Glycogenosis Type 3, Cori-Forbes Disease

Abstract

Glycogen storage disease type III (GSDIII), or Cori-Forbes disease, is typically a benign disorder of childhood, characterized by hepatomegaly, hypoglycemia with seizures, growth retardation, and sometimes cardiac involvement. These symptoms resolve spontaneously, but myopathy often manifests in adult life. Patients with distal myopathy develop wasting of distal leg and intrinsic hand muscles. The association of late-onset weakness and distal atrophy might lead to the diagnosis of motor neuron disease or peripheral neuropathy. Patients with generalized myopathy tend to have more severe weakness, and cardiac evaluation might show left ventricular or biventricular hypertrophy, sometimes responsive to ACE inhibitor therapy. The treatment is dietary, avoiding fasting and hypoglycemia and myoglobinuric attacks, which are very rare in these patients. The disorder is due to a deficiency of glycogen debranching enzyme (Table 64.1), encoded by the AGL gene. The enzyme works with the glycogen phosphorylase to catabolize glycogen and has both a hydrolase and transferase activity. The polysaccharide deposited is abnormal with shorter peripheral chains and is also called limit dextrin.