Glycogenosis due to glucose-6-phosphatase deficiency (G6P) type a, or glycogen storage disease (GSD) type 1a, is a type of glycogenosis due to G6P deficiency (see this term).
Prevalence is unknown. Annual incidence at birth of glycogenosis due to G6P deficiency is around 1/100,000. Type a is the more frequent type, affecting about 80% of patients.
The disease may manifest at birth by enlarged liver or, more commonly, between the ages of three to four months by symptoms of fast-induced hypoglycemia (tremors, seizures, cyanosis, and apnea). Patients present disturbed glucose homeostasis usually characterized by poor tolerance to fasting, significant hepatomegaly (sometimes eight to ten cm below the right costal margin), growth retardation (short stature and delayed puberty), generally improved by an appropriate diet, osteopenia and, in some cases, osteoporosis, round doll-like facial appearance with full cheeks, mild hypotonia, nephromegaly, and platelet dysfunction that may lead to frequent epistaxis. Diarrhea may be encountered. Late complications are hepatic (adenomas with rare but possible transformation into hepatocellular carcinoma) and renal (glomerular hyperfiltration leading to proteinuria and sometimes to renal failure), but also include anemia, sometimes severe, and a risk of hypoglycemic brain damage. Pulmonary hypertension has been reported in few cases.
The disease is due to a dysfunction in the G6P system, a key step in glycemia regulation. Type a is due to mutations in the G6PC gene (17q21), which cause a deficit of the catalytic subunit G6P-alpha expressed in the liver, kidney and intestine. Many mutations have been identified, illustrating the allelic heterogeneity of the condition.
Transmission is autosomal recessive.
Management is similar in both types of glycogenosis due to G6P deficiency (see this term).
Last update: November 2010