Glycogen storage disease type 2 (Pompe disease)
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An infant with severe hypotonia has cardiomegaly with short PR interval. CK is elevated. Acid alpha-glucosidase activity is deficient.
AR; GAA (acid alpha-glucosidase/acid maltase)
- Lysosomal storage disorder
- Infantile: Cardiomegaly (massive), hypotonia, respiratory failure, death in first year
- Late-onset: Progressive myopathy, respiratory weakness
- CK elevated
- ECG: Short PR, LVH
- On RUSP
- On RUSP: flagged by low acid alpha-glucosidase (GAA) activity on newborn screening
- Deficient GAA enzyme activity (dried blood spot, then confirmatory leukocyte/fibroblast assay) is diagnostic
- GAA molecular testing confirms and predicts phenotype; CRIM (cross-reactive immunologic material) status guides immune management before enzyme replacement
- Enzyme replacement therapy (alglucosidase alfa)
PomPe trashes the PumP: the heart (pump) is prominently affected with massive cardiomegaly. Also a lysosomal storage disorder.
"Pumped for MLH": glycogen accumulates in Muscle (hypotonia), Liver (hepatomegaly), and Heart (hypertrophic cardiomyopathy). Also accumulates in the tongue (macroglossia).
Type II GSD x 2 = alpha-1,4: the enzyme (acid maltase/alpha-1,4-glucosidase) cleaves alpha-1,4 linkages. Normal blood glucose (unlike von Gierke and Cori), because the lysosomal pathway is not essential for blood glucose maintenance.