Abstract
Fragile X syndrome is usually caused by expansion of a trinucleotide (CGG) repeat in the 5’-untranslated region of the FMR1 gene. However, both deletions and point mutations in FMR1 have been identified as rare causes of the fragile X syndrome. We have screened the FMR1 gene for mutations by single-stranded conformational polymorphism analysis in 118 mentally retarded males who were referred to us for fragile X testing, and who had a CGG repeat number in the normal size range. We found one patient with a 2-bp deletion in intron 1 and two unrelated patients with identical silent mutations in exon 1. Neither of these mutations were found in 83 controls. Further investigation of the exon 1 silent mutation by Western blot analysis showed normal expression of FMRP in lymphoblastoid cells and reverse-transcription-polymerase chain reaction analysis showed that intron 1 and 2 were spliced out as in the normal control. Furthermore, we found two common polymorphisms, one in intron 1 and one in exon 5. However, no pathogenic FMR1 mutation was found.
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Received: 6 November 1997 / Accepted: 23 December 1997
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Grønskov, K., Hallberg, A. & Brøndum-Nielsen, K. Mutational analysis of the FMR1 gene in 118 mentally retarded males suspected of fragile X syndrome: absence of prevalent mutations. Hum Genet 102, 440–445 (1998). https://doi.org/10.1007/s004390050718
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DOI: https://doi.org/10.1007/s004390050718