Glycogen storage disease type 3 (Cori disease, Forbes disease, or limit dextrinosis) is an autosomal recessive disorder of glycogen debrancher enzyme deficiency. This causes the buildup of abnormal glycogen, which affects the function of the liver, heart, and skeletal muscles. Caused by mutations on the AGL gene. Most patients present with hepatomegaly and hypoglycemia in either infancy or by childhood. Otherwise, presentations can vary widely as the disease has 4 subtypes.

The most common subtype, glycogen storage disease type IIIa, represents patients with affected liver and muscles. Common findings for Type IIIa include seizures, hepatomegaly, hypotonia, ketoacidosis, and hypoglycemia. Type IIIb is second most common, primarily affecting the liver. These patients present with hypotonia, hepatomegaly, short stature, abdominal distension, cardiomyopathy, and hypoglycemia. Very rarely will patients present with types IIIc or IIId, which are characterized by absent activity from either glucosidase or transferase debranching activities.

Patients must eat a special diet to maintain normal glucose levels.