P14.01 * INTEGRATED GENETIC STUDIES OF NEUROFIBROMATOSIS TYPE 1. A TEN YEAR, ITALIAN EXPERIENCE

Abstract

BACKGROUND: Neurofibromatosis type 1 (NF1) is a human autosomal dominant disorders that affects approximately 1 in 3,500 individuals worldwide. The most common features of NF1 are pigmentary abnormalities, such as cafe-au-lait macules, skinfold freckling, Lisch nodules and cutaneous and plexiform neurofibromas (PNs). These signs are age-dependent and present high variability in penetrance and expressivity even between affected members of a family. NF1 is the most common cancer predisposing syndrome affecting the nervous system. Glioma is the most common central nervous system neoplasia in NF1 patients: 15-20% NF1 children develop low grade optic gliomas. PNs occur in 30% of NF1 patients in peripheral nervous system. Patients with PNs have a 20-fold higher risk of developing malignant peripheral nerve sheath tumours (MPNSTs) than other NF1 patients. NF1 is caused by mutations in the neurofibromin gene encoding a negative regulator of Ras guanosine triphosphate (GTP)ase proteins: for this reason is considered a tumor suppressor gene. Mutation detection in the NF1 gene is complex, due to the large size of the gene (>350 kb), the presence of pseudogenes, the lack of hot spots, and the great variety of possible mutations. Hence, the clinical and molecular diagnosis of NF1 may be challenging and its fine-tuning is desirable. METHODS: During 2003-2013 NF1 mutation analysis of genomic DNA was performed in 458 patients using the multiplex ligation-dependent probe amplification (MLPA) to look for deletions or insertions located inside the NF1 gene. Subjects who tested negative for MLPA were investigated using denaturing high pressure liquid chromatography (DHPLC) and sequencing DNA. RNA-based cDNA-PCR sequencing was used in a limited group of patients. RESULTS: 299 of 458 patients were diagnosed according to NIH criteria. 54% were children and about 53% of all NF1 patients were found to have sporadic mutations. We identified 197 single mutations and more than 57% were novel. This genetic protocol permitted us to find mutations in 210 of 299 of clinically diagnosed patients (detection rate: 70%). To improve such detection rate we have recently developed a sensitive, integrated genetic protocol using MLPA and RNA-based cDNA-PCR sequencing. This protocol was validated in a cohort of 33 blood samples from NF1 patients with complete NF1 features, identifying the mutations in 30 cases (91% detection rate). CONCLUSIONS: These data suggest that integrated DNA/RNA-based protocols can improve detection rate in patients suspected to have NF1.