Given that my sister has some form of early on-set dementia, I have concerns about the heredity of conditions that cause dementia.
Apparently, early-onset dementia can be caused by mutations to four genes which are passed from parent to child. These mutations are autosomal dominant and only require one parent to pass them to the child. Even late-onset dementia has a genetic component. Individuals with Down Syndrome have a dramatically increased risk for dementia, specifically Alzheimer's. Despite the genetic component, it appears that not everyone who has the mutated genes ends up with any form of Alzheimer's. As a result, more research is needed.
Knowing the genes that are associated with any of the forms of Alzheimer's, scientists are able to provide tests to help identify those individuals at risk of developing the disease. The question now becomes one of deciding we should be tested or not to see if we have the genetic markers.
Is it worth getting tested? What is the impact of having a set of results which indicates a higher risk factor for something that may or may not happen?
NIH's Alzheimer's Disease Genetics Fact Sheet
Memory in Adults Impacted by Versions of Four Genes
The Nanney/Felts Family: Late-Onset Alzheimer's Genetics