cell line, natural animal model

Table: This compact table summarizes the most actionable disease-knowledge fields for late-onset Pompe disease, including genetics, core phenotypes, mechanisms, diagnostics, therapies, epidemiology, and models. It is designed for rapid knowledge-base curation with conservative ontology suggestions and evidence-linked claims.

1. Disease information

Definition and category. LOPD is the attenuated juvenile/adult spectrum of Pompe disease, a Mendelian lysosomal storage disorder, glycogen storage disease, metabolic myopathy, and autophagic myopathy. Common names are glycogen storage disease type II, acid maltase deficiency, acid α-glucosidase deficiency, non-classic Pompe disease, juvenile-onset Pompe disease, and adult-onset Pompe disease. LOPD is generally defined by onset after infancy and residual enzyme activity; boundaries based on age vary among publications. (aguilargonzalez2022isogenicgaakomurine pages 1-2, ozdamar2023expertopinionon pages 1-2)

Identifiers. Pompe disease is OMIM 232300. Appropriate disease-level mappings include MeSH Pompe Disease, Orphanet Pompe disease, and ICD-10-CM E74.02 (Pompe disease). ICD-11 places Pompe disease under glycogen-storage disorders. The exact LOPD-specific MONDO identifier was not verified in the retrieved evidence and should be resolved directly against the current MONDO release rather than inferred. The evidence summarized here is aggregated from guidelines, cohorts, trials, and disease registries—not individual EHR records.

A concise abstract statement from the 2023 review is: “Pompe disease … is an autosomal recessive disorder caused by mutations in the GAA gene.” Published August 2023; DOI/URL. (labella2023acomprehensiveupdate pages 8-10)

2. Etiology, risk, protection, and gene–environment interaction

The necessary cause is biallelic germline GAA dysfunction. GAA, at chromosome 17q25, encodes lysosomal acid α-glucosidase, which hydrolyzes α-1,4 and α-1,6 glycogen linkages. LOPD commonly retains approximately 2–40% assay-dependent residual activity, versus <1% in classic infantile disease; residual activity broadly predicts phenotype but does not completely explain expressivity. (moschetti2024mutationspectrumof pages 1-2, parenti2024theeuropeanreference pages 6-8)

The major “risk factors” are therefore two pathogenic parental alleles, family history, ancestry-associated founder/common alleles, and consanguinity. The European splice variant NM_000152.5:c.-32-13T>G is particularly common in affected White populations and permits some correctly spliced transcript. In one 18-person LOPD cohort it occurred in 16/18 patients. More than 900 disease-associated GAA variants have been catalogued across missense, nonsense, frameshift, splice, indel, and larger rearrangement classes. (alandydy2019variableclinicalfeatures pages 1-2, moschetti2024mutationspectrumof pages 1-2)

No toxin, infection, smoking behavior, diet, occupation, or radiation exposure is an established primary cause. Exercise, nutrition, intercurrent infection, and respiratory care can alter function or complications but do not determine whether genetically susceptible individuals have Pompe disease. No validated protective GAA allele, environmental prevention, or reproducible disease-modifier gene is established for routine clinical use. Exercise-gene polymorphisms and other modifiers remain investigational. Gene–environment interaction evidence is therefore limited chiefly to how activity, nutrition, aging, infection, and treatment interact with a fixed enzymatic defect.

3. Phenotypes and quality of life

LOPD is heterogeneous and insidious. Core manifestations are:

Proximal lower-limb and limb-girdle weakness (HP:0003701/HP:0003325), difficulty climbing stairs or rising from a chair, waddling gait, and exercise intolerance (HP:0003546).
Axial/paraspinal weakness (HP:0003327), lumbar hyperlordosis, scapular winging, scoliosis (HP:0002650), and later contractures.
Respiratory-muscle and diaphragmatic weakness, restrictive ventilatory defect (HP:0002091), orthopnea/dyspnea, impaired cough, sleep-disordered breathing or sleep apnea (HP:0010535), morning headache, recurrent infection, and respiratory failure (HP:0002093). Respiratory dysfunction may precede conspicuous limb weakness and is the principal cause of morbidity and mortality. (ozdamar2023expertopinionon pages 3-4, ozdamar2023expertopinionon pages 2-3, ozdamar2023expertopinionon pages 1-2)
Laboratory abnormalities: CK may be normal or elevated—sometimes up to 15-fold—while AST/ALT can be mildly elevated. Normal CK does not exclude disease. (ozdamar2023expertopinionon pages 3-4, labella2023acomprehensiveupdate pages 8-10)
Other multisystem findings: fatigue (HP:0012378), myalgia (HP:0003326), dysphagia (HP:0002015), feeding/nutritional difficulties, low bone density/osteoporosis (HP:0000939), and occasional hearing, gastrointestinal, urinary, or cerebrovascular abnormalities. Intracranial aneurysm and vertebrobasilar dolichoectasia have been reported, but their population frequency and screening yield remain uncertain. Cardiac disease is usually absent or mild, although occasional cardiomyopathy occurs. (alandydy2019variableclinicalfeatures pages 1-2, parenti2024theeuropeanreference pages 11-13)

Severity ranges from asymptomatic hyperCKemia to wheelchair and ventilator dependence. In one small cohort, 12/18 used BiPAP, 5/18 had scoliosis, 3/18 cardiomyopathy, and 2/18 cerebral aneurysm; these are descriptive referral-cohort frequencies, not generalizable prevalence estimates. (alandydy2019variableclinicalfeatures pages 1-2)

LOPD impairs mobility, self-care, work, social participation, fatigue, and emotional well-being. PROMIS, EQ-5D-5L, Rasch-built Pompe-specific Activity, and Subject’s Global Impression of Change are relevant instruments. In PROPEL, 90% receiving cipaglucosidase alfa plus miglustat versus 59% receiving alglucosidase/placebo were responders for perceived ability to move around at week 52 (P=0.0005). (byrne2024longtermsafetyand pages 1-2)

4. Genetic and molecular information

Causal gene: GAA; germline, autosomal recessive, loss-of-function. Variants may reduce transcription/splicing, folding, lysosomal trafficking, proteolytic maturation, or catalytic activity. The phenotype reflects the combined residual function of both alleles, but genotype–phenotype correlation is imperfect. In a 2024 Italian screen of 2,934 symptomatic referrals, 39 had low enzyme activity plus two causal variants and 22 carried variants of uncertain significance. (moschetti2024mutationspectrumof pages 2-3, moschetti2024mutationspectrumof pages 3-5)

Variant interpretation should follow ACMG/AMP and ClinGen Lysosomal Diseases Variant Curation Expert Panel specifications. Pseudodeficiency alleles lower activity against artificial substrates without causing Pompe disease. c.271G>A (p.Asp91Asn) was classified as benign in the cited analysis; overcalling it can produce inappropriate ERT and obscure another diagnosis. Sequence analysis should be supplemented by deletion/duplication analysis if two explanatory alleles are not found; RNA studies can resolve cryptic splice variants. Allele frequencies must be checked variant-by-variant in current gnomAD/ClinVar releases. (giliberto2024frompastto pages 12-15)

No recurrent aneuploidy, translocation, repeat expansion, mitochondrial-DNA defect, or somatic driver defines LOPD. CMA, karyotyping, FISH, and repeat-expansion testing are not first-line tests. Disease-specific epigenetic alterations are not validated diagnostic or prognostic markers.

