Home   |   What's NF   |   About NFCA   |   Clinic Info   |   What’s New   |   Support   |   Links   |   Publications

What is Neurofibromatosis (NF)?

Neurofibromatosis (NF) is one of the most common genetic conditions and can affect anyone, regardless of family history, race, gender, or ethnic background.

NF1 affects approximately one out of every 3,000 individuals. NF2 affects one out of every 25,000 individuals. A third classification, Schwannomatosis, is a rare form of NF that has only recently been recognized and appears to affect around 1:40,000 individuals. It is less well understood than NF1 and NF2, and features may vary greatly between patients.

Both NF1 and NF2 are characterized by the growth of benign tumors called neurofibromas. These tumors can grow anywhere in the body where there are nerve cells.
This includes nerves just under the surface of the skin, as well as nerves deeper within the body, spinal cord, and/or brain.

In NF1, neurofibromas most commonly grow on the skin or on the nerve to the eye.  A tumor which grows on the nerve to the eye is called an optic glioma and, if it grows large enough, can cause problems with vision, including blindness.

In NF2, neurofibromas most commonly grow within the spinal cord or brain.  Specifically, the tumors are found on the nerves to the ear, called acoustic neuromas, or the nerves for balance, called vestibular schwannomas.  Acoustic neuromas, if large enough, can lead to deafness.

How is the diagnosis of Neurofibromatosis made?

Features of NF1

To be given the diagnosis of NF1, an individual must have at least two of the following features.  Some people with NF1 have only two, while others can have many of these features:

It is proposed that UBOs "Unidentified Bright Objects" be a diagnostic criterion for NF1 since 43 %-93% of NF children will exhibit areas of increased T2-weighted signal intensity on MRI
screenings.

The Diagnostic Evaluation and Multidisciplinary Management of Neurofibromatosis 1 and Neurofibromatosis 2 (Journal of the American Medical Association, July 2, 1997 278:51-57)


Features of NF2

Individuals with NF2 have fewer outside signs of the condition than individual with NF1.  This form of the disease affects 1 in 35,000 people and has two separate paths to diagnosis:

Patients with NF2 often have hearing loss and cataract formation. These can develop during childhood, but are most common during the teenage years or in the early twenties.

Early management of neurofibromatosis type II

Fact Sheets


Possible NF1 Manifestations At Different Life Stages

Congenital

Preschool

Childhood, Adolescence

Lifelong


How does a person get NF?

NF is caused by a change in our genetic material.  NF1 is caused by a change in a gene carried on chromosome 17.  NF2 is caused by a change in a gene carried on chromosome 22.

The change in the genetic material that causes NF1 and NF2 can be inherited from a parent, referred to as autosomal dominant inheritance, or it can occur spontaneously at conception. The NF gene is always present at birth, though symptoms may not appear until later in life.

Autosomal Dominant Inheritance

If either parent has NF, there is a 50% chance with each pregnancy that the gene causing NF will be passed on to the child.  There is no way to predict whether a child who inherits the gene will be affected more severely, the same, or less than the parent.  If one parent has an autosomal dominant condition such as NF, there is a 50% chance that it will be passed to each child.

Spontaneous Occurrence

In approximately 50% of cases, NF occurs in an individual who has no family history of the disorder. Anyone can be born with NF.  This happens when there is a spontaneous change in the genetic material carried by either the sperm or the egg when pregnancy begins.  There is nothing a parent can do or not do to cause this change. Once a person has the changed gene that causes NF, he or she will have NF and therefore have a 50% chance of passing the gene on to his or her children.


Mosaicism

Neurofibromatosis type 1 and type 2 both occur in mosaic forms. Mosaicism results from somatic mutations. Early somatic mutations cause generalized disease, clinically indistinguishable from nonmosaic forms. Later somatic mutation gives rise to localized disease often described as segmental. In individuals with mosaic or localized manifestations of neurofibromatosis type 1 (segmental neurofibromatosis type 1), disease features are limited to the affected area, which varies from a narrow strip to one quadrant and occasionally to one half of the body. Distribution is usually unilateral but can be bilateral, either in a symmetric or asymmetrical arrangement. Patients with localized neurofibromatosis type 2 have disease-related tumors localized to one part of the nervous system; for example a unilateral vestibular schwannoma with ipsilateral meningiomas or multiple schwannomas in one part of the peripheral nervous system. The recognition of mosaic phenotypes is important. Individuals with the mosaic form, even with a generalized phenotype, are less likely to have severe disease. They also have lower offspring recurrence risk than individuals with the nonmosaic form. The mosaic forms of neurofibromatosis provide a good example of the effects of somatic mutation. It is increasingly recognized that mild and unusual forms of many dominantly inherited disorders are caused by the same mechanism.