CPT® Code 81250

G6PC (glucose-6-phosphatase, catalytic subunit) (eg, Glycogen storage disease, type 1a, von Gierke disease) gene analysis, common variants (eg, R83C, Q347X)

Molecular genetic testing is a critical diagnostic tool used to identify specific mutations in the G6PC (glucose-6-phosphatase, catalytic subunit) gene, which is associated with glycogen storage disease, type 1a, commonly known as von Gierke disease. This gene is located on chromosome 17 and has been found to have as many as 85 different mutations. These mutations typically result in the alteration of a single amino acid within the glucose-6-phosphatase enzyme, which is situated on the membrane of the endoplasmic reticulum. The endoplasmic reticulum is an essential cellular structure involved in the transport and processing of proteins. The glucose-6-phosphatase enzyme works in conjunction with the glucose-6-phosphate translocase protein, produced from the 5LC37A4 gene, to facilitate the breakdown of glucose-6-phosphate into glucose, which is vital for energy production in cells. The glucose-6-phosphatase enzyme plays a crucial role in regulating glucose levels produced by the liver and is also active in the kidneys and intestines. When mutations occur in the G6PC gene, the function of the glucose-6-phosphatase enzyme is impaired, leading to an inability to convert glucose-6-phosphate into glucose. Instead, the process is diverted, resulting in the conversion of glucose-6-phosphate into fat and glycogen. This accumulation of fat and glycogen within cells can cause significant damage to tissues and organs, particularly affecting the kidneys and liver. Von Gierke disease is inherited in an autosomal recessive manner, meaning that individuals must inherit mutations from both parents to develop the disease. Those who inherit the mutation from only one parent are considered carriers and typically do not exhibit symptoms. Symptoms of this genetic disorder can include severe hypoglycemia, constant hunger, irritability, excessive bleeding or bruising, fatigue, abdominal distention, thin extremities, puffy cheeks, inflammatory bowel disease, stunted growth, and delayed puberty. Management of the disease involves dietary restrictions, such as limiting fructose and galactose intake, preventing low blood glucose levels through the consumption of starches like uncooked cornstarch, and administering allopurinol to lower uric acid levels. Molecular genetic testing is particularly indicated for individuals presenting with symptoms consistent with von Gierke disease or those with a family history of the condition.