Neurofibromatosis

By Katelynn Johnson and Katie Duvall

What Is It?

• Neurofibromatosis (NF) is a set of distinct genetic disorders that cause tumors to grow along various types of nerves

• It can affect the development of non-nervous tissues such as bones and skin.

• NF causes tumors to grow anywhere on or in the body.

Types of NF

• Neurofibromatosis 1: • Aka von Recklinghausen NF or Peripheral NF.• Occurring in 1:3,000 births, it is characterized

by multiple spots and neurofibromas on or under the skin.

• Enlargement, deformation of bones, and scoliosis may also occur.

• Sometimes, tumors may develop in the brain, on cranial nerves, or on the spinal cord.

Types of NF cont’d

• Neurofibromatosis 2 (NF2): • NF2 is also known as Bilateral Acoustic NF (BAN), is much

less frequent occurring in 1:25,000 births. • NF2 is characterized by multiple tumors on the cranial and

spinal nerves, and other lesions of the brain and spinal cord.

• Tumors affecting both of the auditory nerves are a classic sign.

• Loss of hearing, which begins in the teens or early twenties is generally the first symptom.

Types of NF cont’d

• Schwannomatosis: a rare form of NF that has only recently been recognized and appears to affect around 1:40,000 individuals.

• It is not yet understood as well as NF1 and NF2, and features may vary greatly between patients.

Symptoms

• 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 characterized by bilateral tumors on the eighth cranial nerve. The tumors cause pressure damage to neighboring nerves. To confirm NF2, a patient must have bilateral eighth nerve tumors and similar signs and symptoms in a parent, sibling, or child.

• 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.

Frequency-Internationally

• NF-1 occurs in approximately 1 of 2500-3300 live births.

• The carrier incidence at birth is 0.0004, • Gene frequency is 0.0002. • The probability of NF-2 is 1 case per 50,000-

120,000 population

Quality of Life

• Various neurologic abnormalities may occur such as acoustic nerve involvement, deafness, and gliomas of the optic nerve

• . Various tumors, such as astrocytoma, meningioma, intramedullary glioma, and ependymoma, occur with greater frequency.

• Tumors may cause increased intracranial pressure, seizure, ataxia, or cranial nerve abnormalities.

• Schwannomas are uncommon in patients with NF-1, but they can present on spinal nerve sheaths. However, in NF-2, they are the most common tumor, involving cranial and peripheral nerves.

Quality of Life cont’d

• Many individuals with neurofibromatosis have below average intelligence.

• Of patients with NF-1, 25-40% may have learning disabilities, while 5-10% may have mental retardation.

• Types of learning disabilities include neuromotor dysfunction and ADHD, as well as deficits in visuospatial processing.

Quality of Life cont’d

• Endocrinologic problems associated with neurofibromatosis are common.

• Short stature and growth hormone deficiency are more common in these patients than in the general population, although the exact probability is not known.

• Also, unusually early sexual development occurs in 3-5% of children who are affected, usually associated with an intracranial tumor.

Genetics!

• NF1 and NF2 are autosomal dominant genetic disorders. • Half of all cases are inherited from a parent who has NF1 or

NF2. However, half of all cases are not inherited. • The cases not inherited are caused by genetic mutation in the

sperm or egg cell. • Each child of a parent with NF1 or NF2 has a 50% chance of

inheriting the gene and developing NF1 or NF2. • The type of NF inherited by the child is always the same as that

of the affected parent. • However, the severity may differ from person to person within a

family.

Genetics cont’d

• Unaffected parents who have a child born with NF1 or NF2 because of a spontaneous mutation do not have a 50-50 risk in future pregnancies.

• Their chance for another child with NF1 is about the same as that of any couple in the general population approximately 1 in 7,000.

Genetics cont’d

• NF1 is located on chromosome 17; NF2 on chromosome 22.

• How inheritance works:• When an egg and sperm, each with 23 single

chromosomes, unite, a new cell is formed which contains the 23 pairs of chromosomes or 46 single chromosomes.

Genetics cont’d

• Thus, a person who has NF1 or NF2 makes two different kinds of reproductive cells.

• If the affected cell happens to be used in conception it will cause a child to have NF, and the would produce an unaffected child if it is the one that happens to be used.

• When a person with NF mates with an unaffected individual, there are four possible combinations of cells. Two will yield a child with NF1 or NF2; two will yield an unaffected child.

Genetics cont’d

Genetics cont’d

Treatment

• Treatments for both NF1 and NF2 are presently aimed at controlling symptoms.

• Treatment may include surgery, radiation, or chemotherapy.• For NF2, improved diagnostic technologies, such as MRI,

can reveal tumors as small as a few millimeters in diameter, thus allowing early treatment.

• Other options include partial removal of tumors, radiation, and if the tumors are not progressing rapidly, the conservative approach of watchful waiting.

• Genetic testing is available for families with documented cases of NF1 and NF2.

Research

• Several years ago, research teams located the exact position of the NF1 gene on chromosome 17.

• The product of the NF1 gene is a large and complex protein called neurofibromin. One portion of this protein is similar to a family of proteins called GAP.

• Scientists have demonstrated that GAP proteins play a significant role in tumor suppression in certain cancers.

• The similarity of the NF1 protein to GAP proteins suggests that the NF1 protein may have a similar switching role in the development of neurofibromas.

Research cont’d

• Scientists theorize that defects in the gene may tamper with the normal output of its protein and allow the irregular cell growth that may lead to tumor development.

• Intensive efforts have led to the identification of the NF2 gene on chromosome 22. The NF2 gene product is a tumor suppressor protein.

• Basic studies in molecular genetics may lead to nonsurgical or pharmacologic treatments aimed at slowing down or stopping tumors associated with the neurofibromatoses.

Research cont’d

• The Interinstitute Medical Genetics Research Program at the NIH Clinical Center conducts NF2 family history research.

• Using samples from some of the families, scientists have isolated and sequenced the NF2 gene and described two different patterns of clinical features. Researchers continue to investigate these samples to find some correspondence between them and mutations.

Organizations

• The Children’s Tumor Foundation• http://www.ctf.org/• National Cancer Institute• http://cancer.gov• Neurofibromatosis, Inc. (NF Inc.)• http://www.nfinc.org• Acoustic Neuroma Association• http://www.anausa.org