Infantile-Onset Pompe Disease

Mendelian MONDO:0017694 Pathograph 34 Show in embeddings browser Pompe Disease Lysosomal Storage Disease

Classic infantile-onset Pompe disease (IOPD) is the most severe form of glycogen storage disease due to acid maltase deficiency, defined by symptom onset before age 12 months together with hypertrophic cardiomyopathy. It is caused by biallelic fully deleterious GAA variants that leave essentially no residual acid alpha-glucosidase activity (typically <1% of control), so lysosomal glycogen accumulates rapidly and massively in cardiac, skeletal, and respiratory muscle. Untreated infants present in the first weeks to months of life with progressive cardiomegaly and hypertrophic cardiomyopathy, profound hypotonia, feeding difficulty and failure to thrive, macroglossia, hepatomegaly, and respiratory distress, and die of cardiopulmonary insufficiency in the first one to two years. Two features distinguish IOPD mechanistically from the late-onset form curated under Pompe Disease. First, the near-total absence of enzyme drives an aggressive cardiac phenotype that late-onset disease does not have. Second, because roughly a quarter of classic infantile patients make no immunologically detectable GAA protein at all (cross-reactive immunologic material, CRIM-negative), recombinant human GAA is seen by the immune system as a foreign protein: these infants mount early, high, sustained anti-rhGAA IgG responses that neutralize enzyme replacement therapy and are associated with death or invasive ventilation despite treatment, unless immune tolerance is induced. Enzyme replacement therapy started early transforms survival and reverses cardiac hypertrophy, and has revealed an emerging long-term survivor phenotype with residual myopathy, hearing loss, dysphagia, osteopenia, and progressive cerebral white-matter abnormalities.

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Classifications

Harrison's Part

Lysosomal Storage

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Mappings

MONDO

MONDO:0009290 glycogen storage disease II DisMech

MONDO:0017694 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

GeneReviews clinical definition of IOPD

GeneReviews defines infantile-onset Pompe disease by onset before age 12 months together with cardiomyopathy; onset before 12 months WITHOUT cardiomyopathy is classified as late-onset disease. Cardiomyopathy, not age alone, is the discriminating criterion.

CASE_DEFINITION

Show evidence (1 reference)

PMID:20301438 SUPPORT Other

"Pompe disease can be classified by age of onset, organ involvement, severity, and rate of progression into infantile-onset Pompe disease (IOPD) (i.e., individuals with onset before age 12 months with cardiomyopathy)"

States the case definition that separates IOPD from LOPD by the presence of cardiomyopathy in the first year.

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Inheritance

Autosomal recessive HP:0000007

IOPD is inherited in an autosomal recessive manner, with affected infants carrying two fully deleterious (null or severely damaging) GAA alleles. The severity of the infantile phenotype tracks the near-complete absence of residual enzyme produced by this fully deleterious genotype.

Autosomal recessive inheritance

Show evidence (3 references)

PMID:12897283 SUPPORT Human Clinical

"The patients have fully deleterious mutations. Acid alpha-glucosidase activity is severely deficient."

The natural-history cohort establishes that classic infantile patients carry fully deleterious GAA genotypes with severely deficient enzyme activity.

PMID:22252923 SUPPORT Human Clinical

"We found that, in most cases, CRIM status can be predicted from GAA mutations, potentially circumventing the need for invasive skin biopsy and time wasted in culturing cells in the future."

Shows that the biallelic GAA genotype determines whether any GAA protein is made, i.e. CRIM status.

PMID:20301438 SUPPORT Other

"If both parents are known to be heterozygous for a GAA pathogenic variant, 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."

The GeneReviews GENETIC COUNSELING section states the autosomal recessive transmission risks that follow from biallelic GAA inheritance.

Discussions and Knowledge Gaps

Does the progressive cerebral white-matter abnormality of ERT-treated IOPD survivors reflect ongoing CNS glycogen storage that intravenous rhGAA cannot reach, and would a brain-penetrant therapy prevent it?

KNOWLEDGE GAP OPEN gap_iopd_cns_glycogen_white_matter

Attached to

pathophysiology#Central nervous system glycogen storage and progressive white matter abnormality

Autopsy evidence now establishes the storage side of this question. A systematic review of 49 classic infantile patients found severe glycogen accumulation in astrocytes and globus pallidus neurons, with white matter among the most frequently affected regions, so CNS glycogen storage is no longer an inference from the muscle phenotype. What remains open is the link between that storage and the clinical trajectory: the review states directly that the mechanisms connecting glycogen accumulation to neurological manifestations are still incompletely understood, and there is still no interventional evidence that reducing CNS glycogen alters the neuropsychological outcome. The same review sharpens the gap rather than closing it, by adding a timing problem that was not previously part of it - pathology is already widespread before 21 months, whereas MRI change appears from 2 to 3 years, biomarker change from about 5 years, and cognitive decline from about 8 to 10, so any causal account has to explain that lag and any trial of a brain-directed therapy has to contend with an endpoint that trails the lesion by years. Preclinical support exists - systemic AAV reversed CNS glycogen storage in Gaa-knockout mice (PMID:37463048, cited on the gene-therapy treatment) - but that has not been shown to change neurological outcome in humans.

Proposed experiments

Longitudinal CNS glycogen and white-matter imaging in treated IOPD

exp_iopd_cns_glycogen_imaging

Correlate a CNS glycogen-burden measure with serial quantitative white-matter MRI and neuropsychological testing in a multi-centre treated IOPD cohort, and compare against recipients of brain-directed enzyme delivery when such therapy becomes available.

Show evidence (3 references)

PMID:29573408 SUPPORT Human Clinical

"Therefore, we advise follow-up programs are expanded to capture CNS involvement in larger, international patient cohorts, to incorporate our findings in the counselling of parents before the start of treatment, and to include the brain as an additional target in the development of..."

The authors frame CNS involvement as an open target rather than a resolved mechanism.

PMID:42538472 SUPPORT Human Clinical

"The mechanisms linking glycogen accumulation to neurological manifestations remain incompletely understood."

The systematic review states that the storage-to-manifestation link is still unresolved, which is what keeps this gap OPEN despite the new tissue-level storage evidence.

PMID:42538472 SUPPORT Human Clinical

"there is a marked temporal gap between the extensive abnormalities observed at autopsy in infancy and later radiological, biochemical, and clinical manifestations"

Adds the timing dimension to this gap - the pathology precedes every clinical means of measuring it by years, which any mechanistic account and any trial endpoint has to account for.

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Pathophysiology

Near-complete acid alpha-glucosidase deficiency

Biallelic fully deleterious GAA variants abolish acid alpha-glucosidase activity, leaving typically less than 1% of control activity in fibroblasts or muscle. This is the quantitative distinction from late-onset disease, where residual activity is higher and the phenotype correspondingly milder and non-cardiac.

GAA hgnc:4065 ↓ DECREASED

acid alpha-glucosidase activity GO:0004558 ↓ DECREASED

Animal models

Lapphund canine Pompe disease (naturally occurring GAA p.W746* homozygote) Dog recapitulates A homozygous premature stop codon abolishes acid alpha-glucosidase, the same class of fully deleterious lesion that produces classic infantile disease in humans.

Downstream

Lysosomal glycogen accumulation Loss of the only lysosomal glycogen-degrading enzyme causes undegraded glycogen to accumulate in the lysosome.

Absence of immunologically detectable GAA protein (CRIM-negative status) Null GAA alleles that produce no protein at all, rather than an inactive protein, yield CRIM-negative status in roughly a quarter of classic infantile patients.

Show evidence (2 references)

PMID:12897283 SUPPORT Human Clinical

"The patients have fully deleterious mutations. Acid alpha-glucosidase activity is severely deficient."

Establishes near-absent enzyme activity as the molecular lesion of the classic infantile form.

PMID:22252923 SUPPORT Human Clinical

"The classical infantile form is rapidly progressive and presents with hypertrophic cardiomyopathy by the first few months of life and has a fatal outcome within the first year of life if left untreated"

Links the severe enzymatic lesion to the rapidly progressive cardiac infantile phenotype.

Lysosomal glycogen accumulation

Undegraded glycogen accumulates progressively within lysosomes of cardiac, skeletal, respiratory, and smooth muscle, and of the central nervous system. In IOPD the accumulation is early and massive because essentially no residual enzyme is available.

Cardiac muscle cell CL:0000746 Skeletal muscle fiber CL:0008002

Glycogen catabolic process GO:0005980 ↓ DECREASED

Downstream

Cardiomyocyte glycogen storage and progressive hypertrophic remodeling Cardiomyocyte glycogen storage drives the cardiomegaly and hypertrophic cardiomyopathy that define IOPD.

Skeletal and respiratory myofiber injury Storage in skeletal and respiratory myofibers produces the profound hypotonia and respiratory distress of untreated IOPD.

Hepatomegaly Hepatic glycogen storage produces the moderate hepatomegaly of infantile disease. The cited cohort attributes it to storage but does not exclude a contribution from cardiac decompensation, so the edge is a partial rather than sole explanation.

Failure of productive autophagy and autophagic buildup Glycogen-laden lysosomes disrupt lysosome-dependent autophagic flux, so autophagic substrate accumulates in muscle.

Central nervous system glycogen storage and progressive white matter abnormality Glycogen storage is not confined to muscle; CNS storage becomes clinically visible only once ERT allows survival into later childhood.

Show evidence (2 references)

ORPHA:365 SUPPORT Other

"A rare lysosomal storage disease characterized by lysosomal accumulation of glycogen particularly in skeletal, cardiac, and respiratory muscles"

Orphanet records the lysosomal glycogen-accumulation lesion and the tissues in which it occurs.

PMID:12897283 SUPPORT Human Clinical

"Infantile Pompe's disease is a lethal cardiac and muscular disorder."

Identifies cardiac and skeletal muscle as the tissues in which the storage lesion is clinically decisive.

Cardiomyocyte glycogen storage and progressive hypertrophic remodeling

Massive cardiomyocyte glycogen storage produces cardiomegaly and hypertrophic cardiomyopathy that is usually already identifiable in the first weeks of life and progresses to left ventricular outflow obstruction and diminished lung volume. Glycogen deposition in conduction tissue shortens the PR interval. This node is the principal mechanistic difference between IOPD and late-onset Pompe disease, which lacks significant cardiac involvement.

Cardiac muscle cell CL:0000746

Cardiac muscle hypertrophy GO:0003300 ↑ INCREASED

Experimental models

Patient-derived iPSC cardiomyocytes (PD-iCMs) IPSC DERIVED MODEL The differentiated cardiomyocytes show reduced GAA activity, lysosomal glycogen accumulation, and hypertrophy - the cellular content of this node - in human cells carrying patient genotypes.

Animal models

Gaa c.1935C>A (p.D645E) knock-in mouse Mouse recapitulates Homozygous knock-in mice develop hypertrophic cardiomyopathy, the cardiac feature that separates infantile-onset from late-onset disease.

Downstream

Hypertrophic cardiomyopathy Cardiomyocyte storage and hypertrophic remodeling manifest clinically as hypertrophic cardiomyopathy.

Shortened PR interval Glycogen deposition in the cardiac conduction system shortens the PR interval on ECG.

Cardiopulmonary insufficiency of infancy Progressive cardiac hypertrophy with outflow obstruction is a principal contributor to fatal cardiopulmonary insufficiency.

Show evidence (2 references)

PMID:20301438 SUPPORT Other

"Cardiomegaly and hypertrophic cardiomyopathy is usually identified in the first weeks of life and progress to left ventricular outflow obstruction and diminished lung volume."

Documents the timing and progression of the cardiac lesion specific to IOPD.

PMID:12897283 SUPPORT Human Clinical

"The diastolic thickness of the left ventricular posterior wall and cardiac weight at autopsy increase significantly with age."

Quantitative natural-history evidence that the cardiac hypertrophy is progressive.

Skeletal and respiratory myofiber injury

Lysosomal glycogen storage in skeletal, respiratory, and bulbar muscle injures myofibers, producing the floppy-infant presentation: generalized hypotonia, severely delayed motor development, feeding difficulty with poor growth, and respiratory distress.

Skeletal muscle fiber CL:0008002

Downstream

Generalized hypotonia Myofiber injury produces the profound generalized hypotonia of the floppy infant.

Generalized muscle weakness The same myofiber injury produces generalized skeletal muscle weakness, which GeneReviews records as a feature distinct from the accompanying hypotonia.

Motor developmental delay Muscle weakness prevents acquisition of major motor milestones.

Respiratory insufficiency Respiratory myofiber injury, compounded by diminished lung volume from cardiomegaly, causes respiratory distress and insufficiency.

Feeding difficulties Bulbar and generalized muscle weakness impair sucking, swallowing, and feeding.

Failure to thrive Growth deviates significantly from normal even once nasogastric tube feeding is started.

Cardiopulmonary insufficiency of infancy Respiratory muscle failure combines with the cardiac lesion to produce fatal cardiopulmonary insufficiency.

Show evidence (2 references)

PMID:20301438 SUPPORT Other

"Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."

Lists the untreated IOPD muscle phenotype produced by myofiber injury.

PMID:12897283 SUPPORT Human Clinical

"Motor development is severely delayed and major developmental milestones are generally not achieved."

Natural-history evidence for the severity of the motor consequence of myofiber injury in IOPD.

Cardiopulmonary insufficiency of infancy

The convergence of hypertrophic cardiomyopathy with outflow obstruction and respiratory muscle failure produces cardiopulmonary insufficiency. In the pre-treatment natural history, symptoms began at a median age of 1.6 months and the median age of death was 6-7.7 months, with only 5-8% of infants surviving beyond one year.

Downstream

Death in infancy Untreated, cardiopulmonary insufficiency is fatal in the first one to two years of life.

Show evidence (1 reference)

PMID:12897283 SUPPORT Human Clinical

"Symptoms start at a median age of 1.6 months in both groups. The median age of death is 7.7 and 6 months, respectively. Five percent of the Dutch patients and 8% of all reported patients survive beyond 1 year of age."

Quantifies the untreated natural history of onset and death that this node represents.

Absence of immunologically detectable GAA protein (CRIM-negative status)

CRIM (cross-reactive immunologic material) status asks a different question from enzyme activity: not whether GAA works, but whether any GAA protein is made at all. Patients with two null alleles produce no GAA protein detectable by Western blot and are CRIM-negative; patients producing a catalytically inactive protein are CRIM-positive. Because a CRIM-negative infant has never been immunologically tolerized to GAA, recombinant human GAA is a foreign antigen. Roughly 20-25% of classic infantile patients are CRIM-negative, and CRIM status is largely predictable from the GAA genotype.

GAA hgnc:4065 ↓ DECREASED

Downstream

High sustained anti-rhGAA antibody response Never having been tolerized to endogenous GAA, CRIM-negative infants mount an early, high-titer, sustained IgG response to infused recombinant human GAA.

Show evidence (2 references)

PMID:22252923 SUPPORT Human Clinical

"CRIM-negative patients make no GAA protein and develop sustained high antibody titers to ERT that render the treatment ineffective."

Defines CRIM-negative status as absence of GAA protein and links it to the antibody response.

PMID:19775921 SUPPORT Human Clinical

"Patients synthesize a non-functional form of GAA or are unable to form native enzyme."

States the CRIM-positive versus CRIM-negative molecular distinction.

High sustained anti-rhGAA antibody response

Sustained high-titer neutralizing IgG against recombinant human GAA blocks the therapeutic benefit of enzyme replacement therapy. This is a treatment-conditioned mechanism with no counterpart in late-onset disease, and it is the reason CRIM status must be determined before the first infusion.

humoral immune response mediated by circulating immunoglobulin GO:0002455 ↑ INCREASED

Downstream

Enzyme replacement therapy failure and clinical decline Neutralizing antibody renders infused rhGAA ineffective, and treated CRIM-negative infants deteriorate.

Show evidence (1 reference)

PMID:22237443 SUPPORT Human Clinical

"Cross-reactive immunologic material negative (CRIM-negative) Pompe patients develop high-titer antibody to the rhGAA and do poorly."

Establishes the high-titer antibody response and its adverse clinical consequence.

Enzyme replacement therapy failure and clinical decline

In the absence of immune tolerance induction, CRIM-negative infants on ERT decline despite treatment: cardiac function and gross motor development improve significantly less than in CRIM-positive infants, and by roughly 27 months all CRIM-negative patients in the original series were dead or invasively ventilated.

Show evidence (2 references)

PMID:19775921 SUPPORT Human Clinical

"By age 27.1 months, all CRIM-negative patients and 4/21 (19.0%) CRIM-positive patients were deceased or invasively ventilated."

Quantifies the divergent treated outcome by CRIM status.

PMID:19775921 SUPPORT Human Clinical

"Cardiac function and gross motor development improved significantly more in the CRIM-positive group."

Shows the treatment benefit gap attributable to CRIM status.

Failure of productive autophagy and autophagic buildup

Autophagy is lysosome-dependent, so the storage lesion disables it. Autophagic vesicles accumulate in type II-rich muscle fibers, disrupting the contractile apparatus. Critically for IOPD, the autophagic buildup also acts as a sink for infused recombinant enzyme and prevents its efficient delivery to lysosomes - a second, non-immune route to poor ERT response that runs in parallel to the CRIM-negative antibody arm.

Skeletal muscle fiber CL:0008002

Autophagy GO:0006914 ↓ DECREASED

Animal models

GAA-knockout mouse Mouse recapitulates Progressive accumulation of autophagic vesicles in type II-rich fibers, with sequestration of infused recombinant enzyme.

Gaa c.1935C>A (p.D645E) knock-in mouse Mouse recapitulates The knock-in mice have near-abolished GAA activity with markedly increased tissue glycogen and impaired autophagy, reproducing the autophagy arm of the mechanism in an allele-specific rather than a null background.

Downstream

Skeletal and respiratory myofiber injury Accumulated autophagosomes disrupt the contractile apparatus of muscle fibers.

Enzyme replacement therapy failure and clinical decline Autophagic buildup sequesters infused recombinant enzyme before it reaches the lysosome, degrading ERT response independently of any antibody response.

Show evidence (1 reference)

PMID:20040311 SUPPORT Model Organism

"we present evidence that a failure of productive autophagy in muscle tissue contributes strongly to disease pathology in both patients with Pompe disease and GAA-knockout mice"

States that failed productive autophagy contributes to pathology in patients as well as in the knockout mouse.

Central nervous system glycogen storage and progressive white matter abnormality

Intravenous rhGAA does not cross the blood-brain barrier, so CNS glycogen storage is untreated. As ERT enables survival into later childhood and adulthood, slowly progressive symmetric white-matter abnormalities emerge - periventricular white matter and centrum semiovale from about age 2, then corpus callosum, capsules and subcortical areas after age 8, and brainstem from age 11 - with variable neuropsychological consequences. This is an ERT-era emerging phenotype rather than part of the classical untreated natural history.

Downstream

Cognitive decline and intellectual disability White-matter involvement is accompanied by neuropsychological decline in a subset of long-term survivors.

Show evidence (1 reference)

PMID:29573408 SUPPORT Human Clinical

"From approximately age 2 years onwards, brain MRI showed involvement of the periventricular white matter and centrum semiovale. After 8 years of age, additional white-matter abnormalities occurred in the corpus callosum, internal and external capsule, and subcortical areas. From 11 years of age,..."

Documents the anatomical progression of white-matter abnormality in treated classic infantile patients.

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Histopathology

Vacuolar myopathy with lysosomal glycogen accumulation

Skeletal muscle in classic infantile-onset disease shows a vacuolar myopathy in which glycogen fills the lysosomes of myofibers. The storage lesion is not confined to muscle: it also involves cardiac and smooth muscle, which is why the same biopsy-level mechanism underlies both the cardiac and the skeletal-muscle arms of the disease. Muscle biopsy is no longer the diagnostic route - enzyme assay and GAA sequencing are - but it remains the tissue-level readout used to judge whether enzyme replacement therapy is reaching muscle.

Show evidence (1 reference)

PMID:17075580 SUPPORT Human Clinical

"glycogen accumulates abnormally in the lysosomes of skeletal, cardiac and smooth muscle, and contributes to clinically progressive and debilitating muscle weakness"

States the tissue distribution of the lysosomal glycogen storage lesion and links it to the weakness.

Variable glycogen clearance on enzyme replacement therapy

Serial quadriceps biopsies taken at baseline, 12 weeks, and 52 weeks in eight infantile-onset patients on weekly recombinant human GAA showed that the extent of glycogen clearance differed widely between patients and tracked clinical outcome. This is the histologic counterpart of the entry's clinical observation that enzyme replacement therapy rescues some infants and not others, and it makes the biopsy an outcome measure rather than only a diagnostic specimen.

Show evidence (1 reference)

PMID:17075580 SUPPORT Human Clinical

"The extent of glycogen clearance varied widely among these patient samples, and correlated well with clinical outcome"

Establishes that histologic glycogen clearance varies between treated infants and predicts how they do clinically.

Baseline histologic predictors of enzyme replacement response

In the same series, low baseline glycogen, mild ultrastructural damage, a high proportion of type I fibers, and young age at baseline all marked patients who responded well histologically. The first two are a statement that the amount of damage already present limits what enzyme replacement can undo, which is the tissue-level argument for treating before symptoms rather than after.

Show evidence (2 references)

PMID:17075580 SUPPORT Human Clinical

"Low glycogen levels, mild ultrastructural damage, a high proportion of type I fibers, and young age at baseline were all features associated with good histologic response"

Names the baseline biopsy features that predict a good histologic response to enzyme replacement therapy.

PMID:17075580 SUPPORT Human Clinical

"There was no correlation between capillary density and glycogen clearance"

Reports a negative result - delivery of enzyme to muscle is not limited by capillary supply - which narrows the candidate explanations for poor response.

Increased activated satellite cells in poorly responding post-treatment biopsies

Confocal analysis of the post-treatment biopsies found higher levels of activated satellite cells in those with a poor histologic response. The finding is correlative, and the study does not establish whether the raised satellite-cell activation is a compensatory regenerative response to continuing myofiber injury or part of what limits the response.

Show evidence (1 reference)

PMID:17075580 SUPPORT Human Clinical

"activated satellite cell levels were shown to be higher in post-treatment biopsies with poor histologic responses"

Reports the satellite-cell measurement and the direction of its association with histologic response.

Widespread CNS glycogen storage with white-matter and deep grey-nucleus predominance

A systematic review of 39 autopsy-based articles covering 49 patients meeting a strict classic-infantile definition (hypertrophic cardiomyopathy, onset under 12 months, GAA deficiency) found histologic abnormality throughout the central nervous system. Cerebral and cerebellar white matter, globus pallidus, dentate nucleus, brainstem motor nuclei, and anterior horn cells were affected most often, and subcortical structures more consistently than cortical ones. This is the tissue-level counterpart of the white-matter abnormality curated as a phenotype and pathophysiology node in this entry, which until now rested on imaging and neuropsychological evidence alone.

