NF1 and central nervous system cancer: While mice with a germline Nf1 gene mutation (Nf1+/− mice) do not develop gliomas, neither do mice in which both copies of the Nf1 gene are inactivated in neuroglial progenitors (40), suggesting that bi-allelic Nf1 gene inactivation in the proper cell of origin is not sufficient for glioma formation.