MUTATIONAL ANALYSIS OF THE CYSTATHIONINE-BETA-SYNTHASE GENE - A SPLICING MUTATION, 2 MISSENSE MUTATIONS AND AN INSERTION IN PATIENTS WITH HOMOCYSTINURIA

RT-PCR and direct sequence analyses were used to define mutations in t he cystathionine beta-synthase (CBS) gene in two unrelated male patien ts with vitamin B6 nonresponsive homocystinuria. Both patients were co mpound heterozygotes for CBS alleles containing point mutations. One p atient had a maternally derived G-->A transition in the splice-donor s ite of intron 1, resulting in aberrant splicing of CBS mRNA. The other allele contained a missense mutation resulting in the previously repo rted E144K mutant CBS protein. The second patient had a maternally der ived 4 bp insertion in exon 17, predicted to cause a CBS peptide of al tered amino acid sequence. A 494G-->A transition was found in exon 4 o f the other allele, predicting a C165Y substitution. Expression of rec ombinant CBS protein, containing the C165Y mutation, had no detectable catalytic activity. Each mutation was confirmed in genomic DNA. (C) 1 998 Wiley-Liss, Inc.