Glycogen storage disease type II (GSD II) is characterized clinically by severe muscle weakness, moderate hepatomegaly, and substantial cardiac enlargement in an infant who appeared "healthy" at birth (see page 622). Hypotonia and cardiomegaly are so extreme that they cannot be missed. This ease of recognition and a new awareness of the existence of the disease explain the apparent increase in the number of cases. Since 1963 when the first patient was recorded at our institution, we have seen 21 children with the disease. Because of the greatly enlarged heart, the condition is also known as cardiac glycogenosis, but generalized GSD is a more adequate term because the glycogen concentration is abnormally increased in every organ examined to date.
Type II GSD is inherited in an autosomal recessive fashion. Carriers are clinically healthy but can be separated from their genotypically normal siblings by the assay of lysosomal acid α-glucosidase in