Show evidence (2 references)

PMID:42538472 SUPPORT Human Clinical

"Histologic abnormalities were found throughout the CNS. The cerebral and cerebellar white matter (WM), globus pallidus, dentate nucleus, motor nuclei of the brainstem, and anterior horn cells were most frequently affected."

Gives the regional distribution of CNS histologic abnormality in autopsied classic infantile patients.

PMID:42538472 SUPPORT Human Clinical

"Cortical neurons were affected with greater variability, and subcortical structures were more frequently involved than cortical ones."

Records the subcortical-over-cortical gradient, which is what makes this a white-matter and deep-nucleus pattern rather than a diffuse encephalopathy.

Severe glycogen accumulation in astrocytes and globus pallidus neurons

Within that CNS pathology, glycogen accumulation was severe specifically in astrocytes and in globus pallidus neurons. This is the storage lesion itself demonstrated in brain tissue from this patient population, rather than inferred from the muscle phenotype - the cell-type-level evidence that the enzyme deficiency produces the same lysosomal storage in the brain that it produces in muscle.

Show evidence (1 reference)

PMID:42538472 SUPPORT Human Clinical

"Glycogen accumulation was severe in astrocytes and in neurons of the globus pallidus."

Identifies the cell types carrying the heaviest CNS glycogen burden in autopsied classic infantile patients.

CNS pathology present in infancy, years before clinical or radiological signs

Autopsy pathology is already early and widespread in children up to 21 months, whereas MRI abnormality typically appears from 2 to 3 years, biomarker change from around 5 years, and cognitive decline from roughly 8 to 10 years. The pathology therefore precedes every clinical means of detecting it by years. This matters for the timing of therapy rather than only for description: by the time CNS involvement is measurable in a treated survivor, the storage lesion is long established.

Show evidence (2 references)

PMID:42538472 SUPPORT Human Clinical

"Histopathological studies from children up to 21 months demonstrate early and widespread CNS pathology."

Establishes that the CNS lesion is present in infancy.

PMID:42538472 SUPPORT Human Clinical

"While white matter pathology is already prominent in young patients, abnormalities on magnetic resonance imaging typically emerge from 2 to 3 years of age, biomarker changes from around 5 years, and cognitive decline, reduced processing speed, and background activity slowing on..."

Quantifies the lag between the pathology and each downstream means of detecting it.

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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

Cardiovascular 3

Hypertrophic cardiomyopathy OBLIGATE HP:0001639

Course: PROGRESSIVE

Show evidence (2 references)

PMID:20301438 SUPPORT Other

Cardiomyopathy is definitional for IOPD, supporting an obligate frequency.

PMID:12897283 SUPPORT Human Clinical

"A progressive cardiac hypertrophy is characteristic for infantile Pompe's disease."

Natural-history evidence that cardiac hypertrophy is characteristic and progressive.

Shortened PR interval HP:0005165

Show evidence (1 reference)

PMID:20301438 SUPPORT Other

"Progressive deposition of glycogen results in conduction defects with shortening of the PR interval on EKG."

Directly documents the shortened PR interval in Pompe disease.

Cardiomegaly VERY_FREQUENT HP:0001640

Show evidence (1 reference)

PMID:16737883 SUPPORT Human Clinical

"Cardiomegaly (92%), hypotonia (88%), cardiomyopathy (88%), respiratory distress (78%), muscle weakness (63%), feeding difficulties (57%), and failure to thrive (53%) appeared after a median age of approximately 4.0 months"

Reports cardiomegaly in 92% of the 168-patient untreated cohort, the highest frequency of any sign listed, which is the basis for the VERY_FREQUENT band.

Digestive 3

Feeding difficulties FREQUENT HP:0011968

Show evidence (2 references)

PMID:20301438 SUPPORT Other

"Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."

Lists feeding difficulties among the typical untreated IOPD manifestations.

PMID:16737883 SUPPORT Human Clinical

Quantifies feeding difficulties at 57% of the 168-patient untreated natural-history cohort, which is the basis for the FREQUENT band.

Hepatomegaly HP:0002240

Show evidence (1 reference)

PMID:12897283 SUPPORT Human Clinical

"The moderate enlargement of the liver is assumed to result from glycogen storage, but may also result from cardiac decompensation."

The natural-history cohort reports moderate hepatomegaly and attributes it to glycogen storage with a cardiac contribution.

Dysphagia HP:0002015

Show evidence (1 reference)

PMID:22538254 SUPPORT Human Clinical

"Commonly present were gross motor weakness, motor speech deficits, sensorineural and/or conductive hearing loss, osteopenia, gastroesophageal reflux, and dysphagia with aspiration risk."

Reports dysphagia with aspiration risk as commonly present in long-term survivors.

Ear 1

Sensorineural hearing impairment HP:0000407

Show evidence (1 reference)

PMID:22538254 SUPPORT Human Clinical

"Commonly present were gross motor weakness, motor speech deficits, sensorineural and/or conductive hearing loss, osteopenia, gastroesophageal reflux, and dysphagia with aspiration risk."

Reports hearing loss among the commonly present features of the long-term survivor phenotype.

Eye 1

Ptosis HP:0000508

Show evidence (2 references)

PMID:41014101 SUPPORT Human Clinical

"Flaccid dysarthria (8/8), ptosis (4/8), and sensorineural hearing loss (6/8) were common."

Reports ptosis in four of eight adult survivors of infantile-onset disease on long-term enzyme replacement therapy.

PMID:41014101 SUPPORT Human Clinical

"Two participants were ambulatory; 6 used wheelchairs."

Records the residual motor disability in the same cohort, which is the context that makes eyelid and bulbar involvement part of a persisting generalized myopathy rather than an isolated ocular finding.

Head and Neck 1

Macroglossia FREQUENT HP:0000158

Show evidence (2 references)

PMID:12897283 SUPPORT Human Clinical

"An enlarged tongue was noticed in 45% of the Dutch patients and 29% of the cases from literature."

Natural-history cohort quantifies tongue enlargement at 45% in the prospectively examined Dutch series, within the FREQUENT band (79-30%); the 29% literature figure is a retrospective case-note count and is treated as under-ascertainment rather than as a competing estimate.

PMID:20301438 SUPPORT Other

"tracheostomy may be considered in those with macroglossia and severe respiratory insufficiency"

GeneReviews management guidance treats macroglossia as a recognised IOPD feature with airway consequences.

Metabolism 1

Elevated creatine kinase Elevated circulating creatine kinase activity HP:0003236

Show evidence (1 reference)

PMID:12897283 SUPPORT Human Clinical

"Levels of aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, creatine kinase, or creatine kinase-myocardial band isoenzyme are typically elevated"

Directly reports elevated CK and CK-MB in the infantile natural-history cohort.

Musculoskeletal 4

Generalized hypotonia VERY_FREQUENT HP:0001252

Show evidence (1 reference)

PMID:20301438 SUPPORT Other

"Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."

GeneReviews lists hypotonia as a typical untreated IOPD feature, supporting a very frequent band.

Generalized muscle weakness VERY_FREQUENT HP:0003324

Show evidence (1 reference)

PMID:20301438 SUPPORT Other

"Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."

GeneReviews lists generalized muscle weakness as a typical untreated IOPD feature, distinct from the hypotonia named in the same sentence, supporting a very frequent band.

Respiratory insufficiency Respiratory insufficiency due to muscle weakness HP:0002747

Show evidence (2 references)

PMID:20301438 SUPPORT Other

"Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."

GeneReviews names respiratory distress directly among the typical untreated IOPD features.

PMID:20301438 SUPPORT Other

"Cardiomegaly and hypertrophic cardiomyopathy is usually identified in the first weeks of life and progress to left ventricular outflow obstruction and diminished lung volume."

Supports the second clause of the description - that the cardiac lesion compounds the respiratory burden by reducing lung volume.

Osteopenia HP:0000938

Show evidence (1 reference)

PMID:22538254 SUPPORT Human Clinical

"Residual muscle weakness, hearing loss, risk for arrhythmias, hypernasal speech, dysphagia with risk for aspiration, and osteopenia were commonly observed findings."

Lists osteopenia among the commonly observed findings in long-term survivors.

Nervous System 4

Motor developmental delay VERY_FREQUENT Motor delay HP:0001270

Show evidence (1 reference)

PMID:12897283 SUPPORT Human Clinical

"Motor development is severely delayed and major developmental milestones are generally not achieved."

Natural-history cohort reports severe motor delay as a general feature, supporting a very frequent band.

Abnormal cerebral white matter morphology HP:0002500

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:29573408 SUPPORT Human Clinical

"From approximately age 2 years onwards, brain MRI showed involvement of the periventricular white matter and centrum semiovale."

Documents the white-matter abnormality and its age of appearance in treated classic infantile patients.

Cognitive decline and intellectual disability HP:0001249

Show evidence (1 reference)

PMID:29573408 SUPPORT Human Clinical

"Cognitive development ranged from stable and normal to declines that lead to intellectual disabilities."

Reports the range of cognitive outcomes, supporting a variably present phenotype.

Flaccid dysarthria HP:0001260

Show evidence (1 reference)

PMID:41014101 SUPPORT Human Clinical

"Flaccid dysarthria (8/8), ptosis (4/8), and sensorineural hearing loss (6/8) were common."

Reports flaccid dysarthria in all eight adult survivors of infantile-onset disease on long-term enzyme replacement therapy.

Voice 1

Hypernasal speech HP:0001611

Show evidence (1 reference)

PMID:22538254 SUPPORT Human Clinical

"Residual muscle weakness, hearing loss, risk for arrhythmias, hypernasal speech, dysphagia with risk for aspiration, and osteopenia were commonly observed findings."

Lists hypernasal speech among commonly observed long-term survivor findings.

Growth 1

Failure to thrive FREQUENT HP:0001508

Show evidence (2 references)

PMID:12897283 SUPPORT Human Clinical

"For the Dutch patient group, growth deviates significantly from normal despite start of nasogastric tube feeding."

Documents growth failure persisting despite feeding support.

PMID:16737883 SUPPORT Human Clinical

Quantifies failure to thrive at 53% of the 168-patient untreated natural-history cohort, which is the basis for the FREQUENT band.

Other 1

Death in infancy

Deliberately left without a phenotype_term. `HP:0001522` (Death in infancy) is the exact concept, but it sits under `HP:0040006` (Mortality/Aging) rather than `HP:0000118` (Phenotypic abnormality), so it is not a legal PhenotypeTerm value in this schema. No mortality term reachable from HP:0000118 expresses it, and no term beats a wrong one.

Show evidence (2 references)

PMID:20301438 SUPPORT Other

"In untreated infants, death commonly occurs in the first two years of life from cardiopulmonary insufficiency."

States the untreated mortality outcome and its cause.

PMID:12897283 SUPPORT Human Clinical

"The median age of death is 7.7 and 6 months, respectively. Five percent of the Dutch patients and 8% of all reported patients survive beyond 1 year of age."

Quantifies median age at death and one-year survival in the untreated natural history.

🧬

Genetic Associations

GAA

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

Show evidence (6 references)

PMID:12897283 SUPPORT Human Clinical

"The patients have fully deleterious mutations. Acid alpha-glucosidase activity is severely deficient."

Establishes fully deleterious biallelic GAA genotypes as the genetic basis of classic infantile disease.

PMID:22252923 SUPPORT Human Clinical

"We found that, in most cases, CRIM status can be predicted from GAA mutations, potentially circumventing the need for invasive skin biopsy and time wasted in culturing cells in the future."

Supports genotype-based prediction of CRIM status from GAA variants.

PMID:39482698 SUPPORT Other

"The GAA gene is localized on chromosome 17 at the 17q25.2–q25.3 locus and contains 20 exons including the 19 coding ones"

Establishes the GAA locus and exon structure.

+ 3 more references

💊

Medical Actions

Enzyme replacement therapy with alglucosidase alfa

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

Agent: alglucosidase alfa NCIT:C65221

Platform: Protein replacement

Intravenous recombinant human GAA is the disease-specific therapy for IOPD. Initiated before age six months and before the need for ventilatory assistance, it improves survival and ventilator-independent survival, reduces cardiac mass, and substantially improves motor skill acquisition. High-dose ERT started immediately on a newborn-screening diagnosis gives the best reported outcomes.

Mechanism Target:

INHIBITS Lysosomal glycogen accumulation — Infused recombinant human GAA supplies the missing lysosomal enzyme and clears stored glycogen.

Show evidence (1 reference)

PMID:20301438 SUPPORT Other

"In those in whom enzyme replacement therapy (ERT) is initiated before age six months and before the need for ventilatory assistance, a majority have improved survival, improved ventilator-independent survival, reduced cardiac mass, and significantly improved acquisition of motor skills compared..."

Reduced cardiac mass and improved survival evidence the reversal of the storage lesion by ERT.

Target Phenotypes: Hypertrophic cardiomyopathy HP:0001639 Motor delay HP:0001270

Show evidence (3 references)

PMID:17151339 SUPPORT Human Clinical

"All patients (100%) survived to 18 months of age. A Cox proportional hazards analysis demonstrated that treatment reduced the risk of death by 99%, reduced the risk of death or invasive ventilation by 92%, and reduced the risk of death or any type of ventilation by 88%, as compared to an..."

Pivotal trial quantifies the survival benefit of rhGAA in infantile-onset disease.

PMID:32373469 SUPPORT Human Clinical

"High-dose ERT instituted immediately at newborn screening seems to give the best outcome, and a dosage increase is necessary upon - or, even better, before - a rise in biomarker levels."

Real-world cohort supports early, high-dose ERT initiation at newborn screening.

PMID:32373469 SUPPORT Human Clinical

"In patients with classical IOPD diagnosed through newborn screening, those late in ERT initiation (p = .006) or late in high-dosage ERT initiation (p = .044) had a higher risk of motor decline."

Quantifies the penalty of delayed ERT initiation on motor outcome in classic IOPD.

Avalglucosidase alfa

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

Agent: avalglucosidase alfa NCIT:C169795

Platform: Protein replacement

A next-generation recombinant human GAA with enhanced mannose-6-phosphate receptor binding. In the Mini-COMET phase 2 trial, children with IOPD who had declined or responded suboptimally to alglucosidase alfa were switched to avalglucosidase alfa, with persistent normalization of left ventricular mass z score, falling disease-burden biomarkers, and improved or stable motor function through 97 weeks.

Mechanism Target:

INHIBITS Lysosomal glycogen accumulation — Avalglucosidase alfa delivers recombinant GAA to the lysosome via enhanced mannose-6-phosphate receptor uptake.

Show evidence (1 reference)

PMID:40449831 SUPPORT Human Clinical

"Compared with baseline, biomarkers of Pompe disease burden decreased, and motor function improved or stabilized."

Falling disease-burden biomarkers evidence reduction of the glycogen storage lesion.

Target Phenotypes: Hypertrophic cardiomyopathy HP:0001639

Show evidence (1 reference)

PMID:40449831 SUPPORT Human Clinical

"Echocardiography revealed persistent left ventricular mass z score normalization. Compared with baseline, biomarkers of Pompe disease burden decreased, and motor function improved or stabilized."

Mini-COMET reports cardiac, biomarker, and motor outcomes for avalglucosidase alfa in IOPD.

Immune tolerance induction with rituximab and methotrexate

Action: immune tolerance induction Ontology label: Pharmacotherapy NCIT:C15986

Agent: rituximab NCIT:C1702 methotrexate NCIT:C642

Platform: Monoclonal antibody

Because CRIM-negative infants neutralize rhGAA, immune tolerance induction is given prophylactically at ERT initiation, or therapeutically once antibodies appear. Rituximab (anti-CD20 B-cell depletion) plus methotrexate, with or without intravenous immunoglobulin, eliminated established anti-rhGAA antibody and conferred durable tolerance off all immune therapy with B-cell recovery. It is most effective before an entrenched high-titer response develops, which is why CRIM status should be known before the first infusion.

Mechanism Target:

INHIBITS High sustained anti-rhGAA antibody response — B-cell depletion plus antimetabolite immunomodulation prevents or eliminates the neutralizing anti-rhGAA IgG response.

Show evidence (1 reference)

PMID:22237443 SUPPORT Human Clinical

"In both patients treated therapeutically, anti-rhGAA was eliminated after 3 and 19 months. All four patients are immune tolerant to rhGAA, off immune therapy, showing B-cell recovery while continuing to receive ERT"

Directly evidences elimination of the antibody response and durable tolerance.

Show evidence (2 references)

PMID:22237443 SUPPORT Human Clinical

"All patients show clinical response to ERT, in stark contrast to the rapid deterioration of their nontolerized CRIM-negative counterparts."

Contrasts tolerized with non-tolerized CRIM-negative infants, supporting the clinical value of tolerance induction.

PMID:20301438 SUPPORT Other

"individuals who do not produce CRIM (i.e., who are CRIM negative) generally develop high titer anti-rhGAA antibodies during ERT and require modified therapy protocols using immunomodulation early in the treatment course, optimally before the first infusion."

Management guidance specifying immunomodulation for CRIM-negative infants, optimally before the first infusion.

Intravenous immunoglobulin adjunct

Action: immunoglobulin therapy Ontology label: Immunoglobulin Therapy NCIT:C62710

Platform: Other

Intravenous gammaglobulin was used alongside rituximab and methotrexate in the therapeutic (post-antibody) tolerance-induction regimen; the prophylactic regimen given at ERT initiation used a short rituximab-plus-methotrexate course essentially without IVIG.

Mechanism Target:

INHIBITS High sustained anti-rhGAA antibody response — IVIG was part of the therapeutic tolerance-induction combination that eliminated established anti-rhGAA antibody.

Show evidence (1 reference)

PMID:22237443 SUPPORT Human Clinical

"The combination of rituximab with methotrexate ± intravenous gammaglobulins (IVIG) is an option for tolerance induction of CRIM-negative Pompe to ERT when instituted in the naïve setting or following antibody development."

Names IVIG as a component of the tolerance-induction combination.

Show evidence (1 reference)

PMID:22237443 SUPPORT Human Clinical

"Two CRIM-negative patients with preexisting anti-GAA antibodies were treated therapeutically with rituximab, methotrexate, and gammaglobulins."

Describes the therapeutic regimen in which IVIG was used.

Respiratory support

Action: artificial respiration Ontology label: Mechanical Ventilation NCIT:C70909

Platform: Device

Respiratory support for respiratory insufficiency may include CPAP and BiPAP; tracheostomy may be considered in infants with macroglossia and severe respiratory insufficiency. Invasive ventilator-free survival is the primary outcome measure in IOPD trials.

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

Show evidence (1 reference)

PMID:20301438 SUPPORT Other

"Respiratory support for those with respiratory insufficiency may include CPAP and BiPAP; tracheostomy may be considered in those with macroglossia and severe respiratory insufficiency."

Specifies the respiratory support options in Pompe disease management.

Feeding therapy and gastrostomy

Action: Dietary management Ontology label: Dietary Intervention NCIT:C15447

Platform: Behavioral / lifestyle

Feeding therapy with consideration of a gastrostomy tube is recommended for infants with feeding and nutritional difficulties, though growth may still deviate from normal despite tube feeding.

Target Phenotypes: Feeding difficulties HP:0011968 Failure to thrive HP:0001508

Show evidence (1 reference)

PMID:20301438 SUPPORT Other

"Feeding therapy and consideration of a gastrostomy tube is recommended for those who have feeding/nutritional difficulties."

States the recommended feeding intervention.

Cardiac management with Pompe-specific drug precautions

Action: supportive care Ontology label: Supportive Care NCIT:C15747

Medical intervention for cardiomyopathy must be individualized because standard cardiac drugs may be contraindicated at certain disease stages; digoxin, inotropes, diuretics, and afterload-reducing agents may worsen left ventricular outflow obstruction.

Target Phenotypes: Hypertrophic cardiomyopathy HP:0001639

Show evidence (2 references)

PMID:20301438 SUPPORT Other

"The use of digoxin, ionotropes, diuretics, and afterload-reducing agents may worsen left ventricular outflow"

Lists cardiac drugs that may worsen outflow obstruction in Pompe disease.

PMID:39482698 SUPPORT Other

"ECG and Echocardiogram should be performed at diagnosis, and at regular intervals (every 12 months or more frequently, depending on patients’ conditions, in the presence of cardiomyopathy)."

The MetabERN European clinical pathway recommendations set the cardiac surveillance schedule that accompanies this individualized cardiac management.

AAV9-mediated GAA gene therapy

Action: AAV9-delivered GAA gene transfer Ontology label: Gene Therapy NCIT:C15238

Platform: Gene therapy

A single intravenous infusion of an adeno-associated virus serotype 9 vector carrying codon-optimized human GAA cDNA, given at 1.2 x 10^14 vector genomes per kilogram. In a reported infantile-onset series, three of four treated patients had improved cardiac outcomes and motor function over 52 weeks and no anti-GAA antibodies were detected; one patient was withdrawn and subsequently died. The rationale is that a single administration of a gene that the body then expresses avoids both the every-other-week infusion burden of enzyme replacement and the anti-rhGAA antibody response that defeats it in CRIM-negative infants - but this is an early-phase result in four patients, not established therapy.

Mechanism Target:

RESTORES Near-complete acid alpha-glucosidase deficiency — Vector-delivered GAA cDNA supplies the missing enzyme from the patient's own transduced cells, addressing the initiating lesion rather than a downstream consequence.

Show evidence (1 reference)

PMID:40561529 SUPPORT Human Clinical

"Four patients with infantile-onset Pompe's disease received a single intravenous injection of an adeno-associated virus serotype 9 vector carrying codon-optimized complementary DNA encoding human acid α-glucosidase (GAA)"

Describes the intervention acting on the enzyme-deficiency node in infantile-onset patients.

Target Phenotypes: Hypertrophic cardiomyopathy HP:0001639

Show evidence (7 references)

PMID:40561529 SUPPORT Human Clinical

"The other patients had improvement in cardiac outcomes and motor function over a 52-week observation period."

Reports the cardiac and motor benefit observed in the treated infantile-onset patients.

PMID:40561529 SUPPORT Human Clinical

"Anti-GAA antibodies were not detected in any of the patients during the observation period."

Reports that no anti-GAA antibody response was detected over the observation period. The publication does not report the CRIM status of these four patients, so this does not by itself speak to the CRIM-negative antibody-mediated failure curated elsewhere in this entry.

PMID:40561529 REFUTE Human Clinical

"One patient was withdrawn from the study and subsequently died."

Records the outcome in the fourth patient, which counts against reading this four-patient series as an established benefit.

+ 4 more references

🔬

Biochemical Markers

Acid alpha-glucosidase enzyme activity

Context: Diagnosis rests on deficient GAA enzyme activity in isolated lymphocytes or mixed leukocytes (or fibroblasts/muscle), with classic infantile patients showing severely deficient activity, typically less than 1% of the control mean.

