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 11years, 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.
Highlights
Neurofibromatosis type 1 (NF1) is a human autosomal dominant disorder that affects approximately 1 in 3500 individuals worldwide (Carey et al 1986; Friedman 1999)
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
Mutations were found in 70% of the 293 patients studied by DHPLC, thereby fulfilling the NIH criterion for the clinical diagnosis of NF1; 87% of the patients studied by RNA sequencing were genetically characterized
Summary
Neurofibromatosis type 1 (NF1) is a human autosomal dominant disorder that affects approximately 1 in 3500 individuals worldwide (Carey et al 1986; Friedman 1999). The most common features of NF1 are pigmentary abnormalities such as cafe-au-lait macules (CALs) and skinfold freckling, Lisch nodules (LNs), cutaneous and plexiform neurofibromas (PNs), optic gliomas, and bone lesions. These symptoms are age-dependent (with a full clinical manifestation typically by 12 years of age) and present high variability in expressivity, even among affected members of the same family (Jett and Friedman 2010). NF1 is caused by mutations in the neurofibromin gene (17q11.2.5-7; NM_000267.3), which encodes a negative regulator of the Ras guanosine triphosphate (GTP)ase proteins and acts as a tumor suppressor gene. Small changes are most frequently identified in NF1 (approximately 80–90%) and often cause premature stop codons.
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