Distribution of 13 truncating mutations in the neurofibromatosis 1 gene

Abstract

Neurofibromatosis 1 (NF1) is a common genetic disorder characterized by abnormalities of tissues derived from the neural crest. To define germ-line mutations in the NF1 gene, we studied 20 patients with familial or sporadic cases of NF1 diagnosed clinically and one patient with only café-au-lait spots and no other diagnostic criteria. A protein truncation assay identified abnormal polypeptides synthesized in vitro from five RT-PCR products that represented the entire NF1 coding region. Truncated polypeptides were observed in 14 individuals. The mutations responsible for the generation of abnormal polypeptides were characterized by DNA sequencing. Thirteen previously unpublished mutations were characterized in the 14 individuals. The mutation 2027insC was observed in two unrelated individuals; the other 12 mutations were unique. The sequence changes included seven nonsense and four frameshift mutations that created premature translation termination signals, and two large in-frame deletions that led to the synthesis of truncated polypeptides. One of the mutations was found in the child with a single clinical diagnostic criterion, providing her with a presumptive diagnosis of NF1. Our results confirm that truncating mutations are frequent in both familial and sporadic NF1 cases. The identification of mutations in 14 of 21 individuals studied (67%) suggests that the use of protein truncation assays will rapidly accelerate the rate of identification of NF1 mutations. Because we scanned the entire NF1 coding region in each individual, the distribution of NF1 truncating mutations was discerned for the first time. The mutations were relatively evenly distributed throughout the coding region with no evidence for clustering.

Identification of forty-five novel and twenty-three knownNF1 mutations in Chinese patients with neurofibromatosis type 1

“…Approximately two-thirds of the mutations (43/63) are predicted to cause premature termination of the peptide sequence, which is also consistent with previous data. Fifteen mutations observed in the present cohort have also been reported in other populations [Purandare et al, 1994;Heim et al, 1995;Park and Pivnick, 1998;Fahsold et al, 2000;Messiaen et al, 2000;Toliat et al, 2000]. Whether they have a common ancestor or constitute de novo repeat mutations will require additional studies to resolve.…”

NF1 inactivation cooperates with N-Ras in in vivo lymphogenesis activating Erk by a mechanism independent of its Ras-GTPase accelerating activity

“…In contrast, human GAP can inhibit wild type-ras but not mutant rasdependent growth in yeast (Ballester et al, 1989). (3) Most of the mutations found in NF1 patients leave the GRD domain intact (Heim et al, 1995;Upadhyaya et al, 1994;Shen et al, 1996), suggesting that alterations of functions other than the GTPase accelerating activity of NF1 may be associated with tumorigenesis. In addition, a GAP-related domain peptide of NF1 carrying a mutation that confers greatly diminished GAP activity, but a normal binding a nity for Ras-GTP, suppresses tumor formation by the HCT116 human colon carcinoma cell line (Li and White, 1996).…”

Three different premature stop codons lead to skipping of exon 7 in neurofibromatosis type I patients

“…The protein truncation test (PTT) provides the advantage over other methods to screen the entire coding region of the NF1 gene for nonsense or frameshift mutations which represent about 80% of the characterised mutations in the NF1 gene so far (Shen et al, 1996). This technique also allows the detection of aberrantly spliced transcripts (Heim et al, 1995;Messiaen et al, 1997;Hoffmeyer et al, 1998;Park and Pivnick, 1998). Usually, aberrant transcripts are indicative for mutations in splice or branching sites of exons.…”