Prenatal diagnosis of glycogen storage disease type Ia, presenting a new mutation in the glucose-6-phosphatase gene

Molecular genetic analysis and phenotypic characteristics of a consanguineous family with glycogen storage disease type Ia

Glycogen storage disease type‑Ia (GSD‑Ia) is a rare autosomal recessive disease caused by a mutation in the gene encoding glucose‑6‑phosphate‑α (G6PC). The present study reported the case of a 3‑month‑old female Chinese patient with GSD‑Ia born to consanguineous parents. The aim of the present study was to identify the precise mutation of the G6PC gene associated with this family and to describe the phenotypic characteristics of the patient. A comprehensive examination was performed on the patient, including physical examination, vein blood gas analysis, abdominal sonography and biochemical analyses. In addition, gene sequencing was performed on the coding region of the G6PC gene to identify the mutation. The patient was diagnosed with GSD‑Ia and a G6PC missense mutation of c.518T>C (p.L173P) located in a highly conserved area was identified. The mutation is in a non‑helical region of the protein, which previous studies have suggested should result in a lesser effect on G6PC enzymatic activity and milder phenotypic characteristics compared with mutations located in helical regions. However, the severity of the disease phenotype in the subject of the present study was inconsistent with that predicted from her genotype. The patient suffered from serious hypoglycemia, lactic acidosis, increased triglycerides, hepatic dysfunction, clear hepatomegaly and nephromegaly. The incidence of the p.L173P mutation may be relatively high in the Chinese population. Knowledge of the various phenotypic presentations of the p.L173P mutation may beneficial for future investigations.

Mutations in the glucose-6-phosphatase-alpha (G6PC) gene that cause type Ia glycogen storage disease

Glucose-6-phosphatase-alpha (G6PC) is a key enzyme in glucose homeostasis that catalyzes the hydrolysis of glucose-6-phosphate to glucose and phosphate in the terminal step of gluconeogenesis and glycogenolysis. Mutations in the G6PC gene, located on chromosome 17q21, result in glycogen storage disease type Ia (GSD-Ia), an autosomal recessive metabolic disorder. GSD-Ia patients manifest a disturbed glucose homeostasis, characterized by fasting hypoglycemia, hepatomegaly, nephromegaly, hyperlipidemia, hyperuricemia, lactic acidemia, and growth retardation. G6PC is a highly hydrophobic glycoprotein, anchored in the membrane of the endoplasmic reticulum with the active center facing into the lumen. To date, 54 missense, 10 nonsense, 17 insertion/deletion, and three splicing mutations in the G6PC gene have been identified in more than 550 patients. Of these, 50 missense, two nonsense, and two insertion/deletion mutations have been functionally characterized for their effects on enzymatic activity and stability. While GSD-Ia is not more prevalent in any ethnic group, mutations unique to Caucasian, Oriental, and Jewish populations have been described. Despite this, GSD-Ia patients exhibit phenotypic heterogeneity and a stringent genotype-phenotype relationship does not exist.