What are the neurofibromatoses?
The neurofibromatoses are a group of three genetically distinct but related disorders of the nervous system that cause tumors to grow around the nerves. Tumors begin in the cells that make up the myelin sheath, a thin membrane that envelops and protects nerve fibers, and often spread into adjacent areas. The type of tumor that develops depends on its location in the body and the kind of cells involved. The most common tumors are neurofibromas, which develop in the tissue surrounding peripheral nerves. Most tumors are non-cancerous, although occasionally they become cancerous over time.
Why these tumors occur still isn't completely known, but it appears to be mainly related to mutations in genes that play key roles in suppressing tumor growth in the nervous system. These mutations keep the genes - identified as NF1 and NF2 - from making specific proteins that control cell production. Without these proteins, cells multiply out of control and form tumors.
An estimated 100,000 Americans have a neurofibromatosis (the singular form of neurofibromatoses) disorder, which occurs in both sexes and in all races and ethnic groups. Scientists have classified the disorders as neurofibromatosis type 1 (NF1), neurofibromatosis type 2 (NF2), and a type that was once considered to be a variation of NF2 but is now called schwannomatosis.
What is Neurofibromatosis?
The neurofibromatoses are genetic disorders of the nervous system that primarily affect the development and growth of neural (nerve) cell tissues. These disorders cause tumors to grow on nerves and produce other abnormalities such as skin changes and bone deformities. Although many affected persons inherit the disorder, between 30 and 50 percent of new cases arise spontaneously through mutation (change) in an individual's genes. Once this change has taken place, the mutant gene can be passed on to succeeding generations. Scientists have classified the disorders as neurofibromatosis type 1 (NF1) and neurofibromatosis type 2 (NF2). NF1 is the more common type of the neurofibromatoses. In diagnosing NF1, a physician looks for changes in skin appearance, tumors, or bone abnormalities, and/or a parent, sibling, or child with NF1. Symptoms of NF1, particularly those on the skin, are often evident at birth or during infancy and almost always by the time a child is about 10 years old. NF2 is less common. NF2 is characterized by bilateral (occurring on both sides of the body) tumors on the eighth cranial nerve. The tumors cause pressure damage to neighboring nerves. To determine whether an individual has NF2, a physician looks for bilateral eighth nerve tumors and similar signs and symptoms in a parent, sibling, or child. Affected individuals may notice hearing loss as early as the teen years. Other early symptoms may include tinnitus (ringing noise in the ear) and poor balance. Headache, facial pain, or facial numbness, caused by pressure from the tumors, may also occur.
