NOVEL POINT MUTATION WITHIN INTRON-10 OF FMR-1 GENE CAUSING FRAGILE-X-SYNDROME

The majority of cases involving fragile X syndrome are due to expansio n of a (CGG)n trinucleotide repeat at the 5' untranslated region of th e FMR-1 gene. Deletion and intragenic loss of function mutations of th e FMR-1 gene also have been reported. Here, we report a C to T point m utation at the 14(th) nucleotide in intron 10 of the FMR-1 gene in thr ee unrelated fragile X patients, However, the (CGG)n repeat of FMR-1 i n those patients does not expand. To determine the effect of this muta tion on the patients' FMR-1 transcripts, total RNA from peripheral blo od cells was reverse transcribed and amplified by polymerase chain rea ction (RT-PCR). Direct and subcloned sequencing of the RT-PCR products revealed that the transcripts from the allele with C to T mutation sk ip exon 10 entirely, resulting in a joining of exons 9 and 11. Deletio n of exon 10 results in frame-shift and premature termination of trans lation, which removes the highly conserved region that encoding the KH 2 and RGG box domains of FMRP. Interestingly, a male of the three pati ents has another G to A substitution in exon 15. However, the intron 1 0 mutation is sufficient for development of fragile X syndrome. (C) 19 97 Wiley-Liss, Inc.