5. Environmental information

Environmental, infectious, and lifestyle causes are not applicable as primary etiology. Respiratory infections can precipitate decompensation; immobility aggravates deconditioning, osteoporosis, and contractures. Carefully prescribed aerobic and resistance activity, adequate protein/energy intake, vaccination, airway clearance, and avoidance of prolonged inactivity support health but do not correct GAA deficiency.

6. Mechanism and pathophysiology

The causal chain is:

biallelic GAA loss → deficient lysosomal glycogen hydrolysis → glycogen-filled/swollen lysosomes → lysosomal rupture/trafficking disturbance and failed autophagosome–lysosome fusion → autophagic debris, p62/SQSTM1 and ubiquitinated-protein accumulation → AMPK activation, reduced mTORC1 signaling, altered TFEB activity, oxidative stress and mitochondrial dysfunction → myofibrillar disorganization, apoptosis/regeneration, weakness and respiratory failure. (monceau2024decodingthemuscle pages 1-2, do2024failureofautophagy pages 7-8, do2024failureofautophagy pages 5-7, do2024failureofautophagy pages 4-5)

Autophagic lesions in adult muscle may exceed the apparent lysosomal enlargement; biopsies show autophagic vacuoles in approximately 30–40% of fibers, and buildup can occupy up to 40% of fiber volume in knockout mice. Type II myofibers are particularly affected in models. Autophagic debris also impedes recombinant-enzyme delivery, helping explain incomplete skeletal-muscle response. TFEB overexpression or experimental mTORC1 restoration can reverse buildup in model systems, but neither is established human therapy. Suggested annotations include GO glycogen catabolic process, macroautophagy, lysosome organization, response to oxidative stress, and GO cellular components lysosome and autophagosome. Principal CL mapping is skeletal muscle cell/myofiber; macrophages and regenerative myogenic cells are downstream participants. (do2024failureofautophagy pages 7-8, do2024failureofautophagy pages 5-7, do2024failureofautophagy pages 4-5)

Recent multi-omics. A 2024 study applied single-nucleus RNA-seq to biopsies from eight LOPD patients and four matched controls and spatially compared normal, non-vacuolated, and vacuolated fibers. Early non-vacuolated fibers had reduced glycolysis with increased lipid/amino-acid metabolism; affected tissue showed more slow/regenerative fibers and macrophages, autophagy upregulation, reduced ribosomal/mitochondrial programs, and defective oxidative phosphorylation. Inflammation, apoptosis, and regeneration were concentrated in vacuolated fibers. Published July 2024; DOI/URL. (monceau2024decodingthemuscle pages 1-2, monceau2024decodingthemuscle pages 2-3)

Proteomics identified 178 altered muscle proteins, of which only 47 normalized after one year of ERT; oxidative metabolism, contractile regulation, cytoskeletal remodeling, ER stress, unfolded-protein response, and lysosomal-tethering abnormalities persisted. Published March 2021; DOI/URL. (moriggi2021muscleproteomicprofile pages 1-2, moriggi2021muscleproteomicprofile pages 16-17)

7. Anatomical structures

Primary involvement is bilateral, generally symmetric skeletal muscle: pelvic-girdle, hip extensors, thigh, paraspinal/axial, abdominal-wall, diaphragm, and intercostal muscles. Respiratory muscle involvement may be disproportionate. Secondary targets include bulbar/swallowing musculature, bone, smooth muscle, and cerebral arterial walls. The relevant subcellular compartments are lysosome, autophagosome, mitochondrion, ER, and cytosol. Suggested UBERON mappings include skeletal muscle tissue, diaphragm, abdominal muscle, paraspinal muscle, respiratory system, and cerebral artery. (parenti2024theeuropeanreference pages 11-13, labella2023acomprehensiveupdate pages 8-10)

8. Temporal development

Onset may occur from childhood through late adulthood and is usually chronic and insidious. Disease is lifelong, variably progressive, and does not spontaneously remit. Diagnostic delay is commonly 5–30 years, and nearly one-third of patients may initially receive another diagnosis. Untreated natural-history summaries report detectable FVC deterioration within approximately two years and 6-minute-walk deterioration over longer intervals, around nine years, although individual trajectories vary greatly. Early treatment is the main modifiable prognostic opportunity because established fatty replacement and autophagic destruction are incompletely reversible. (ozdamar2023expertopinionon pages 3-4, ozdamar2023expertopinionon pages 4-6)

9. Inheritance and population

Inheritance is autosomal recessive: each pregnancy of two heterozygous carriers has a 25% affected, 50% carrier, and 25% unaffected/non-carrier probability. Penetrance for genuinely pathogenic biallelic genotypes is high but age-dependent; expressivity is markedly variable. Anticipation is not recognized. Germline mosaicism is theoretically possible but not a characteristic feature.

Frequently cited overall Pompe prevalence is approximately 1:40,000–1:57,000, but newborn sequencing estimates suggest underdiagnosis and marked ancestry variation. Population-database modeling estimated carrier frequencies of 1.7% in Koreans and 0.7% in Japanese, corresponding to predicted genetic prevalences of 1:13,657 and 1:78,013; such predictions include uncertainty from penetrance and variant classification. Both sexes are affected approximately equally. (alandydy2019variableclinicalfeatures pages 1-2, aguilargonzalez2022isogenicgaakomurine pages 1-2)

10. Diagnostics and screening

Recommended pathway: recognize unexplained proximal/axial weakness, diaphragmatic restriction, exercise intolerance, or hyperCKemia → dried-blood-spot GAA assay → confirm low activity in leukocytes, fibroblasts, or muscle and identify two pathogenic/likely pathogenic GAA alleles. A second independent method is important because sample quality and pseudodeficiency can cause false positives. (ozdamar2023expertopinionon pages 3-4, ozdamar2023expertopinionon pages 1-2)

Assess CK, AST/ALT, urinary Glc4/Hex4, seated and supine FVC, maximal inspiratory/expiratory pressures, sleep study/oximetry, cough flow, MRC strength, dynamometry, timed tests, and 6MWT. A >25% seated-to-supine FVC fall suggests diaphragmatic weakness. EMG may show myopathy and paraspinal myotonic discharges without clinical myotonia. MRI characteristically identifies paraspinal, abdominal, and hip-extensor involvement. Biopsy—now reserved for unresolved cases—shows PAS-positive, acid-phosphatase-positive glycogen vacuoles and autophagic pathology. (ozdamar2023expertopinionon pages 3-4, labella2023acomprehensiveupdate pages 8-10)

Potential monitoring biomarkers include urinary Glc4/Hex4, CK, BNP/pro-BNP where cardiac disease is suspected, vacuolated PAS-positive lymphocytes, miR-1-3p/miR-133a-3p/miR-206, and neurofilament light; none replaces clinical respiratory and motor assessment. (parenti2024theeuropeanreference pages 6-8, labella2023acomprehensiveupdate pages 21-22)

Differentials include limb-girdle muscular dystrophy, inflammatory or mitochondrial myopathy, other glycogenoses, spinal muscular disease, congenital myopathy, Danon disease, and oculopharyngeal muscular dystrophy. Normal CK, EMG, or biopsy does not exclude LOPD. (giliberto2024frompastto pages 12-15, ozdamar2023expertopinionon pages 3-4, parenti2024theeuropeanreference pages 11-13)

WES/WGS or neuromuscular panels are useful when phenotype is atypical or single-gene analysis is incomplete; RNA sequencing can establish splice effects. Newborn screening, presymptomatic sibling testing, carrier/cascade screening, prenatal diagnosis, and preimplantation genetic testing are technically feasible after familial variants are known.