Show evidence (2 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"

States the diagnostic enzyme assay for Pompe disease.

PMID:12897283 SUPPORT Human Clinical

"Acid alpha-glucosidase activity is severely deficient."

Confirms severe enzyme deficiency in the classic infantile cohort.

Urinary glucose tetrasaccharide (Glc4/Hex4)

Context: Urinary glucose tetrasaccharide is a glycogen-burden biomarker used to monitor treatment response in IOPD. Together with creatine kinase, low levels correlate with favourable response to enzyme replacement therapy, and uGlc4 is the more stable of the two.

Show evidence (3 references)

PMID:32373469 SUPPORT Human Clinical

"Low CK and uGlc4 levels were correlated with favorable response to ERT in IOPD patients, although CK may be more fluctuated than uGlc4."

Establishes urinary Glc4 as a monitoring biomarker of ERT response in IOPD.

PMID:15886040 SUPPORT Human Clinical

"Both urinary Glc4 and plasma Hex4 levels decreased after initiation of ERT for all patients."

Establishes the direction of the biomarker's response to enzyme replacement therapy - it falls in every treated patient, so a fall is not by itself a marker of good response.

PMID:15886040 SUPPORT Human Clinical

"In contrast, levels fluctuated and were persistently elevated above the control ranges in those patients with a less favorable clinical response"

Supplies the discriminating observation - persistent elevation above the control range, rather than the initial fall, is what marks a poorer clinical response.

Anti-rhGAA IgG antibody titer

Context: Serial anti-recombinant-human-GAA IgG titers stratify treatment response. CRIM-negative infants develop earlier, higher, and more sustained titers; by contrast, long-term survivors of IOPD had low or undetectable anti-alglucosidase alfa antibody titers.

Show evidence (2 references)

PMID:19775921 SUPPORT Human Clinical

"IgG antibodies to rhGAA developed earlier and serotiters were higher and more sustained in the CRIM-negative group."

Reports the antibody-titer difference by CRIM status that makes this a decision-relevant biomarker.

PMID:22538254 SUPPORT Human Clinical

"All long-term survivors had low or undetectable anti-alglucosidase alfa antibody titers."

Shows the association between low antibody titer and long-term survival on ERT.

🔬

Diagnosis

Newborn screening for GAA deficiency

Pompe disease is screened in newborns by measuring acid alpha-glucosidase activity in dried blood spots. The European clinical pathway calls newborn screening essential specifically for the infantile-onset forms, and this entry's own histopathology section supplies the tissue-level reason: the amount of damage already present at baseline limits what enzyme replacement therapy can undo, so identifying an affected infant before symptoms appear is what decides the outcome. The dried blood spot assay is a screening test only - a low result needs confirmation, and sequencing also yields the genotype used to predict CRIM status before enzyme replacement therapy is started.

newborn dried blood spot screening for GAA deficiency NCIT:C81178

Results: A low dried-blood-spot GAA activity result must be confirmed before it is treated as a diagnosis; confirmation is by enzyme assay in leukocytes and/or biallelic pathogenic GAA variants on molecular testing.

Show evidence (7 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)"

States the assay on which newborn screening for this disease is based.

PMID:39482698 SUPPORT Other

"Newborn screening is essential for timely identification and treatment of patients with the infantile-onset forms of the disease."

The European clinical pathway singles out the infantile-onset forms as the ones for which newborn screening is essential, which is what makes this a diagnosis entry on this disease rather than on Pompe disease generally.

PMID:39482698 SUPPORT Other

"the assay in dried blood spots is only a screening test and is not sufficient for definitive diagnosis"

Records the limitation that makes confirmatory testing mandatory rather than optional.

+ 4 more references

CRIM status determination before starting enzyme replacement therapy

Cross-reactive immunologic material status is established before enzyme replacement therapy begins, because it decides whether prophylactic immune tolerance induction is needed alongside it. A systematic review addressed how CRIM status is determined in practice, how CRIM-negative status affects outcome, and which immune tolerance induction regimens are actually used. CRIM status is not a measure of enzyme activity: both CRIM-positive and CRIM-negative infants have essentially none, and the question is whether any GAA protein exists for the immune system to recognise as self.

CRIM status determination NCIT:C18020

Results: A CRIM-negative result calls for prophylactic immune tolerance induction started with, or before, enzyme replacement therapy rather than after antibodies appear. The review reports that starting immune tolerance induction at or before the first enzyme dose improves prognosis in CRIM-positive patients as well, so a CRIM-positive result is not by itself a reason to withhold it.

Show evidence (3 references)

PMID:41583481 SUPPORT Other

"CRIM status should be determined before initiating ERT since CRIM-negative patients have a very high risk of developing an immune response against ERT, potentially leading to treatment failure"

States the claim this entry makes - that CRIM status is established before enzyme replacement therapy starts - and the reason, which is the risk of an immune response that defeats the therapy.

PMID:41583481 SUPPORT Other

"Initiating ITI therapy concurrent or prior to the first dose of ERT can improve the prognosis of patients with IOPD with either CRIM-negative or CRIM-positive status"

Supports the results field - immune tolerance induction started with or before the first enzyme dose rather than after antibodies appear. Note the scope is wider than the results text; the review reports benefit for CRIM-positive patients too, not only CRIM-negative ones.

PMID:41583481 SUPPORT Other

"Recently, there has been a major shift from direct CRIM testing using western blotting and mutation analysis to CRIM status prediction based on genetic variant analysis."

Records how the determination is actually made now, which is why the binding here is the generic Diagnostic Procedure rather than a protein-assay or a genetic-testing term - both routes are in use.

📈

Progression

Presentation and diagnosis

Age: Median symptom onset 2.0 months, median diagnosis 4.7 months

Symptoms typically begin within the first months of life, with diagnosis following a median of under three months later. This phase and the two that follow describe the pre-enzyme-replacement natural history against which treated cohorts are benchmarked; they are not the expected course of a child treated early today. The medians fall inside the first year, but the cohort's reported death range extends to 73.4 months, so individual courses are not uniformly that short.

Show evidence (1 reference)

PMID:16737883 SUPPORT Human Clinical

"The median age at symptom onset was 2.0 months (range 0 to 12 months), 4.7 months at diagnosis"

Gives the median ages at symptom onset and diagnosis in the 168-patient natural-history cohort.

Ventilator-dependent phase

Age: Median age at first ventilator support 5.9 months (range 0.1 to 31.1 months)

Ventilatory support becomes necessary before most affected infants reach their first birthday. The cohort reports the median age at first ventilator support and the median age at death as separate marginal figures, so the interval between the two is not derivable from them and is deliberately not asserted here.

Show evidence (2 references)

PMID:16737883 SUPPORT Human Clinical

"5.9 months at first ventilator support (range 0.1 to 31.1 months), and 8.7 months at death"

Gives the median age at first ventilator support, and the median age at death that bounds the phase that follows.

PMID:16737883 SUPPORT Human Clinical

"Survival rates at 12 months of age were 25.7% overall and 16.9% ventilator-free; at 18 months 12.3% and 6.7%"

Quantifies how few untreated infants reach 12 and 18 months, and how many of those are ventilator-free.

Untreated terminal phase

Age: Median age at death 8.7 months (range 0.3 to 73.4 months)

Earlier symptom onset carries a higher risk of early death, which is the natural-history counterpart of the treated-era finding that earlier enzyme replacement gives better outcomes. The mode of death is curated in the pathophysiology chain (Cardiopulmonary insufficiency of infancy) rather than asserted here, since the cohort abstract reports timing rather than cause.

Show evidence (2 references)

PMID:16737883 SUPPORT Human Clinical

"To characterize the natural progression of infantile-onset Pompe disease. ... Retrospective chart reviews of 168 patients with documented acid alpha-glucosidase deficiency and symptom onset by 12 months of age; ... The median age at symptom onset was 2.0 months (range 0 to 12 months), 4.7 months..."

Reports infantile-onset Pompe natural-history mortality and survival in a retrospective cohort. The excerpt does not explicitly distinguish enzyme-replacement-naive patients from other therapeutic interventions.

PMID:16737883 SUPPORT Human Clinical

"Despite frequent therapeutic interventions, infantile-onset Pompe disease remains lethal"

States the pre-enzyme-replacement conclusion that supportive care alone does not alter the fatal outcome.

📊

Prevalence

Global live births

Birth Prevalence 1.0 per 100,000 (0.5–1.5) 1–9 per 1,000,000 (births)

Pooled global birth prevalence of infantile-onset Pompe disease specifically, from a 2024 systematic review and meta-analysis (1.0 per 100,000 live births, 95% CI 0.5-1.5), against 2.0 per 100,000 for Pompe disease overall.

Show evidence (1 reference)

PMID:39424261 SUPPORT Human Clinical

"Global birth prevalence of infantile-onset Pompe disease was 1.0 cases (95% CI: 0.5-1.5) per 100,000 live births."

Meta-analysis reports the birth prevalence of the infantile-onset form specifically.

📊

Related Datasets

GAA deficiency (Pompe Disease) in infantile-onset patients geo:GSE38680

Microarray expression profiling of biceps and quadriceps muscle from two cohorts of infantile-onset Pompe patients, used to identify transcriptional differences contributing to the disease phenotype. This is the only dataset located that is both human and restricted to the infantile-onset form, so it is the direct transcriptomic counterpart of this entry's skeletal-myofiber-injury node.

human MICROARRAY n=58

PMID:22658377

Discovered via `just discover-datasets Infantile-Onset_Pompe_Disease` as a DIRECT match - the infantile-onset form is named in the dataset's own title - and retained after manual relevance triage. Verified with `just verify-datasets`. Retrieved 2026-09-01.

Show evidence (2 references)

PMID:22658377 SUPPORT Human Clinical

"we used microarrays to examine gene expression from the muscle of two cohorts of infantile-onset Pompe patients to identify transcriptional differences that may contribute to the disease phenotype"

Establishes that this dataset profiles muscle from infantile-onset patients specifically, which is what makes it on-topic for this entry rather than for Pompe disease generally.

PMID:22658377 SUPPORT Human Clinical

"infantile-onset Pompe patient muscle had a gene expression pattern characteristic of immature or regenerating muscle, and exhibited many transcriptional markers of inflammation, despite having few overt signs of inflammatory infiltrate"

Reports the dataset's principal finding, a regenerative and inflammatory transcriptional signature in infantile-onset patient muscle without matching histologic infiltrate.

Transcriptomic profile of three-dimensional tissue-engineered human skeletal muscle model of Pompe disease and recombinant protein therapy geo:GSE159062

RNA-seq of a three-dimensional tissue-engineered human skeletal muscle ("myobundle") model of infantile-onset Pompe disease with and without recombinant human GAA, giving a transcriptomic readout of the muscle response to the therapy this entry curates as its principal treatment. The model reproduces reduced GAA activity, elevated glycogen and lysosome abundance, and contractile sensitivity to metabolic stress.

human BULK RNA SEQ n=10

PMID:33953320

Discovered via `just discover-datasets` as a DIRECT match and retained after manual relevance triage: the source publication describes the myobundles explicitly as a model of infantile-onset Pompe disease. Relevance caveat: it is an engineered in vitro system, so it bears on the GAA-deficiency mechanism and the enzyme-replacement response in human muscle rather than on the cardiac severity or infantile course observed in patients. The companion SuperSeries GSE159064 is deliberately not curated separately, since it contains this series. Verified with `just verify-datasets`. Retrieved 2026-09-01.

Show evidence (2 references)

PMID:33953320 SUPPORT In Vitro

"we report a three-dimensional primary human skeletal muscle ("myobundle") model of infantile-onset Pompe disease (IOPD) that recapitulates hallmark pathological features including reduced GAA enzyme activity, elevated glycogen content and lysosome abundance"

Establishes that the profiled system is a model of the infantile-onset form specifically, and which disease features it reproduces.

PMID:33953320 SUPPORT In Vitro

"In vitro treatment of IOPD myobundles with rhGAA or adeno-associated virus (AAV)-mediated hGAA expression yields increased GAA activity and robust glycogen clearance, but no improvements in stress-induced functional deficits."

Reports the dissociation this dataset captures - glycogen clears while a functional deficit persists - which is the in vitro counterpart of the incomplete skeletal-muscle response to enzyme replacement therapy curated in this entry.

Gene expression profile of tibialis anterior from Gaa-/- mice compared to wild type mice geo:GSE293648

Microarray profiling of tibialis anterior muscle from Gaa-knockout mice against wild type, generated in a study of membrane-repair proteins and satellite-cell failure in Pompe muscle. It is the transcriptomic layer of the same knockout model this entry curates under animal_models for the autophagic-buildup node.

house mouse MICROARRAY n=32

PMID:42337614

Discovered via `just discover-datasets` as a GENE_ONLY candidate and retained after manual relevance triage: the GEO title and summary describe Gaa-knockout mouse muscle with glycogen-filled lysosomes and autophagic build-up, which is this entry's mechanism. Relevance caveat: it is a mouse knockout, so it models GAA deficiency rather than the infantile onset or the cardiac severity that define IOPD, and the source publication's human validation arm is late-onset patients rather than infantile-onset ones. Verified with `just verify-datasets`. Retrieved 2026-09-01.

Show evidence (2 references)

PMID:42337614 SUPPORT Model Organism

"Longitudinal transcriptomic analysis of skeletal muscle from a Pompe disease mouse model, combined with immunohistochemical and biochemical approaches, showed early and sustained overexpression of dysferlin (DYSF), annexin A2 (ANXA2), and AHNAK2."

Describes the transcriptomic analysis this dataset is the primary data for, and its principal result in the mouse muscle profiled.

PMID:42337614 SUPPORT Model Organism

"in the mouse model, we observed persistent post-transcriptional accumulation of mature myostatin (MSTN), a key negative regulator of muscle growth, alongside a decrease in the phospho-SMAD3/SMAD3 ratio and reduced SMAD7 expression"

Reports the second result obtained from this mouse model, a myostatin-axis change relevant to the muscle-wasting arm of the disease.

🔬

Clinical Trials

NCT03019406 PHASE_II ACTIVE_NOT_RECRUITING

Mini-COMET: a phase 2, open-label, ascending-dose, three-cohort study of avalglucosidase alfa in children with infantile-onset Pompe disease who were declining or responding suboptimally to prior alglucosidase alfa.

Target Phenotypes: Hypertrophic cardiomyopathy HP:0001639

Show evidence (1 reference)

PMID:40449831 SUPPORT Human Clinical

"The Mini-COMET clinical trial, a phase 2, open-label, ascending-dose, 3-cohort study, has a 25-week primary analysis period (PAP) and an extension treatment period (ETP)."

Describes the design of the registered Mini-COMET trial in infantile-onset Pompe disease.

NCT04910776 PHASE_III ACTIVE_NOT_RECRUITING

Baby-COMET: a phase 3, open-label, single-group study of avalglucosidase alfa in treatment-naive pediatric participants with infantile-onset Pompe disease. It is the first-line counterpart of Mini-COMET, which enrolled only children already declining on alglucosidase alfa, and so speaks to whether avalglucosidase alfa is an alternative to alglucosidase alfa at diagnosis rather than a salvage option.

Target Phenotypes: Hypertrophic cardiomyopathy HP:0001639 Generalized muscle weakness HP:0003324

Show evidence (1 reference)

clinicaltrials:NCT04910776 SUPPORT Human Clinical

"This is a single group, treatment, Phase 3, open-label study to assess efficacy, safety, pharmacokinetic (PK), pharmacodynamics (PD) of avalglucosidase alfa in treatment-naïve male and female participants with IOPD."

The registry record establishes the phase, design, and treatment-naive IOPD population of the trial.

ChiCTR2200063229 PHASE_I RECRUITING

Single-arm, single-centre, open-label Phase 1 study of GC301, an adeno-associated virus injection, for safety, tolerability, and efficacy in patients with infantile-onset Pompe disease. This is the registration behind the AAV9-GAA gene-therapy series curated as a treatment in this entry; the trial identifier is named in that publication.

Target Phenotypes: Hypertrophic cardiomyopathy HP:0001639

Show evidence (1 reference)

ICTRP:ChiCTR2200063229 SUPPORT Other

"| Register | ChiCTR |"

WHO ICTRP registration record establishing the trial's identity and register of origin.

🧫

Experimental Models

Patient-derived iPSC cardiomyocytes (PD-iCMs) IPSC_DERIVED_MODEL

Cardiomyocytes differentiated from Pompe patient induced pluripotent stem cells. They reproduce the cardiac storage lesion in a human genetic background - decreased GAA activity, lysosomal glycogen accumulation, and hypertrophy - and were used to show that mitochondrial dysfunction accompanies the hypertrophy, in human cardiomyocytes carrying patient genotypes rather than in a rodent background. Supplementing the cultures with recombinant human GAA improved mitochondrial function and mitigated the cardiac pathology, making this a system in which the disease lesion and its response to the actual clinical therapy are both observable.

Organism

human NCBITaxon:9606

Cell source

Patient-derived induced pluripotent stem cells

Publication

PMID:37916452

Pathograph links

Cardiomyocyte glycogen storage and progressive hypertrophic remodeling recapitulates fidelity: moderate The differentiated cardiomyocytes show reduced GAA activity, lysosomal glycogen accumulation, and hypertrophy - the cellular content of this node - in human cells carrying patient genotypes.

Limitations: iPSC-derived cardiomyocytes are immature relative to adult myocardium and are cultured without haemodynamic load, so the hypertrophy they show is not the pressure-loaded ventricular remodeling of the intact infant heart. The source publication describes the donors as Pompe disease patients without stating that they are the classic infantile form, so the genotype-to-onset link is not established by this study alone.

Readouts

Mitochondrial number, respiratory function, and ATP production

Direction: DECREASED

Interpretation: Mitochondrial deficit accompanying the storage and hypertrophy phenotype in patient-derived cardiomyocytes.

Show evidence (1 reference)

PMID:37916452 SUPPORT In Vitro

"The defective mitochondria were involved in the cardiac pathology as shown by the significantly decreased number of mitochondria and impaired respiratory function and ATP production in PD-iCMs"

Reports the mitochondrial measurements and their direction in the patient-derived cardiomyocytes.

Rescue of mitochondrial function and cardiac pathology by recombinant human GAA

Direction: RESTORED

Interpretation: Supplying the missing enzyme partially reverses the model phenotype, which is the in vitro counterpart of the cardiac response to enzyme replacement therapy.

Show evidence (1 reference)

PMID:37916452 SUPPORT In Vitro

"This was alleviated by supplementation with recombinant human acid alpha-glucosidase that improved the mitochondrial function and concomitantly mitigated the cardiac pathology."

Reports the rescue arm and what it restored.

Show evidence (1 reference)

PMID:37916452 SUPPORT In Vitro

"PD patient-specific induced pluripotent stem cells were differentiated into cardiomyocytes (PD-iCMs) that exhibited cardiomyopathic features of PD, including decreased acid alpha-glucosidase activity, lysosomal glycogen accumulation and hypertrophy"

Supports treating these cardiomyocytes as informative for the cardiac storage and hypertrophy node.

Show evidence (1 reference)

PMID:37916452 SUPPORT In Vitro

"Therefore, this study suggests that defective mitochondria underlie the pathogenesis of cardiomyopathy in patients with PD."

States the conclusion this model system was built to support, and so what the model is being curated as evidence for.

🐁

Animal Models

GAA-knockout mouse

The GAA-knockout mouse reproduces the lysosomal glycogen storage lesion and was the system in which the autophagic-buildup arm of Pompe muscle pathology, and its interference with enzyme replacement therapy, was established.

Species

Mouse

Genotype

Gaa knockout (GAA-null)

Publication

PMID:20040311

Pathograph links

Failure of productive autophagy and autophagic buildup recapitulates fidelity: moderate Progressive accumulation of autophagic vesicles in type II-rich fibers, with sequestration of infused recombinant enzyme.

Limitations: The autophagic buildup in this model is restricted to type II-rich fibers, and mouse and human skeletal muscle differ in fiber-type composition, so the proportion of muscle affected does not transfer directly. The model is also not specific to the infantile form: it models GAA deficiency, not the age of onset or cardiac severity that defines IOPD, and it says nothing about CRIM status, the other determinant of ERT response in infants.

Readouts

Autophagic vesicle accumulation in type II-rich muscle fibers

Direction: INCREASED

Interpretation: Histological correlate of the autophagic-buildup node in this model.

Show evidence (1 reference)

PMID:20040311 SUPPORT Model Organism

"In the GAA-knockout mouse model, progressive accumulation of autophagic vesicles is restricted to Type II-rich muscle fibers."

Reports the measurement and its direction in the knockout mouse.

Show evidence (1 reference)

PMID:20040311 SUPPORT Model Organism

"we present evidence that a failure of productive autophagy in muscle tissue contributes strongly to disease pathology in both patients with Pompe disease and GAA-knockout mice"

Supports treating the knockout mouse as informative for the autophagy node in human disease.

Show evidence (1 reference)

PMID:20040311 SUPPORT Model Organism

"Not only does this build-up of autophagosomes disrupt the contractile apparatus in the muscle fibers, it also interferes with enzyme replacement therapy by acting as a sink for the recombinant enzyme and preventing its efficient delivery to the lysosomes."

Reports the knockout-mouse finding that makes this model informative here - autophagic buildup both damages the contractile apparatus and sequesters infused recombinant enzyme.

Lapphund canine Pompe disease (naturally occurring GAA p.W746* homozygote)

A naturally occurring canine Pompe disease found in Finnish Lapphunds, Swedish Lapphunds, and Lapponian Herders. The dogs are homozygous for a GAA nonsense variant at the codon whose human counterpart causes infantile disease when paired with a second fully deleterious allele, and they reproduce the infantile form both genetically and clinico-pathologically. Unlike the engineered mouse models, this is a spontaneous large-animal disease, which is what makes it the preferred system for preclinical gene-therapy work.

Species

Dog

Genotype

GAA c.2237G>A (premature stop at residue 746) homozygous

Publication

PMID:23457621

Pathograph links

Near-complete acid alpha-glucosidase deficiency recapitulates fidelity: moderate A homozygous premature stop codon abolishes acid alpha-glucosidase, the same class of fully deleterious lesion that produces classic infantile disease in humans.

Limitations: The dogs are homozygous for one nonsense allele, whereas human infantile-onset disease usually arises from two different deleterious alleles, so the model does not reproduce the human allelic heterogeneity or its effect on residual protein. The publication reports genetic and clinico-pathological similarity to the human infantile form but does not itself establish CRIM status or the anti-rhGAA antibody behaviour that governs enzyme replacement response in infants, so it says nothing about that axis of the disease.

Show evidence (2 references)

PMID:23457621 SUPPORT Model Organism

"The affected dogs from both the Finnish as well as the Swedish breed mimic infantile-onset Pompe disease genetically, but also clinico-pathologically."

