Somatic alterations of the NF1 gene in an NF1 individual with multiple benign tumours (internal and external) and malignant tumour types

Abstract

Neurofibromatosis type 1 is a common familial cancer syndrome, affecting about 1 in every 4,000 individuals worldwide. We have carried out NF1 gene mutation analysis on DNA isolated from 25 tumours (dermal and plexiform neurofibromas, malignant peripheral nerve sheath tumour, MPNST), obtained at post-mortem from an NF1 patient. Macro and micro sequence alterations of the NF1 gene were studied by dHPLC, microsatellite, RFLP markers and multiplex ligation probe amplification (MLPA). The underlying germline mutation involves a deletion of exons 2 and 3. Of the 25 tumours studied from this patient, characterised somatic mutations were identified in 9 tumours, these were six small deletions (748del T, 2534-2557 del 24bp, 2843delA, 3047-3048 del GT, 4743del G, 7720-7721 delAA), an insertion 649 ins 73 bp, a non-sense mutation R1513X and a single splice site mutation, IVS4C-1 G>A, eight of these represent novel sequence changes in the gene. Evidence for loss of heterozygosity (LOH) was identified in DNA from 7 of the tumours. Each of the tumours analysed contained a different somatic NF1 mutation, indicating that each tumour is the result of an independent somatic event. The somatic mutation detection rate in this study is 64% (16/25), is one of the highest rates in genomic DNA reported so far in a single NF1 patient. Only 68 characterised NF1 somatic mutations have so far been reported and so our data will contribute to NF1 somatic mutational spectrum of the NF1 gene and will be important for understanding the molecular basis of NF1 tumorigenesis.