NF1 Molecular Characterization and Neurofibromatosis Type I Genotype-Phenotype Correlation: The French Experience

Abstract

Neurofibromatosis type 1 (NF1) affects about one in 3,500 people in all ethnic groups. Most NF1 patients have private loss-of-function mutations scattered along the NF1 gene. Here, we present an original NF1 investigation strategy and report a comprehensive mutation analysis of 565 unrelated patients from the NF-France Network. A NF1 mutation was identified in 546 of the 565 patients, giving a mutation detection rate of 97%. The combined cDNA/DNA approach showed that a significant proportion of NF1 missense mutations (30%) were deleterious by affecting pre-mRNA splicing. Multiplex ligation-dependent probe amplification allowed the identification of restricted rearrangements that would have been missed if only sequencing or microsatellite analysis had been performed. In four unrelated families, we identified two distinct NF1 mutations within the same family. This fortuitous association points out the need to perform an exhaustive NF1 screening in the case of molecular discordant-related patients. A genotype-phenotype study was performed in patients harboring a truncating (N = 368), in-frame splicing (N = 36), or missense (N = 35) mutation. The association analysis of these mutation types with 12 common NF1 clinical features confirmed a weak contribution of the allelic heterogeneity of the NF1 mutation to the NF1 variable expressivity.

126 novel mutations in Italian patients with neurofibromatosis type 1

“…2013; Sabbagh et al. 2013) 95% was reached by Messiaen et al. (2000) through a comprehensive protocol including cytogenetic analysis, MLPA, RNA analysis and DNA sequencing.…”

“…2007; Sabbagh et al. 2013). However, RNA approach usually identify 30–34% of splicing alterations (Messiaen et al.…”

“…Sabbagh and colleagues verified that approximately 31.1% of missense mutations actually disturb NF1 transcript splicing (Sabbagh et al. 2013). …”

Neurofibromatosis type 1 molecular diagnosis: what can NGS do for you when you have a large gene with loss of function mutations?

“…A huge number of different pathogenic NF1 mutations have been reported (Leiden Open Variation Database, LOVD: www.lovd.nl/NF1). [5][6][7][8][9][10][11] Over 1300 NF1 mutations have been reported by The Human Gene Mutation Database (HGMD, Institute of Medical Genetics, Cardiff, http://www.hgmd.org/). Among them, 5-10% are large 17q11.2 deletions encompassing the entire NF1 locus and neighbouring genes.…”

“…This high sensitivity can be obtained with a multistep approach including a cDNA and/or DNA Sanger sequencing and copy number alteration (CNA) study. [8][9][10][11] As NF1 is a tumour suppressor gene, it is expected that tumorigenesis will occur when a second somatic mutation disrupts the remaining functional copy of this gene. In keeping with this expectation and consistent with Knudson's two hit hypothesis, a somatic loss of the second wild-type NF1 allele can be found in NF1-associated tumours, including neurofibromas and MPNSTs.…”