Investigation of NF1 gene mutations with next generation sequencing technology in neurofibromatosis type1 cases

Neurofibromatosis Type 1 (NF1), also known as Von Recklinghausen disease, is a common familial cancer syndrome independent of ethnic and racial origins, Itaffects approximately 1 in 3000 to 4000 people worldwide. This disease is an inherited disorder caused by dominant mutations in the NF1 gene. The NF1 gene encodes a cytoplasmic protein called neurofibromin (NM_000267) that is a negative regulator of the RASpathway. Previous studies have shown increased expression of neurofibromin in NF1-related tumors. The diagnostic criteria for NF1 defined by National Institutes of Health are multiple cafe-au-lait (CAL) spots, benign peripheral nerve sheath tumors (neurofibromas), Lischnodules, axillary and inguinal freckles, optic glioma, spesific bone lesions and family history. Other clinical manifestations associated with NF1 include neurological, renal, cardiovascular, gastrointestinal, endocrine and orthopedic, learning and intellectual disabilities, attention deficit, and peripheral nerve sheath or central nervous system malignancies. About a quarter of NF1 cases eventually develop one or more of theseclinical complications that lead to significant morbidity and mortality. Although Characterization of the germline and somatic mutations in tumor tissues provided information about the type, nature and frequency of NF1 gene mutation, information about the molecular mechanisms of the tumor formation is still limited. In addition, somes sendromes present clinical findings that overlap with neurofibromatosis, and this can lead to problems in diagnosis, especially in the prenatal period. Therefore, understanding the frequency of molecular etiopathogenesis of neurofibromatosis is important for the follow-up of prenatal and postnatalcases. Given the clinical heterogeneity of NF1, rapid, accurate parallel sequencing of this gene and deletion / duplication analysis (when necessary) is required for proper diagnosis. In this study, we performed sequencing of the NF1 gene with in-house-designednext generation sequencing (NGS) targeted NF1 gene, using an Ion Torrentplatform, coveringng all exons and exon-intron boundaries in 27 families diagnosed with neurofibromatosis type 1. When sequencing did not yield any pathologic variants, the gene was analysed with MLPA for deletion/duplications. If MLPA showed a deletion, a possible microdeletion involving the NF1 gene was investigated with array-CGH. As a result, we identified 11 previously reported possible related variants and 11 variants that were not previously reported in the literature. Thus the frequency of diagnosis was 94% in this study. The results of our research are expected to contribute to the present knowledge about NF1 gene mutation types and frequencies in the Turkish population. This will provide follow-up opportunities which will allow early detection of benign and malignant tumors as well as proper genetic counseling including prenatal or pre-implantation genetic diagnosis.