States that this naturally occurring canine disease reproduces the human infantile-onset form at both the genetic and the pathological level.

+ 1 more reference

Show evidence (1 reference)

PMID:23457621 SUPPORT Model Organism

"The affected dogs are homozygous for the GAA c.2237G>A mutation leading to a premature stop codon at amino acid position 746."

Establishes the causal genotype of this naturally occurring canine disease, which is what makes it a model of GAA deficiency rather than an unrelated canine myopathy.

Gaa c.1935C>A (p.D645E) knock-in mouse

A CRISPR-Cas9 knock-in mouse carrying the human GAA c.1935C>A (p.Asp645Glu) variant, which is the most frequent infantile-onset allele in people of Southern Han Chinese ancestry. By three months these mice have both skeletal muscle weakness and hypertrophic cardiomyopathy, the two features that define the human infantile form, which is the basis on which the authors present it as a model of the infantile-onset disease rather than of GAA deficiency in general.

Species

Mouse

Genotype

Gaaem1935C>A (p.Asp645Glu) homozygous knock-in

Publication

PMID:36517654

Pathograph links

Cardiomyocyte glycogen storage and progressive hypertrophic remodeling recapitulates fidelity: moderate Homozygous knock-in mice develop hypertrophic cardiomyopathy, the cardiac feature that separates infantile-onset from late-onset disease.

Limitations: The mice show no premature mortality, so the model reproduces the cardiac and muscle lesions without the fatal course that defines the untreated human disease. It also models one specific missense allele rather than the null genotypes behind most classic infantile disease, and the characterization reported is at a single three-month timepoint.

Readouts

Hypertrophic cardiomyopathy and skeletal muscle weakness at 3 months

Direction: INCREASED

Interpretation: Presence of the defining cardiac lesion of infantile-onset disease in the knock-in model.

Show evidence (1 reference)

PMID:36517654 SUPPORT Model Organism

"Three-month-old mice demonstrated skeletal muscle weakness and hypertrophic cardiomyopathy but no premature mortality."

Reports the measurement, its direction, and the negative survival result in the same sentence.

Show evidence (1 reference)

PMID:36517654 SUPPORT Model Organism

"The Gaaem1935C>A knock-in mouse model recapitulates multiple salient aspects of human IOPD caused by the GAA c.1935C>A pathogenic variant."

Supports treating this knock-in line as informative for the infantile-onset cardiac phenotype.

Failure of productive autophagy and autophagic buildup recapitulates fidelity: moderate The knock-in mice have near-abolished GAA activity with markedly increased tissue glycogen and impaired autophagy, reproducing the autophagy arm of the mechanism in an allele-specific rather than a null background.

Limitations: Autophagy is reported as impaired at three months without the longitudinal characterization available for the knockout line, and the mice do not progress to the fatal outcome, so the model does not show how far the autophagic lesion goes in untreated disease.

Show evidence (1 reference)

PMID:36517654 SUPPORT Model Organism

"Homozygous Gaaem1935C>A knock-in mice exhibited normal Gaa mRNA expression levels relative to wild-type mice, had near-abolished GAA enzymatic activity, markedly increased tissue glycogen storage, and concomitantly impaired autophagy."

Reports abolished enzyme activity, glycogen storage, and impaired autophagy together in this model.

Show evidence (1 reference)

PMID:36517654 SUPPORT Model Organism

"The c.1935C>A (p.Asp645Glu) variant, the most frequent GAA pathogenic mutation in people of Southern Han Chinese ancestry, causes infantile-onset Pompe disease (IOPD)"

Establishes that the knocked-in allele is itself a human infantile-onset-causing variant, which is the basis for treating this line as an IOPD model rather than a generic GAA-deficiency model.

