Should I test my family members for vestibular schwannoma?
This inevitably becomes a burning question to all patients diagnosed with a vestibular vestibular schwannoma. Should I have my family tested? Is my condition genetic or hereditary, and did I inherit it from my parents? Can I transmit it to my offspring? What is the risk of my other siblings having it? Should I have children? These are only a few questions that may arise, and hopefully, I can give some guidance on the road forward.
About the risk of my vestibular schwannoma being hereditary.
Vestibular schwannoma or acoustic neuromas are benign growths that occur at an incidence of 2 per 100 000 per year. It can occur in children but is more common in the elderly.
When ordering an MRI, usually for a non-related reason, a solitary (single) vestibular schwannoma may be an incidental finding. Of all vestibular schwannomas diagnosed, 95% appear as solitary tumours and are non-genetic.
In less than 5% of cases, a genetic predisposition may be present. In most cases, this diagnosis may lead to anxiety and uncertainty. Patients would like to know the risks are for their children or other direct family members, to develop this condition.
The related genetic conditions.
Neurofibromatosis type 2 (NF2) and schwannomatosis are two genetic conditions responsible for the development of vestibular schwannoma. These genetic conditions may be responsible for less than 5% of all vestibular schwannomas. Yet, it is still justified that patients ask about hereditary and the risk of transmitting the disease.
What is genetic testing, and who is INVITAE?
Genetic testing is a medical test of gene material, genes, chromosomes and proteins to establish hereditary. Its main aim is to confirm suspected genetic conditions and help determine a patient’s risk of developing and passing on a genetic disorder to children and siblings.
INVITAE is a company that conducts an array of genetic testing utilised by many doctors worldwide. Their main office and laboratory are based in San Francisco in the USA. Their mission is to bring comprehensive genetic information into mainstream medicine to improve healthcare for billions of people.
Neurofibromatosis type 2 (NF2).
Neurofibromatosis type 2 (NF2) is a genetic disorder predisposing affected individuals to develop benign central nervous system tumours, including the spinal cord. These tumours include vestibular schwannomas, typically bilateral, meningiomas, ependymomas, and, very rarely, astrocytomas. Vestibular schwannomas typically develop before 30 years of age.
Children present with single nerve involvement( neuropathy), which progresses to the involvement of numerous nerves (polyneuropathy). The presenting symptoms of vestibular neuroma specifically include hearing loss, tinnitus, balance problems, vertigo and facial numbness/weakness.
It is estimated that the prevalence of NF2 is 1 in 33,000 individuals. It is inherited in an autosomal dominant way, meaning that you only have to get an abnormal gene from one of your parents in order to develop the condition. 50% of cases are inherited from an affected parent, and 50% result from a spontaneous mutation. In 25%-30% of apparently sporadic cases, the affected individual has constitutional mosaicism for an NF2 pathogenic variant.
Schwannomatosis
Schwannomatosis is a genetic disorder where patients develop multiple schwannomas throughout their bodies, usually presenting with pain. Other symptoms include numbness, tingling and weakness, mainly related to nerve involvement.
Schwannomatosis patients usually develop vestibular schwannomas after the age of 30.
Before developing vestibular schwannomas, NF2 can be difficult to distinguish from schwannomatosis. The development of vestibular schwannomas, usually by age 30, is a hallmark of NF2, whereas, in schwannomatosis, vestibular schwannomas are absent.
The clinical history, management, mortality and genetic risks of patients with schwannomatosis are different from NF2. It is of clinical importance to distinguish between them. One can add a test for the schwannomatosis gene at no cost when ordering an NF2 panel from INVITAE.
Who should consider testing?
Consider the analysis of the NF2 gene if you have a personal or family history of the following lesions,
- Vestibular schwannomas
- Gliomas
- Multiple meningiomas
- Neurofibromas
- Posterior subcapsular lenticular opacities
- Cataracts
How accurate are these tests?
According to INVITAE, the mutations picked up in the NF2 gene occur in greater than 92% of familial cases and approximately 70% of simplex cases (i.e., a single occurrence in a family).
What does testing involve?
Currently, testing cannot be performed in South Africa. Blood, saliva, sputum or other DNA samples will be collected locally and then sent overseas for analysis. INVITAE testing is performed in the USA. The turnaround time of the test is 21 days.
It is advised to consult with a geneticist before requesting testing. The geneticist will help the patient in interpreting the results and explaining the significance of findings as it relates to treatment and further management, also of family members and potential future pregnancies.
If you have any questions or require a referral to a geneticist, kindly contact my rooms` for further information.
