Different mutations in the NF1 gene are associated with Neurofibromatosis-Noonan syndrome (NFNS)

The association of the Noonan phenotype with neurofibromatosis type 1 (NF1) was first noted by Allanson et al. [Am J Med Genet 1985;21:457-462.] and 30 further cases have subsequently been reported. It has been suggested that this phenotype is more common than previously appreciated, as Colley et al. [Clin Genet 1996;49:59-64.] examined 94 sequentially identified patients with NF1 from their genetic register and found Noonan features in 12. A 3-bp deletion of exon 17 of the NF1 neurofibromin gene was described in one family by Carey et al. [Proc Greenwood Genet Center 1997;17:52-53]. However, it remains unclear whether Neurofibromatosis-Noonan syndrome (NFNS) represents a form of NF1 (with mutations in the NF1 neurofibromin gene) or a separate syndrome. We have used a new, rapid sequence analysis technique-comparative sequence analysis (CSA)-to examine the NF1 gene in six patients with NFNS. None of the six patients had the previously identified mutation, nor did we observe other mutations within this exon. However, two other mutations were found: in exon 25, a 3-bp deletion 4312 del GAA, and in exon 23-2, a 2-bp insertion 4095 ins TG. The PTPN11 gene, now known to cause over 50% of Noonan syndrome was also examined in four cases of NFNS, and no mutations were found. These results show that NFNS can in some cases result from different mutations in the NF1 gene and therefore represents a variant form of NF1