Neurofibromatoses are a group of genetic disorders that cause tumors to form on nerve tissue. These tumors can develop anywhere in the nervous system, including the brain, spinal cord and nerves. There are three types of neurofibromatosis: neurofibromatosis 1 (NF1), neurofibromatosis 2 (NF2) and schwannomatosis. NF1 is usually diagnosed in childhood, while NF2 and schwannomatosis are usually diagnosed in early adulthood.
The tumors in these disorders are usually noncancerous (benign), but sometimes can become cancerous (malignant). Symptoms are often mild. However, complications of neurofibromatosis can include hearing loss, learning impairment, heart and blood vessel (cardiovascular) problems, loss of vision, and severe pain.
Neurofibromatosis treatment focuses on encouraging healthy growth and development in children who are affected by the disorder and on early management of complications. When neurofibromatosis causes large tumors or tumors that press on a nerve, surgery can reduce symptoms. Some people may benefit from other therapies, such as stereotactic radiosurgery or medications to control pain. A new medication is available to treat tumors in children, and other new treatments are being developed.
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There are three types of neurofibromatosis, each with different signs and symptoms.
Neurofibromatosis 1 (NF1) is usually diagnosed during childhood. Signs are often noticeable at birth or shortly afterward and almost always by age 10. Signs and symptoms are often mild to moderate, but can vary in severity.
Signs and symptoms include:
- Flat, light brown spots on the skin (cafe au lait spots). These harmless spots are common in many people. Having more than six cafe au lait spots suggests NF1. They are usually present at birth or appear during the first years of life. After childhood, new spots stop appearing.
- Freckling in the armpits or groin area. Freckling usually appears by ages 3 to 5. Freckles are smaller than cafe au lait spots and tend to occur in clusters in skin folds.
- Tiny bumps on the iris of the eye (Lisch nodules). These harmless nodules can't easily be seen and don't affect vision.
- Soft, pea-sized bumps on or under the skin (neurofibromas). These benign tumors usually develop in or under the skin, but can also grow inside the body. Sometimes, a growth will involve many nerves (plexiform neurofibroma). Plexiform neurofibromas, when located on the face, can cause disfigurement. Neurofibromas may increase in number with age.
- Bone deformities. Abnormal bone development and a deficiency in bone mineral density can cause bone deformities such as a curved spine (scoliosis) or a bowed lower leg.
- Tumor on the optic nerve (optic glioma). These tumors usually appear by age 3, rarely in late childhood and adolescence, and almost never in adults.
- Learning disabilities. Impaired thinking skills are common in children who have NF1 but are usually mild. Often there is a specific learning disability, such as a problem with reading or mathematics. Attention-deficit/hyperactivity disorder (ADHD) and speech delay also are common.
- Larger than average head size. Children with NF1 tend to have a larger than average head size due to increased brain volume.
- Short stature. Children who have NF1 often are below average in height.
Neurofibromatosis 2 (NF2) is much less common than NF1. Signs and symptoms of NF2 usually result from the development of benign, slow-growing tumors in both ears (acoustic neuromas), which can cause hearing loss. Also known as vestibular schwannomas, these tumors grow on the nerve that carries sound and balance information from the inner ear to the brain.
Signs and symptoms generally appear during the late teen and early adult years, and can vary in severity. Signs and symptoms can include:
- Gradual hearing loss
- Ringing in the ears
- Poor balance
Sometimes NF2 can lead to the growth of schwannomas in other nerves, including the cranial, spinal, visual (optic) and peripheral nerves. People who have NF2 may also develop other benign tumors.
Signs and symptoms of these tumors can include:
- Numbness and weakness in the arms or legs
- Balance difficulties
- Facial drop
- Vision problems or cataracts
This rare type of neurofibromatosis usually affects people after age 20. Symptoms usually appear between ages 25 and 30. Schwannomatosis causes tumors to develop on the cranial, spinal and peripheral nerves — but rarely on the nerve that carries sound and balance information from the inner ear to the brain. Tumors don't usually grow on both hearing nerves, so people who have schwannomatosis don't experience the same hearing loss as people who have NF2.
