neurofibromatosis

Neurofibromatosis is a group of inherited disorders in which tumors tend to grow on or around nerves throughout the body. The tumors are usually noncancerous, but they can appear on the skin, under it, and deep along nerves, and they vary enormously from person to person, from a few harmless bumps to many. Often the first signs are flat, light-brown skin patches present from childhood.

The most common form, neurofibromatosis type 1 (NF1), is autosomal dominant, so a single altered copy of the NF1 gene causes it, and each child of an affected parent has a 50 percent chance of inheriting it. The NF1 gene is a tumor-suppressor gene: it normally helps keep cell growth in check, so losing its function allows nerve-associated cells to grow into tumors. About half of cases arise from a new mutation, with no previous family history.

The disorder shows highly variable expressivity, meaning the same mutation can cause very mild or more significant features even within one family, while its penetrance is high, so nearly everyone with the mutation shows at least some signs. A separate, rarer disorder, NF2, involves a different gene and tends to cause tumors of the hearing-and-balance nerves. This entry is educational, not medical advice.