{ }

Source YAML

click to show

name: Infantile-Onset Pompe Disease
creation_date: '2026-08-18T00:00:00Z'
category: Mendelian
description: >
  Classic infantile-onset Pompe disease (IOPD) is the most severe form of glycogen
  storage disease due to acid maltase deficiency, defined by symptom onset before
  age 12 months together with hypertrophic cardiomyopathy. It is caused by
  biallelic fully deleterious GAA variants that leave essentially no residual acid
  alpha-glucosidase activity (typically <1% of control), so lysosomal glycogen
  accumulates rapidly and massively in cardiac, skeletal, and respiratory muscle.
  Untreated infants present in the first weeks to months of life with progressive
  cardiomegaly and hypertrophic cardiomyopathy, profound hypotonia, feeding
  difficulty and failure to thrive, macroglossia, hepatomegaly, and respiratory
  distress, and die of cardiopulmonary insufficiency in the first one to two years.
  Two features distinguish IOPD mechanistically from the late-onset form curated
  under Pompe Disease. First, the near-total absence of enzyme drives an aggressive
  cardiac phenotype that late-onset disease does not have. Second, because roughly a
  quarter of classic infantile patients make no immunologically detectable GAA
  protein at all (cross-reactive immunologic material, CRIM-negative), recombinant
  human GAA is seen by the immune system as a foreign protein: these infants mount
  early, high, sustained anti-rhGAA IgG responses that neutralize enzyme replacement
  therapy and are associated with death or invasive ventilation despite treatment,
  unless immune tolerance is induced. Enzyme replacement therapy started early
  transforms survival and reverses cardiac hypertrophy, and has revealed an emerging
  long-term survivor phenotype with residual myopathy, hearing loss, dysphagia,
  osteopenia, and progressive cerebral white-matter abnormalities.
disease_term:
  preferred_term: Infantile-onset Pompe disease
  term:
    id: MONDO:0017694
    label: glycogen storage disease due to acid maltase deficiency, infantile onset
synonyms:
- IOPD
- Classic infantile Pompe disease
- Glycogen storage disease type II, infantile onset
- Acid maltase deficiency, infantile onset
- Pompe disease, infantile onset
classifications:
  harrisons_chapter:
  - classification_value: ENDOCRINOLOGY_METABOLISM
    evidence:
    - reference: PMID:22252923
      reference_title: "Predicting cross-reactive immunological material (CRIM) status in Pompe disease using GAA mutations: lessons learned from 10 years of clinical laboratory testing experience."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Pompe disease (Glycogen Storage Disease type II; acid maltase deficiency; OMIM# 232300) is an autosomal recessive disorder of glycogen metabolism caused by deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA)"
      explanation: Identifies the disease as an inherited disorder of glycogen metabolism, placing it in the metabolic chapter.
  lysosomal_storage_category:
    classification_value: disorder of glycogen metabolism
    evidence:
    - reference: ORPHA:365
      reference_title: "Glycogen storage disease due to acid maltase deficiency"
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "A rare lysosomal storage disease characterized by lysosomal accumulation of glycogen particularly in skeletal, cardiac, and respiratory muscles"
      explanation: Orphanet classifies acid maltase deficiency, of which IOPD is the infantile form, as a lysosomal glycogen-storage disorder.
definitions:
- name: GeneReviews clinical definition of IOPD
  definition_type: CASE_DEFINITION
  derivation_basis: ESTABLISHED_CRITERIA
  description: >
    GeneReviews defines infantile-onset Pompe disease by onset before age 12 months
    together with cardiomyopathy; onset before 12 months WITHOUT cardiomyopathy is
    classified as late-onset disease. Cardiomyopathy, not age alone, is the
    discriminating criterion.
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Pompe disease can be classified by age of onset, organ involvement, severity, and rate of progression into infantile-onset Pompe disease (IOPD) (i.e., individuals with onset before age 12 months with cardiomyopathy)"
    explanation: States the case definition that separates IOPD from LOPD by the presence of cardiomyopathy in the first year.
parents:
- Pompe Disease
- Lysosomal Storage Disease
inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >
    IOPD is inherited in an autosomal recessive manner, with affected infants
    carrying two fully deleterious (null or severely damaging) GAA alleles. The
    severity of the infantile phenotype tracks the near-complete absence of residual
    enzyme produced by this fully deleterious genotype.
  evidence:
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patients have fully deleterious mutations. Acid alpha-glucosidase activity is severely deficient."
    explanation: The natural-history cohort establishes that classic infantile patients carry fully deleterious GAA genotypes with severely deficient enzyme activity.
  - reference: PMID:22252923
    reference_title: "Predicting cross-reactive immunological material (CRIM) status in Pompe disease using GAA mutations: lessons learned from 10 years of clinical laboratory testing experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found that, in most cases, CRIM status can be predicted from GAA mutations, potentially circumventing the need for invasive skin biopsy and time wasted in culturing cells in the future."
    explanation: Shows that the biallelic GAA genotype determines whether any GAA protein is made, i.e. CRIM status.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "If both parents are known to be heterozygous for a GAA pathogenic variant, 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: The GeneReviews GENETIC COUNSELING section states the autosomal recessive transmission risks that follow from biallelic GAA inheritance.
prevalence:
- population: Global live births
  measure_type: BIRTH_PREVALENCE
  prevalence_class: BAND_1_9_PER_1000000
  rate_per_100000: 1.0
  rate_low: 0.5
  rate_high: 1.5
  notes: >-
    Pooled global birth prevalence of infantile-onset Pompe disease specifically,
    from a 2024 systematic review and meta-analysis (1.0 per 100,000 live births,
    95% CI 0.5-1.5), against 2.0 per 100,000 for Pompe disease overall.
  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 infantile-onset Pompe disease was 1.0 cases (95% CI: 0.5-1.5) per 100,000 live births."
    explanation: Meta-analysis reports the birth prevalence of the infantile-onset form specifically.
progression:
- phase: Presentation and diagnosis
  age_range: Median symptom onset 2.0 months, median diagnosis 4.7 months
  notes: >-
    Symptoms typically begin within the first months of life, with diagnosis
    following a median of under three months later. This phase and the two that
    follow describe the pre-enzyme-replacement natural history against which treated
    cohorts are benchmarked; they are not the expected course of a child treated
    early today. The medians fall inside the first year, but the cohort's reported
    death range extends to 73.4 months, so individual courses are not uniformly that
    short.
  evidence:
  - reference: PMID:16737883
    reference_title: "A retrospective, multinational, multicenter study on the natural history of infantile-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The median age at symptom onset was 2.0 months (range 0 to 12 months), 4.7 months at diagnosis"
    explanation: Gives the median ages at symptom onset and diagnosis in the 168-patient natural-history cohort.
- phase: Ventilator-dependent phase
  age_range: Median age at first ventilator support 5.9 months (range 0.1 to 31.1 months)
  notes: >-
    Ventilatory support becomes necessary before most affected infants reach their
    first birthday. The cohort reports the median age at first ventilator support and
    the median age at death as separate marginal figures, so the interval between the
    two is not derivable from them and is deliberately not asserted here.
  evidence:
  - reference: PMID:16737883
    reference_title: "A retrospective, multinational, multicenter study on the natural history of infantile-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "5.9 months at first ventilator support (range 0.1 to 31.1 months), and 8.7 months at death"
    explanation: Gives the median age at first ventilator support, and the median age at death that bounds the phase that follows.
  - reference: PMID:16737883
    reference_title: "A retrospective, multinational, multicenter study on the natural history of infantile-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Survival rates at 12 months of age were 25.7% overall and 16.9% ventilator-free; at 18 months 12.3% and 6.7%"
    explanation: Quantifies how few untreated infants reach 12 and 18 months, and how many of those are ventilator-free.
- phase: Untreated terminal phase
  age_range: Median age at death 8.7 months (range 0.3 to 73.4 months)
  notes: >-
    Earlier symptom onset carries a higher risk of early death, which is the
    natural-history counterpart of the treated-era finding that earlier enzyme
    replacement gives better outcomes. The mode of death is curated in the
    pathophysiology chain (Cardiopulmonary insufficiency of infancy) rather than
    asserted here, since the cohort abstract reports timing rather than cause.
  evidence:
  - reference: PMID:16737883
    reference_title: "A retrospective, multinational, multicenter study on the natural history of infantile-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      To characterize the natural progression of infantile-onset Pompe disease. ... Retrospective
      chart reviews of 168 patients with documented acid alpha-glucosidase deficiency and symptom
      onset by 12 months of age; ... The median age at symptom onset was 2.0 months (range 0 to 12
      months), 4.7 months at diagnosis (range: prenatal to 4.2 months), 5.9 months at first
      ventilator support (range 0.1 to 31.1 months), and 8.7 months at death (range 0.3 to 73.4
      months). Survival rates at 12 months of age were 25.7% overall and 16.9% ventilator-free; at
      18 months 12.3% and 6.7%. ... Multiple covariate analysis confirmed that early symptom onset
      increased risk of early death. CONCLUSION: Despite frequent therapeutic interventions,
      infantile-onset Pompe disease remains lethal.
    explanation: >-
      Reports infantile-onset Pompe natural-history mortality and survival in a retrospective
      cohort. The excerpt does not explicitly distinguish enzyme-replacement-naive patients from
      other therapeutic interventions.
  - reference: PMID:16737883
    reference_title: "A retrospective, multinational, multicenter study on the natural history of infantile-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Despite frequent therapeutic interventions, infantile-onset Pompe disease remains lethal"
    explanation: States the pre-enzyme-replacement conclusion that supportive care alone does not alter the fatal outcome.
pathophysiology:
- name: Near-complete acid alpha-glucosidase deficiency
  biological_scale: MOLECULAR
  description: >
    Biallelic fully deleterious GAA variants abolish acid alpha-glucosidase activity,
    leaving typically less than 1% of control activity in fibroblasts or muscle. This
    is the quantitative distinction from late-onset disease, where residual activity
    is higher and the phenotype correspondingly milder and non-cardiac.
  gene:
    preferred_term: GAA
    description: Acid alpha-glucosidase, the lysosomal enzyme that hydrolyzes alpha-1,4 and alpha-1,6 glycosidic linkages in 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
  evidence:
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patients have fully deleterious mutations. Acid alpha-glucosidase activity is severely deficient."
    explanation: Establishes near-absent enzyme activity as the molecular lesion of the classic infantile form.
  - reference: PMID:22252923
    reference_title: "Predicting cross-reactive immunological material (CRIM) status in Pompe disease using GAA mutations: lessons learned from 10 years of clinical laboratory testing experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The classical infantile form is rapidly progressive and presents with hypertrophic cardiomyopathy by the first few months of life and has a fatal outcome within the first year of life if left untreated"
    explanation: Links the severe enzymatic lesion to the rapidly progressive cardiac infantile phenotype.
  downstream:
  - target: Lysosomal glycogen accumulation
    description: Loss of the only lysosomal glycogen-degrading enzyme causes undegraded glycogen to accumulate in the lysosome.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:22252923
      reference_title: "Predicting cross-reactive immunological material (CRIM) status in Pompe disease using GAA mutations: lessons learned from 10 years of clinical laboratory testing experience."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Pompe disease (Glycogen Storage Disease type II; acid maltase deficiency; OMIM# 232300) is an autosomal recessive disorder of glycogen metabolism caused by deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA)"
      explanation: States the enzyme-deficiency-to-glycogen-storage relationship that defines the disease.
  - target: Absence of immunologically detectable GAA protein (CRIM-negative status)
    description: >
      Null GAA alleles that produce no protein at all, rather than an inactive protein,
      yield CRIM-negative status in roughly a quarter of classic infantile patients.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:22252923
      reference_title: "Predicting cross-reactive immunological material (CRIM) status in Pompe disease using GAA mutations: lessons learned from 10 years of clinical laboratory testing experience."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "CRIM-negative patients make no GAA protein and develop sustained high antibody titers to ERT that render the treatment ineffective."
      explanation: Directly links the null genotype to absence of GAA protein and CRIM-negative status.
- name: Lysosomal glycogen accumulation
  biological_scale: CELLULAR
  conforms_to: "lysosomal_substrate_accumulation#Lysosomal Substrate Accumulation"
  description: >
    Undegraded glycogen accumulates progressively within lysosomes of cardiac,
    skeletal, respiratory, and smooth muscle, and of the central nervous system. In
    IOPD the accumulation is early and massive because essentially no residual enzyme
    is available.
  cell_types:
  - preferred_term: Cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  - preferred_term: Skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: Glycogen catabolic process
    modifier: DECREASED
    term:
      id: GO:0005980
      label: glycogen catabolic process
  chemical_entities:
  - preferred_term: glycogen
    modifier: INCREASED
    term:
      id: CHEBI:28087
      label: glycogen
  evidence:
  - reference: ORPHA:365
    reference_title: "Glycogen storage disease due to acid maltase deficiency"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "A rare lysosomal storage disease characterized by lysosomal accumulation of glycogen particularly in skeletal, cardiac, and respiratory muscles"
    explanation: Orphanet records the lysosomal glycogen-accumulation lesion and the tissues in which it occurs.
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Infantile Pompe's disease is a lethal cardiac and muscular disorder."
    explanation: Identifies cardiac and skeletal muscle as the tissues in which the storage lesion is clinically decisive.
  downstream:
  - target: Cardiomyocyte glycogen storage and progressive hypertrophic remodeling
    description: Cardiomyocyte glycogen storage drives the cardiomegaly and hypertrophic cardiomyopathy that define IOPD.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:12897283
      reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "A progressive cardiac hypertrophy is characteristic for infantile Pompe's disease."
      explanation: Natural-history data establish progressive cardiac hypertrophy as the characteristic infantile consequence of storage.
  - target: Skeletal and respiratory myofiber injury
    description: Storage in skeletal and respiratory myofibers produces the profound hypotonia and respiratory distress of untreated IOPD.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."
      explanation: GeneReviews attributes the untreated IOPD muscle and respiratory phenotype to the storage lesion.
  - target: Hepatomegaly
    description: >
      Hepatic glycogen storage produces the moderate hepatomegaly of infantile disease.
      The cited cohort attributes it to storage but does not exclude a contribution from
      cardiac decompensation, so the edge is a partial rather than sole explanation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:12897283
      reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The moderate enlargement of the liver is assumed to result from glycogen storage, but may also result from cardiac decompensation."
      explanation: Attributes the hepatomegaly to glycogen storage while explicitly leaving a cardiac contribution open, which is why this is PARTIAL rather than SUPPORT.
  - target: Failure of productive autophagy and autophagic buildup
    description: Glycogen-laden lysosomes disrupt lysosome-dependent autophagic flux, so autophagic substrate accumulates in muscle.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38785980
      reference_title: "Failure of Autophagy in Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "The autophagic pathway is largely responsible for the delivery of cytosolic glycogen to the lysosome where it is degraded to glucose via acid α-glucosidase."
      explanation: Places the autophagic pathway downstream of, and dependent on, the acid alpha-glucosidase step that is lost here.
  - target: Central nervous system glycogen storage and progressive white matter abnormality
    description: >
      Glycogen storage is not confined to muscle; CNS storage becomes clinically
      visible only once ERT allows survival into later childhood.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:29573408
      reference_title: "Classic infantile Pompe patients approaching adulthood: a cohort study on consequences for the brain."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "AIM: To examine the long-term consequences of glycogen storage in the central nervous system (CNS) for classic infantile Pompe disease using enzyme replacement therapy."
      explanation: Frames CNS glycogen storage as the substrate of the long-term brain phenotype in classic infantile disease.
- name: Cardiomyocyte glycogen storage and progressive hypertrophic remodeling
  biological_scale: TISSUE
  description: >
    Massive cardiomyocyte glycogen storage produces cardiomegaly and hypertrophic
    cardiomyopathy that is usually already identifiable in the first weeks of life and
    progresses to left ventricular outflow obstruction and diminished lung volume.
    Glycogen deposition in conduction tissue shortens the PR interval. This node is
    the principal mechanistic difference between IOPD and late-onset Pompe disease,
    which lacks significant cardiac involvement.
  cell_types:
  - preferred_term: Cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  biological_processes:
  - preferred_term: Cardiac muscle hypertrophy
    modifier: INCREASED
    term:
      id: GO:0003300
      label: cardiac muscle hypertrophy
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Cardiomegaly and hypertrophic cardiomyopathy is usually identified in the first weeks of life and progress to left ventricular outflow obstruction and diminished lung volume."
    explanation: Documents the timing and progression of the cardiac lesion specific to IOPD.
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diastolic thickness of the left ventricular posterior wall and cardiac weight at autopsy increase significantly with age."
    explanation: Quantitative natural-history evidence that the cardiac hypertrophy is progressive.
  downstream:
  - target: Hypertrophic cardiomyopathy
    description: Cardiomyocyte storage and hypertrophic remodeling manifest clinically as hypertrophic cardiomyopathy.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Cardiomegaly and hypertrophic cardiomyopathy is usually identified in the first weeks of life"
      explanation: Directly links the cardiac storage lesion to the hypertrophic cardiomyopathy phenotype.
  - target: Shortened PR interval
    description: Glycogen deposition in the cardiac conduction system shortens the PR interval on ECG.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Progressive deposition of glycogen results in conduction defects with shortening of the PR interval on EKG."
      explanation: GeneReviews attributes the shortened PR interval directly to glycogen deposition.
  - target: Cardiopulmonary insufficiency of infancy
    description: Progressive cardiac hypertrophy with outflow obstruction is a principal contributor to fatal cardiopulmonary insufficiency.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "In untreated infants, death commonly occurs in the first two years of life from cardiopulmonary insufficiency."
      explanation: Names cardiopulmonary insufficiency as the mode of death in untreated IOPD.
- name: Skeletal and respiratory myofiber injury
  biological_scale: TISSUE
  description: >
    Lysosomal glycogen storage in skeletal, respiratory, and bulbar muscle injures
    myofibers, producing the floppy-infant presentation: generalized hypotonia,
    severely delayed motor development, feeding difficulty with poor growth, and
    respiratory distress.
  cell_types:
  - preferred_term: Skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."
    explanation: Lists the untreated IOPD muscle phenotype produced by myofiber injury.
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Motor development is severely delayed and major developmental milestones are generally not achieved."
    explanation: Natural-history evidence for the severity of the motor consequence of myofiber injury in IOPD.
  downstream:
  - target: Generalized hypotonia
    description: Myofiber injury produces the profound generalized hypotonia of the floppy infant.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness"
      explanation: GeneReviews links untreated IOPD to hypotonia and generalized muscle weakness.
  - target: Generalized muscle weakness
    description: >
      The same myofiber injury produces generalized skeletal muscle weakness, which
      GeneReviews records as a feature distinct from the accompanying hypotonia.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness"
      explanation: GeneReviews attributes generalized muscle weakness to untreated IOPD, alongside but separate from hypotonia.
  - target: Motor developmental delay
    description: Muscle weakness prevents acquisition of major motor milestones.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:12897283
      reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Motor development is severely delayed and major developmental milestones are generally not achieved."
      explanation: Directly supports severe motor delay as a consequence of the infantile muscle lesion.
  - target: Respiratory insufficiency
    description: Respiratory myofiber injury, compounded by diminished lung volume from cardiomegaly, causes respiratory distress and insufficiency.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."
      explanation: Respiratory distress is listed among the untreated IOPD manifestations of muscle involvement.
  - target: Feeding difficulties
    description: Bulbar and generalized muscle weakness impair sucking, swallowing, and feeding.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."
      explanation: Lists feeding difficulties alongside the muscle weakness that produces them.
  - target: Failure to thrive
    description: Growth deviates significantly from normal even once nasogastric tube feeding is started.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:12897283
      reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "For the Dutch patient group, growth deviates significantly from normal despite start of nasogastric tube feeding."
      explanation: Growth failure persisting despite feeding support indicates intermediates beyond reduced intake alone.
  - target: Cardiopulmonary insufficiency of infancy
    description: Respiratory muscle failure combines with the cardiac lesion to produce fatal cardiopulmonary insufficiency.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "In untreated infants, death commonly occurs in the first two years of life from cardiopulmonary insufficiency."
      explanation: Names cardiopulmonary insufficiency, to which respiratory muscle failure contributes, as the mode of death.
- name: Cardiopulmonary insufficiency of infancy
  biological_scale: ORGANISM
  description: >
    The convergence of hypertrophic cardiomyopathy with outflow obstruction and
    respiratory muscle failure produces cardiopulmonary insufficiency. In the
    pre-treatment natural history, symptoms began at a median age of 1.6 months and
    the median age of death was 6-7.7 months, with only 5-8% of infants surviving
    beyond one year.
  evidence:
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Symptoms start at a median age of 1.6 months in both groups. The median age of death is 7.7 and 6 months, respectively. Five percent of the Dutch patients and 8% of all reported patients survive beyond 1 year of age."
    explanation: Quantifies the untreated natural history of onset and death that this node represents.
  downstream:
  - target: Death in infancy
    description: Untreated, cardiopulmonary insufficiency is fatal in the first one to two years of life.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "In untreated infants, death commonly occurs in the first two years of life from cardiopulmonary insufficiency."
      explanation: Directly supports the fatal outcome of untreated IOPD from cardiopulmonary insufficiency.
- name: Absence of immunologically detectable GAA protein (CRIM-negative status)
  biological_scale: MOLECULAR
  description: >
    CRIM (cross-reactive immunologic material) status asks a different question from
    enzyme activity: not whether GAA works, but whether any GAA protein is made at
    all. Patients with two null alleles produce no GAA protein detectable by Western
    blot and are CRIM-negative; patients producing a catalytically inactive protein
    are CRIM-positive. Because a CRIM-negative infant has never been immunologically
    tolerized to GAA, recombinant human GAA is a foreign antigen. Roughly 20-25% of
    classic infantile patients are CRIM-negative, and CRIM status is largely
    predictable from the GAA genotype.
  gene:
    preferred_term: GAA
    description: Null GAA alleles producing no detectable protein define CRIM-negative status.
    modifier: DECREASED
    term:
      id: hgnc:4065
      label: GAA
  evidence:
  - reference: PMID:22252923
    reference_title: "Predicting cross-reactive immunological material (CRIM) status in Pompe disease using GAA mutations: lessons learned from 10 years of clinical laboratory testing experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CRIM-negative patients make no GAA protein and develop sustained high antibody titers to ERT that render the treatment ineffective."
    explanation: Defines CRIM-negative status as absence of GAA protein and links it to the antibody response.
  - reference: PMID:19775921
    reference_title: "Cross-reactive immunologic material status affects treatment outcomes in Pompe disease infants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients synthesize a non-functional form of GAA or are unable to form native enzyme."
    explanation: States the CRIM-positive versus CRIM-negative molecular distinction.
  downstream:
  - target: High sustained anti-rhGAA antibody response
    description: >
      Never having been tolerized to endogenous GAA, CRIM-negative infants mount an
      early, high-titer, sustained IgG response to infused recombinant human GAA.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:19775921
      reference_title: "Cross-reactive immunologic material status affects treatment outcomes in Pompe disease infants."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "IgG antibodies to rhGAA developed earlier and serotiters were higher and more sustained in the CRIM-negative group."
      explanation: Directly supports the CRIM-negative-to-antibody-response edge with comparative titer data.
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "individuals who do not produce CRIM (i.e., who are CRIM negative) generally develop high titer anti-rhGAA antibodies during ERT"
      explanation: Management guidance confirms CRIM-negative status predicts a high-titer anti-rhGAA response.
- name: High sustained anti-rhGAA antibody response
  biological_scale: ORGANISM
  description: >
    Sustained high-titer neutralizing IgG against recombinant human GAA blocks the
    therapeutic benefit of enzyme replacement therapy. This is a treatment-conditioned
    mechanism with no counterpart in late-onset disease, and it is the reason CRIM
    status must be determined before the first infusion.
  biological_processes:
  - preferred_term: humoral immune response mediated by circulating immunoglobulin
    modifier: INCREASED
    term:
      id: GO:0002455
      label: humoral immune response mediated by circulating immunoglobulin
  evidence:
  - reference: PMID:22237443
    reference_title: "Successful immune tolerance induction to enzyme replacement therapy in CRIM-negative infantile Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cross-reactive immunologic material negative (CRIM-negative) Pompe patients develop high-titer antibody to the rhGAA and do poorly."
    explanation: Establishes the high-titer antibody response and its adverse clinical consequence.
  downstream:
  - target: Enzyme replacement therapy failure and clinical decline
    description: Neutralizing antibody renders infused rhGAA ineffective, and treated CRIM-negative infants deteriorate.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:19775921
      reference_title: "Cross-reactive immunologic material status affects treatment outcomes in Pompe disease infants."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Following 52 weeks of treatment, 6/11 (54.5%) CRIM-negative and 1/21 (4.8%) CRIM-positive patients were deceased or invasively ventilated (p<0.0001)."
      explanation: Quantifies the treatment-failure outcome that follows the CRIM-negative antibody response.
    - reference: PMID:22252923
      reference_title: "Predicting cross-reactive immunological material (CRIM) status in Pompe disease using GAA mutations: lessons learned from 10 years of clinical laboratory testing experience."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "CRIM-negative patients make no GAA protein and develop sustained high antibody titers to ERT that render the treatment ineffective."
      explanation: States that the sustained antibody response renders ERT ineffective.
- name: Enzyme replacement therapy failure and clinical decline
  biological_scale: ORGANISM
  description: >
    In the absence of immune tolerance induction, CRIM-negative infants on ERT decline
    despite treatment: cardiac function and gross motor development improve
    significantly less than in CRIM-positive infants, and by roughly 27 months all
    CRIM-negative patients in the original series were dead or invasively ventilated.
  evidence:
  - reference: PMID:19775921
    reference_title: "Cross-reactive immunologic material status affects treatment outcomes in Pompe disease infants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "By age 27.1 months, all CRIM-negative patients and 4/21 (19.0%) CRIM-positive patients were deceased or invasively ventilated."
    explanation: Quantifies the divergent treated outcome by CRIM status.
  - reference: PMID:19775921
    reference_title: "Cross-reactive immunologic material status affects treatment outcomes in Pompe disease infants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac function and gross motor development improved significantly more in the CRIM-positive group."
    explanation: Shows the treatment benefit gap attributable to CRIM status.
