Neurofibromatoses are a group of three genetically distinct disorders that cause tumors to grow in the nervous system. Tumors begin in the supporting cells that make up the nerve and the myelin sheath (the thin membrane that envelops and protects the nerves), rather than the cells that actually transmit information. The type of tumor that develops depends on the type of supporting cells involved. Scientists have classified the disorders as neurofibromatosis type 1 (NF1, also called von Recklinghaus disease), neurofibromatosis type 2 (NF2), and a type that was once considered to be a variation of NF2 but is now called schwannomatosis. An estimated 100,000 Americans have a neurofibromatosis disorder, which occurs in both sexes and in all races and ethnic groups.