Neurofibromatosis Type 2 (NF2)
Neurofibromatosis Type 2 (NF2) is a genetic disorder in which tumors called schwannomas are found on nerves in the inner ear. These tumours can also develop on nerves in other areas of the brain or spinal cord. Persons with NF2 are at high risk for developing brain tumors and most of all affected individuals develop tumors on both nerves to the ears (also called the eighth cranial nerve). This nerve has two portions: the acoustic (hearing) which carries information about sound to the brain and the vestibular nerve which carries balance information to the brain.
Signs and symptoms usually appear during adolescence or in the early 20s. The most common early symptoms are hearing loss, ringing in the ears (tinnitus), and loss of balance caused by tumors growing on the nerve from the ear to the brain. If tumors are growing in other parts of the brain, signs and symptoms vary according to location and can include seizures, changes in vision or sensation, and fluid build up in the brain. Some people with Neurofibromatosis 2 also develop cataracts (clouding of the lens in the eye) at an early age.
Although tumors on the eighth cranial nerve are most common, persons with NF2 can develop tumors on other nerves also. These tumors are called schwannomas because they arise from the Schwann cells. Schwann cells support and protect nerve cells and provide nerves with the insulation they require to conduct information. The symptoms of a schwannoma will depend on its location in the body.
In addition to schwannomas, persons with NF2 occasionally develop other sorts of tumors which grow on the coverings of the brain and spinal cord. These tumors (called ependymomas and meningiomas) may cause many different kinds of neurological symptoms depending on their location. As with schwannomas, a physician may detect signs of a tumor on a detailed neurological examination before a patient can detect symptoms in everyday life.
NF2 individuals can develop a special sort of cataract, know as a juvenile posterior sublenticular opacity or have other problems with the eyes. Since cataracts are likely to impair vision if not removed, it is important for all persons with NF2 to have a detailed eye exam by a specialist familiar with NF2.
Onset is unique to each individual with NF2. Some get their first symptoms during late teenage years or in their early 20’s. A few people develop symptoms in childhood and some do not have problems until their 40’s. Neurofibromatosis type 2 is far less common than neurofibromatosis1 affecting about 1 in 40,000 births.
Mutations in the NF2 gene cause Neurofibromatosis 2. Normally, the NF2 gene produces a protein that inhibits cell division particularly in the specialized cells that insulate the nerve cells of the brain and spinal cord (Schwann cells). The mutated gene produces an abnormal protein that cannot properly control cell division, leading to tumor development.
How do people inherit NF2?
NF2 is inherited in an autosomal dominant pattern which means only one copy of the altered gene is necessary to cause the disorder. In about half of all cases, an affected person has one affected parent. The other half result from new mutations which means that neither parent is affected. All individuals have a 50% chance of passing the disorder on to their children. NF2 affects both genders equally and is located on the 22 chromosome.
What other names do people use for NF2?
- BANF- Bilateral Acoustic Neurofibromatosis
- Bilateral Acoustic Neurofibromatosis
- Central NF2 Neurofibromatosis
- Familial Acoustic Neuromas
- Neurofibromatosis Type 2
- Neurofibromatosis Type II
- Schwannoma, Acoustic, Bilateral
What treatments are available for NF2?
Presently, the only treatments available for the tumors of NF2 are surgery and radiation therapy. Most individuals with NF2 require at least one operation during their lifetime. Since these tumors lie on nerves and or near the brain and spinal cord, their surgical removal is not without risk. Surgery in small and delicate places may cause further injury to nerves and further neurological problems. For these reasons an attempt should be made to postpone surgery until the risk of further damage by the tumor itself out weights the risk of the surgical damage. When surgery is no longer an option for a particular person because of their medical problems or the size or location of a tumor, radiation therapy may be considered. As with any surgery, radiation therapy has both risks and benefits which must be carefully considered.
There are two very common tests that may be helpful in defining its nature and progression. An MRI (magnetic resonance imaging) scan and audiometry (a hearing test). MRI scans are used to visualize the anatomy of the body. They are most commonly taken of the brain, but may also be used to “see” the spine or nerves in the arms and legs.