11. Outcome and prognosis

Respiratory insufficiency, infection, and progressive neuromuscular disability dominate morbidity and mortality. Adult survival is reduced, but robust contemporary 5- or 10-year survival percentages are not established because of rarity, phenotypic heterogeneity, and treatment-era change. Prognosis is better with earlier diagnosis, greater baseline motor/FVC reserve, lower fixed fatty replacement, and sustained treatment. ERT generally improves or stabilizes function initially but does not reliably reverse advanced disease; many patients plateau after two to three years and subsequently decline. (byrne2024longtermsafetyand pages 1-2, labella2023acomprehensiveupdate pages 11-12)

12. Treatment and real-world implementation

Alglucosidase alfa: recombinant human GAA, 20 mg/kg IV every two weeks; first approved in 2006. The 90-person LOTS trial improved/stabilized 6MWD and percent-predicted FVC. Infusion reactions and anti-drug antibodies occur; skeletal-muscle uptake and durability are limited. (labella2023acomprehensiveupdate pages 11-12, parenti2024theeuropeanreference pages 13-14)
Avalglucosidase alfa: second-generation rhGAA enriched for mannose-6-phosphate receptor targeting, 20 mg/kg every two weeks. COMET established non-inferiority to alglucosidase; an expert summary reported week-49 FVC gains of 2.89 versus 0.46 percentage points, without statistically confirmed superiority. FDA approval was in 2021 and EMA approval in 2022. (ozdamar2023expertopinionon pages 4-6, labella2023acomprehensiveupdate pages 11-12)
Cipaglucosidase alfa plus miglustat: high-M6P rhGAA plus an oral enzyme stabilizer. A phase I/II regimen used cipaglucosidase 20 mg/kg IV plus miglustat 260 mg orally every two weeks. At up to 48 months, ambulatory ERT-experienced patients maintained approximately 5–6% predicted 6MWD improvement, while ERT-naïve patients had approximately 10–12%; FVC was stable in experienced patients and improved 3–8% in the small naïve cohort. CK and Hex4 improved, with safety resembling alglucosidase. EMA approval occurred in 2023; subsequent US approval applies to selected adults inadequately responding to current ERT. Published December 2024; DOI/URL. (byrne2024longtermsafetyand pages 1-2, parenti2024theeuropeanreference pages 13-14)

Suggested NCIT intervention concepts are enzyme replacement therapy, alglucosidase alfa, avalglucosidase alfa, cipaglucosidase alfa, miglustat, noninvasive ventilation, physical therapy, and gene therapy; exact codes should be validated against the current NCIT release.

Supportive management includes individualized submaximal aerobic/resistance therapy without overwork injury, stretching and contracture prevention, mobility aids, noninvasive ventilation, airway-clearance/cough-assist techniques, vaccination, prompt infection treatment, swallowing and nutritional assessment, bone-health care, occupational therapy, and psychosocial support. ERT should begin promptly in symptomatic patients and in presymptomatic patients with objective weakness or respiratory abnormality; clinically silent individuals require approximately six-month surveillance. (ozdamar2023expertopinionon pages 4-6, parenti2024theeuropeanreference pages 11-13)

Experimental therapy. RESOLUTE (NCT04093349) is an active-not-recruiting phase 1/2 dose-escalation study of AAV vector SPK-3006 in adults previously treated with ERT; four participants were enrolled, with five-year safety and immune follow-up. ClinicalTrials.gov. Gene therapy’s goals are sustained endogenous GAA secretion and cross-correction, but capsid immunity, transgene immunity, dose toxicity, durability, and skeletal-muscle delivery remain unresolved. (NCT04093349 chunk 1)

13. Prevention

There is no vaccine, exposure avoidance, or lifestyle intervention that prevents the genetic disease. Primary genetic prevention/options include carrier testing, genetic counseling, prenatal diagnosis, and preimplantation genetic testing. Secondary prevention comprises newborn/cascade screening and treatment before irreversible weakness. Tertiary prevention includes ERT, respiratory surveillance/support, vaccination, airway clearance, safe exercise, fall/contracture prevention, bone care, and nutrition. Each sibling of an affected individual should receive targeted familial-variant and/or enzyme testing.

14. Natural disease in other species

Pompe-like natural GAA deficiency has been described in Japanese quail (Coturnix japonica, NCBI Taxon 93934), with additional spontaneous glycogen-storage models reported across domestic species. It is inherited/metabolic, not transmissible or zoonotic. Comparative pathology includes lysosomal glycogen storage and muscle dysfunction, although species differ in severity, cardiac involvement, and treatment response. (aguilargonzalez2022isogenicgaakomurine pages 1-2)

15. Model organisms

The principal model is the Gaa-knockout mouse (Mus musculus, Taxon 10090), which reproduces absent enzyme, skeletal/cardiac glycogen storage, weakness, autophagic buildup, and impaired ERT delivery. Its limitations are severe/null-genotype biology, strain-dependent phenotype, and imperfect modeling of decades-long human LOPD. Japanese quail offers a natural model. CRISPR-generated GAA-knockout murine myotubes reproduce absent activity, glycogen excess, increased autophagy, and reduced cation-independent mannose-6-phosphate receptor and support ERT/gene-therapy screening. Human fibroblasts, primary myoblasts, and patient-derived iPSC muscle systems provide genotype-specific in-vitro models but incompletely reproduce mature muscle architecture and systemic respiratory disease. (aguilargonzalez2022isogenicgaakomurine pages 1-2, do2024failureofautophagy pages 7-8)

Evidence limitations

Phenotype percentages are highly cohort-dependent; several manifestations lack population-level frequency estimates. Variant frequencies and ontology identifiers should be revalidated against live ClinVar, gnomAD, HPO, MONDO, UBERON, GO, CL, CHEBI, and NCIT releases before database ingestion. Most retrieved sources reported DOI rather than PMID metadata; therefore, DOI-linked primary papers are supplied rather than inventing unverified PMIDs. The strongest 2023–2024 evidence comprises expert pathways/reviews, small rare-disease cohorts, and extension studies; comparative long-term effectiveness among newer ERTs remains uncertain without direct head-to-head trials.

