Neurofibromatosis (NF) is a genetic disorder in which tumors grow on nerve cells, affecting their growth and development. The skin and bones can also be affected. About half of those with NF inherit the disorder, while other cases are the result of a spontaneous genetic mutation. There are two types: NF 1, involving a gene defect on chromosome 17, with symptoms that include spots on the skin, scoliosis, and learning disabilities; and NF 2, involving a gene on defect on chromosome 22, with symptoms that include hearing loss and tumors on the cranial, spinal and auditory nerves. NF 1 occurs about 10 times more frequently than NF 2.