Neurofibromatosis: An Autosomal Dominant Genetic Disorder
written by: Nirvanagrewal•edited by: Paul Arnold•updated: 6/27/2009
Neurofibromatosis is an autosomal dominant genetic disorder that produces non-cancerous tumors in the nerve cells and along the skin. The problems are caused by the growths compressing nerves and tissues.
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Types of Neurofibromatosis
Neurofibromatosis is a condition affecting nerves and skin in any organ system of the body. There are two main types of Neurofibromatosis but a rare third type also exists.
Two main types are:-
1)Neurofibromatosis 1 - or peripheral neurofibromatosis
2)Neurofibromatosis 2 - or central neurofibromatosis
3)Schwannomatosis is a rare type that produces multiple benign tumors in the Schwann cells of peripheral nerves.
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Causes of Neurofibromatosis
Neurofibromatosis 1: It is caused by a mutation of the NF1 gene and it is transmitted on chromosome 17.
Neurofibromatosis 2: It is caused by a mutation of the NF 2 gene and is passed on to the next generation on chromosome 22.
The NF 1 gene codes for an enzyme called Neurofibromin. It is a tumor suppressor protein and a mutation can render it inactive or defective, allowing the rapid growth of tumors.
The NF 2 gene codes for a protein known as Merlin, which also acts as a tumor suppressor.
Being an autosomal dominant genetic disorder means that only one copy of the mutated gene needs to be passed on for the disease to be apparent. An NF 1 or NF 2 parent and an unaffected parent will have a 50% chance of passing the condition onto their children.
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Signs and symptoms
In Neurofibromatosis 1, multiple areas of hyper pigmentation of the skin appears a few days after the birth. These spots are known as “café au lait". Large numbers of benign tumors occur above and under the skin surface that may become malignant later in life.
In Neurofibromatosis 2, benign tumors occur in the cranial and spinal nerves. The most common nerve affected in NF 2 is the eighth cranial nerve and therefore the patient may experience hearing loss, and loss of balance.
Due to the nervous system being affected many children suffering with NF may experience learning disabilities. They will have below average intelligence and some children may become mentally retarded.
Bones are also affected due to the development of tumors on bone tissue. As a result bowing of the long bones, scoliosis, and bone hypertrophy may occur.
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Diagnosis and treatment
Diagnosis is carried out on the basis of the presence of one or more of the signs given below:
Presence of café-au-lait spots
Presence of neurofibromas
Family history of NF
Freckling on the armpits and groin.
Treatment includes surgical removal of the benign neurofibromas. High energy X-rays can also be used to shrink the tumors.
Children are referred to specialists to correct other disorders associated with NF - such as auditory dysfunction, bone abnormalities, ophthalmic abnormalities, and learning disabilities.