The neurofibromatosis (NF) are genetic disorders of the ...
The neurofibromatoses (NF) are genetic disorders of the nervous system. At this time two
distinct forms are known: NF1 and NF2. One baby in every four thousand is born in the
United States with NF1. It is one of the most common genetic disorders, affecting some
one hundred thousand americans. NF2 is less common and occurs in only one and every
forty thousand births. In both forms of NF severity of symptoms vary greatly.
The effects can be severely disabling, mildly disfiguring or can even go undetected.
Several other names for this disorder have been used in the past but recent advancements
in understanding the disorder made some of those terms obsolete.
NF1 was previously known as peripheral neurofibromatosis, or von Recklinghouasen’s
disease after the doctor who first described it in 1882. NF2 was called bilateral acoustic
nuerofibromatosis, central neurofibromatosis, or vestibular schwannoma.
NF is found in every racial and ethnic group throughout the world and
affects both sexes equally. Both neurofibromatosis1 and neurofibromitosis2 are caused
by abnormal genes. This disease cannot be "caught" from someone who has it already. .
A common early sign of NF1 is six or more tan spots on the skin. They are
called "cafe-au-lait" (French for "coffee with milk") spots. These spots are
often present at birth, and may increase in size and number with age. They
also may become darker. More than half of affected children have some signs
of NF1 by 2 years of age.
Benign tumors (lumps), under the skin or deeper, may appear at any age but
especially during adolescence. The tumors, which grow on nerves, are made
up of cells that surround nerves and other cell types, and are called
neurofibromas. An affected person may have any number of neurofibromas,
from none to hundreds. The tumors, which vary in size, may or may not be
painful. A person also may have a single neurofibroma without having NF.
Some tumors may grow on the optic (eye) nerves and in rare cases may
interfere with vision. Tiny tan or brown "Lisch nodules" (small tumors) often
appear on the iris (colored part of the eye), but these cause no trouble. They
usually show up around age 6 to 10 years and may help a doctor diagnose
NF1. NF2 is characterized by tumors that grow on what is referred to as the
8th cranial nerve (one of 12 pairs of nerves that enter or emerge from the brain). These
tumors often cause pressure on the acoustic (hearing) nerves, resulting in hearing loss.
Persons with NF2 also may develop other tumors of the brain or spinal cord, and
sometimes develop cataracts at an early age. Persons with NF2 have few, if any, cafe-au-
lait spots or tumors under the skin. Symptoms of NF2 may not begin until after puberty.
NF1 and NF2 are caused by two separate abnormal genes. The abnormal gene in each
form of NF can either be inherited from one parent who has the disorder or can result
from a new mutation (change) in the gene. Thus, NF can occur in a person who has no
family history of the condition. About 50 percent of NF1 and NF2 cases are caused by
new mutations. An individual with NF caused by a new mutation can have the same
variety of signs and symptoms as a person who inherited it from an affected parent.
Inheritance of the gene is "autosomal dominant", so that the child of a parent with NF has
a 50-50 chance of inheriting the NF gene and showing at least some signs of
neurofibromatosis sooner or later. The child also has a 50-50 chance of inheriting the NF
gene's normal partner (since genes come in pairs) and remaining free of NF.
In most cases of NF1, symptoms are mild and affected individuals live a normal life.
Some individuals have many skin neurofibromas (lumps on the nerves) on the face and
body. Neurofibromas also can grow inside the body. Neurofibromas may increase during
puberty and pregnancy because of hormonal changes. Scoliosis (a progressive curvature
of the spine) is common in NF and can begin at an early age.
Some children with NF1 have learning disabilities, speech problems and/or seizures, and
may be hyperactive. Some affected children and adults have large heads. This usually
does not reflect a serious medical problem. Eye tumors may cause bulging of the eye, or
visual difficulties. A variety of bone defects may be present at birth, including bowing of
the legs below the knee. Children with NF1 appear to be at increased risk of certain
cancers, though these are rare.
Symptoms of NF2 may include hearing loss, ringing in the ears, dizziness, balance
problems, headaches or seizures. Early removal of small auditory nerve tumors
sometimes helps to preserve hearing. A diagnostic technique called magnetic resonance
imaging has improved early diagnosis of tumors.
There is no way of predicting the degree of severity either form of NF will have.
As with many other genetic disorders, psychological problems may occur in NF patients.
Some become lonely and withdrawn because they feel "different" from others. They may
be concerned about whether or not to have children. They often are worried about further
complications.
There is no cure for NF, but there are ways to treat some of its effects. Painful or
disfiguring skin tumors can be removed by surgery. However, they may grow back.
Tumors on the eye or ear nerves sometimes can be removed or treated with radiation or
chemotherapy. Scoliosis may be treated by surgery, a brace, or both.
There are a number of multidisciplinary NF clinics throughout the United States that
address specific medical concerns and routine NF-related health care issues of
individuals and families affected by NF.
Recent research advances may lead to improved treatments for NF1 and NF2.
Researchers have found the gene for NF1 on the 17th chromosome, and the gene for NF2
on the 22nd chromosome. Scientists are using this information to develop precise tests
aimed at definitively diagnosing these disorders, even before an individual develops
symptoms. Early diagnosis should allow doctors to treat symptoms sooner, possibly
preventing some serious complications. Researchers also have identified the protein
products these genes dictate, and are beginning to understand the functions of these
proteins. This may lead to the development of drugs to treat some of the symptoms of
these disorders.
In rare instances, cases of NF occur that are not consistent with NF1 or NF2, or have
features of both. Very little is known about these rare conditions.
NF1 and NF2 usually can be diagnosed on the basis of signs and symptoms alone.
However, genetic testing is available and can be used in some cases for prenatal
diagnosis and to help evaluate individuals with a family history of these disorders who do
not yet show symptoms.
There are two major types of genetic testing. The first is called linkage analysis, and is
used for families in which there are more than two affected members. Linkage analysis
requires blood tests on multiple family members, and it tracks the chromosome that
harbors the disease-causing gene through two or more generations. In general, linkage
testing is more than 95 percent accurate in predicting whether or not an individual has
NF. The second test, direct gene mutation analysis, does not require the testing of other
family members. However, it is not useful in all cases, since it misses about one-third of
the mutations that cause NF1 and NF2. These methods are supposed to improve over the
next few years. NF is not a rare disorder, it is the most common neurological disorder
caused by a single gene. NF can lead to disfigurement; blindness; deafness; skeletal
abnormalities; dermal, brain and spinal tumors; loss of limbs; malignancies; and learning
disabilities. The NF gene has been implicated in the development of several of the most
common and most serious human cancers.
Because NF1 and NF2 are genetically-determined disorders which affect more than
100,000 Americans; this makes NF more prevalent than Cystic Fibrosis, Hereditary
Muscular Dystrophy, Huntington’s Disease, and Tay Sachs combined.
To be diagnosed with NF1 you must have two of the following symptom’s:
six or more café au lait macules over 5 mm in greatest diameter in prepubertal
individuals and over 15 mm in greatest diameter in postpubertal individuals,
two or more neurofibromas of any type or one plexiform neurofibroma,
freckling in the axillary or inguinal regions, optic glioma ,
two or more Lisch nodules (iris harmartomas) ,and a distinctive osseous lesion such as
sphenoid dysplasia or thinning of long bone cortex with or without pseudoarthrosis .
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