Summary
Glycogen storage disease type II (GSD II) is a lysosomal storage disease due to acid alpha-1,4-glucosidase deficiency. This enzyme hydrolyses glycogen into glucose, and its deficient action causes glycogen to accumulate in lysosomes (see also Danon disease for differential diagnosis). The disorder is autosomal recessive. Although the deficiency is ubiquitous, it is only expressed in certain organs (mainly heart and/or skeletal muscles). The infantile form, or Pompe's disease, begins before the age of 3 months with major hypotonia, suckling and swallowing difficulties, hypertrophic cardiomyopathy, and progressive hepatomegaly. It is fatal within a maximum of two years. Juvenile and adult forms present as limb-girdle muscular dystrophy beginning in the lower limbs. Final outcome depends on respiratory muscle failure. A continuous spectrum exist between these 2 presentations. Biologically, evidence of enzymatic deficiency in fibroblasts, lymphocytes, or a trophoblast biopsy is diagnostic. Rare pseudodeficient alleles can complicate prenatal diagnosis. The gene has been located on chromosome 17q23. Although a small number of mutations are most frequently encountered, many have been identified, in agreement with the clinical heterogeneity of the disease. Besides symptomatic treatment, recombinant enzyme therapy is available in Europe for treatment of Pompe's disease and clinical trials of enzyme replacement therapy have started in juvenile patients and will start soon in adults. *Authors: Dr I. Maire, Dr R. Froissart (February 2005)*.
