Two new mutations in the glucose-6-phosphatase gene cause glycogen storage disease in Hungarian patients.

Glycogen storage disease type 1a (von Gierke disease, GSD-1A) is caused by the deficiency of microsomal glucose-6-phosphatase (G6Pase) activity which catalyzes the final common step of glycogenolysis and gluconeogenesis. The cloning of the G6Pase cDNA and characterization of the human G6Pase gene enabled the identification of the mutations causing GSD-1a. This, in turn, allows the development of non-invasive DNA-based diagnosis that provides reliable carrier testing and prenatal diagnosis. Here we report on two new mutations E110Q and D38V causing GSD-1a in two Hungarian patients. The analyses of these mutations by site-directed mutagenesis followed by transient expression assays demonstrated that E110Q retains 17% of G6Pase enzymatic activity while the D38V abolishes the enzymatic activity. The patient with the E110Q has G222R as his other mutation. G222R was also shown to preserve about 4% of the G6Pase enzymatic activity. Nevertheless, the patient presented with the classical severe symptomatology of the GSD-1a.

Molecular basis of heat labile hexosaminidase B among Jews and Arabs.

Genotyping individuals for Tay-Sachs disease (TSD) is mainly based on the heat lability of beta-hexosaminidase (Hex) A (alphabeta) and the heat stability of Hex B (betabeta). Mutations in the HEXB gene encoding the beta-subunits of Hex that result in heat-labile Hex B thus may lead to erroneous enzymatic genotyping regarding TSD. Utilizing single strand conformation polymorphism (SSCP) analysis for all 14 exons of HEXB followed by direct sequencing of aberrant fragments, we screened individuals whose Hex B was heat labile. A novel heat labile mutation, previously concluded to exist in the HEXB gene, was identified among Jews and Arabs as 1627 G-->A. One individual with heat labile Hex B (HLB) was negative for this novel mutation and for the known 1514 G-->A HLB mutation, proving that there exists at least one other unidentified HLB mutation. Based on these results, it is advisable to perform DNA tests for 1627 G-->A mutation in suspected HLB individuals.