Glycogen storage disease type IIIa presenting as non-ketotic hypoglycemia: use of a newly approved commercially available mutation analysis to non-invasively confirm the diagnosis.

Glycogen storage disease type III (GSD-III) is an autosomal recessive disorder caused by the lack of amylo-1,6-glucosidase (AGL), one of the catalytic domains of the glycogen debranching enzyme. Deficiency of this enzyme classically results in hepatomegaly and ketotic hypoglycemia. The diagnosis of the disorder was previously confirmed with a liver biopsy demonstrating abnormal liver glycogen content and absent enzyme activity. We describe an 11 month-old African-American Jehovah's Witness male with non-ketotic hypoglycemia (NKH), hepatomegaly, cardiomyopathy, and a flat glucagon response confirmed to have GSD-IIIa by mutation analysis of the AGL gene. The present case represents an unusual presentation (NKH) of GSD-IIIa and emphasizes the utility of the newly approved commercially available Clinical Laboratory Improvement Advisory Committee (CLIA) mutation analysis test.