Neurofibromatosis type 1: Expanded variant spectrum with multiplex ligation-dependent probe amplification and genotype-phenotype correlation in 138 Turkish patients.

OBJECTIVE: To investigate the variant spectrum and genotype-phenotype correlations in a Turkish cohort with Neurofibromatosis Type-1 (NF1). MATERIALS AND METHODS: We retrospectively investigated the clinical and molecular data of 138 NF1 patients from 129 families who had been followed-up for a median of 3.9 (1.25-18.5) years. RESULTS: NF1 sequencing revealed 73 different intragenic variants, 19 of which were novel. Seven large deletions were detected by multiplex ligation-dependent probe amplification (MLPA) analyses. The total detection rate of pathogenic NF1 variants was found to be 87.1%. Comparing age groups, cutaneous neurofibromas, freckling, and Lisch nodules were more prevalent in patients older than 12 years (p > .05). Optic glioma detected in 17.3% of the patients and was significantly more common before the age of 6 (p > .001). Other solid tumors developed in 5% of the patients. There was no genotype-phenotype correlation between patients with truncating and nontruncating variants. However, six out of seven patients with large deletions had significant developmental delay, one patient with the c.2970_2972delAAT (p.Met992del) variant had only typical pigmentary features, and another patient with the c.4267A > G (p.Lys1423Glu) variant had CALMs, freckling, neurofibromas, and Noonan-like phenotype. CONCLUSIONS: We described 19 novel variants and seven large deletions in NF1. Applying MLPA assay in NF1 is useful in expanding the molecular diagnosis. Although very limited genotype-phenotype correlation has been reported in NF1, the fact that specific phenotypic findings were observed in our patients with large deletions and two intragenic variants supports the studies published recently.