References

(parenti2024theeuropeanreference pages 11-13): Giancarlo Parenti, Simona Fecarotta, Marianna Alagia, Federica Attaianese, Alessandra Verde, Antonietta Tarallo, Vincenza Gragnaniello, Athanasia Ziagaki, Maria Jose’ Guimaraes, Patricio Aguiar, Andreas Hahn, Olga Azevedo, Maria Alice Donati, Beata Kiec-Wilk, Maurizio Scarpa, Nadine A. M. E. van der Beek, Mireja Del Toro Riera, Dominique P. Germain, Hidde Huidekoper, Johanna M. P. van den Hout, Ans T. van der Ploeg, Ivo Baric, Spyros Batzios, Nadia Belmatoug, Andrea Bordugo, Annet M. Bosch, Anais Brassier, Alberto Burlina, David Cassiman, Brigitte Chabrol, Efstathia Chronopoulou, Maria Luz Couce-Pico, Niklas Darin, Anibh M. Das, Francois G. Debray, Patrick Deegan, Luisa M. de Abreu Freire Diogo Matos, Javier De Las Heras Montero, Maja Di Rocco, Dries Dobbelaere, Francois Eyskens, Ana Ferreira, Ana M. Gaspar, Serena Gasperini, Antonio González-Meneses López, Salvatore Grosso, Nathalie Guffon-Fouilhoux, Julia Hennermann, Tarekegn G. Hiwot, Simon Jones, Sandra Kingma, Veroniki Komninaka, Elena Martín-Hernández, Esmeralda Martins, Diana Miclea, György Pfliegler, Esmeralda Rodrigues, Dariusz Rokicki, Dominique Roland, Frank Rutsch, Alessandro Salviati, Ivailo Tournev, Kurt Ullrich, Peter M. van Hasselt, Suresh Vijay, Natalie Weinhold, Peter Witters, and Jiri Zeman. The european reference network for metabolic diseases (metabern) clinical pathway recommendations for pompe disease (acid maltase deficiency, glycogen storage disease type ii). Orphanet Journal of Rare Diseases, Nov 2024. URL: https://doi.org/10.1186/s13023-024-03373-w, doi:10.1186/s13023-024-03373-w. This article has 28 citations and is from a peer-reviewed journal.
(parenti2024theeuropeanreference pages 6-8): Giancarlo Parenti, Simona Fecarotta, Marianna Alagia, Federica Attaianese, Alessandra Verde, Antonietta Tarallo, Vincenza Gragnaniello, Athanasia Ziagaki, Maria Jose’ Guimaraes, Patricio Aguiar, Andreas Hahn, Olga Azevedo, Maria Alice Donati, Beata Kiec-Wilk, Maurizio Scarpa, Nadine A. M. E. van der Beek, Mireja Del Toro Riera, Dominique P. Germain, Hidde Huidekoper, Johanna M. P. van den Hout, Ans T. van der Ploeg, Ivo Baric, Spyros Batzios, Nadia Belmatoug, Andrea Bordugo, Annet M. Bosch, Anais Brassier, Alberto Burlina, David Cassiman, Brigitte Chabrol, Efstathia Chronopoulou, Maria Luz Couce-Pico, Niklas Darin, Anibh M. Das, Francois G. Debray, Patrick Deegan, Luisa M. de Abreu Freire Diogo Matos, Javier De Las Heras Montero, Maja Di Rocco, Dries Dobbelaere, Francois Eyskens, Ana Ferreira, Ana M. Gaspar, Serena Gasperini, Antonio González-Meneses López, Salvatore Grosso, Nathalie Guffon-Fouilhoux, Julia Hennermann, Tarekegn G. Hiwot, Simon Jones, Sandra Kingma, Veroniki Komninaka, Elena Martín-Hernández, Esmeralda Martins, Diana Miclea, György Pfliegler, Esmeralda Rodrigues, Dariusz Rokicki, Dominique Roland, Frank Rutsch, Alessandro Salviati, Ivailo Tournev, Kurt Ullrich, Peter M. van Hasselt, Suresh Vijay, Natalie Weinhold, Peter Witters, and Jiri Zeman. The european reference network for metabolic diseases (metabern) clinical pathway recommendations for pompe disease (acid maltase deficiency, glycogen storage disease type ii). Orphanet Journal of Rare Diseases, Nov 2024. URL: https://doi.org/10.1186/s13023-024-03373-w, doi:10.1186/s13023-024-03373-w. This article has 28 citations and is from a peer-reviewed journal.
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Late-Onset Pompe Disease (LOPD): Comprehensive Disease Characteristics Report

openscientist-autonomous 52 citations 2026-09-01T11:04:16.178208

Late-Onset Pompe Disease (LOPD): Comprehensive Disease Characteristics Report

Disease: Late-Onset Pompe Disease (LOPD) Synonyms: Glycogen storage disease type II (GSD-II), acid maltase deficiency (AMD), acid α-1,4-glucosidase deficiency, glycogenosis type II Category: Mendelian, autosomal recessive lysosomal storage disorder Suggested MONDO ID: MONDO:0009290 (Pompe disease); OMIM: 232300; Gene: GAA (HGNC:4065, 17q25.3)

Summary

Late-Onset Pompe Disease (LOPD) is an autosomal-recessive lysosomal storage disorder caused by biallelic partial loss-of-function variants in the GAA gene, which encodes the lysosomal enzyme acid α-1,4-glucosidase (acid maltase). Residual enzyme deficiency leads to progressive intralysosomal glycogen accumulation, secondary failure of autophagy, and disruption of the contractile apparatus — preferentially in type II (fast-twitch) skeletal and respiratory muscle fibers. Unlike the infantile-onset form (IOPD), which is dominated by lethal hypertrophic cardiomyopathy, LOPD presents after the first year of life (childhood through late adulthood) as a slowly progressive limb-girdle and axial myopathy with disproportionately early diaphragmatic/respiratory insufficiency and minimal cardiac involvement. Respiratory failure is the leading cause of death.

The molecular hallmark is the "leaky" splice variant c.-32-13T>G (IVS1), which appears in ~90% of Caucasian late-onset patients and permits low-level production of functional enzyme (hence a comparatively mild, adult phenotype and generally CRIM-positive immunological status). Diagnosis rests on demonstrating reduced GAA activity on a dried blood spot (fluorometry or FIA-MS/MS), confirmed by GAA sequencing, with urinary glucose tetrasaccharide (Glc4/Hex4) and serum creatine kinase (CK) as supporting biomarkers. Pseudodeficiency alleles (notably p.[G576S;E689K], common in East Asians) are an important cause of screening false positives.

Management centers on enzyme replacement therapy (ERT). Three agents are now approved: alglucosidase alfa (>15 years standard of care), avalglucosidase alfa (enhanced bis-M6P mannose-6-phosphate uptake), and cipaglucosidase alfa co-administered with the chaperone miglustat. ERT modifies but does not halt the disease: respiratory and ambulatory function improve initially then decline gradually over 10–15 years. Next-generation ERTs show superiority signals over alglucosidase alfa in walk distance, lung function, biomarker normalization, and patient-reported outcomes. Multidisciplinary supportive care — respiratory support, supervised resistance/respiratory-muscle training, and high-protein nutrition — provides meaningful adjuvant benefit. Gene therapy (AAV-GAA) is in trials but has documented risks (dorsal-root-ganglion sensory neuronopathy).

Section 1 — Disease Information

LOPD is a rare inherited neuromuscular glycogen storage disorder resulting from deficiency of the lysosomal enzyme acid α-glucosidase (GAA), which normally degrades lysosomal glycogen to glucose. When enzyme activity is only partially reduced and symptoms appear after 12 months of age, the condition is termed late-onset to distinguish it from the severe classic infantile form.

Key identifiers (suggested):

Resource	Identifier
MONDO	MONDO:0009290 (Pompe disease)
OMIM	232300 (Glycogen storage disease II)
Gene (HGNC)	GAA, HGNC:4065
ICD-10	E74.02 (Pompe disease)
MeSH	D006009 (Glycogen Storage Disease Type II)
Orphanet	ORPHA:308552 (late-onset form) / ORPHA:365 (GSD-II)

Synonyms/alternative names: Glycogen storage disease type II (GSD-II), acid maltase deficiency, acid α-1,4-glucosidase deficiency, glycogenosis type II, adult/juvenile-onset Pompe disease.

Information is derived predominantly from aggregated disease-level resources — international patient registries (e.g., the International Pompe Registry, n=485), newborn screening cohorts, and randomized controlled trials — rather than from single-patient EHR data. LOPD is described in the literature as "a rare autosomal recessive multisystemic disorder" that substantially impacts daily activities and health-related quality of life (PMID: 39535661).

