Neurofibromatosis (NF), or von Recklinghausen disease, is a genetic disease in which patients develop many soft tumors (neurofibromas) under the skin and throughout the nervous system. The tumors develop from cells called neural crest cells, which are found in developing fetuses (unborn babies). Normally, neural crest cells turn into other types of cells that form nerves; bony structures of the head and neck; and pigment cells, which provide color to body structures. But in a person with neurofibromatosis, a genetic defect causes the neural crest cells to develop abnormally, producing tumors and malformations of the nerves, bones, and skin.

About one in every 4,000 babies born has neurofibromatosis (NF). Two types of NF exist, NF-1 (90% of all cases), and NF-2 (10% of all cases). The chance of a person with NF passing on the genetic defect to a child is 50%. However, not all cases of NF are inherited. About half...