Glycogen storage diseases (GSDs) are characterized by abnormal inherited
glycogen metabolism in the liver, muscle, and brain and divided into types 0 to X. GSD type I,
glucose 6-phosphatase system, has types Ia, Ib, Ic, and Id,
glucose 6-phosphatase,
glucose 6-phosphate translocase,
pyrophosphate translocase, and
glucose translocase deficiencies, respectively. GSD type II is caused by defective
lysosomal alpha-glucosidase (GAA), subdivided into 4 onset forms. GSD type III,
amylo-1,6-glucosidase deficiency, is subdivided into 6 forms. GSD type IV,
Andersen disease or
amylopectinosis, is caused by deficiency of the
glycogen-branching enzyme in numerous forms. GSD type V,
McArdle disease or
muscle phosphorylase deficiency, is divided into 2 forms. GSD type VI is characterized by liver
phosphorylase deficiency. GSD type VII,
phosphofructokinase deficiency, has 2 subtypes. GSD types VIa, VIII, IX, or X are supposedly caused by tissue-specific
phosphorylase kinase deficiency. GSD type 0,
glycogen synthase deficiency, is divided into 2 subtypes.