126 novel mutations in Italian patients with neurofibromatosis type 1

Abstract

Genetic analysis of Neurofibromatosis type 1 (NF1) may facilitate the identification of patients in early phases of the disease. Here, we present an overview of our diagnostic research spanning the last 11 years, with a focus on the description of 225 NF1 mutations, 126 of which are novel, found in a series of 607 patients (513 unrelated) in Italy. Between 2003 and 2013, 443 unrelated patients were profiled by denaturing high pressure liquid chromatography (DHPLC) analysis of 60 amplicons derived from genomic NF1 DNA and subsequent sequencing of heterozygotic PCR products. In addition, a subset of patients was studied by multiplex ligation‐dependent probe amplification (MLPA) to identify any duplications, large deletions or microdeletions present at the locus. Over the last year, 70 unrelated patients were investigated by MLPA and sequencing of 22 amplicons spanning the entire NF1 cDNA. Mutations were found in 70% of the 293 patients studied by DHPLC, thereby fulfilling the NIH criterion for the clinical diagnosis of NF1 (detection rate: 70%); furthermore, 87% of the patients studied by RNA sequencing were genetically characterized. Mutations were also found in 36 of the 159 patients not fulfilling the NIH clinical criteria. We confirmed a higher incidence of intellectual disability in patients harboring microdeletion type 1 and observed a correlation between a mild phenotype and the small deletion c.2970_2972delAAT or the missense alteration in amino acid residue 1809 (p.Arg1809Cys). These data support the use of RNA‐based methods for genetic analysis and provide novel information for improving the management of symptoms in oligosymptomatic patients.

Risk of Optic Pathway Glioma in Neurofibromatosis Type 1: No Evidence of Genotype–Phenotype Correlations in a Large Independent Cohort

“…Constitutional intragenic NF1 mutations were determined by means of standard techniques using gDNA and, more recently, cDNA; that is, Sanger sequencing and NGS to test for point mutations, and MLPA to test for intragenic deletion/duplication [11,38].…”

“…The enormous number of reported pathogenic NF1 variations consist of intragenic NF1 mutations, which are found in about 90% of NF1 patients, and large 17q11.2 deletions encompassing the entire NF1 gene and a number of flanking genes (the NF1 microdeletion), which are found in 5%-10% [9]. Point mutations are observed in all exons and are mostly nulling or protein-truncating mutations, while a minority (9.4%-15%) are missense mutations [10][11][12].…”

“…The reported detection rates range from 60% to 97% depending on the technique used and the source of the tissues. Advances in genetic investigation techniques have allowed a molecular diagnosis to be made in the majority of cases using multiple gene DNA and RNA screening approaches: Sanger sequencing, next-generation sequencing (NGS), multiplex ligation-dependent probe amplification (MLPA), and array comparative genomic hybridisation CGH [9][10][11].…”

Genetic analyses of the NF1 gene in Turkish neurofibromatosis type I patients and definition of three novel variants

“…Determining the pathogenic variant can assist in diagnosing the patients who have an uncertain diagnosis of NF1 [ 12 , 13 ]. Advances in preimplantation genetic diagnosis (PGD) and prenatal genetic testing might be helpful for the individuals who have a pathogenic variant causing NF1 [ 14 ].…”

Extent of surgery for phaeochromocytomas in the genomic era

“…Mutation analysis of NF1 is complicated by the large size of the gene, the presence of 36 pseudogenes and the apparent absence of hotspot regions, which necessitates the use of multiple detection methods, including DNA/RNA sequencing or multiplex ligation‐dependent probe amplification assays. The span of NF1 genotypes includes missense mutations, truncating mutations, deletions and small duplications, but no reliable genotype–phenotype correlations of clinical value have yet been found. Patients with NF1 presenting with features of MEN2A (medullary thyroid carcinoma and hyperparathyroidism) but without RET mutation have been described, suggesting that RAS‐mediated signals downstream of RET hyperactivation represent a convergence point for transformative processes that are induced by NF1 and RET mutations, and lead to the development of mainly adrenergic adrenal chromaffin tumours with a malignancy potential below 10 per cent.…”