Identification of a Novel NF1 Frameshift Variant in a Chinese Family with Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is a progressive neurocutaneous disorder in humans, mainly characterized by cafe-au-lait macules (CALMs) and neurofibromas. NF1 is caused by variants of the neurofibromin 1 gene (NF1), which encodes a Ras-GTPase-activating protein called neurofibromin. NF1 variants may result in loss of neurofibromin function and elevation of cell proliferation and tumor formation. In this study, a Chinese NF1 family with an autosomal dominant inheritance pattern was recruited. Exome sequencing and Sanger sequencing were performed to discover the causative variant responsible for the family, followed by molecular analysis of effect of the mutated NF1 protein on Ras activity. A novel frameshift variant c.541dupC (p.(Gln181Profs*20)) in the NF1 gene was identified in all three affected family members. The variant cosegregated with the disease phenotypes in the pedigree and was absent in 100 healthy controls. Bioinformatic analysis showed that the variant c.541dupC (p.(Gln181Profs*20)) was pathogenic. The further molecular analysis verified the cells expressing NF1 variant p.(Gln181Profs*20) partially enhanced Ras activity and elevated cell proliferation and tumor formation due to loss of neurofibromin function caused by the variant. Taken together, the data strongly advocate the c.541dupC (p.(Gln181Profs*20)) variant as the underlying genetic cause of the Chinese family with NF1. Moreover, our findings broaden the spectrum of NF1 variants and provide molecular insights into the pathogenesis of NF1.