Section 2 — Etiology

Primary cause (genetic): LOPD is caused by biallelic pathogenic variants in GAA producing partial (rather than complete) loss of acid α-glucosidase function. The dominant late-onset allele is the intron-1 leaky splice variant c.-32-13T>G, which allows a small fraction of normally spliced transcript and thus residual enzyme. "This splicing variant occurs in 90% of Caucasian late onset patients, and is associated with a broad range of symptom onset" (PMID: 30922962).

Genetic risk/modifier factors: The cis synonymous variant c.510C>T acts as a genetic modifier — "c.510C>T is a genetic modifier in compound heterozygous and homozygous IVS1 patients" — reducing residual wild-type splicing and lowering the age of onset (PMID: 30922962). Rare variants in autophagy and non-autophagy genes have been proposed as additional disease modifiers explaining variable severity among patients sharing the same GAA genotype (PMID: 33807278).

Environmental/lifestyle risk factors: No established environmental cause; this is a Mendelian disorder. Physical deconditioning may exacerbate weakness; conversely, structured exercise is protective of function (see Section 12). No infectious agents are involved.

Protective factors: The single most important "protective" genetic feature is the leaky c.-32-13T>G allele itself, whose residual enzyme production yields the milder late-onset phenotype. There are no established dietary or lifestyle protective factors that prevent disease, though high-protein diet and exercise mitigate functional decline.

Gene–environment interactions: Minimal. The main modifiable interaction is treatment (ERT) and supportive exercise/nutrition acting on the genetically determined enzyme deficiency.

Section 3 — Phenotypes

LOPD is a progressive proximal and axial myopathy with early respiratory involvement. Key phenotypes, with suggested HPO terms and frequencies:

Phenotype	HPO term (suggested)	Type	Frequency / notes
Limb-girdle / proximal muscle weakness	HP:0003701 (proximal muscle weakness)	Clinical sign	~85% (limb-girdle phenotype 85.3%)
Respiratory / ventilatory insufficiency (diaphragm)	HP:0002093 (respiratory insufficiency); HP:0002878	Clinical sign	~61%
Axial / paraspinal weakness	HP:0003327 (axial muscle weakness)	Clinical sign	Common; early-degenerating
Elevated serum creatine kinase (hyperCKemia)	HP:0003236	Lab abnormality	Common
Exercise intolerance / fatigue	HP:0003546; HP:0012378	Symptom	Common
Minor/mild cardiac involvement	HP:0001638	Clinical sign	Minor (contrast with IOPD)
Rigid spine / scoliosis	HP:0003306; HP:0002650	Physical manifestation	Subset

The most common clinical presentation in confirmed LOPD is "a limb-girdle phenotype (85.3%) combined with ventilatory insufficiency (61%)" (PMID: 27170567). LOPD "typically show[s] progressive muscle weakness, respiratory dysfunction and minor cardiac involvement" — distinguishing it from IOPD (PMID: 31811531).

Characteristics: onset ranges from childhood to late adulthood (age-of-onset HPO: HP:0003581 adult onset); severity variable; progression slow but relentless; respiratory failure often precedes loss of ambulation.

Quality of life: LOPD "substantially impacts patients' day-to-day activities, outcomes, and health-related quality of life" (PMID: 39535661). Validated instruments used include PROMIS Physical Function/Fatigue, R-PAct (Pompe-specific activity), EQ-5D-5L, SF-36, and 6-minute walk distance.

Section 4 — Genetic / Molecular Information

Causal gene: GAA (acid alpha-glucosidase), chromosome 17q25.3, HGNC:4065, OMIM 606800. LOPD is "a rare autosomal recessive lysosomal disorder caused by loss-of-function of the [GAA gene]" (PMID: 40225932).

Pathogenic variants:

Feature	Detail
Most common late-onset allele	c.-32-13T>G (IVS1), splice-site, "leaky" — ~90% of Caucasian LOPD
Genetic modifier	c.510C>T (cis synonymous), lowers age of onset
Variant classes	splice-site, missense, nonsense, frameshift/indels
Pseudodeficiency alleles	c.[1726G>A;2065G>A] p.[G576S;E689K] — ~4% homozygous in East Asians
Origin	germline (biallelic)
Functional consequence	loss of function (partial residual activity in LOPD)

Variant classification follows ACMG/AMP criteria (pathogenic / likely pathogenic / VUS); ClinVar and HGMD are primary catalogs. In LOPD, at least one allele is typically the leaky c.-32-13T>G producing residual enzyme; pairing with a "null" second allele yields disease. Pseudodeficiency alleles reduce measured enzyme activity without causing disease and "may present as false positives in newborn screening programs especially in Asian populations" (PMID: 18301443).

Modifier genes/epigenetics: Beyond c.510C>T, rare variants in autophagy-related genes have been proposed as modifiers (PMID: 33807278). No established disease-specific DNA-methylation/histone signature. Chromosomal abnormalities: none characteristic.

Section 5 — Environmental Information

LOPD is a monogenic Mendelian disorder with no environmental, toxic, occupational, or infectious cause. No lifestyle factor initiates disease. Physical activity and nutrition modulate functional outcome rather than disease occurrence (see Section 12). No infectious agents are implicated.

Section 6 — Mechanism / Pathophysiology

Ordered causal chain

Biallelic partial-LoF GAA variants (commonly c.-32-13T>G) → reduced synthesis/activity of acid α-glucosidase in the lysosome (demonstrated).
Deficient GAA → failure to degrade lysosomal glycogen → progressive intralysosomal glycogen accumulation, first in cardiac and skeletal muscle (demonstrated).
Glycogen-laden lysosomes swell and rupture, spilling glycogen and hydrolases into the cytoplasm; concurrently an acidification defect develops in a subset of late endosomes/lysosomes (demonstrated in Gaa-KO myoblasts).
In parallel (branch), autophagy fails at the termination stage — impaired autophagosome–lysosome fusion → massive autophagic buildup restricted to type II-rich fibers (demonstrated).
Autophagic buildup disrupts the contractile apparatus → progressive myofiber damage and weakness; it also acts as a sink for recombinant enzyme, reducing ERT delivery/efficacy (demonstrated → mechanism of ERT resistance).
Downstream: lipofuscin accumulation, mitochondrial dysfunction/defective oxidative phosphorylation, inflammation, apoptosis, and muscle regeneration in vacuolated fibers (demonstrated by transcriptomics).
Preferential involvement of diaphragm and axial/proximal muscles → respiratory insufficiency and limb-girdle weakness → clinical LOPD, with respiratory failure as the leading cause of death (demonstrated).
(Branch, largely inferred for LOPD but demonstrated in models) CNS lysosomal glycogen accumulation occurs and is not corrected by current ERTs (which do not cross the blood–brain barrier).

Detail by category

Molecular pathways / cellular processes: The core lesion is a lysosomal catabolism defect (GO:0005764 lysosome; GO:0005980 glycogen catabolic process) with secondary macroautophagy dysfunction (GO:0016236; GO:0000045 autophagosome assembly; GO:0061909 autophagosome-lysosome fusion). "The autophagic process in Pompe skeletal muscle is affected at the termination stage—impaired autophagosomal-lysosomal fusion" (PMID: 25183957). "Progressive accumulation of autophagic vesicles is restricted to Type II-rich muscle fibers" and "it also interferes with enzyme replacement therapy by acting as a sink for the recombinant enzyme and preventing its efficient delivery to the lysosomes" (PMID: 20040311).

Protein dysfunction / biochemical abnormality: Loss of function of acid α-glucosidase (EC 3.2.1.20), a lysosomal exo-1,4-α-glucosidase. Substrate CHEBI: glycogen (CHEBI:28087); product glucose (CHEBI:17234).

