Genetic testing can help individuals learn if their family has a known FTD genetic variant.
The results are more conclusive if the family member with symptoms of FTD is tested first. Once the genetic cause for their FTD is known, other relatives can decide to test for that specific genetic variant. If the person with FTD is unwilling or unable to be tested, family members without symptoms could still get tested for all the known genes associated with FTD, but the results may not be conclusive.
A family history of FTD or related conditions is a strong indication of a genetic cause. However, a small number of people with no family history of FTD have an identifiable genetic cause, which could be passed on to the next generation. This can happen if:
- The family history is limited or not well known
- Previous conditions in the family were incorrectly diagnosed
- Information about family relationships is inaccurate or incomplete
- A relative passed away before symptoms developed or a diagnosis was made
- The person with FTD is the first person in the family to have a genetic variant. This is known as a de novo variant. Although not inherited, de novo variants can still be passed to the next generation. Therefore, AFTD recommends that people diagnosed with FTD who have no family history consider genetic counseling
All known forms of genetic FTD are inherited in an autosomal dominant fashion, meaning that each child (or sibling) of an affected person has a 50% chance of inheriting the FTD-causing genetic variant. (While the diagram above shows a couple with four children - two unaffected, two affected - it is important to note that each child is a new “event,” with an equal chance to inherit, or not inherit, the FTD-causing variant. In other words, every time a person with genetic FTD has a child, there is a 1 in 2 chance of passing along the FTD-causing variant to that child.)