Type

Enzyme

Clinical features

Ia

Glucose 6-phosphatase

Presentation in early infancy, severe hypoglycemia, hepatomegaly, unable to tolerate starvation [3, 5]

Ib

Glucose-6-phosphate specific transporter deficiency

Presentation in early infancy, severe hypoglycemia, hepatomegaly, unable to tolerate starvation, neutropenia, frequent infections, enterocolitis (IBD-like symptoms), renal involvement [4, 5]

II

Lysosomal acid alpha-1,4-glucosidase

Currently classified as lysosomal storage disease. Onset in early infancy, muscle weakness, cardiomyopathy, abnormal brain myelination, no hypoglycemia, no hepatomegaly [1, 7]

III

Debranching enzyme deficiency

Presentation in infancy, usually (>85 % of cases type IIIa) combined liver and skeletal muscle involvement, liver only (type IIIb 15 %), cardiomyopathy, lactic acidosis and hyperuricemia are less severe than in GSD type I [4, 6]

IV

Branching enzyme deficiency

Presentation in late infancy, poor growth, mild hypoglycemia, hepatosplenomegaly, progressive liver fibrosis and portal hypertension, muscle involvement, broad spectrum of severity [1, 7]

V

Muscle phosphorylase deficiency

Myopathy, exercise intolerance, rhabdomyolysis, no hypoglycemia, no liver involvement [1, 7]

VI

Liver phosphorylase deficiency

Presentation in childhood, mild hypoglycemia, hepatomegaly [2, 8]

VII

Muscle phosphofructokinase deficiency

Myopathy, exercise intolerance, no hypoglycemia, no liver involvement, mild hemolytic anemia [1, 7]

IX

Phosphorylase kinase deficiency

presentation in childhood, mild hypoglycemia, hepatomegaly, mild myopathy [1, 2, 7, 8]