MRI (Magnetic Resonance Imaging)
To scan the patient has to lie very still on a small bed which slides into a donut-shaped machine. Magnets are activated around the patient. At some point the patient may be injected with a dye that enhances the appearance of some parts of the brain. No x-irradiation is used. Although MRI scans can show a very detailed structural information (what your body looks like), they cannot show functional information (how well your body is working). Audiometry test how well the hearing portion of the eighth cranial nerve is working. To undergo audiometry a person puts on earphones in a soundproof room.
Sounds of different intensity and frequency are given to each ear and the ability to detect them is monitored. Information from the audiometry augments the structural information form an MRI.
- If a person has NF2 but no one else in her family has NF2 what are the chances that her child will be affected?
50-50, although new genetic alterations are common in NF2 they do not alter the risk of passing along the gene.
- What is the most common problem that people with NF2 have? What are other problems that people with NF2 have?
The most common clinical problems are tinnitus (ringing in the ears), hearing loss and balance dysfunction. Anatomically, the most common problem is tumor on the nerve to the ear (the eighth cranial nerve), also know as vestibular schwannoma or acoustic neuroma. Other less common problems include spinal tumors, skin tumors and cataracts.
- Do all people with NF2 become deaf? When a person with NF2 loses his hearing does it occur suddenly or gradually?
No, some people with NF2 retain hearing, especially on one side. Hearing loss may occur gradually over months or years, or suddenly over a day or week.
- Do people with NF2 ever develop NF1?
No. These two disorders appear to be genetically and functionally distinct. The NF1 defect lies on Chromosome 17 where NF2 lies on Chromosome 22.
- Are all NF2 associated brain tumors immediately treated?
Not all NF2 associated tumors are treated as soon as they are detected because many are quite slow growing and may remain for years without causing significant problems. Since treatment may cause neurological damage on its own, it is often more prudent to learn the natural history of a tumor before operating on it.
- How are NF2 tumors different from cancer?
The tumors of NF2 are slow growing and do not spread to other areas of the body.
- Is there a cure for NF2?
Although great advances are being made by researchers in the NF field, there is no cure?yet! NF1 and NF2 care is aimed at treating symptoms at present. Several clinical trials are in progress at the National Cancer Institute in the States. These trials are aimed at stopping the progression of tumor growth.
- Is there a blood test to detect NF2?
A blood test has become available to detect a second family individual with NF2. This means there is an arduous process in order to find the first family member who is diagnosed with NF2 but once the process has been done in a family; it is much easier to find other affected family members with a blood test. One must remember that the blood test will not determine how affected a person with the defect will be.
- Do people with NF2 have a higher incidence of becoming senile?
There is no evidence that individuals with NF2 become “senile” more often than the general population.
- If I have NF2 will I die at a young age because of this disorder?
In past studies, the average life span of individuals with NF2 was considerably shortened compared to people without NF2. With improvements in diagnosis, monitoring and surgical techniques this data may not be applicable to individuals living now.
- Do prenatal factors cause or influence the course of NF2?
There is evidence that exposure of the father to toxic chemicals before conception may increase the incidence of new cases of NF1 and other tumors. This has not been looked at for NF2. In utero exposures would not be expected to alter the probability that an infant would be born with NF2, but it is unknown if they may alter the course if the fetus is already affected with NF2.
- If a child is at risk for NF2, at what age should MRI scanning begin and at what age can it safely be stopped?
Since the average age of onset of symptoms in NF2 is late teens and early twenties, scanning has traditionally begun at that time. It is not clear if earlier studies would be beneficial. It is also not known at what age monitoring can safely be stopped. Although there are NF2 affected individuals who do not have symptoms until their 50’s it is possible that “silent” tumors would always be seen on an MRI scan earlier.
- What effects do puberty, pregnancy and menopause have on NF2 tumours?
One of the tumor types associated with NF2 (the meningiomas) is known to frequently be responsive to female hormones in its non-genetic form. There are also individual reports of acceleration of tumor growth in women with NF2 during exposures to female hormones. However, in the largest study to date of women with NF2, no significant changes were seen in the patients of their tumors during 100 individual pregnancies.
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