Neurofibromin is a product of the tumor suppressor gene, Neurofibromatosis type I. Neurofibromin is known to have GTPase activity that modulates the ras pathway. The absence of or alteration of the neurofibromin protein may lead to Neurofibromatosis disease. This protein has not been purified, therefore, most of the information regarding this protein has been deduced from homology analysis of its gene sequence.