- name: Failure of productive autophagy and autophagic buildup
  biological_scale: CELLULAR
  description: >
    Autophagy is lysosome-dependent, so the storage lesion disables it. Autophagic
    vesicles accumulate in type II-rich muscle fibers, disrupting the contractile
    apparatus. Critically for IOPD, the autophagic buildup also acts as a sink for
    infused recombinant enzyme and prevents its efficient delivery to lysosomes -
    a second, non-immune route to poor ERT response that runs in parallel to the
    CRIM-negative antibody arm.
  biological_processes:
  - preferred_term: Autophagy
    modifier: DECREASED
    term:
      id: GO:0006914
      label: autophagy
  cell_types:
  - preferred_term: Skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  evidence:
  - reference: PMID:20040311
    reference_title: "Autophagy in skeletal muscle: implications for Pompe disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "we present evidence that a failure of productive autophagy in muscle tissue contributes strongly to disease pathology in both patients with Pompe disease and GAA-knockout mice"
    explanation: States that failed productive autophagy contributes to pathology in patients as well as in the knockout mouse.
  downstream:
  - target: Skeletal and respiratory myofiber injury
    description: Accumulated autophagosomes disrupt the contractile apparatus of muscle fibers.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20040311
      reference_title: "Autophagy in skeletal muscle: implications for Pompe disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In the GAA-knockout mouse model, progressive accumulation of autophagic vesicles is restricted to Type II-rich muscle fibers."
      explanation: Localizes the autophagic buildup to the muscle fibers whose injury this edge asserts.
  - target: Enzyme replacement therapy failure and clinical decline
    description: >
      Autophagic buildup sequesters infused recombinant enzyme before it reaches the
      lysosome, degrading ERT response independently of any antibody response.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20040311
      reference_title: "Autophagy in skeletal muscle: implications for Pompe disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Not only does this build-up of autophagosomes disrupt the contractile apparatus in the muscle fibers, it also interferes with enzyme replacement therapy by acting as a sink for the recombinant enzyme and preventing its efficient delivery to the lysosomes."
      explanation: Directly evidences the enzyme-sequestration route from autophagic buildup to reduced ERT efficacy.
- name: Central nervous system glycogen storage and progressive white matter abnormality
  biological_scale: TISSUE
  description: >
    Intravenous rhGAA does not cross the blood-brain barrier, so CNS glycogen storage
    is untreated. As ERT enables survival into later childhood and adulthood, slowly
    progressive symmetric white-matter abnormalities emerge - periventricular white
    matter and centrum semiovale from about age 2, then corpus callosum, capsules and
    subcortical areas after age 8, and brainstem from age 11 - with variable
    neuropsychological consequences. This is an ERT-era emerging phenotype rather than
    part of the classical untreated natural history.
  evidence:
  - reference: PMID:29573408
    reference_title: "Classic infantile Pompe patients approaching adulthood: a cohort study on consequences for the brain."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "From approximately age 2 years onwards, brain MRI showed involvement of the periventricular white matter and centrum semiovale. After 8 years of age, additional white-matter abnormalities occurred in the corpus callosum, internal and external capsule, and subcortical areas. From 11 years of age, white-matter abnormalities were also found in the brainstem."
    explanation: Documents the anatomical progression of white-matter abnormality in treated classic infantile patients.
  downstream:
  - target: Cognitive decline and intellectual disability
    description: White-matter involvement is accompanied by neuropsychological decline in a subset of long-term survivors.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:29573408
      reference_title: "Classic infantile Pompe patients approaching adulthood: a cohort study on consequences for the brain."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In our long-term survivors treated intravenously with enzyme replacement therapy, we found slowly progressive symmetric white-matter abnormalities. Cognitive development varied from stable and normal to declines towards intellectual disabilities."
      explanation: Directly links progressive white-matter abnormality to the range of cognitive outcomes observed.
phenotypes:
- name: Hypertrophic cardiomyopathy
  category: Cardiovascular
  description: >
    Cardiomegaly with hypertrophic cardiomyopathy, usually identifiable in the first
    weeks of life and progressing to left ventricular outflow obstruction. Its
    presence in an infant with GAA deficiency is what defines classic infantile
    disease rather than late-onset disease.
  frequency: OBLIGATE
  phenotype_term:
    preferred_term: Hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Pompe disease can be classified by age of onset, organ involvement, severity, and rate of progression into infantile-onset Pompe disease (IOPD) (i.e., individuals with onset before age 12 months with cardiomyopathy)"
    explanation: Cardiomyopathy is definitional for IOPD, supporting an obligate frequency.
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A progressive cardiac hypertrophy is characteristic for infantile Pompe's disease."
    explanation: Natural-history evidence that cardiac hypertrophy is characteristic and progressive.
- name: Shortened PR interval
  category: Cardiovascular
  description: >
    Glycogen deposition in the cardiac conduction system produces conduction defects
    with a short PR interval on ECG.
  phenotype_term:
    preferred_term: Shortened PR interval
    term:
      id: HP:0005165
      label: Shortened PR interval
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Progressive deposition of glycogen results in conduction defects with shortening of the PR interval on EKG."
    explanation: Directly documents the shortened PR interval in Pompe disease.
- name: Cardiomegaly
  category: Cardiovascular
  description: >
    Radiographic and echocardiographic cardiac enlargement, the single most frequent
    presenting sign in the untreated natural history and the finding that most often
    brings an affected infant to attention. It is the imaging correlate of the
    hypertrophic remodeling curated separately as a phenotype in its own right.
  phenotype_term:
    preferred_term: Cardiomegaly
    term:
      id: HP:0001640
      label: Cardiomegaly
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:16737883
    reference_title: "A retrospective, multinational, multicenter study on the natural history of infantile-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiomegaly (92%), hypotonia (88%), cardiomyopathy (88%), respiratory distress (78%), muscle weakness (63%), feeding difficulties (57%), and failure to thrive (53%) appeared after a median age of approximately 4.0 months"
    explanation: Reports cardiomegaly in 92% of the 168-patient untreated cohort, the highest frequency of any sign listed, which is the basis for the VERY_FREQUENT band.
- name: Generalized hypotonia
  category: Neuromuscular
  description: >
    Profound generalized hypotonia and muscle weakness - the classic floppy infant
    presentation of IOPD.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."
    explanation: GeneReviews lists hypotonia as a typical untreated IOPD feature, supporting a very frequent band.
- name: Generalized muscle weakness
  category: Neuromuscular
  description: >
    Generalized skeletal muscle weakness from glycogen-laden myofiber injury. GeneReviews
    names this alongside, and separately from, hypotonia among the typical untreated IOPD
    features, so it is curated as its own phenotype rather than folded into the hypotonia
    entry.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Generalized muscle weakness
    term:
      id: HP:0003324
      label: Generalized muscle weakness
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."
    explanation: GeneReviews lists generalized muscle weakness as a typical untreated IOPD feature, distinct from the hypotonia named in the same sentence, supporting a very frequent band.
- name: Motor developmental delay
  category: Neuromuscular
  description: >
    Motor development is severely delayed and major motor milestones are generally
    never achieved in untreated infants.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Motor delay
    term:
      id: HP:0001270
      label: Motor delay
  evidence:
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Motor development is severely delayed and major developmental milestones are generally not achieved."
    explanation: Natural-history cohort reports severe motor delay as a general feature, supporting a very frequent band.
- name: Respiratory insufficiency
  category: Respiratory
  description: >
    Respiratory distress and insufficiency from respiratory muscle involvement,
    compounded by diminished lung volume secondary to cardiomegaly.
  phenotype_term:
    preferred_term: Respiratory insufficiency due to muscle weakness
    term:
      id: HP:0002747
      label: Respiratory insufficiency due to muscle weakness
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."
    explanation: GeneReviews names respiratory distress directly among the typical untreated IOPD features.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Cardiomegaly and hypertrophic cardiomyopathy is usually identified in the first weeks of life and progress to left ventricular outflow obstruction and diminished lung volume."
    explanation: Supports the second clause of the description - that the cardiac lesion compounds the respiratory burden by reducing lung volume.
- name: Feeding difficulties
  category: Gastrointestinal
  description: >
    Bulbar and generalized weakness cause feeding difficulty requiring nasogastric or
    gastrostomy feeding.
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  frequency: FREQUENT
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Untreated individuals with IOPD typically have hypotonia, generalized muscle weakness, feeding difficulties, poor growth, and respiratory distress."
    explanation: Lists feeding difficulties among the typical untreated IOPD manifestations.
  - reference: PMID:16737883
    reference_title: "A retrospective, multinational, multicenter study on the natural history of infantile-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiomegaly (92%), hypotonia (88%), cardiomyopathy (88%), respiratory distress (78%), muscle weakness (63%), feeding difficulties (57%), and failure to thrive (53%) appeared after a median age of approximately 4.0 months"
    explanation: "Quantifies feeding difficulties at 57% of the 168-patient untreated natural-history cohort, which is the basis for the FREQUENT band."
- name: Failure to thrive
  category: Growth
  description: >
    Growth deviates significantly from normal despite nasogastric tube feeding.
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  frequency: FREQUENT
  evidence:
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "For the Dutch patient group, growth deviates significantly from normal despite start of nasogastric tube feeding."
    explanation: Documents growth failure persisting despite feeding support.
  - reference: PMID:16737883
    reference_title: "A retrospective, multinational, multicenter study on the natural history of infantile-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiomegaly (92%), hypotonia (88%), cardiomyopathy (88%), respiratory distress (78%), muscle weakness (63%), feeding difficulties (57%), and failure to thrive (53%) appeared after a median age of approximately 4.0 months"
    explanation: "Quantifies failure to thrive at 53% of the 168-patient untreated natural-history cohort, which is the basis for the FREQUENT band."
- name: Macroglossia
  category: Craniofacial
  description: >
    Glycogen storage in the tongue produces an enlarged tongue, which contributes to
    feeding and airway difficulty and is one of the considerations weighing in favour
    of tracheostomy in infants with severe respiratory insufficiency.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Macroglossia
    term:
      id: HP:0000158
      label: Macroglossia
  evidence:
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "An enlarged tongue was noticed in 45% of the Dutch patients and 29% of the cases from literature."
    explanation: Natural-history cohort quantifies tongue enlargement at 45% in the prospectively examined Dutch series, within the FREQUENT band (79-30%); the 29% literature figure is a retrospective case-note count and is treated as under-ascertainment rather than as a competing estimate.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "tracheostomy may be considered in those with macroglossia and severe respiratory insufficiency"
    explanation: GeneReviews management guidance treats macroglossia as a recognised IOPD feature with airway consequences.
- name: Hepatomegaly
  category: Hepatic
  description: >
    Moderate liver enlargement, attributed to hepatic glycogen storage though cardiac
    decompensation may also contribute. No frequency band is asserted: the cohort
    reports 90% in the Dutch series against 29% in the literature cases, a spread too
    wide to map onto a single band.
  phenotype_term:
    preferred_term: Hepatomegaly
    term:
      id: HP:0002240
      label: Hepatomegaly
  evidence:
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The moderate enlargement of the liver is assumed to result from glycogen storage, but may also result from cardiac decompensation."
    explanation: The natural-history cohort reports moderate hepatomegaly and attributes it to glycogen storage with a cardiac contribution.
- name: Elevated creatine kinase
  category: Laboratory
  description: >
    Serum creatine kinase, CK-MB, transaminases, and lactate dehydrogenase are
    typically elevated, with AST, ALT and LDH rising significantly with age.
  phenotype_term:
    preferred_term: Elevated circulating creatine kinase activity
    term:
      id: HP:0003236
      label: Elevated circulating creatine kinase activity
  evidence:
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Levels of aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, creatine kinase, or creatine kinase-myocardial band isoenzyme are typically elevated"
    explanation: Directly reports elevated CK and CK-MB in the infantile natural-history cohort.
- name: Death in infancy
  category: Mortality
  description: >
    Untreated, death commonly occurs in the first two years of life from
    cardiopulmonary insufficiency; median age of death in the pre-treatment era was
    6-7.7 months.
  notes: >
    Deliberately left without a phenotype_term. `HP:0001522` (Death in infancy) is
    the exact concept, but it sits under `HP:0040006` (Mortality/Aging) rather than
    `HP:0000118` (Phenotypic abnormality), so it is not a legal PhenotypeTerm value
    in this schema. No mortality term reachable from HP:0000118 expresses it, and no
    term beats a wrong one.
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "In untreated infants, death commonly occurs in the first two years of life from cardiopulmonary insufficiency."
    explanation: States the untreated mortality outcome and its cause.
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The median age of death is 7.7 and 6 months, respectively. Five percent of the Dutch patients and 8% of all reported patients survive beyond 1 year of age."
    explanation: Quantifies median age at death and one-year survival in the untreated natural history.
- name: Abnormal cerebral white matter morphology
  category: Neurological
  description: >
    Slowly progressive symmetric cerebral white-matter abnormalities emerging in
    ERT-treated long-term survivors, beginning in periventricular white matter and
    centrum semiovale around age 2 years.
  phenotype_term:
    preferred_term: Abnormal cerebral white matter morphology
    term:
      id: HP:0002500
      label: Abnormal cerebral white matter morphology
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:29573408
    reference_title: "Classic infantile Pompe patients approaching adulthood: a cohort study on consequences for the brain."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "From approximately age 2 years onwards, brain MRI showed involvement of the periventricular white matter and centrum semiovale."
    explanation: Documents the white-matter abnormality and its age of appearance in treated classic infantile patients.
- name: Cognitive decline and intellectual disability
  category: Neurological
  description: >
    Neuropsychological outcome in ERT-treated long-term survivors ranges from stable
    and normal cognitive development to decline towards intellectual disability.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:29573408
    reference_title: "Classic infantile Pompe patients approaching adulthood: a cohort study on consequences for the brain."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cognitive development ranged from stable and normal to declines that lead to intellectual disabilities."
    explanation: Reports the range of cognitive outcomes, supporting a variably present phenotype.
- name: Sensorineural hearing impairment
  category: Auditory
  description: >
    Sensorineural and/or conductive hearing loss is commonly present in ERT-treated
    long-term survivors of infantile Pompe disease.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:22538254
    reference_title: "The emerging phenotype of long-term survivors with infantile Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Commonly present were gross motor weakness, motor speech deficits, sensorineural and/or conductive hearing loss, osteopenia, gastroesophageal reflux, and dysphagia with aspiration risk."
    explanation: Reports hearing loss among the commonly present features of the long-term survivor phenotype.
- name: Osteopenia
  category: Skeletal
  description: >
    Osteopenia is a commonly observed finding in long-term survivors of IOPD on
    enzyme replacement therapy.
  phenotype_term:
    preferred_term: Osteopenia
    term:
      id: HP:0000938
      label: Osteopenia
  evidence:
  - reference: PMID:22538254
    reference_title: "The emerging phenotype of long-term survivors with infantile Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Residual muscle weakness, hearing loss, risk for arrhythmias, hypernasal speech, dysphagia with risk for aspiration, and osteopenia were commonly observed findings."
    explanation: Lists osteopenia among the commonly observed findings in long-term survivors.
- name: Dysphagia
  category: Gastrointestinal
  description: >
    Dysphagia with aspiration risk is common in ERT-treated long-term survivors.
  phenotype_term:
    preferred_term: Dysphagia
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: PMID:22538254
    reference_title: "The emerging phenotype of long-term survivors with infantile Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Commonly present were gross motor weakness, motor speech deficits, sensorineural and/or conductive hearing loss, osteopenia, gastroesophageal reflux, and dysphagia with aspiration risk."
    explanation: Reports dysphagia with aspiration risk as commonly present in long-term survivors.
- name: Hypernasal speech
  category: Neuromuscular
  description: >
    Hypernasal speech from velopharyngeal weakness is commonly observed in long-term
    survivors of infantile Pompe disease.
  phenotype_term:
    preferred_term: Hypernasal speech
    term:
      id: HP:0001611
      label: Hypernasal speech
  evidence:
  - reference: PMID:22538254
    reference_title: "The emerging phenotype of long-term survivors with infantile Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Residual muscle weakness, hearing loss, risk for arrhythmias, hypernasal speech, dysphagia with risk for aspiration, and osteopenia were commonly observed findings."
    explanation: Lists hypernasal speech among commonly observed long-term survivor findings.
- name: Flaccid dysarthria
  category: Neuromuscular
  description: >
    Bulbar weakness producing flaccid dysarthria in long-term enzyme-replacement
    survivors. It was present in every survivor in a cohort followed for two decades,
    and belongs to the residual multisystem morbidity that persists once treatment has
    removed the cardiac and respiratory causes of early death.
  phenotype_term:
    preferred_term: Flaccid dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
  evidence:
  - reference: PMID:41014101
    reference_title: "Infantile-onset Pompe disease entering adulthood: Insights from 2 decades of enzyme replacement therapy experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Flaccid dysarthria (8/8), ptosis (4/8), and sensorineural hearing loss (6/8) were common."
    explanation: Reports flaccid dysarthria in all eight adult survivors of infantile-onset disease on long-term enzyme replacement therapy.
- name: Ptosis
  category: Ophthalmologic
  description: >
    Ptosis in long-term enzyme-replacement survivors, present in about half of one
    two-decade cohort. Extraocular and eyelid muscle involvement is part of the same
    residual myopathy that leaves most survivors non-ambulatory, and is an example of
    a muscle group that infused enzyme does not adequately reach.
  phenotype_term:
    preferred_term: Ptosis
    term:
      id: HP:0000508
      label: Ptosis
  evidence:
  - reference: PMID:41014101
    reference_title: "Infantile-onset Pompe disease entering adulthood: Insights from 2 decades of enzyme replacement therapy experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Flaccid dysarthria (8/8), ptosis (4/8), and sensorineural hearing loss (6/8) were common."
    explanation: Reports ptosis in four of eight adult survivors of infantile-onset disease on long-term enzyme replacement therapy.
  - reference: PMID:41014101
    reference_title: "Infantile-onset Pompe disease entering adulthood: Insights from 2 decades of enzyme replacement therapy experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two participants were ambulatory; 6 used wheelchairs."
    explanation: Records the residual motor disability in the same cohort, which is the context that makes eyelid and bulbar involvement part of a persisting generalized myopathy rather than an isolated ocular finding.
histopathology:
- name: Vacuolar myopathy with lysosomal glycogen accumulation
  description: >-
    Skeletal muscle in classic infantile-onset disease shows a vacuolar myopathy in
    which glycogen fills the lysosomes of myofibers. The storage lesion is not
    confined to muscle: it also involves cardiac and smooth muscle, which is why the
    same biopsy-level mechanism underlies both the cardiac and the skeletal-muscle
    arms of the disease. Muscle biopsy is no longer the diagnostic route - enzyme
    assay and GAA sequencing are - but it remains the tissue-level readout used to
    judge whether enzyme replacement therapy is reaching muscle.
  diagnostic: false
  evidence:
  - reference: PMID:17075580
    reference_title: "Characterization of pre- and post-treatment pathology after enzyme replacement therapy for Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "glycogen accumulates abnormally in the lysosomes of skeletal, cardiac and smooth muscle, and contributes to clinically progressive and debilitating muscle weakness"
    explanation: States the tissue distribution of the lysosomal glycogen storage lesion and links it to the weakness.
- name: Variable glycogen clearance on enzyme replacement therapy
  description: >-
    Serial quadriceps biopsies taken at baseline, 12 weeks, and 52 weeks in eight
    infantile-onset patients on weekly recombinant human GAA showed that the extent
    of glycogen clearance differed widely between patients and tracked clinical
    outcome. This is the histologic counterpart of the entry's clinical observation
    that enzyme replacement therapy rescues some infants and not others, and it makes
    the biopsy an outcome measure rather than only a diagnostic specimen.
  diagnostic: false
  evidence:
  - reference: PMID:17075580
    reference_title: "Characterization of pre- and post-treatment pathology after enzyme replacement therapy for Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The extent of glycogen clearance varied widely among these patient samples, and correlated well with clinical outcome"
    explanation: Establishes that histologic glycogen clearance varies between treated infants and predicts how they do clinically.
- name: Baseline histologic predictors of enzyme replacement response
  description: >-
    In the same series, low baseline glycogen, mild ultrastructural damage, a high
    proportion of type I fibers, and young age at baseline all marked patients who
    responded well histologically. The first two are a statement that the amount of
    damage already present limits what enzyme replacement can undo, which is the
    tissue-level argument for treating before symptoms rather than after.
  diagnostic: false
  evidence:
  - reference: PMID:17075580
    reference_title: "Characterization of pre- and post-treatment pathology after enzyme replacement therapy for Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Low glycogen levels, mild ultrastructural damage, a high proportion of type I fibers, and young age at baseline were all features associated with good histologic response"
    explanation: Names the baseline biopsy features that predict a good histologic response to enzyme replacement therapy.
  - reference: PMID:17075580
    reference_title: "Characterization of pre- and post-treatment pathology after enzyme replacement therapy for Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There was no correlation between capillary density and glycogen clearance"
    explanation: Reports a negative result - delivery of enzyme to muscle is not limited by capillary supply - which narrows the candidate explanations for poor response.
- name: Increased activated satellite cells in poorly responding post-treatment biopsies
  description: >-
    Confocal analysis of the post-treatment biopsies found higher levels of activated
    satellite cells in those with a poor histologic response. The finding is
    correlative, and the study does not establish whether the raised satellite-cell
    activation is a compensatory regenerative response to continuing myofiber injury
    or part of what limits the response.
  diagnostic: false
  evidence:
  - reference: PMID:17075580
    reference_title: "Characterization of pre- and post-treatment pathology after enzyme replacement therapy for Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "activated satellite cell levels were shown to be higher in post-treatment biopsies with poor histologic responses"
    explanation: Reports the satellite-cell measurement and the direction of its association with histologic response.
- name: Widespread CNS glycogen storage with white-matter and deep grey-nucleus predominance
  description: >-
    A systematic review of 39 autopsy-based articles covering 49 patients meeting a
    strict classic-infantile definition (hypertrophic cardiomyopathy, onset under 12
    months, GAA deficiency) found histologic abnormality throughout the central
    nervous system. Cerebral and cerebellar white matter, globus pallidus, dentate
    nucleus, brainstem motor nuclei, and anterior horn cells were affected most
    often, and subcortical structures more consistently than cortical ones. This is
    the tissue-level counterpart of the white-matter abnormality curated as a
    phenotype and pathophysiology node in this entry, which until now rested on
    imaging and neuropsychological evidence alone.
  diagnostic: false
  evidence:
  - reference: PMID:42538472
    reference_title: "Central nervous system histopathological findings in classic infantile Pompe disease: a systematic review with clinical relevance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histologic abnormalities were found throughout the CNS. The cerebral and cerebellar white matter (WM), globus pallidus, dentate nucleus, motor nuclei of the brainstem, and anterior horn cells were most frequently affected."
    explanation: Gives the regional distribution of CNS histologic abnormality in autopsied classic infantile patients.
  - reference: PMID:42538472
    reference_title: "Central nervous system histopathological findings in classic infantile Pompe disease: a systematic review with clinical relevance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cortical neurons were affected with greater variability, and subcortical structures were more frequently involved than cortical ones."
    explanation: Records the subcortical-over-cortical gradient, which is what makes this a white-matter and deep-nucleus pattern rather than a diffuse encephalopathy.
- name: Severe glycogen accumulation in astrocytes and globus pallidus neurons
  description: >-
    Within that CNS pathology, glycogen accumulation was severe specifically in
    astrocytes and in globus pallidus neurons. This is the storage lesion itself
    demonstrated in brain tissue from this patient population, rather than inferred
    from the muscle phenotype - the cell-type-level evidence that the enzyme
    deficiency produces the same lysosomal storage in the brain that it produces in
    muscle.
  diagnostic: false
  evidence:
  - reference: PMID:42538472
    reference_title: "Central nervous system histopathological findings in classic infantile Pompe disease: a systematic review with clinical relevance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Glycogen accumulation was severe in astrocytes and in neurons of the globus pallidus."
    explanation: Identifies the cell types carrying the heaviest CNS glycogen burden in autopsied classic infantile patients.
- name: CNS pathology present in infancy, years before clinical or radiological signs
  description: >-
    Autopsy pathology is already early and widespread in children up to 21 months,
    whereas MRI abnormality typically appears from 2 to 3 years, biomarker change
    from around 5 years, and cognitive decline from roughly 8 to 10 years. The
    pathology therefore precedes every clinical means of detecting it by years. This
    matters for the timing of therapy rather than only for description: by the time
    CNS involvement is measurable in a treated survivor, the storage lesion is long
    established.
  diagnostic: false
  evidence:
  - reference: PMID:42538472
    reference_title: "Central nervous system histopathological findings in classic infantile Pompe disease: a systematic review with clinical relevance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histopathological studies from children up to 21 months demonstrate early and widespread CNS pathology."
    explanation: Establishes that the CNS lesion is present in infancy.
  - reference: PMID:42538472
    reference_title: "Central nervous system histopathological findings in classic infantile Pompe disease: a systematic review with clinical relevance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "While white matter pathology is already prominent in young patients, abnormalities on magnetic resonance imaging typically emerge from 2 to 3 years of age, biomarker changes from around 5 years, and cognitive decline, reduced processing speed, and background activity slowing on electroencephalogram from approximately 8-10 years onward."
    explanation: Quantifies the lag between the pathology and each downstream means of detecting it.
genetic:
- name: GAA
  notes: >
    Biallelic fully deleterious GAA variants cause IOPD. The specific pair of alleles
    also determines CRIM status: two alleles that produce no protein at all yield
    CRIM-negative status, whereas alleles producing a catalytically inactive protein
    yield CRIM-positive status. CRIM status can in most cases be predicted from the
    GAA genotype, avoiding a skin biopsy and the weeks of fibroblast culture that
    Western-blot CRIM testing requires - a decisive advantage in a disease where
    treatment delay is measured in weeks.

