Dementia is a dominate trait that is carried on both the X and Y chromosome. There is a larger chance of inheriting it someone's siblings has it as well. Depending on the other diseases someone has the chromosome that can be mutated is either chromosome 14 or chromosome 21.

Dementia usually affects elderly but it can affect young adults as well. Dementia is variably expressed. If someone lives in a dangerous environment it is easier to sustain a brain injury. Other diseases or brain injuries can cause dementia. If one lives in an low income country it'll be harder to afford treatment and that can affect one negatively.

Genetic Makeup of Dementia