Genetics

The three forms of neurofibromatosis (NF), NF1, NF2 -Related Schwannomatosis and Schwannomatosis, are genetic conditions.

The genes involved in NF are important in controlling and stopping cell growth and division.

If there is a gene mutation that causes the gene not to function correctly, cells continue to divide and a tumour forms.  Therefore, the genes are referred to as ‘tumour suppressor genes’ because in their normal form they stop uncontrolled cell division.

Inheritance

NF can occur in any family.

About 50% of people who are diagnosed with NF1 or NF2 have inherited the condition from one of their parents. The other half of those diagnosed are considered to be the result of a new or spontaneous mutation of the gene.

If a child inherits the NF gene, they will always show symptoms of the condition, however, it is difficult to predict the severity, especially in NF1. This is called ‘variable expressivity’. If a child of someone with NF does not inherit the NF gene, they do not have NF and therefore cannot pass it on to their future children. That is to say, NF cannot “skip a generation.”

The inheritance of schwannomatosis is less well understood and appears to involve more than one gene. Regardless, the majority of cases of schwannomatosis appear to occur by chance and are not inherited.

Segmental/Mosaic NF

Some people only have features of NF1, NF2 or Schwannomatosis on only one part of their body, although this is much less common. These people may be diagnosed with segmental or mosaic NF1, NF2 or Schwannomatosis. For people with this diagnosis the chance of passing on the condition to their children may be as low as it is for the general population, but this depends on which part of the body is affected. If the affected area includes the ovaries or testes, then the chance could be as high as 50%.

Genetic Counseling

Genetic counseling can help families affected by NF to talk about and understand; a new diagnosis, the decision-making process in regards to starting a family, having another child, genetic testing and health management for those who have the condition.

Genetic Testing

While the diagnosis of NF1 and NF2 is usually based on clinical findings, there are now genetic tests available for people affected by or with a family history of NF. However, clinical diagnosis remains the standard for diagnosing NF.

For this reason, genetic testing is mainly used for families who want to pursue pre-implantation genetic diagnosis (PGD) or a prenatal diagnosis. As the technology becomes more accessible, choices for genetic screening will expand.

Click here to learn more about the BC Provincial Medical Genetics Program.