    Locus and allelic spectrum. GAA lies at 17q25.2-q25.3 and contains 20 exons. The
    allelic spectrum is highly heterogeneous - missense, nonsense, splice-site,
    partial deletions and insertions - and the Pompe disease variant database lists
    well over 900 disease-associated variants, so IOPD genotypes are typically
    private compound heterozygous pairs rather than recurrent founder alleles.

    Copy-number variants are a real diagnostic blind spot. Large deletions are about
    1.5% of known GAA variants and are invisible to exon sequencing, so when
    sequencing returns fewer than two explanatory alleles in a patient with deficient
    enzyme activity, MLPA or another dosage assay should be run before the genetic
    diagnosis is called incomplete.
  gene_term:
    preferred_term: GAA
    term:
      id: hgnc:4065
      label: GAA
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  evidence:
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patients have fully deleterious mutations. Acid alpha-glucosidase activity is severely deficient."
    explanation: Establishes fully deleterious biallelic GAA genotypes as the genetic basis of classic infantile disease.
  - reference: PMID:22252923
    reference_title: "Predicting cross-reactive immunological material (CRIM) status in Pompe disease using GAA mutations: lessons learned from 10 years of clinical laboratory testing experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found that, in most cases, CRIM status can be predicted from GAA mutations, potentially circumventing the need for invasive skin biopsy and time wasted in culturing cells in the future."
    explanation: Supports genotype-based prediction of CRIM status from GAA variants.
  - 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 GAA gene is localized on chromosome 17 at the 17q25.2–q25.3 locus and contains 20 exons including the 19 coding ones"
    explanation: Establishes the GAA locus and exon structure.
  - 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: "There is a high allelic heterogeneity/diversity: missense, nonsense, splice-site variants, partial deletions, and insertions have been reported to be causative of the disease."
    explanation: Documents the breadth of GAA variant classes underlying the disease.
  - 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: "For MLPA, large deletions make up only 1.5% of known variants, and the deletion of exon 18 was a common variant in Caucasian patients."
    explanation: Quantifies the large-deletion share of the GAA allelic spectrum, which is the fraction missed by sequencing alone.
  - 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: "This method revealed in four subjects the presence of exonic deletions in the GAA gene causative of PD in association with other causative point mutations."
    explanation: Demonstrates that MLPA recovers causative exonic deletions in patients whose sequencing found only one explanatory allele, supporting the dosage-assay recommendation.
biochemical:
- name: Acid alpha-glucosidase enzyme activity
  context: >
    Diagnosis rests on deficient GAA enzyme activity in isolated lymphocytes or mixed
    leukocytes (or fibroblasts/muscle), with classic infantile patients showing
    severely deficient activity, typically less than 1% of the control mean.
  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"
    explanation: States the diagnostic enzyme assay for Pompe disease.
  - reference: PMID:12897283
    reference_title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Acid alpha-glucosidase activity is severely deficient."
    explanation: Confirms severe enzyme deficiency in the classic infantile cohort.
- name: Urinary glucose tetrasaccharide (Glc4/Hex4)
  context: >
    Urinary glucose tetrasaccharide is a glycogen-burden biomarker used to monitor
    treatment response in IOPD. Together with creatine kinase, low levels correlate
    with favourable response to enzyme replacement therapy, and uGlc4 is the more
    stable of the two.
  evidence:
  - reference: PMID:32373469
    reference_title: "Earlier and higher dosing of alglucosidase alfa improve outcomes in patients with infantile-onset Pompe disease: Evidence from real-world experiences."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Low CK and uGlc4 levels were correlated with favorable response to ERT in IOPD patients, although CK may be more fluctuated than uGlc4."
    explanation: Establishes urinary Glc4 as a monitoring biomarker of ERT response in IOPD.
  - reference: PMID:15886040
    reference_title: "Glucose tetrasaccharide as a biomarker for monitoring the therapeutic response to enzyme replacement therapy for Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Both urinary Glc4 and plasma Hex4 levels decreased after initiation of ERT for all patients."
    explanation: Establishes the direction of the biomarker's response to enzyme replacement therapy - it falls in every treated patient, so a fall is not by itself a marker of good response.
  - reference: PMID:15886040
    reference_title: "Glucose tetrasaccharide as a biomarker for monitoring the therapeutic response to enzyme replacement therapy for Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In contrast, levels fluctuated and were persistently elevated above the control ranges in those patients with a less favorable clinical response"
    explanation: Supplies the discriminating observation - persistent elevation above the control range, rather than the initial fall, is what marks a poorer clinical response.
- name: Anti-rhGAA IgG antibody titer
  context: >
    Serial anti-recombinant-human-GAA IgG titers stratify treatment response.
    CRIM-negative infants develop earlier, higher, and more sustained titers; by
    contrast, long-term survivors of IOPD had low or undetectable anti-alglucosidase
    alfa antibody titers.
  evidence:
  - reference: PMID:19775921
    reference_title: "Cross-reactive immunologic material status affects treatment outcomes in Pompe disease infants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "IgG antibodies to rhGAA developed earlier and serotiters were higher and more sustained in the CRIM-negative group."
    explanation: Reports the antibody-titer difference by CRIM status that makes this a decision-relevant biomarker.
  - reference: PMID:22538254
    reference_title: "The emerging phenotype of long-term survivors with infantile Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All long-term survivors had low or undetectable anti-alglucosidase alfa antibody titers."
    explanation: Shows the association between low antibody titer and long-term survival on ERT.
treatments:
- name: Enzyme replacement therapy with alglucosidase alfa
  description: >
    Intravenous recombinant human GAA is the disease-specific therapy for IOPD.
    Initiated before age six months and before the need for ventilatory assistance, it
    improves survival and ventilator-independent survival, reduces cardiac mass, and
    substantially improves motor skill acquisition. High-dose ERT started immediately
    on a newborn-screening diagnosis gives the best reported outcomes.
  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
  target_phenotypes:
  - preferred_term: Hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
  - preferred_term: Motor delay
    term:
      id: HP:0001270
      label: Motor delay
  target_mechanisms:
  - target: Lysosomal glycogen accumulation
    treatment_effect: INHIBITS
    description: Infused recombinant human GAA supplies the missing lysosomal enzyme and clears stored glycogen.
    evidence:
    - reference: PMID:20301438
      reference_title: "Pompe Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "In those in whom enzyme replacement therapy (ERT) is initiated before age six months and before the need for ventilatory assistance, a majority have improved survival, improved ventilator-independent survival, reduced cardiac mass, and significantly improved acquisition of motor skills compared to untreated individuals."
      explanation: Reduced cardiac mass and improved survival evidence the reversal of the storage lesion by ERT.
  evidence:
  - reference: PMID:17151339
    reference_title: "Recombinant human acid [alpha]-glucosidase: major clinical benefits in infantile-onset Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients (100%) survived to 18 months of age. A Cox proportional hazards analysis demonstrated that treatment reduced the risk of death by 99%, reduced the risk of death or invasive ventilation by 92%, and reduced the risk of death or any type of ventilation by 88%, as compared to an untreated historical control group."
    explanation: Pivotal trial quantifies the survival benefit of rhGAA in infantile-onset disease.
  - reference: PMID:32373469
    reference_title: "Earlier and higher dosing of alglucosidase alfa improve outcomes in patients with infantile-onset Pompe disease: Evidence from real-world experiences."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "High-dose ERT instituted immediately at newborn screening seems to give the best outcome, and a dosage increase is necessary upon - or, even better, before - a rise in biomarker levels."
    explanation: Real-world cohort supports early, high-dose ERT initiation at newborn screening.
  - reference: PMID:32373469
    reference_title: "Earlier and higher dosing of alglucosidase alfa improve outcomes in patients with infantile-onset Pompe disease: Evidence from real-world experiences."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In patients with classical IOPD diagnosed through newborn screening, those late in ERT initiation (p = .006) or late in high-dosage ERT initiation (p = .044) had a higher risk of motor decline."
    explanation: Quantifies the penalty of delayed ERT initiation on motor outcome in classic IOPD.
- name: Avalglucosidase alfa
  description: >
    A next-generation recombinant human GAA with enhanced mannose-6-phosphate receptor
    binding. In the Mini-COMET phase 2 trial, children with IOPD who had declined or
    responded suboptimally to alglucosidase alfa were switched to avalglucosidase
    alfa, with persistent normalization of left ventricular mass z score, falling
    disease-burden biomarkers, and improved or stable motor function through 97 weeks.
  therapeutic_modality: PROTEIN_REPLACEMENT
  treatment_term:
    preferred_term: enzyme replacement therapy
    term:
      id: NCIT:C16221
      label: Protein Replacement Therapy
    therapeutic_agent:
    - preferred_term: avalglucosidase alfa
      term:
        id: NCIT:C169795
        label: Avalglucosidase Alfa
  target_phenotypes:
  - preferred_term: Hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
  target_mechanisms:
  - target: Lysosomal glycogen accumulation
    treatment_effect: INHIBITS
    description: Avalglucosidase alfa delivers recombinant GAA to the lysosome via enhanced mannose-6-phosphate receptor uptake.
    evidence:
    - reference: PMID:40449831
      reference_title: "The Mini-COMET Clinical Trial: Safety and Efficacy of Avalglucosidase Alfa after 97 Weeks of Treatment in Children with Infantile-Onset Pompe Disease Previously Treated with Alglucosidase Alfa."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Compared with baseline, biomarkers of Pompe disease burden decreased, and motor function improved or stabilized."
      explanation: Falling disease-burden biomarkers evidence reduction of the glycogen storage lesion.
  evidence:
  - reference: PMID:40449831
    reference_title: "The Mini-COMET Clinical Trial: Safety and Efficacy of Avalglucosidase Alfa after 97 Weeks of Treatment in Children with Infantile-Onset Pompe Disease Previously Treated with Alglucosidase Alfa."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Echocardiography revealed persistent left ventricular mass z score normalization. Compared with baseline, biomarkers of Pompe disease burden decreased, and motor function improved or stabilized."
    explanation: Mini-COMET reports cardiac, biomarker, and motor outcomes for avalglucosidase alfa in IOPD.
- name: Immune tolerance induction with rituximab and methotrexate
  description: >
    Because CRIM-negative infants neutralize rhGAA, immune tolerance induction is
    given prophylactically at ERT initiation, or therapeutically once antibodies
    appear. Rituximab (anti-CD20 B-cell depletion) plus methotrexate, with or without
    intravenous immunoglobulin, eliminated established anti-rhGAA antibody and
    conferred durable tolerance off all immune therapy with B-cell recovery. It is
    most effective before an entrenched high-titer response develops, which is why
    CRIM status should be known before the first infusion.
  therapeutic_modality: MONOCLONAL_ANTIBODY
  treatment_term:
    preferred_term: immune tolerance induction
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: rituximab
      term:
        id: NCIT:C1702
        label: Rituximab
    - preferred_term: methotrexate
      term:
        id: NCIT:C642
        label: Methotrexate
  target_mechanisms:
  - target: High sustained anti-rhGAA antibody response
    treatment_effect: INHIBITS
    description: B-cell depletion plus antimetabolite immunomodulation prevents or eliminates the neutralizing anti-rhGAA IgG response.
    evidence:
    - reference: PMID:22237443
      reference_title: "Successful immune tolerance induction to enzyme replacement therapy in CRIM-negative infantile Pompe disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In both patients treated therapeutically, anti-rhGAA was eliminated after 3 and 19 months. All four patients are immune tolerant to rhGAA, off immune therapy, showing B-cell recovery while continuing to receive ERT"
      explanation: Directly evidences elimination of the antibody response and durable tolerance.
  evidence:
  - reference: PMID:22237443
    reference_title: "Successful immune tolerance induction to enzyme replacement therapy in CRIM-negative infantile Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients show clinical response to ERT, in stark contrast to the rapid deterioration of their nontolerized CRIM-negative counterparts."
    explanation: Contrasts tolerized with non-tolerized CRIM-negative infants, supporting the clinical value of tolerance induction.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "individuals who do not produce CRIM (i.e., who are CRIM negative) generally develop high titer anti-rhGAA antibodies during ERT and require modified therapy protocols using immunomodulation early in the treatment course, optimally before the first infusion."
    explanation: Management guidance specifying immunomodulation for CRIM-negative infants, optimally before the first infusion.
- name: Intravenous immunoglobulin adjunct
  description: >
    Intravenous gammaglobulin was used alongside rituximab and methotrexate in the
    therapeutic (post-antibody) tolerance-induction regimen; the prophylactic regimen
    given at ERT initiation used a short rituximab-plus-methotrexate course
    essentially without IVIG.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: immunoglobulin therapy
    term:
      id: NCIT:C62710
      label: Immunoglobulin Therapy
  target_mechanisms:
  - target: High sustained anti-rhGAA antibody response
    treatment_effect: INHIBITS
    description: IVIG was part of the therapeutic tolerance-induction combination that eliminated established anti-rhGAA antibody.
    evidence:
    - reference: PMID:22237443
      reference_title: "Successful immune tolerance induction to enzyme replacement therapy in CRIM-negative infantile Pompe disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The combination of rituximab with methotrexate ± intravenous gammaglobulins (IVIG) is an option for tolerance induction of CRIM-negative Pompe to ERT when instituted in the naïve setting or following antibody development."
      explanation: Names IVIG as a component of the tolerance-induction combination.
  evidence:
  - reference: PMID:22237443
    reference_title: "Successful immune tolerance induction to enzyme replacement therapy in CRIM-negative infantile Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two CRIM-negative patients with preexisting anti-GAA antibodies were treated therapeutically with rituximab, methotrexate, and gammaglobulins."
    explanation: Describes the therapeutic regimen in which IVIG was used.
- name: Respiratory support
  description: >
    Respiratory support for respiratory insufficiency may include CPAP and BiPAP;
    tracheostomy may be considered in infants with macroglossia and severe respiratory
    insufficiency. Invasive ventilator-free survival is the primary outcome measure in
    IOPD trials.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: artificial respiration
    term:
      id: NCIT:C70909
      label: Mechanical Ventilation
  target_phenotypes:
  - preferred_term: Respiratory insufficiency due to muscle weakness
    term:
      id: HP:0002747
      label: Respiratory insufficiency due to muscle weakness
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Respiratory support for those with respiratory insufficiency may include CPAP and BiPAP; tracheostomy may be considered in those with macroglossia and severe respiratory insufficiency."
    explanation: Specifies the respiratory support options in Pompe disease management.
- name: Feeding therapy and gastrostomy
  description: >
    Feeding therapy with consideration of a gastrostomy tube is recommended for
    infants with feeding and nutritional difficulties, though growth may still deviate
    from normal despite tube feeding.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Dietary management
    term:
      id: NCIT:C15447
      label: Dietary Intervention
  target_phenotypes:
  - preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  - preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Feeding therapy and consideration of a gastrostomy tube is recommended for those who have feeding/nutritional difficulties."
    explanation: States the recommended feeding intervention.
- name: Cardiac management with Pompe-specific drug precautions
  description: >
    Medical intervention for cardiomyopathy must be individualized because standard
    cardiac drugs may be contraindicated at certain disease stages; digoxin,
    inotropes, diuretics, and afterload-reducing agents may worsen left ventricular
    outflow obstruction.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_phenotypes:
  - preferred_term: Hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
  evidence:
  - 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"
    explanation: Lists cardiac drugs that may worsen outflow obstruction in Pompe disease.
  - 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: "ECG and Echocardiogram should be performed at diagnosis, and at regular intervals (every 12 months or more frequently, depending on patients’ conditions, in the presence of cardiomyopathy)."
    explanation: The MetabERN European clinical pathway recommendations set the cardiac surveillance schedule that accompanies this individualized cardiac management.
- name: AAV9-mediated GAA gene therapy
  description: >-
    A single intravenous infusion of an adeno-associated virus serotype 9 vector
    carrying codon-optimized human GAA cDNA, given at 1.2 x 10^14 vector genomes per
    kilogram. In a reported infantile-onset series, three of four treated
    patients had improved cardiac outcomes and motor function over 52 weeks and no
    anti-GAA antibodies were detected; one patient was withdrawn and subsequently
    died. The rationale is that a single administration of a gene that the body then
    expresses avoids both the every-other-week infusion burden of enzyme replacement
    and the anti-rhGAA antibody response that defeats it in CRIM-negative infants -
    but this is an early-phase result in four patients, not established therapy.
  therapeutic_modality: GENE_THERAPY
  treatment_term:
    preferred_term: AAV9-delivered GAA gene transfer
    term:
      id: NCIT:C15238
      label: Gene Therapy
  target_mechanisms:
  - target: Near-complete acid alpha-glucosidase deficiency
    treatment_effect: RESTORES
    description: >-
      Vector-delivered GAA cDNA supplies the missing enzyme from the patient's own
      transduced cells, addressing the initiating lesion rather than a downstream
      consequence.
    evidence:
    - reference: PMID:40561529
      reference_title: "AAV9-Mediated Gene Therapy for Infantile-Onset Pompe's Disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Four patients with infantile-onset Pompe's disease received a single intravenous injection of an adeno-associated virus serotype 9 vector carrying codon-optimized complementary DNA encoding human acid α-glucosidase (GAA)"
      explanation: Describes the intervention acting on the enzyme-deficiency node in infantile-onset patients.
  target_phenotypes:
  - preferred_term: Hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
  evidence:
  - reference: PMID:40561529
    reference_title: "AAV9-Mediated Gene Therapy for Infantile-Onset Pompe's Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The other patients had improvement in cardiac outcomes and motor function over a 52-week observation period."
    explanation: Reports the cardiac and motor benefit observed in the treated infantile-onset patients.
  - reference: PMID:40561529
    reference_title: "AAV9-Mediated Gene Therapy for Infantile-Onset Pompe's Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Anti-GAA antibodies were not detected in any of the patients during the observation period."
    explanation: Reports that no anti-GAA antibody response was detected over the observation period. The publication does not report the CRIM status of these four patients, so this does not by itself speak to the CRIM-negative antibody-mediated failure curated elsewhere in this entry.
  - reference: PMID:40561529
    reference_title: "AAV9-Mediated Gene Therapy for Infantile-Onset Pompe's Disease."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "One patient was withdrawn from the study and subsequently died."
    explanation: Records the outcome in the fourth patient, which counts against reading this four-patient series as an established benefit.
  - reference: PMID:42142433
    reference_title: "Sensory neuronopathy secondary to gene therapy with AT845 for Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Injury to dorsal root ganglion neurons has been reported in animal models treated with gene therapy using recombinant AAV, but there are limited reports of AAV-mediated sensory neuronopathy in clinical trials."
    explanation: Records dorsal-root-ganglion toxicity as a recognised class risk of recombinant AAV gene therapy, and states plainly how thin the clinical evidence for it currently is.
  - reference: PMID:42142433
    reference_title: "Sensory neuronopathy secondary to gene therapy with AT845 for Pompe disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We describe the clinical, electrophysiological and response to treatment features of a 49-year-old woman with Pompe disease who developed a sensory neuronopathy after receiving AT845, an investigational adeno-associated virus (AAV) gene replacement therapy"
    explanation: The single reported case grounding that class risk in Pompe disease specifically. Note the scope limits, which are why this is a class-level caution rather than a finding about the treatment curated here - the patient was an adult with late-onset disease, and the product was AT845, not the AAV9-GAA vector this entry curates.
  - reference: PMID:37463048
    reference_title: "AAV-mediated delivery of secreted acid α-glucosidase with enhanced uptake corrects neuromuscular pathology in Pompe mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "adeno-associated virus-mediated (AAV-mediated) systemic gene transfer reversed glycogen storage in all key therapeutic targets - skeletal and cardiac muscles, the diaphragm, and the central nervous system - in both young and severely affected old Gaa-knockout mice"
    explanation: The preclinical basis for systemic AAV in this disease, and the reason it is of interest beyond enzyme replacement therapy - it reversed storage in the central nervous system, which infused enzyme does not reach.
  - reference: PMID:37463048
    reference_title: "AAV-mediated delivery of secreted acid α-glucosidase with enhanced uptake corrects neuromuscular pathology in Pompe mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "the therapy reversed secondary cellular abnormalities in skeletal muscle, such as those in autophagy and mTORC1/AMPK signaling"
    explanation: Shows the same intervention reversing the autophagic abnormality curated as a pathophysiology node in this entry, not only the glycogen storage upstream of it.
  notes: >-
    Investigational. The series is four patients in a single-arm Phase 1 study
    (ChiCTR2200063229, curated under clinical_trials), followed for 52 weeks, so it
    establishes neither durability nor a survival benefit over enzyme replacement
    therapy.
diagnosis:
- name: Newborn screening for GAA deficiency
  description: >-
    Pompe disease is screened in newborns by measuring acid alpha-glucosidase
    activity in dried blood spots. The European clinical pathway calls newborn
    screening essential specifically for the infantile-onset forms, and this entry's
    own histopathology section supplies the tissue-level reason: the amount of damage
    already present at baseline limits what enzyme replacement therapy can undo, so
    identifying an affected infant before symptoms appear is what decides the
    outcome. The dried blood spot assay is a screening test only - a low result needs
    confirmation, and sequencing also yields the genotype used to predict CRIM status
    before enzyme replacement therapy is started.
  diagnosis_term:
    preferred_term: newborn dried blood spot screening for GAA deficiency
    term:
      id: NCIT:C81178
      label: Newborn Screening
  results: >-
    A low dried-blood-spot GAA activity result must be confirmed before it is treated
    as a diagnosis; confirmation is by enzyme assay in leukocytes and/or biallelic
    pathogenic GAA variants on molecular testing.
  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: States the assay on which newborn screening for this disease is based.
  - 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 is essential for timely identification and treatment of patients with the infantile-onset forms of the disease."
    explanation: The European clinical pathway singles out the infantile-onset forms as the ones for which newborn screening is essential, which is what makes this a diagnosis entry on this disease rather than on Pompe disease generally.
  - 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 assay in dried blood spots is only a screening test and is not sufficient for definitive diagnosis"
    explanation: Records the limitation that makes confirmatory testing mandatory rather than optional.
  - reference: PMID:20301438
    reference_title: "Pompe Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "identification of biallelic pathogenic (or likely pathogenic) variants in GAA by molecular genetic testing in a proband with an out-of-range newborn screening result and/or suggestive clinical features"
    explanation: GeneReviews states what confirms the diagnosis after an out-of-range newborn screening result.
  - reference: PMID:42320386
    reference_title: "High prevalence of GAA c.[752C > T;761C > T] haplotype complicates high-risk screening for Pompe disease in the Chinese population."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pseudodeficiency alleles pose a significant challenge to Pompe disease (PD) newborn and high-risk screening by causing false-positive enzyme reductions without clinical manifestations."
    explanation: Names the dominant false-positive mechanism in newborn screening for this disease, which is why a low dried-blood-spot result is not a diagnosis.
  - reference: PMID:42320386
    reference_title: "High prevalence of GAA c.[752C > T;761C > T] haplotype complicates high-risk screening for Pompe disease in the Chinese population."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "individuals homozygous for the haplotype or carrying it in trans with a single pathogenic variant remained asymptomatic, despite dried blood spot (DBS) GAA activity falling below the diagnostic threshold"
    explanation: Shows the failure mode concretely - enzyme activity below the screening threshold in people who never develop the disease - which is what second-tier genotyping is for.
  - reference: PMID:42320386
    reference_title: "High prevalence of GAA c.[752C > T;761C > T] haplotype complicates high-risk screening for Pompe disease in the Chinese population."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the haplotype is markedly enriched in East Asian populations"
    explanation: Records that the false-positive burden is ancestry-stratified, so screening performance is not uniform across populations.
- name: CRIM status determination before starting enzyme replacement therapy
  description: >-
    Cross-reactive immunologic material status is established before enzyme
    replacement therapy begins, because it decides whether prophylactic immune
    tolerance induction is needed alongside it. A systematic review addressed how
    CRIM status is determined in practice, how CRIM-negative status affects outcome,
    and which immune tolerance induction regimens are actually used. CRIM status is
    not a measure of enzyme activity: both CRIM-positive and CRIM-negative infants
    have essentially none, and the question is whether any GAA protein exists for the
    immune system to recognise as self.
  diagnosis_term:
    preferred_term: CRIM status determination
    term:
      id: NCIT:C18020
      label: Diagnostic Procedure
  results: >-
    A CRIM-negative result calls for prophylactic immune tolerance induction started
    with, or before, enzyme replacement therapy rather than after antibodies appear.
    The review reports that starting immune tolerance induction at or before the first
    enzyme dose improves prognosis in CRIM-positive patients as well, so a
    CRIM-positive result is not by itself a reason to withhold it.
  evidence:
  - reference: PMID:41583481
    reference_title: "Insights into immunogenicity and therapeutic strategies to mitigate the immune response in infantile-onset Pompe disease: a comprehensive systematic literature review."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "CRIM status should be determined before initiating ERT since CRIM-negative patients have a very high risk of developing an immune response against ERT, potentially leading to treatment failure"
    explanation: States the claim this entry makes - that CRIM status is established before enzyme replacement therapy starts - and the reason, which is the risk of an immune response that defeats the therapy.
  - reference: PMID:41583481
    reference_title: "Insights into immunogenicity and therapeutic strategies to mitigate the immune response in infantile-onset Pompe disease: a comprehensive systematic literature review."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Initiating ITI therapy concurrent or prior to the first dose of ERT can improve the prognosis of patients with IOPD with either CRIM-negative or CRIM-positive status"
    explanation: "Supports the results field - immune tolerance induction started with or before the first enzyme dose rather than after antibodies appear. Note the scope is wider than the results text; the review reports benefit for CRIM-positive patients too, not only CRIM-negative ones."
  - reference: PMID:41583481
    reference_title: "Insights into immunogenicity and therapeutic strategies to mitigate the immune response in infantile-onset Pompe disease: a comprehensive systematic literature review."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Recently, there has been a major shift from direct CRIM testing using western blotting and mutation analysis to CRIM status prediction based on genetic variant analysis."
    explanation: Records how the determination is actually made now, which is why the binding here is the generic Diagnostic Procedure rather than a protein-assay or a genetic-testing term - both routes are in use.
clinical_trials:
- name: NCT03019406
  phase: PHASE_II
  status: ACTIVE_NOT_RECRUITING
  description: >
    Mini-COMET: a phase 2, open-label, ascending-dose, three-cohort study of
    avalglucosidase alfa in children with infantile-onset Pompe disease who were
    declining or responding suboptimally to prior alglucosidase alfa.
  target_phenotypes:
  - preferred_term: Hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
  evidence:
  - reference: PMID:40449831
    reference_title: "The Mini-COMET Clinical Trial: Safety and Efficacy of Avalglucosidase Alfa after 97 Weeks of Treatment in Children with Infantile-Onset Pompe Disease Previously Treated with Alglucosidase Alfa."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The Mini-COMET clinical trial, a phase 2, open-label, ascending-dose, 3-cohort study, has a 25-week primary analysis period (PAP) and an extension treatment period (ETP)."
    explanation: Describes the design of the registered Mini-COMET trial in infantile-onset Pompe disease.
- name: NCT04910776
  phase: PHASE_III
  status: ACTIVE_NOT_RECRUITING
  description: >
    Baby-COMET: a phase 3, open-label, single-group study of avalglucosidase alfa in
    treatment-naive pediatric participants with infantile-onset Pompe disease. It is
    the first-line counterpart of Mini-COMET, which enrolled only children already
    declining on alglucosidase alfa, and so speaks to whether avalglucosidase alfa is
    an alternative to alglucosidase alfa at diagnosis rather than a salvage option.
  target_phenotypes:
  - preferred_term: Hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
  - preferred_term: Generalized muscle weakness
    term:
      id: HP:0003324
      label: Generalized muscle weakness
  evidence:
  - reference: clinicaltrials:NCT04910776
    reference_title: "An Open-label, Multinational, Multicenter, Intravenous Infusion Study of the Efficacy, Safety, Pharmacokinetics, and Pharmacodynamics of Avalglucosidase Alfa in Treatment naïve Pediatric Participants With Infantile-Onset Pompe Disease (IOPD)"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is a single group, treatment, Phase 3, open-label study to assess efficacy, safety, pharmacokinetic (PK), pharmacodynamics (PD) of avalglucosidase alfa in treatment-naïve male and female participants with IOPD."
    explanation: The registry record establishes the phase, design, and treatment-naive IOPD population of the trial.
- name: ChiCTR2200063229
  phase: PHASE_I
  status: RECRUITING
  description: >-
    Single-arm, single-centre, open-label Phase 1 study of GC301, an adeno-associated
    virus injection, for safety, tolerability, and efficacy in patients with
    infantile-onset Pompe disease. This is the registration behind the AAV9-GAA
    gene-therapy series curated as a treatment in this entry; the trial identifier is
    named in that publication.
  target_phenotypes:
  - preferred_term: Hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
  evidence:
  - reference: ICTRP:ChiCTR2200063229
    reference_title: "A single-arm, single-center, open-label clinical study on safety, tolerability, and efficacy of GC301 injection for the treatment of patients with Infantile-onset pompe disease"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "| Register | ChiCTR |"
    explanation: WHO ICTRP registration record establishing the trial's identity and register of origin.
  notes: >-
    Registered on ChiCTR rather than ClinicalTrials.gov, so it is keyed on its WHO
    ICTRP identifier. Recruitment status and last refresh date are as recorded in the
    cached ICTRP record and are not independently re-verified here.
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0009290
      label: glycogen storage disease II
    mapping_predicate: skos:broadMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0017694 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.
discussions:
- discussion_id: gap_iopd_cns_glycogen_white_matter
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Central nervous system glycogen storage and progressive white matter abnormality
  prompt: >-
    Does the progressive cerebral white-matter abnormality of ERT-treated IOPD
    survivors reflect ongoing CNS glycogen storage that intravenous rhGAA cannot
    reach, and would a brain-penetrant therapy prevent it?
  rationale: >-
    Autopsy evidence now establishes the storage side of this question. A systematic
    review of 49 classic infantile patients found severe glycogen accumulation in
    astrocytes and globus pallidus neurons, with white matter among the most
    frequently affected regions, so CNS glycogen storage is no longer an inference
    from the muscle phenotype. What remains open is the link between that storage and
    the clinical trajectory: the review states directly that the mechanisms
    connecting glycogen accumulation to neurological manifestations are still
    incompletely understood, and there is still no interventional evidence that
    reducing CNS glycogen alters the neuropsychological outcome. The same review
    sharpens the gap rather than closing it, by adding a timing problem that was not
    previously part of it - pathology is already widespread before 21 months, whereas
    MRI change appears from 2 to 3 years, biomarker change from about 5 years, and
    cognitive decline from about 8 to 10, so any causal account has to explain that
    lag and any trial of a brain-directed therapy has to contend with an endpoint
    that trails the lesion by years. Preclinical support exists - systemic AAV
    reversed CNS glycogen storage in Gaa-knockout mice (PMID:37463048, cited on the
    gene-therapy treatment) - but that has not been shown to change neurological
    outcome in humans.
  proposed_experiments:
  - experiment_id: exp_iopd_cns_glycogen_imaging
    name: Longitudinal CNS glycogen and white-matter imaging in treated IOPD
    description: >-
      Correlate a CNS glycogen-burden measure with serial quantitative
      white-matter MRI and neuropsychological testing in a multi-centre treated
      IOPD cohort, and compare against recipients of brain-directed enzyme
      delivery when such therapy becomes available.
  evidence:
  - reference: PMID:29573408
    reference_title: "Classic infantile Pompe patients approaching adulthood: a cohort study on consequences for the brain."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Therefore, we advise follow-up programs are expanded to capture CNS involvement in larger, international patient cohorts, to incorporate our findings in the counselling of parents before the start of treatment, and to include the brain as an additional target in the development of next-generation therapeutic strategies for classic infantile Pompe disease.
    explanation: The authors frame CNS involvement as an open target rather than a resolved mechanism.
  - reference: PMID:42538472
    reference_title: "Central nervous system histopathological findings in classic infantile Pompe disease: a systematic review with clinical relevance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mechanisms linking glycogen accumulation to neurological manifestations remain incompletely understood."
    explanation: The systematic review states that the storage-to-manifestation link is still unresolved, which is what keeps this gap OPEN despite the new tissue-level storage evidence.
  - reference: PMID:42538472
    reference_title: "Central nervous system histopathological findings in classic infantile Pompe disease: a systematic review with clinical relevance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "there is a marked temporal gap between the extensive abnormalities observed at autopsy in infancy and later radiological, biochemical, and clinical manifestations"
    explanation: Adds the timing dimension to this gap - the pathology precedes every clinical means of measuring it by years, which any mechanistic account and any trial endpoint has to account for.

