IDENTIFICATION OF A SPLICE-SITE MUTATION IN THE CYSTATHIONINE BETA-SYNTHASE GENE RESULTING IN VARIABLE AND NOVEL SPLICING DEFECTS OF PRE-MESSENGER-RNA

We used single-strand conformational polymorphism and direct nucleotid e sequencing to identify a novel mutation in the cystathionine beta-sy nthase (CBS) gene of two siblings with homocystinuria. Both patients a re heterozygous carriers of the G(919)A transition and the novel mutat ion which involves a G-to-A transition in the intron 12 splice donor s ite. Reverse transcription of RNA harvested from transformed lymphocyt es followed by PCR showed a normal size product along with two shorter products involving the deletion of either exon 12 alone or both exons 11 and 12. To our knowledge, the skipping of more than one exon throu gh a single base substitution at a splice-donor site has not been prev iously reported. The normal size splice product was found to have eith er a G or an A at nucleotide position 919, indicating that normal size mRNA was produced by both alleles. (C) 1997 Academic Press.