Glycogen storage disease type Ia: Molecular diagnosis of 51 Japanese patients and characterization of splicing mutations by analysis of ectopically transcribed mRNA from lymphoblastoid cells

Glycogen storage disease type Ia (GSD-Ia) is an autosomal recessive disorde r of glycogen metabolism caused by a deficiency of glucose-6-phosphatase (G 6Pase) that is expressed in the liver, kidney, and intestinal mucosa. Clini cal manifestations include short stature, hepatomegaly, hypoglycemia, hyper uricemia, and lactic acidemia. To elucidate a spectrum of the G6Pase gene m utations and their frequencies, we analyzed mutations in 51 unrelated Japan ese patients with GSD-Ia. The most prevalent mutation was g727t, accounting for 88 of 102 mutant alleles examined, followed by R170X mutation, which a ccounted for 6 mutant alleles, and R83H mutation which was observed in 3 mu tant alleles. In addition, 3 different, novel mutations, IVS1-1g<a, Gly122- to-Asp (G122D) and His179-to-Pro (H179P), were identified. We were able to detect "ectopically" transcribed G6Pase-mRNA in Epstein-Barr virus-transfor med lymphoblastoid cells and observed aberrant mRNA splicing associated wit h the g727t and IVS1-1g<a mutations. To our knowledge, this is the first re port that ectopic expression can be utilized for the characterization of GS D-Ia mutations. Our findings suggest that a screening for the g727t, R170X, and R83H mutations by simple DNA-based diagnostic methods can detect 95% o f the G6Pase mutant alleles in Japanese patients with GSD-Ia, and remaining mutations can be identified and characterized by the direct sequencing of genomic DNA and/or the analysis of ectopically expressed mRNA. The noninvas ive molecular diagnosis for GSD-Ia may ultimately replace the conventional means of enzymatic diagnosis that requires liver biopsy. (C) 2000 Wiley-Lis s, Inc.