animal_models:
- name: GAA-knockout mouse
  species: Mouse
  genotype: Gaa knockout (GAA-null)
  publication: PMID:20040311
  description: >
    The GAA-knockout mouse reproduces the lysosomal glycogen storage lesion and was
    the system in which the autophagic-buildup arm of Pompe muscle pathology, and its
    interference with enzyme replacement therapy, was established.
  evidence:
  - reference: PMID:20040311
    reference_title: "Autophagy in skeletal muscle: implications for Pompe disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Not only does this build-up of autophagosomes disrupt the contractile apparatus in the muscle fibers, it also interferes with enzyme replacement therapy by acting as a sink for the recombinant enzyme and preventing its efficient delivery to the lysosomes."
    explanation: Reports the knockout-mouse finding that makes this model informative here - autophagic buildup both damages the contractile apparatus and sequesters infused recombinant enzyme.
  modeled_mechanisms:
  - target: Failure of productive autophagy and autophagic buildup
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >
      Progressive accumulation of autophagic vesicles in type II-rich fibers, with
      sequestration of infused recombinant enzyme.
    limitations: >-
      The autophagic buildup in this model is restricted to type II-rich fibers, and
      mouse and human skeletal muscle differ in fiber-type composition, so the
      proportion of muscle affected does not transfer directly. The model is also not
      specific to the infantile form: it models GAA deficiency, not the age of onset
      or cardiac severity that defines IOPD, and it says nothing about CRIM status,
      the other determinant of ERT response in infants.
    readouts:
    - name: Autophagic vesicle accumulation in type II-rich muscle fibers
      target: Failure of productive autophagy and autophagic buildup
      direction: INCREASED
      interpretation: Histological correlate of the autophagic-buildup node in this model.
      evidence:
      - reference: PMID:20040311
        reference_title: "Autophagy in skeletal muscle: implications for Pompe disease."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "In the GAA-knockout mouse model, progressive accumulation of autophagic vesicles is restricted to Type II-rich muscle fibers."
        explanation: Reports the measurement and its direction in the knockout mouse.
    evidence:
    - reference: PMID:20040311
      reference_title: "Autophagy in skeletal muscle: implications for Pompe disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "we present evidence that a failure of productive autophagy in muscle tissue contributes strongly to disease pathology in both patients with Pompe disease and GAA-knockout mice"
      explanation: Supports treating the knockout mouse as informative for the autophagy node in human disease.
- name: Lapphund canine Pompe disease (naturally occurring GAA p.W746* homozygote)
  species: Dog
  genotype: GAA c.2237G>A (premature stop at residue 746) homozygous
  publication: PMID:23457621
  description: >-
    A naturally occurring canine Pompe disease found in Finnish Lapphunds, Swedish
    Lapphunds, and Lapponian Herders. The dogs are homozygous for a GAA nonsense
    variant at the codon whose human counterpart causes infantile disease when paired
    with a second fully deleterious allele, and they reproduce the infantile form
    both genetically and clinico-pathologically. Unlike the engineered mouse models,
    this is a spontaneous large-animal disease, which is what makes it the preferred
    system for preclinical gene-therapy work.
  evidence:
  - reference: PMID:23457621
    reference_title: "A nonsense mutation in the acid α-glucosidase gene causes Pompe disease in Finnish and Swedish Lapphunds."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The affected dogs are homozygous for the GAA c.2237G>A mutation leading to a premature stop codon at amino acid position 746."
    explanation: Establishes the causal genotype of this naturally occurring canine disease, which is what makes it a model of GAA deficiency rather than an unrelated canine myopathy.
  modeled_mechanisms:
  - target: Near-complete acid alpha-glucosidase deficiency
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      A homozygous premature stop codon abolishes acid alpha-glucosidase, the same
      class of fully deleterious lesion that produces classic infantile disease in
      humans.
    limitations: >-
      The dogs are homozygous for one nonsense allele, whereas human infantile-onset
      disease usually arises from two different deleterious alleles, so the model
      does not reproduce the human allelic heterogeneity or its effect on residual
      protein. The publication reports genetic and clinico-pathological similarity
      to the human infantile form but does not itself establish CRIM status or the
      anti-rhGAA antibody behaviour that governs enzyme replacement response in
      infants, so it says nothing about that axis of the disease.
    evidence:
    - reference: PMID:23457621
      reference_title: "A nonsense mutation in the acid α-glucosidase gene causes Pompe disease in Finnish and Swedish Lapphunds."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The affected dogs from both the Finnish as well as the Swedish breed mimic infantile-onset Pompe disease genetically, but also clinico-pathologically."
      explanation: States that this naturally occurring canine disease reproduces the human infantile-onset form at both the genetic and the pathological level.
    - reference: PMID:23457621
      reference_title: "A nonsense mutation in the acid α-glucosidase gene causes Pompe disease in Finnish and Swedish Lapphunds."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Therefore this canine model provides a valuable tool for preclinical studies aimed at the development of gene therapy in Pompe disease."
      explanation: Supports treating the canine disease as a preclinical model, which is the use this entry makes of it alongside the gene-therapy treatment.
- name: Gaa c.1935C>A (p.D645E) knock-in mouse
  species: Mouse
  genotype: Gaaem1935C>A (p.Asp645Glu) homozygous knock-in
  publication: PMID:36517654
  description: >-
    A CRISPR-Cas9 knock-in mouse carrying the human GAA c.1935C>A (p.Asp645Glu)
    variant, which is the most frequent infantile-onset allele in people of Southern
    Han Chinese ancestry. By three months these mice have both skeletal muscle
    weakness and hypertrophic cardiomyopathy, the two features that define the human
    infantile form, which is the basis on which the authors present it as a model of
    the infantile-onset disease rather than of GAA deficiency in general.
  evidence:
  - reference: PMID:36517654
    reference_title: "CRISPR-mediated generation and characterization of a Gaa homozygous c.1935C>A (p.D645E) Pompe disease knock-in mouse model recapitulating human infantile onset-Pompe disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The c.1935C>A (p.Asp645Glu) variant, the most frequent GAA pathogenic mutation in people of Southern Han Chinese ancestry, causes infantile-onset Pompe disease (IOPD)"
    explanation: Establishes that the knocked-in allele is itself a human infantile-onset-causing variant, which is the basis for treating this line as an IOPD model rather than a generic GAA-deficiency model.
  modeled_mechanisms:
  - target: Cardiomyocyte glycogen storage and progressive hypertrophic remodeling
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Homozygous knock-in mice develop hypertrophic cardiomyopathy, the cardiac
      feature that separates infantile-onset from late-onset disease.
    limitations: >-
      The mice show no premature mortality, so the model reproduces the cardiac and
      muscle lesions without the fatal course that defines the untreated human
      disease. It also models one specific missense allele rather than the null
      genotypes behind most classic infantile disease, and the characterization
      reported is at a single three-month timepoint.
    readouts:
    - name: Hypertrophic cardiomyopathy and skeletal muscle weakness at 3 months
      target: Cardiomyocyte glycogen storage and progressive hypertrophic remodeling
      direction: INCREASED
      interpretation: Presence of the defining cardiac lesion of infantile-onset disease in the knock-in model.
      evidence:
      - reference: PMID:36517654
        reference_title: "CRISPR-mediated generation and characterization of a Gaa homozygous c.1935C>A (p.D645E) Pompe disease knock-in mouse model recapitulating human infantile onset-Pompe disease."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Three-month-old mice demonstrated skeletal muscle weakness and hypertrophic cardiomyopathy but no premature mortality."
        explanation: Reports the measurement, its direction, and the negative survival result in the same sentence.
    evidence:
    - reference: PMID:36517654
      reference_title: "CRISPR-mediated generation and characterization of a Gaa homozygous c.1935C>A (p.D645E) Pompe disease knock-in mouse model recapitulating human infantile onset-Pompe disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The Gaaem1935C>A knock-in mouse model recapitulates multiple salient aspects of human IOPD caused by the GAA c.1935C>A pathogenic variant."
      explanation: Supports treating this knock-in line as informative for the infantile-onset cardiac phenotype.
  - target: Failure of productive autophagy and autophagic buildup
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      The knock-in mice have near-abolished GAA activity with markedly increased
      tissue glycogen and impaired autophagy, reproducing the autophagy arm of the
      mechanism in an allele-specific rather than a null background.
    limitations: >-
      Autophagy is reported as impaired at three months without the longitudinal
      characterization available for the knockout line, and the mice do not progress
      to the fatal outcome, so the model does not show how far the autophagic lesion
      goes in untreated disease.
    evidence:
    - reference: PMID:36517654
      reference_title: "CRISPR-mediated generation and characterization of a Gaa homozygous c.1935C>A (p.D645E) Pompe disease knock-in mouse model recapitulating human infantile onset-Pompe disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Homozygous Gaaem1935C>A knock-in mice exhibited normal Gaa mRNA expression levels relative to wild-type mice, had near-abolished GAA enzymatic activity, markedly increased tissue glycogen storage, and concomitantly impaired autophagy."
      explanation: Reports abolished enzyme activity, glycogen storage, and impaired autophagy together in this model.
experimental_models:
- name: Patient-derived iPSC cardiomyocytes (PD-iCMs)
  description: >-
    Cardiomyocytes differentiated from Pompe patient induced pluripotent stem cells.
    They reproduce the cardiac storage lesion in a human genetic background -
    decreased GAA activity, lysosomal glycogen accumulation, and hypertrophy - and
    were used to show that mitochondrial dysfunction accompanies the hypertrophy, in
    human cardiomyocytes carrying patient genotypes rather than in a rodent
    background. Supplementing the
    cultures with recombinant human GAA improved mitochondrial function and mitigated
    the cardiac pathology, making this a system in which the disease lesion and its
    response to the actual clinical therapy are both observable.
  experimental_model_type: IPSC_DERIVED_MODEL
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_types:
  - preferred_term: iPSC-derived cardiomyocyte
    term:
      id: CL:0000746
      label: cardiac muscle cell
  cell_source: Patient-derived induced pluripotent stem cells
  publication: PMID:37916452
  evidence:
  - reference: PMID:37916452
    reference_title: "Mitochondrial dysfunction is associated with hypertrophic cardiomyopathy in Pompe disease-specific induced pluripotent stem cell-derived cardiomyocytes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Therefore, this study suggests that defective mitochondria underlie the pathogenesis of cardiomyopathy in patients with PD."
    explanation: States the conclusion this model system was built to support, and so what the model is being curated as evidence for.
  modeled_mechanisms:
  - target: Cardiomyocyte glycogen storage and progressive hypertrophic remodeling
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      The differentiated cardiomyocytes show reduced GAA activity, lysosomal glycogen
      accumulation, and hypertrophy - the cellular content of this node - in human
      cells carrying patient genotypes.
    limitations: >-
      iPSC-derived cardiomyocytes are immature relative to adult myocardium and are
      cultured without haemodynamic load, so the hypertrophy they show is not the
      pressure-loaded ventricular remodeling of the intact infant heart. The source
      publication describes the donors as Pompe disease patients without stating that
      they are the classic infantile form, so the genotype-to-onset link is not
      established by this study alone.
    readouts:
    - name: Mitochondrial number, respiratory function, and ATP production
      target: Cardiomyocyte glycogen storage and progressive hypertrophic remodeling
      direction: DECREASED
      interpretation: >-
        Mitochondrial deficit accompanying the storage and hypertrophy phenotype in
        patient-derived cardiomyocytes.
      evidence:
      - reference: PMID:37916452
        reference_title: "Mitochondrial dysfunction is associated with hypertrophic cardiomyopathy in Pompe disease-specific induced pluripotent stem cell-derived cardiomyocytes."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: "The defective mitochondria were involved in the cardiac pathology as shown by the significantly decreased number of mitochondria and impaired respiratory function and ATP production in PD-iCMs"
        explanation: Reports the mitochondrial measurements and their direction in the patient-derived cardiomyocytes.
    - name: Rescue of mitochondrial function and cardiac pathology by recombinant human GAA
      target: Cardiomyocyte glycogen storage and progressive hypertrophic remodeling
      direction: RESTORED
      interpretation: >-
        Supplying the missing enzyme partially reverses the model phenotype, which is
        the in vitro counterpart of the cardiac response to enzyme replacement therapy.
      evidence:
      - reference: PMID:37916452
        reference_title: "Mitochondrial dysfunction is associated with hypertrophic cardiomyopathy in Pompe disease-specific induced pluripotent stem cell-derived cardiomyocytes."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: "This was alleviated by supplementation with recombinant human acid alpha-glucosidase that improved the mitochondrial function and concomitantly mitigated the cardiac pathology."
        explanation: Reports the rescue arm and what it restored.
    evidence:
    - reference: PMID:37916452
      reference_title: "Mitochondrial dysfunction is associated with hypertrophic cardiomyopathy in Pompe disease-specific induced pluripotent stem cell-derived cardiomyocytes."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "PD patient-specific induced pluripotent stem cells were differentiated into cardiomyocytes (PD-iCMs) that exhibited cardiomyopathic features of PD, including decreased acid alpha-glucosidase activity, lysosomal glycogen accumulation and hypertrophy"
      explanation: Supports treating these cardiomyocytes as informative for the cardiac storage and hypertrophy node.
datasets:
- accession: geo:GSE38680
  title: GAA deficiency (Pompe Disease) in infantile-onset patients
  description: >-
    Microarray expression profiling of biceps and quadriceps muscle from two cohorts
    of infantile-onset Pompe patients, used to identify transcriptional differences
    contributing to the disease phenotype. This is the only dataset located that is
    both human and restricted to the infantile-onset form, so it is the direct
    transcriptomic counterpart of this entry's skeletal-myofiber-injury node.
  data_type: MICROARRAY
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  sample_count: 58
  genes:
  - preferred_term: GAA
    term:
      id: hgnc:4065
      label: GAA
  publication: PMID:22658377
  evidence:
  - reference: PMID:22658377
    reference_title: "Transcriptional response to GAA deficiency (Pompe disease) in infantile-onset patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we used microarrays to examine gene expression from the muscle of two cohorts of infantile-onset Pompe patients to identify transcriptional differences that may contribute to the disease phenotype"
    explanation: Establishes that this dataset profiles muscle from infantile-onset patients specifically, which is what makes it on-topic for this entry rather than for Pompe disease generally.
  - reference: PMID:22658377
    reference_title: "Transcriptional response to GAA deficiency (Pompe disease) in infantile-onset patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "infantile-onset Pompe patient muscle had a gene expression pattern characteristic of immature or regenerating muscle, and exhibited many transcriptional markers of inflammation, despite having few overt signs of inflammatory infiltrate"
    explanation: Reports the dataset's principal finding, a regenerative and inflammatory transcriptional signature in infantile-onset patient muscle without matching histologic infiltrate.
  notes: >-
    Discovered via `just discover-datasets Infantile-Onset_Pompe_Disease` as a DIRECT
    match - the infantile-onset form is named in the dataset's own title - and
    retained after manual relevance triage. Verified with `just verify-datasets`.
    Retrieved 2026-09-01.
- accession: geo:GSE159062
  title: Transcriptomic profile of three-dimensional tissue-engineered human skeletal
    muscle model of Pompe disease and recombinant protein therapy
  description: >-
    RNA-seq of a three-dimensional tissue-engineered human skeletal muscle
    ("myobundle") model of infantile-onset Pompe disease with and without recombinant
    human GAA, giving a transcriptomic readout of the muscle response to the therapy
    this entry curates as its principal treatment. The model reproduces reduced GAA
    activity, elevated glycogen and lysosome abundance, and contractile sensitivity to
    metabolic stress.
  data_type: BULK_RNA_SEQ
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  sample_count: 10
  genes:
  - preferred_term: GAA
    term:
      id: hgnc:4065
      label: GAA
  publication: PMID:33953320
  evidence:
  - reference: PMID:33953320
    reference_title: "Three-dimensional tissue-engineered human skeletal muscle model of Pompe disease."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "we report a three-dimensional primary human skeletal muscle (\"myobundle\") model of infantile-onset Pompe disease (IOPD) that recapitulates hallmark pathological features including reduced GAA enzyme activity, elevated glycogen content and lysosome abundance"
    explanation: Establishes that the profiled system is a model of the infantile-onset form specifically, and which disease features it reproduces.
  - reference: PMID:33953320
    reference_title: "Three-dimensional tissue-engineered human skeletal muscle model of Pompe disease."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In vitro treatment of IOPD myobundles with rhGAA or adeno-associated virus (AAV)-mediated hGAA expression yields increased GAA activity and robust glycogen clearance, but no improvements in stress-induced functional deficits."
    explanation: Reports the dissociation this dataset captures - glycogen clears while a functional deficit persists - which is the in vitro counterpart of the incomplete skeletal-muscle response to enzyme replacement therapy curated in this entry.
  notes: >-
    Discovered via `just discover-datasets` as a DIRECT match and retained after
    manual relevance triage: the source publication describes the myobundles
    explicitly as a model of infantile-onset Pompe disease. Relevance caveat: it is
    an engineered in vitro system, so it bears on the GAA-deficiency mechanism and
    the enzyme-replacement response in human muscle rather than on the cardiac
    severity or infantile course observed in patients. The companion
    SuperSeries GSE159064 is deliberately not curated separately, since it contains
    this series. Verified with `just verify-datasets`. Retrieved 2026-09-01.
- accession: geo:GSE293648
  title: Gene expression profile of tibialis anterior from Gaa-/- mice compared to
    wild type mice
  description: >-
    Microarray profiling of tibialis anterior muscle from Gaa-knockout mice against
    wild type, generated in a study of membrane-repair proteins and satellite-cell
    failure in Pompe muscle. It is the transcriptomic layer of the same knockout
    model this entry curates under animal_models for the autophagic-buildup node.
  data_type: MICROARRAY
  organism:
    preferred_term: house mouse
    term:
      id: NCBITaxon:10090
      label: Mus musculus
  sample_count: 32
  genes:
  - preferred_term: GAA
    term:
      id: hgnc:4065
      label: GAA
  publication: PMID:42337614
  evidence:
  - reference: PMID:42337614
    reference_title: "Accumulation of membrane repair-associated proteins and mature myostatin are novel markers of muscle pathophysiology in Pompe disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Longitudinal transcriptomic analysis of skeletal muscle from a Pompe disease mouse model, combined with immunohistochemical and biochemical approaches, showed early and sustained overexpression of dysferlin (DYSF), annexin A2 (ANXA2), and AHNAK2."
    explanation: Describes the transcriptomic analysis this dataset is the primary data for, and its principal result in the mouse muscle profiled.
  - reference: PMID:42337614
    reference_title: "Accumulation of membrane repair-associated proteins and mature myostatin are novel markers of muscle pathophysiology in Pompe disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "in the mouse model, we observed persistent post-transcriptional accumulation of mature myostatin (MSTN), a key negative regulator of muscle growth, alongside a decrease in the phospho-SMAD3/SMAD3 ratio and reduced SMAD7 expression"
    explanation: Reports the second result obtained from this mouse model, a myostatin-axis change relevant to the muscle-wasting arm of the disease.
  notes: >-
    Discovered via `just discover-datasets` as a GENE_ONLY candidate and retained
    after manual relevance triage: the GEO title and summary describe Gaa-knockout
    mouse muscle with glycogen-filled lysosomes and autophagic build-up, which is
    this entry's mechanism. Relevance caveat: it is a mouse knockout, so it models
    GAA deficiency rather than the infantile onset or the cardiac severity that
    define IOPD, and the source publication's human validation arm is late-onset
    patients rather than infantile-onset ones. Verified with `just verify-datasets`.
    Retrieved 2026-09-01.
notes: >
  Scope. This entry curates MONDO:0017694, the classic infantile-onset form of
  glycogen storage disease due to acid maltase deficiency. It is a child of
  Pompe Disease (MONDO:0009290), which remains the umbrella entry covering the
  whole GAA-deficiency continuum; the late-onset form is a separate concept
  (MONDO:0018485). Shared mechanism - GAA deficiency, lysosomal glycogen
  accumulation - is stated here because dismech entries are self-contained rather
  than inheriting, but the content that justifies a separate entry is the
  IOPD-specific material: near-total enzyme deficiency, the obligate cardiac
  phenotype, the untreated infantile natural history, the CRIM-status/anti-rhGAA
  antibody axis with its immune-tolerance-induction therapy, and the ERT-era
  long-term-survivor phenotype including CNS white-matter disease.

  Terminology caution. IOPD is defined by onset before 12 months WITH
  cardiomyopathy. Onset before 12 months WITHOUT cardiomyopathy is classified by
  GeneReviews as late-onset disease, so "infantile" in the literature does not
  always mean IOPD in this sense; some sources call the latter atypical or
  non-classical infantile disease. Clinical snippets quoted here were checked to be
  about the classic cardiac infantile form. Two classes of item deliberately are
  not, and say so where they sit: mechanism sources that describe the shared
  GAA-deficiency lesion across the whole spectrum, and model and dataset records,
  whose `limitations` and `notes` state where the model or cohort is Pompe disease
  generally rather than the infantile form.

  CRIM status is not the same as enzyme activity. Enzyme activity asks whether GAA
  works; CRIM asks whether any GAA protein exists. Both CRIM-positive and
  CRIM-negative IOPD patients have essentially no enzyme activity - the difference
  is immunological, and it is what determines whether enzyme replacement therapy
  works.
references:
- reference: PMID:12897283
  title: "The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature."
- reference: PMID:19775921
  title: "Cross-reactive immunologic material status affects treatment outcomes in Pompe disease infants."
- reference: PMID:22252923
  title: "Predicting cross-reactive immunological material (CRIM) status in Pompe disease using GAA mutations: lessons learned from 10 years of clinical laboratory testing experience."
- reference: PMID:22237443
  title: "Successful immune tolerance induction to enzyme replacement therapy in CRIM-negative infantile Pompe disease."
- reference: PMID:22538254
  title: "The emerging phenotype of long-term survivors with infantile Pompe disease."
- reference: PMID:29573408
  title: "Classic infantile Pompe patients approaching adulthood: a cohort study on consequences for the brain."
- reference: PMID:32373469
  title: "Earlier and higher dosing of alglucosidase alfa improve outcomes in patients with infantile-onset Pompe disease: Evidence from real-world experiences."
- reference: PMID:40449831
  title: "The Mini-COMET Clinical Trial: Safety and Efficacy of Avalglucosidase Alfa after 97 Weeks of Treatment in Children with Infantile-Onset Pompe Disease Previously Treated with Alglucosidase Alfa."
- reference: PMID:20040311
  title: "Autophagy in skeletal muscle: implications for Pompe disease."
- reference: PMID:38785980
  title: "Failure of Autophagy in Pompe Disease."
- reference: PMID:20301438
  title: "Pompe Disease."
  tags:
    - GeneReviews
- reference: PMID:17151339
  title: "Recombinant human acid [alpha]-glucosidase: major clinical benefits in infantile-onset Pompe disease."
- reference: PMID:39482698
  title: "The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)."
- reference: PMID:39273088
  title: "Mutation Spectrum of GAA Gene in Pompe Disease: Current Knowledge and Results of an Italian Study."
- reference: PMID:16737883
  title: "A retrospective, multinational, multicenter study on the natural history of infantile-onset Pompe disease."
- reference: PMID:17075580
  title: "Characterization of pre- and post-treatment pathology after enzyme replacement therapy for Pompe disease."
- reference: PMID:23457621
  title: "A nonsense mutation in the acid α-glucosidase gene causes Pompe disease in Finnish and Swedish Lapphunds."
- reference: PMID:36517654
  title: "CRISPR-mediated generation and characterization of a Gaa homozygous c.1935C>A (p.D645E) Pompe disease knock-in mouse model recapitulating human infantile onset-Pompe disease."
- reference: PMID:40561529
  title: "AAV9-Mediated Gene Therapy for Infantile-Onset Pompe's Disease."
- reference: PMID:37916452
  title: "Mitochondrial dysfunction is associated with hypertrophic cardiomyopathy in Pompe disease-specific induced pluripotent stem cell-derived cardiomyocytes."
- reference: PMID:22658377
  title: "Transcriptional response to GAA deficiency (Pompe disease) in infantile-onset patients."
- reference: PMID:33953320
  title: "Three-dimensional tissue-engineered human skeletal muscle model of Pompe disease."
- reference: PMID:42337614
  title: "Accumulation of membrane repair-associated proteins and mature myostatin are novel markers of muscle pathophysiology in Pompe disease."
- reference: ICTRP:ChiCTR2200063229
  title: "A single-arm, single-center, open-label clinical study on safety, tolerability, and efficacy of GC301 injection for the treatment of patients with Infantile-onset pompe disease"
- reference: PMID:41014101
  title: "Infantile-onset Pompe disease entering adulthood: Insights from 2 decades of enzyme replacement therapy experience."
- reference: PMID:42538472
  title: "Central nervous system histopathological findings in classic infantile Pompe disease: a systematic review with clinical relevance."
- reference: PMID:42320386
  title: "High prevalence of GAA c.[752C > T;761C > T] haplotype complicates high-risk screening for Pompe disease in the Chinese population."
- reference: PMID:42142433
  title: "Sensory neuronopathy secondary to gene therapy with AT845 for Pompe disease."
- reference: PMID:15886040
  title: "Glucose tetrasaccharide as a biomarker for monitoring the therapeutic response to enzyme replacement therapy for Pompe disease."
- reference: PMID:37463048
  title: "AAV-mediated delivery of secreted acid α-glucosidase with enhanced uptake corrects neuromuscular pathology in Pompe mice."
- reference: PMID:41583481
  title: "Insights into immunogenicity and therapeutic strategies to mitigate the immune response in infantile-onset Pompe disease: a comprehensive systematic literature review."

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References & Deep Research

References

PMID:12897283

The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature.