PMID 20301760


Glycogen storage disease type VI (GSD VI), a disorder of glycogenolysis caused by deficiency of hepatic glycogen phosphorylase, is characterized in the untreated child by hepatomegaly, growth retardation, ketotic hypoglycemia after an overnight fast, and mild hypoglycemia after prolonged fasting (e.g., during an illness). It is usually a relatively mild disorder that presents in infancy and childhood; however, severe and recurrent hypoglycemia, severe hepatomegaly, and post-prandial lactic acidosis have been described. The risk of hepatic adenoma formation in late childhood and adulthood is theoretically increased. Clinical and biochemical abnormalities may resolve with age; most adults are asymptomatic. Hypoglycemia can occur during pregnancy. Although assay of hepatic glycogen phosphorylase enzyme activity can be performed on erythrocytes, leukocytes, and liver cells, false negative results are common. For this reason, molecular genetic testing of GSD VI is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk relatives and prenatal diagnosis for pregnancies at increased risk are possible if the pathogenic variants in the family are known.