Neurofibromatosis type 2 (NF2) is caused by a genetic mutation in a gene called NF2.
Genes are the instructions used to produce all human characteristics. A genetic mutation is a permanent change in the DNA sequence that makes up a gene.
Normally, the NF2 gene produces a protein called merlin (also called schwannomin). This protein plays an important role in regulating the growth of nerve tissue.
In someone with NF2, this gene is faulty. This results in the cells producing an incomplete protein, or no protein at all. Without an effective merlin protein, areas of uncontrolled growth (tumours) can develop in the nervous system.
The faulty gene that causes NF2 is found on chromosome number 22.
In around half of all cases of NF2, the mutated gene is passed down from a parent to their child.
The NF2 mutation is known as an autosomal dominant mutation. This means that only one parent has to have the faulty gene for a child to be at risk of developing the condition.
If either the mother or father has the faulty gene, there's a one in two chance that each child they have will develop NF2.
Males and females have the same chance of developing the condition.
In around half of NF2 cases, the mutation appears to happen spontaneously in either the sperm or egg just before conception. This is known as a sporadic mutation. It's unclear what causes it or whether anything increases the risk of it happening.
If you have a child who develops NF2 as a result of a sporadic mutation, it's highly unlikely that any further children you have will also develop the condition.
A person who develops NF2 sporadically can pass the condition to their children. The chances of this happening are usually the same as those for someone who inherited the condition (see above), unless they develop a form of NF2 called mosaic NF2 (see below).
About one third of people with NF2 just have a mild form of the disease, called mosaic NF2.
Mosaic NF2 develops when the mutation occurs after an embryo has been conceived. This is different from "normal" NF2, where the mutation is already present in the sperm or the egg before conception takes place.
As the mutation takes place later in the development of the embryo, not all the cells of the body are affected in mosaic NF2. Therefore, the symptoms of mosaic NF2 are milder and are often restricted to a certain area or side of the body.
As the genetic mutation isn't in all the cells of someone with mosaic NF2, the risk of having a child with NF2 is less than the usual 50%. However, if the child of someone with mosaic NF2 is affected, they'll have the more common form of the condition.