Transcriptomic profiling: Single-nucleus RNA-seq plus spatial transcriptomics of LOPD muscle showed "an increase in the proportion of slow and regenerative muscle fibres and macrophages," reduced glycolysis, increased lipid/amino-acid metabolism in non-vacuolated fibers (early metabolic abnormality), "upregulation of autophagy genes and downregulation of the genes involved in ribosomal and mitochondrial function leading to defective oxidative phosphorylation," with inflammation/apoptosis/regeneration confined to vacuolated fibers (PMID: 39045638).

Early pathology: Even in asymptomatic patients, residual glycogen accumulates in muscle lysosomes with early glycogenin/STBD1 detection, suggesting a pre-symptomatic window and candidate biomarker (PMID: 41923452).

Immune involvement: Immunometabolic profiling of Pompe patient and mouse cells revealed "heightened expression of activation markers in effector T cells compared to controls," reduced regulatory T cells, and mitophagy defects — relevant to anti-rhGAA antibody responses (PMID: 41840212).

Cell types (suggested CL terms): fast-twitch/type II skeletal myocyte (CL:0000190 striated muscle cell; CL:0002211 fast muscle cell), cardiac muscle cell (CL:0000746), macrophage (CL:0000235), motor neuron / CNS neurons (CL:0000100).

Section 7 — Anatomical Structures Affected

Organ/system level (primary): skeletal muscle (UBERON:0001134), especially proximal limb-girdle and axial/paraspinal muscles; diaphragm (UBERON:0001103) → respiratory system involvement. Secondary/minor: heart (UBERON:0000948) — minor in LOPD.

Muscle involvement pattern (imaging): "The first muscles to degenerate in Pompe disease are hamstring and paraspinals" with elevated glycogen (1.8–2.2× controls) preceding fatty replacement; calves are relatively spared (PMID: 41093637). Quantitative MRI identifies the adductor magnus and the age-independent adductor-magnus/rectus-femoris fat-fraction ratio as sensitive early markers (PMID: 41554264; PMID: 42223341).

Tissue/cell level: striated muscle tissue; type II (fast-twitch) myofibers preferentially; macrophage infiltration in vacuolated fibers. CNS neurons (motor neurons, anterior horn) in models.

Subcellular level (GO cellular component): lysosome (GO:0005764) — primary site of glycogen storage; autophagosome (GO:0005776); late endosome (GO:0005770) with acidification defect; mitochondria (GO:0005739) — secondary dysfunction.

Localization/lateralization: bilateral, symmetric proximal and axial muscle involvement.

Section 8 — Temporal Development

Onset: After 12 months of age by definition; ranges from childhood to the seventh–eighth decade. Insidious, chronic onset. In the Pompe Registry (n=485), "median ages at symptom onset, diagnosis, and alglucosidase alfa initiation were 34.3, 41.1, and 44.9 years" (PMID: 38896264) — highlighting a substantial diagnostic delay of ~7 years.

Progression: Slowly progressive and lifelong. Without ERT, forced vital capacity and ambulation decline steadily; respiratory muscle weakness drives morbidity and mortality. With alglucosidase alfa, FVC%predicted rose during the first 6 months ("slope 1.83%/year") then declined (−0.54%/yr from >6 months–5 years; −1.00%/yr from >5–13 years) (PMID: 38896264). Network/observational data show initial 1–3 year gains followed by gradual 10–15 year decline (PMID: 41696977).

Critical periods: Pre-symptomatic residual-glycogen accumulation (PMID: 41923452) and subclinical qMRI changes preceding clinical decline (PMID: 42223341) define a window for early intervention. No spontaneous remission occurs.

Section 9 — Inheritance and Population

Inheritance: Autosomal recessive. Penetrance is effectively complete for biallelic pathogenic genotypes but age of onset and expressivity are highly variable, partly explained by the residual activity of the leaky allele and by modifier variants (c.510C>T; autophagy-gene variants). No anticipation (not a repeat-expansion disorder).

Epidemiology (birth prevalence from newborn screening): LOPD "ranged from 1 in 82,914 in Taiwan to 1 in 17,133 in Pennsylvania" (PMID: 40329343). In the Pennsylvania program, 531,139 newborns were screened; combined IOPD+LOPD incidence was 1:16,095 (rising to 1:8,431 including suspected LOPD) (PMID: 33202836). In Chinese newborn genomic screening, GSD-II was among the more common lysosomal disorders detected (PMID: 40355959).

Enriched clinical populations: Among adults with hyperCKemia and/or limb-girdle weakness, LOPD prevalence is 2.4% (74/3076), with ~95% carrying the common c.-32-13T>G splice variant (PMID: 27170567).

Carrier frequency / founder effects: GAA carriers are appreciable in the general population; in Taiwanese carrier screening, GAA was among the top autosomal-recessive genes identified, supporting reverse cascade testing (PMID: 38135707; PMID: 40673334). The c.-32-13T>G allele constitutes a Northern-European–enriched allele; pseudodeficiency alleles are enriched in East Asians (~4% homozygous) (PMID: 18301443).

Sex ratio: Approximately equal (autosomal). Consanguinity increases risk of biallelic disease as for any AR disorder.

Section 10 — Diagnostics

First-line enzyme test: Reduced GAA activity on a dried blood spot (DBS) by fluorometry or flow-injection tandem mass spectrometry (FIA-MS/MS). In Pennsylvania NBS, "Alpha-Glucosidase (GAA) enzyme activity is measured by flow-injection tandem mass spectrometry" with reflex full GAA sequencing (PMID: 33202836).

Confirmatory genetic test: GAA sequencing (single-gene or multigene NGS panel). Large biochemical + genetic testing programs confirm this two-step approach in >30,000 symptomatic patients (PMID: 40225932). NGS panels effectively distinguish LOPD from LGMD: "NGS effectively diagnosed 86.2% and 13.8% of patients with LGMD and Pompe disease, respectively" (PMID: 39678382).

Biomarkers: Urinary glucose tetrasaccharide Glc4/Hex4 (Glcα1-6Glcα1-4Glcα1-4Glc) and serum CK. Baseline urinary Glc4 (34.2±11.3 mmol/mol creatinine) and plasma Hex4 (1.7±0.8 µM) are elevated vs controls (6.1±5.1; 0.22±0.15) and "both urinary Glc4 and plasma Hex4 levels decreased after initiation of ERT for all patients" (PMID: 15886040).

Imaging: Quantitative muscle MRI (Dixon fat fraction, water T2) detects subclinical involvement and disease progression before clinical decline (PMID: 41554264; PMID: 42223341); 7-Tesla imaging quantifies muscle glycogen distribution (PMID: 41093637).

Electrophysiology / biopsy: EMG shows myopathic ± myotonic discharges, especially in paraspinals; muscle biopsy shows rimmed/autophagic vacuoles with PAS-positive glycogen and acid-phosphatase positivity (PMID: 32419263).

Differential diagnosis: LGMD subtypes (GNE, LDB3/ZASP, MYOT, DES, GYG1, TRIM32), Danon disease (LAMP2), inflammatory myopathies, and other late-onset vacuolar myopathies. "An important differential diagnosis among patients presenting with proximal muscle weakness (PMW) is late-onset Pompe disease (LOPD)... which often presents with early respiratory insufficiency" (PMID: 31931849). Danon disease (X-linked LAMP2) is a key mimic with glycogen-filled autophagic vacuoles (PMID: 42154863).