Symptoms of schwannomatosis include:
- Chronic pain, which can occur anywhere in the body and can be disabling
- Numbness or weakness in various parts of the body
- Loss of muscle
When to see a doctor
See your doctor if you or your child develop signs or symptoms of neurofibromatosis. The tumors associated with neurofibromatosis are often benign and slow growing.
Neurofibromatosis is caused by genetic defects (mutations) that either are passed on by a parent or occur spontaneously at conception. The specific genes involved depend on the type of neurofibromatosis:
- NF1. The NF1 gene is located on chromosome 17. This gene produces a protein called neurofibromin that helps regulate cell growth. The mutated gene causes a loss of neurofibromin, which allows cells to grow uncontrolled.
- NF2. The NF2 gene is located on chromosome 22, and produces a protein called merlin (also called schwannomin), which suppresses tumors. The mutated gene causes a loss of merlin, leading to uncontrolled cell growth.
- Schwannomatosis. So far, two genes are known to cause schwannomatosis. Mutations of the genes SMARCB1 and LZTR1, which suppress tumors, are associated with this type of neurofibromatosis.
Autosomal dominant inheritance pattern
Autosomal dominant inheritance pattern
In an autosomal dominant disorder, the altered gene is a dominant gene located on one of the nonsex chromosomes, called autosomes. You need only one altered gene to be affected by this type of disorder. A person with an autosomal dominant disorder — in this case, the father — has a 50% chance of having an affected child with one altered gene. The person has a 50% chance of having an unaffected child with two normal genes, known as recessive genes.
The biggest risk factor for neurofibromatosis is a family history of the disorder. About half of people who have NF1 and NF2 inherited the disease from an affected parent. People who have NF1 and NF2 and whose relatives aren't affected are likely to have a new gene mutation.
NF1 and NF2 are both autosomal dominant disorders, meaning that any child of a parent who is affected by the disorder has a 50% chance of inheriting the genetic mutation.
The inheritance pattern for schwannomatosis is less clear. Researchers currently estimate that the risk of inheriting schwannomatosis from an affected parent is about 15%.
Complications of neurofibromatosis vary, even within the same family. Generally, complications result from tumors that affect nerve tissue or press on internal organs.
Complications of NF1 include:
- Neurological problems. Learning and thinking difficulties are the most common neurological problems associated with NF1. Uncommon complications include epilepsy and the buildup of excess fluid in the brain.
- Concerns with appearance. Visible signs of neurofibromatosis — such as extensive cafe au lait spots, many neurofibromas in the facial area or large neurofibromas — can cause anxiety and emotional distress, even if they're not medically serious.
- Skeletal problems. Some children have abnormally formed bones, which can result in bowing of the legs and fractures that sometimes don't heal. NF1 can cause curvature of the spine (scoliosis) that may need bracing or surgery. NF1 is also associated with decreased bone mineral density, which increases the risk of weak bones (osteoporosis).
- Vision problems. Sometimes a tumor develops on the optic nerve (optic glioma), which can affect vision.
- Problems during times of hormonal change. Hormonal changes associated with puberty or pregnancy might cause an increase in neurofibromas. Most women who have NF1 have healthy pregnancies but will likely need monitoring by an obstetrician who is familiar with the disorder.
- Cardiovascular problems. People who have NF1 have an increased risk of high blood pressure and may develop blood vessel abnormalities.
- Breathing problems. Rarely, plexiform neurofibromas can put pressure on the airway.
- Cancer. An estimated 3% to 5% of people who have NF1 develop cancerous tumors. These usually arise from neurofibromas under the skin or from plexiform neurofibromas. People who have NF1 also have a higher risk of other forms of cancer, such as breast cancer, leukemia, colorectal cancer, brain tumors and some types of soft tissue cancer. Women who have NF1 should start screening for breast cancer at an earlier age than the general population.
- Benign adrenal gland tumor (pheochromocytoma). This noncancerous tumor secretes hormones that raise your blood pressure. Surgery is usually needed to remove the pheochromocytoma.
Complications of NF2 include:
- Partial or total deafness
- Facial nerve damage
- Vision problems
- Small benign skin tumors (skin schwannomas)
- Weakness or numbness in the extremities
- Multiple benign brain tumors or spinal tumors (meningiomas) requiring frequent surgeries
The pain caused by schwannomatosis can be debilitating and may require surgical treatment or management by a pain specialist.
Jan. 21, 2021