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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

8

Leaky GAA Splicing and Partial Residual Enzyme Activity

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.

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

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

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

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

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

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

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

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.

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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

"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."

Establishes these inclusions as the ERT-resistant residual pathology of LOPD skeletal muscle.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

11

Digestive 1

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.

Metabolism 1

Elevated creatine kinase Elevated circulating creatine kinase concentration 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 4

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

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.

Constitutional 2

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.

Other 3

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.

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.

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.

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Genetic Associations

1

GAA leaky splice-site variants (Causative)

Gene: GAA hgnc:4065 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.

💊

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

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

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

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

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

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.

📊

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.

🔬

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.

{ }

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.
- 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.
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. Glycogen storage in
    vascular smooth muscle is the proposed substrate, but the mechanism is not
    established here and is deliberately not asserted.
  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 concentration
    term:
      id: HP:0003236
      label: Elevated circulating creatine kinase concentration
  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.
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: "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."
    explanation: Establishes these inclusions as the ERT-resistant residual pathology of LOPD skeletal muscle.
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.

  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.
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

1

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

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(monceau2024decodingthemuscle pages 2-3): Alexandra Monceau, Rasya Gokul Nath, Xavier Suárez-Calvet, Olimpia Musumeci, Antonio Toscano, Biruta Kierdaszuk, Anna Kostera-Pruszczyk, Cristina Domínguez-González, Aurelio Hernández-Lain, Carmen Paradas, Eloy Rivas, George Papadimas, Constantinos Papadopoulos, Margarita Chrysanthou-Piterou, Eduard Gallardo, Montse Olivé, James Lilleker, Mark E Roberts, Domenica Marchese, Giulia Lunazzi, Holger Heyn, Esther Fernández-Simón, Elisa Villalobos, James Clark, Panos Katsikis, Catherine Collins, Priyanka Mehra, Zoe Laidler, Amy Vincent, Giorgio Tasca, Chiara Marini-Bettolo, Michela Guglieri, Volker Straub, Nina Raben, and Jordi Díaz-Manera. Decoding the muscle transcriptome of patients with late-onset pompe disease reveals markers of disease progression. Brain, 147:4213-4226, Jul 2024. URL: https://doi.org/10.1093/brain/awae249, doi:10.1093/brain/awae249. This article has 9 citations and is from a highest quality peer-reviewed journal.
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(labella2023acomprehensiveupdate pages 21-22): Beatrice Labella, Stefano Cotti Piccinelli, Barbara Risi, Filomena Caria, Simona Damioli, Enrica Bertella, Loris Poli, Alessandro Padovani, and Massimiliano Filosto. A comprehensive update on late-onset pompe disease. Biomolecules, 13:1279, Aug 2023. URL: https://doi.org/10.3390/biom13091279, doi:10.3390/biom13091279. This article has 76 citations.
(byrne2024longtermsafetyand pages 1-2): Barry J. Byrne, Benedikt Schoser, Priya S. Kishnani, Drago Bratkovic, Paula R. Clemens, Ozlem Goker-Alpan, Xue Ming, Mark Roberts, Matthias Vorgerd, Kumaraswamy Sivakumar, Ans T. van der Ploeg, Mitchell Goldman, Jacquelyn Wright, Fred Holdbrook, Vipul Jain, Elfrida R. Benjamin, Franklin Johnson, Sheela Sitaraman Das, Yasmine Wasfi, and Tahseen Mozaffar. 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). Journal of Neurology, 271:1787-1801, Dec 2024. URL: https://doi.org/10.1007/s00415-023-12096-0, doi:10.1007/s00415-023-12096-0. This article has 24 citations and is from a domain leading peer-reviewed journal.
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Inheritance

Discussions and Knowledge Gaps

Pathophysiology

Histopathology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Biochemical Markers

Diagnosis

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Prevalence

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Late-Onset Pompe Disease: Comprehensive Disease-Characteristics Report

Executive summary

1. Disease information

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

3. Phenotypes and quality of life

4. Genetic and molecular information

5. Environmental information

6. Mechanism and pathophysiology

7. Anatomical structures

8. Temporal development

9. Inheritance and population

10. Diagnostics and screening

11. Outcome and prognosis

12. Treatment and real-world implementation

13. Prevention

14. Natural disease in other species

15. Model organisms

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