What Is Glycogen Storage Disease Type III?
Glycogen Storage Disease Type III (GSD III), also known as Cori disease or Forbes disease, is an inherited condition in which the body lacks the glycogen debranching enzyme. GSD III is caused by mutations in the AGL gene. A deficiency of the glycogen debranching enzyme prevents the body from breaking down glycogen, a stored form of sugar. As a result, glycogen cannot properly be used to energize and fuel the body and glycogen molecules accumulate in the body. This results in various complications, notably involving the liver and muscles.
Symptoms of GSD III often appear in infancy or childhood. The liver is enlarged (hepatomegaly), leading to a noticeably swollen abdomen. This enlargement usually subsides with puberty, although there may be long-term liver damage. Low blood sugar (hypoglycemia) may occur. The majority of people with GSD III experience muscle weakness. This weakness can be severe at times and may worsen in adulthood. Children with the disease may experience delayed growth but usually reach normal adult height. Some people with the disease also develop an enlarged heart, though its function is usually normal.
Some individuals with GSD III do not have symptoms until adulthood. This later onset typically corresponds with milder symptoms.
How Common Is Glycogen Storage Disease Type III?
The incidence of GDS III is 1 in 100,000. This disease is more common in Sephardic Jews of North African descent and in individuals from the Faroe Islands of the North Atlantic.
How Is Glycogen Storage Disease Type III Treated?
GSD III is managed mainly by frequent, small meals and a high-protein diet with cornstarch supplementation. Cornstarch, which breaks down slowly into simple sugars, may alleviate symptoms of low blood sugar between meals. Parents of infants should be particularly careful and monitor the child's diet to avoid hypoglycemic seizures. Physicians will monitor the liver, heart, and muscles in affected individuals and recommend physical therapy when necessary to promote better movement.
What Is the Prognosis for an Individual with Glycogen Storage Disease Type III?
Among infants with GSD III, there is an increased rate of fatalities due to seizures caused by low blood sugar. While an exact lifespan is unknown, many individuals with GSD III live well into adulthood. Liver disease and muscle weakness may contribute to a cause of death in the long term.