Two independent mutations in a family with neurofibromatosis type 1 (NF1)

We report on two independent alterations of the NF1 gene in a three-generat ion kindred with neurofibromatosis type 1 (NF1). Using temperature gradient gel electrophoresis (TGGE) in a mutation analysis of exon 31 of the NF1 ge ne we detected the previously reported nonsense mutation R1947X, This C-to- T transition at codon 1947 in exon 31 is considered to represent a mutation "hot spot" of the NF1 gene due to (5m)CpG deamination. All living family m embers together with their genomic DNA were included in this investigation. However, the mutation R1947X was absent from two undoubtedly affected sibl ings of the propositus, Another NF1 mutation (889-2A-->G) was identified in the two sibs by the protein truncation test (PTT), The novel splice site m utation 889-2A-->G results in a skip of NF1 exon 7 during splicing and prot ein truncation due to frameshift, The two NF1 alterations are linked to dif ferent paternal haplotypes. In our study of a three-generation kindred, R19 47X represents a de novo mutation whereas 889-2A-->G is an inherited splice mutation, Implications for phenotype variation are discussed. (C) 1999 Wil ey-liss, Inc.