Glycogen Storage Disease Type III is a genetic condition where the body lacks an enzyme called glycogen debranching enzyme.
This enzyme is vital for breaking down stored sugar (glycogen) into energy. When this enzyme is missing, the body struggles to use glycogen properly, leading to various issues, especially in the liver and muscles. Children with this disease might have an enlarged liver, causing a swollen abdomen. They could also experience low blood sugar, leading to weakness and, in severe cases, hypoglycemic seizures. Muscle weakness is a common symptom, and some individuals might develop an enlarged heart, although it usually functions normally. While some symptoms might improve with age, muscle weakness can worsen in adulthood. In some cases, people might not show symptoms until adulthood, and these symptoms are generally milder. To manage GSD III, individuals need to have frequent, small meals and a diet rich in protein. Cornstarch supplements, which break down into sugars slowly, can help maintain blood sugar levels between meals. With proper management and care, individuals with GSD III can lead relatively normal lives despite their condition.
GSD III is caused by pathogenic (disease-causing) variants in the AGL gene and exhibits autosomal recessive inheritance. This means that both parents must be carriers to have a 25% chance to have a child with the condition. The risk of being a carrier is based on a person’s ancestry or ethnic background. For example, individuals of Sephardic Jewish descent have a 1 in 34 chance to be a carrier.
Other names for this condition are Cori disease or Forbes disease.