Is family history a big risk factor for Alzheimer's?

When a family member has Alzheimer's disease, people often wonder about their own chances of developing the disease. Family history is indeed a risk factor for Alzheimer's. If you have a parent or sibling with Alzheimer's, you're more likely to develop the disease than someone who does not have a first-degree relative with this condition. Risk rises further if you have more than one first-degree relative with Alzheimer's. But while heredity is a major factor in a small number of families, for most people, genetics seem to play only a minor role or none at all. As scientists continue to mine new research on genes associated with late-onset Alzheimer's, though, our current understanding may shift.

Genetics is most important in families with a history of early-onset Alzheimer's (occurring before age 50) stretching back for several generations. (The early-onset form accounts for less than 1% of all Alzheimer's cases.) Mutations in three genes are known to cause this type of Alzheimer's: amyloid precursor protein gene (APP), presenilin 1, and presenilin 2. All three genetic mutations increase the production of beta-amyloid, which is deposited in the plaques found in Alzheimer's disease. Excessive amounts of beta-amyloid fragments are thought to be toxic to nerve cells.

If one parent has any of these mutations, each child has a 50% chance of inheriting the mutated form. A child who inherits the mutated gene will inevitably develop early-onset Alzheimer's disease.