Glycogen storage disease type III (GSD III)—also known as Cori disease or Forbes disease—is an inherited condition in which the deficiency of an enzyme called glycogen debranching enzyme results in various complications, notably involving the liver and muscles. The lack of this enzyme means the body cannot properly break down glycogen, a stored form of sugar. As a result, glycogen cannot properly be used to energize the body and glycogen molecules accumulate in the body.
Symptoms of GSD III often appear in infancy or childhood. The liver is enlarged, leading to a noticeably swollen abdomen. This enlargement usually subsides with puberty, although there may be long term liver damage.
Muscle weakness is a problem seen in 85% of people with GSD III. This weakness can at times be severe and may worsen in adulthood. Children with the disease may experience delayed growth, but usually reach normal adult height. A minority of people with the disease also have a mildly enlarged heart, though its function is usually normal.
Low blood sugar and feelings of tiredness may occur with GSD III, although they are less common and less severe than with another form of GSD, type I.
The onset of the disease may occur in adulthood, which typically corresponds with milder symptoms.
About 1 in 100,000 U.S. births is affected by GSD III. This disease is much more common in Israeli Jews of North African descent, where 1 in 35 are carriers and 1 in 5,400 babies has the disease. The highest rate is found among people on the Faroe Islands of the North Atlantic, where 1 in 30 is a carrier and 1 in 3,600 babies is affected.
There is no treatment for the cause of GSD III. Physicians will monitor the liver, heart, and muscles in affected people and recommend physical therapy when necessary to promote better movement. Frequent small meals and a high-protein diet may also be beneficial. Physicians may recommend consuming corn starch, which breaks down slowly into simple sugars and may alleviate symptoms of low blood sugar between meals. Parents of infants should be particularly careful to monitor the child’s diet to avoid hypoglycemic seizures.
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 people with GSD III live well into adulthood. Liver disease and muscle weakness may contribute to a cause of death long-term.
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