Screening: Newborn screening (DBS enzyme + reflex sequencing); carrier and reverse cascade testing in families (PMID: 40673334). Pseudodeficiency alleles must be recognized to avoid false positives (PMID: 18301443).

Section 11 — Outcome / Prognosis

Mortality: Respiratory failure from progressive diaphragmatic weakness is the leading cause of death. ERT substantially improves survival: in a Chinese single-center cohort (n=68), "the mortality rate was 6.4%, compared to 57.1% in the 21 patients who did not receive ERT" (PMID: 42131243).

Morbidity / function: Progressive loss of ambulation and respiratory capacity; many patients ultimately require ventilatory support and mobility aids. Quality-of-life burden is substantial across PROMIS, R-PAct, EQ-5D-5L, and SF-36 measures (PMID: 39535661; PMID: 39318718).

Disease course with treatment: ERT changes the natural history but effectiveness wanes over time; initial 1–3 year gains are followed by gradual decline over 10–15 years (PMID: 41696977). A proposed "therapeutic corridor of stability" defines FVC change of approximately −1% to +5%/year and 6MWD stability within ±25 m of peak as adequate response (PMID: 42538546).

Prognostic factors/biomarkers: Age at ERT initiation, baseline muscle involvement (qMRI fat fraction), FVC, 6MWD, and biomarker trajectory (Glc4/Hex4, CK). Persistently elevated Glc4 tracks limited motor improvement (PMID: 15886040).

Section 12 — Treatment

Enzyme replacement therapy (ERT) — mainstay

Three approved agents (suggested NCIT: Enzyme Replacement Therapy):

Agent	Key feature	Pivotal trial
Alglucosidase alfa	Standard of care >15 years	LOTS
Avalglucosidase alfa	Enhanced bis-M6P → improved muscle uptake	COMET (NCT02782741)
Cipaglucosidase alfa + miglustat	Enzyme + chaperone stabilizer	PROPEL (NCT03729362)

Alglucosidase alfa "has been available for more than 15 years and is the standard treatment... although the effectiveness of the treatment reduces over time" (PMID: 41453611).

Comparative efficacy: In network meta-analysis, ERT-naïve patients showed "significant 6MWD improvements vs. placebo: ~25 m with alglucosidase alfa and ~54 m with avalglucosidase alfa" at ~1 year (PMID: 40842017; PMID: 41696977). Real-world data confirm "avalglucosidase alfa and cipaglucosidase alfa plus miglustat have demonstrated that both treatments are at least as efficacious as alglucosidase alfa" (PMID: 40471681). Indirect comparisons numerically favor avalglucosidase over cipa+mig for FVC and 6MWT (PMID: 40920287; PMID: 41757410).

Switching: ERT-experienced patients switched from alglucosidase to cipaglucosidase alfa+miglustat improved or stabilized across most outcomes, with SGIC responder rates "90 vs. 59% responders in the cipa+mig vs. the alg+pbo group" (PMID: 39535661; PMID: 40342075). Switching to avalglucosidase is likewise feasible and safe (PMID: 38313679).

Advanced therapeutics

Gene therapy: Systemic AAV9-GAA is in development, including novel liver/muscle-restricted promoters (G6PC, CRM4-G6PC) that evade transgene-specific immune responses in mice (PMID: 41485391). However, safety risks exist: "a late onset Pompe disease patient who developed sensory neuronopathy after initiating gene therapy with AT845" (DRG toxicity) (PMID: 42142433).

Supportive / rehabilitative (adjuvant to ERT)

Supervised resistance training (24 weeks) plus respiratory-muscle training improved leg extensor strength (+10.5±3.2 Nm, p<0.01), leg flexors (+12.1±4.1 Nm, p<0.01) and maximal inspiratory pressure (+8.5±3.7 cmH₂O) in ERT-treated LOPD patients (PMID: 35365393). High-protein diet plus physical training improved muscle strength, fatigue, and physical QoL in pediatric Pompe patients (PMID: 37002894). Structured adapted physical activity and pulmonary rehabilitation are recommended (PMID: 31811531; PMID: 31970320).

Immunogenicity considerations

Anti-rhGAA antibodies can reduce ERT efficacy. "ERT response depends on several factors, including ERT initiation age, dose, and cross-reactive immunological material (CRIM) status, especially in infantile-onset Pompe disease" (PMID: 41583481). Most LOPD patients carry the leaky allele producing some GAA protein (CRIM-positive) and develop lower titers, but immunomodulation (rituximab + methotrexate + IVIG) is critical mainly for CRIM-negative IOPD, where "the inability of CRIM-negative IOPD patients to produce native GAA exposes them to a high risk of development of anti-rhGAA IgG antibody titers, leading to treatment failure" (PMID: 39314994).

Section 13 — Prevention

There is no primary prevention for this Mendelian disorder. Secondary prevention relies on early detection: newborn screening (DBS GAA enzyme + reflex sequencing) enables presymptomatic identification and timely ERT (PMID: 33202836; PMID: 40355959), and carrier / reverse cascade testing identifies at-risk relatives (PMID: 40673334; PMID: 38135707). Genetic counseling, carrier screening, prenatal testing, and preimplantation genetic diagnosis inform reproductive decisions. Tertiary prevention (preventing complications) comprises ERT, respiratory support, vaccination against respiratory infections, exercise/nutrition, and multidisciplinary follow-up per LOPD management recommendations (PMID: 41453611).

Section 14 — Other Species / Natural Disease

Naturally occurring GAA/Pompe disease ("generalized glycogenosis") is well documented in animals. "Generalized glycogenosis is a lethal autosomal recessive disease caused by a deficient activity of the acidic 1,4-α-glucosidase enzyme and characterized by an accumulation of glycogen within lysosomes" in cattle (PMID: 31377960).

Cattle (Bos taurus, NCBI:txid9913): Loss-of-function GAA alleles are established in Brahman (E13, 1783C>T), Shorthorn (E18, 2454delCA), and Droughtmaster/Braford (E7, 1057delTA), all causing premature translation termination; carrier frequency ~12% in Argentinean Brahman-derived herds. Homozygous calves show multisystem pathology: "Pathology consistent with generalised glycogenosis was found in the skeletal and cardiac muscle and spinal cord of both of the affected calves" (PMID: 28444756). Bovine GAA is "highly conserved compared with the human alpha-glucosidase gene (86% and 83% identity respectively)" (PMID: 10723725). Heterozygote detection can be confounded by haemopoietic chimaerism in twin cattle (PMID: 8161014).

Other species: Naturally occurring acid maltase deficiency is reported in dogs (e.g., Lapland dog), cats, sheep, and Japanese quail — the last historically used as an avian therapy-development model. Orthologous gene: GAA is conserved; suggested resources: OMIA, NCBI Gene, HomoloGene.

Section 15 — Model Organisms

Mammalian genetic models: The Gaa-knockout mouse is the principal model; newer CRISPR knock-in / compound-heterozygous mice recapitulate the metabolic hallmark. "CHet mice exhibited reduced GAA activity and elevated plasma glycogen levels, recapitulating the metabolic hallmark of human PD" (PMID: 41742217). Models reproduce cardiac, skeletal, diaphragmatic and hepatic glycogenosis with type II fiber-restricted autophagic buildup and an endosomal/lysosomal acidification defect (PMID: 16532490; PMID: 20040311).

