Type I glycogen storage diseases: disorders of the glucose-6-phosphatase complex.
Glycogen storage disease type I (GSD-I) is a group of autosomal recessive disorders with an incidence of 1 in 100,000. The two major subtypes are GSD-Ia (MIM232200), caused by a deficiency of glucose-6-phosphatase (G6Pase), and GSD-Ib (MIM232220), caused by a deficiency in the glucose-6-phosphate transporter (G6PT). Both G6Pase and G6PT are associated with the endoplasmic reticulum (ER) membrane. G6PT translocates glucose-6-phosphate (G6P) from the cytoplasm into the lumen of the ER, where G6Pase hydrolyses the G6P into glucose and phosphate. Together G6Pase and G6PT maintain glucose homeostasis. G6Pase is expressed in gluconeogenic tissues, the liver, kidney, and intestine. However G6PT, which transports G6P efficiently only in the presence of G6Pase, is expressed ubiquitously. This suggests that G6PT may play other roles in tissues lacking G6Pase. Both GSD-Ia and GSD-Ib patients manifest phenotypic G6Pase deficiency, characterized by growth retardation, hypoglycemia, hepatomegaly, nephromegaly, hyperlipidemia, hyperuricemia, and lactic academia and the current treatment is a dietary therapy. GSD-Ib patients also suffer from chronic neutropenia and functional deficiencies of neutrophils and monocytes, which is treated with granulocyte colony stimulating factor to restore myeloid function. The GSD-Ia and GSD-Ib genes have been cloned. To date, 76 G6Pase and 69 G6PT mutations have been identified in GSD-I patients. A database of the residual enzymatic activity retained by the G6Pase missense mutants is facilitating the correlation of the disease phenotype with the patients' genotype. While the molecular basis for the GSD-I disorders are now known and symptomatic therapies are available, many aspects of the diseases are still poorly understood, and there are no cures. Recently developed animal models of the disorders are now being exploited to delineate the disease more precisely and develop new, more causative therapies.
Chou
Janice Yang
JY
Section on Cellular Differentiation, Heritable Disorders Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA. chou@helix.nih.gov
Matern
Dietrich
D
Mansfield
Brian C
BC
Chen
Yuan-Tsong
YT
D020413:3' Untranslated Regions; D020121:5' Untranslated Regions; D000328:Adult; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015152:Blotting, Northern; D002675:Child, Preschool; D018076:DNA, Complementary / Q000378:metabolism; D004195:Disease Models, Animal; D005091:Exons; D015316:Genetic Therapy; D005838:Genotype; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D005953:Glycogen Storage Disease Type I / Q000175:diagnosis / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D007223:Infant; D007668:Kidney; D008099:Liver / Q000378:metabolism; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D013997:Time Factors; D014018:Tissue Distribution
D020413:3' Untranslated Regions; D020121:5' Untranslated Regions; D018076:DNA, Complementary; D005952:Glucose-6-Phosphatase