It is necessary to draw a distinction between dementia and Alzheimer's disease.  "Dementia" refers to a set of symptoms displayed due to loss of brain function that can be brought on by various conditions and illnesses.  There are reversible and non-reversible types of dementia.  Alzheimer's diseas' is a (nonreversible) type of dementia, and is the most common type.  In regards to your concerns for your own risk of developing Alzheimer's-type dementia, it is important to understand the difference between the two categories of Alzheimer's disease:  young (or early) onset and late onset.  Young onset affects people who are usually younger than 65 or even as young as the late-thirties.  "Familial" early onset is an inherited form of the disease that is due to genetic mutations.  This sub-type has a very strong history in families, and the odds of future generations developing the illness are significantly higher than the odds for someone without such a family history.  The late onset category of Alzheimer's disease,  also known as "sporadic" Alzheimer's disease is also thought to have a genetic predisposition component to it (though this component differs from that seen in the familial early-onset version).  Only about 20% of families with a history of sporadic Alzheimer's disease are at greater risk for developing the illness in future generations. It is important to understand that having the genetic predisposition for the disease does not necessarily mean an individual will, in fact, go on to develop the disease. And, while genetics are believed to play some role in who develops Alzheimer's disease, but it is not the only factor.  At this time, it is thought that environment and lifestyle choices also play a part. If you have any concerns and/or are experiencing symptoms, it is recommended that you discuss them with your primary care physician.