Two novel mutations affecting mRNA splicing of the neurofibromatosis type 1 (NF1) gene

INTRODUCTION Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disorder with an incidence of 1 in 3,500 in all ethnic groups (Riccardi and Eichner, 1986), characterized by cutaneous or subcutaneous neurofibromas, hyperpigmented cafe-au-lait skin patches, and Lisch nodules of the iris. The NF1 gene, which contains 57 exons, produces a messenger RNA of -13 kilobases (Wallace et al., 1990). Over 80 mutations of the gene have been reported to date, including chromosome rearrangements, large and small deletions and insertions, and point mutations. The great majority of mutations are nonsense rather than missense (Upadhyaya et al., 1994; Viskochil et al., 1993; NNFF Int. Consort. 1994). We have screened 42 unrelated NFI patients by reverse transcription and polymerase chain reaction (RT-PCR), using a set of seven primer pairs to amplify the coding region of the NF1 cDNA. In only three patients were abnormal RT-PCR products detected; the first of these, leading to the skipping of exon 33, has been described elsewhere (Hutter et al., 1994). This report describes two new splice site mutations: the first generates a cryptic splice site in intron 30 and results in the creation of abnormal supplementary exons, whereas the second, in the acceptor site of intron 17, is responsible for the skipping of exon 18.