The neurofibromin 1 protein is associated with neurofibromatosis type I (neurofibromatosis, von Recklinghausen disease, Watson disease), also known as NF1. Mutations linked to neurofibromatosis type 1 led to the identification of NF1.

NF1 encodes the protein neurofibromin, which appears to be a negative regulator of the ras signal transduction pathway. In addition to type 1 neurofibromatosis, mutations in NF1 can also lead to juvenile myelomonocytic leukemia. Although alternatively-spliced NF1 mRNA transcripts have been isolated, their functional differences, if any, remain unclear.Stimulates the GTPase activity of Ras. NF1 shows greater affinity for Ras GAP, but lower specific activity. May be a regulator of Ras activity.