Applications & extensions: - CNS involvement: "none of the approved therapies are known to cross the blood brain barrier (BBB) and patients with PD have progressive central nervous system (CNS)-associated impairments due to lysosomal glycogen accumulation in the CNS" — motivating focused-ultrasound BBB opening for ERT delivery (PMID: 41349290). - Gene therapy: AAV9-GAA with novel promoters evading immune responses (PMID: 41485391). - Immunometabolism: heightened effector T-cell activation and mitophagy defects in Gaa-/- immune cells (PMID: 41840212).

Limitations: Mouse models show variable fidelity to the slowly progressive, respiratory-predominant adult human phenotype; the human leaky splice allele (a splicing phenomenon) is difficult to model directly. Satellite-cell dysfunction may contribute to impaired regeneration across neuromuscular disorders including Pompe (PMID: 35302338). Databases: MGI, IMPC, IMSR; cellular models include patient iPSC-derived myotubes.

Mechanistic Model / Interpretation

 Biallelic partial-LoF GAA variants (leaky c.-32-13T>G + null allele)
    │  (partial residual acid α-glucosidase)
    ▼
   Impaired lysosomal glycogen degradation → intralysosomal glycogen ↑
    │
      ┌─────────────┴──────────────┐
      ▼                            ▼
 Lysosomal swelling/rupture   Autophagy termination defect
 + acidification defect       (impaired autophagosome–lysosome fusion)
      │                            │ (restricted to TYPE II fibers)
      │                            ▼
      │                    Massive autophagic buildup
      │                    ── acts as SINK for recombinant enzyme → ERT resistance
      └──────────────┬─────────────┘
     ▼
   Disruption of contractile apparatus; mitochondrial dysfunction,
   lipofuscin, inflammation, apoptosis, impaired regeneration
     │
      ┌──────────────┼───────────────────────┐
      ▼              ▼                        ▼
 Proximal/axial   Diaphragm weakness    CNS glycogen accumulation
 limb-girdle       → respiratory         (not corrected by current
 weakness           insufficiency         ERTs — no BBB penetration)
      │              │
      └──────┬───────┘
     ▼
     Progressive LOPD; respiratory failure = leading cause of death

The unifying insight is that LOPD is not simply a lysosomal storage problem but a disorder of failed autophagy in a specific fiber type. The type II-fiber-restricted autophagic buildup both damages muscle and blunts ERT delivery, explaining why enzyme therapy modifies without curing the disease and why next-generation, higher-uptake enzymes and adjuvant strategies matter.

Evidence Base — Key Literature

PMID	Contribution	Relationship to findings
30922962	c.-32-13T>G in ~90% of Caucasian LOPD; c.510C>T modifier	Supports F001 (genetics)
20040311	Type II-restricted autophagic buildup; ERT "sink"	Supports F002 (mechanism)
25183957	Impaired autophagosome-lysosome fusion	Supports F002
16532490	Endocytic/autophagic dysfunction, acidification defect	Supports F002
40329343	NBS birth prevalence range	Supports F003 (epidemiology)
27170567	2.4% LOPD in hyperCKemia/LGMW; phenotype frequencies	Supports F003, F004
18301443	Pseudodeficiency alleles → NBS false positives	Supports F003
38896264	Registry timeline; FVC trajectory on ERT	Supports F004
42131243	Mortality 6.4% (ERT) vs 57.1% (no ERT)	Supports F004
40842017 / 41696977	ERT 6MWD network meta-analysis	Supports F005
40471681	Next-gen ERTs ≥ alglucosidase	Supports F005
42142433	Gene therapy AT845 sensory neuronopathy	Supports F005 (risk)
41742217	Compound-het mouse recapitulates hallmark	Supports F006
41349290	CNS glycogen; ERT no BBB penetration	Supports F006
41840212	Immunometabolic dysregulation	Supports F006
39535661	Multisystem/QoL; PRO on switching	Supports F007
39678382 / 31931849 / 32419263	LGMD/vacuolar-myopathy differential; NGS	Supports F008
41583481 / 39314994	CRIM/immunogenicity	Supports F009
28444756 / 31377960 / 10723725	Bovine natural disease; GAA conservation	Supports F010
31811531 / 35365393 / 37002894	Rehab/nutrition adjuncts; minor cardiac	Supports F011
15886040	Glc4/Hex4 biomarker	Supports F012

Limitations and Knowledge Gaps

Prevalence estimates vary widely by ascertainment method (newborn screening vs. clinical cohorts) and geography (1:17,133 to 1:82,914 for LOPD from NBS); true adult clinical prevalence is uncertain because of diagnostic delay (~7 years).
Genotype–phenotype correlation is imperfect: patients with identical GAA genotypes vary in onset and severity, implicating incompletely characterized modifier genes and epigenetic factors (PMID: 33807278).
Comparative ERT efficacy rests largely on indirect/network comparisons rather than head-to-head trials; long-term (10–15 year) comparative outcomes for next-generation agents are immature (PMID: 41696977).
CNS involvement in human LOPD is inferred largely from models; its clinical significance and the value of BBB-crossing therapies remain to be established.
Gene therapy safety (DRG toxicity) requires resolution before broad application.
Biomarkers (Glc4/Hex4, qMRI) need longitudinal validation as surrogate endpoints and for optimal timing of therapy initiation.

Proposed Follow-up Experiments / Actions

Longitudinal qMRI + biomarker validation: Prospectively validate adductor-magnus fat fraction and urinary Glc4 as surrogate endpoints and triggers for pre-symptomatic ERT initiation.
Modifier-gene discovery: Genome-wide/whole-genome sequencing of discordant siblings sharing GAA genotype to identify severity modifiers beyond c.510C>T and autophagy-gene variants.
Head-to-head next-generation ERT trial: Randomized comparison of avalglucosidase alfa vs. cipaglucosidase alfa+miglustat with harmonized endpoints (FVC, 6MWD, Glc4, PROs).
CNS-directed therapy translation: Advance focused-ultrasound BBB-opening and CNS-tropic AAV-GAA approaches, with rigorous DRG-toxicity monitoring informed by the AT845 signal.
Autophagy-targeted adjuvant strategies: Test agents that restore autophagosome-lysosome fusion to relieve the "enzyme sink" and improve ERT delivery to type II fibers.
Standardized exercise/nutrition protocols: Multi-center RCT of resistance + respiratory-muscle training plus high-protein diet as adjuvant to next-generation ERT.
Reverse cascade testing implementation: Operationalize family-wide screening following NBS-positive LOPD to shorten diagnostic delay in relatives.

Evidence source types: findings are drawn from human clinical cohorts and registries, randomized controlled trials, newborn-screening programs, model-organism (mouse, cattle) studies, in vitro/muscle-biopsy transcriptomics, and quantitative imaging. All mechanistic and clinical claims are cited to primary literature by PMID.

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Outcome	Count
References checked	52
Resolved	52
Unresolved (possible confabulation)	0
Unverifiable	0
References weighed for topical relevance	52
On topic	45
Off topic	0

All extracted references resolved successfully.

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Outcome	Count
Terms checked	33
Resolved	30
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	3
Terms whose name was checked	5
Terms named correctly	3
Terms named as a different term	1
Terms whose name is worth a second look	1

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HP:0003236 (1 mention) - the report calls it "Elevated serum creatine kinase (hyperCKemia)"; HP calls it Elevated circulating creatine kinase activity, and lists "Elevated serum creatine kinase" among its other names

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Late-Onset Pompe Disease (LOPD): Comprehensive Research Report

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Late-Onset Pompe Disease: Comprehensive Disease-Characteristics Report

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Late-Onset Pompe Disease (LOPD): Comprehensive Disease Characteristics Report

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