What are neurofibromatoses?

Neurofibromatoses are a group of three genetically distinct disorders that cause tumors to grow in the nervous system. Tumors begin in supporting cells that make up the nerve and the myelin sheath (a thin membrane that envelops and protects nerves) rather than in cells that actually transmit information. The type of tumor that develops depends on the types of supporting cells involved.

Scientists have classified disorders as neurofibromatosis type 1 (NF1), which is also called von Recklinghausen's 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 genders and in all races and ethnic groups.

The most common nerve-associated tumors in NF1 are neurofibromas (tumors of peripheral nerves). On the other hand, schwannomas (tumors that begin in Schwann cells that help form the myelin sheath) are most common in NF2 and schwannomatosis. Most tumors are benign, but occasionally, they may become cancerous.

Why these tumors occur is still not completely known, but it appears to be related mainly to mutations in genes that play key roles in suppressing cell growth in the nervous system. These mutations keep the genes?identified as NF1, NF2, and SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 (SMARCB1)/INI1?from making normal proteins that control cell production. Without the normal function of these proteins, cells multiply out of control and form tumors.