Glycogen storage disease type III (GSD III) is a very rare disorder caused by a deficiency in the activities of glycogen debranching enzymes (amylo-1-6-glucosidase and 4-α-glucanotransferase). GSD III is characterized by the accumulation of abnormal glycogen in the liver and skeletal muscle. The primary clinical manifestations are hepatomegaly, fasting hypoglycemia, and hyperlipidemia in infants. We report a rare case of GSD III in an adult. A 52-year-old woman presented to our clinic due to dyspnea on exertion, severe general weakness, and hepatomegaly. Hypertrophic cardiomyopathy was diagnosed based on echocardiogram findings. The microscopic findings of liver and skeletal muscle biopsies were consistent with the diagnosis of GSD. DNA analysis prompted by clinical and pathologic findings led to a definitive diagnosis of GSD IIIa. Diet therapy with cornstarch was started, and the patient was followed closely. This represents the first reported case of GSD IIIa diagnosed in an adult in Korea. (Korean J Hepatol 2008;14:219-225)
