Is Alzheimer's Disease Inherited?
Every illness in life is a product of genes and environment. As a result, all illnesses are, to some extent or another, inherited. In some families, Alzheimer's disease occurs quite commonly. As a rule, for research purposes, we would define Alzheimer's disease as likely inherited when more than one first-degree relative (e.g. a brother or a sister, but not a cousin) is affected in more than one generation. In general, of all people who come to a memory clinic with Alzheimer's disease, only about 5% will have the strongly inherited form.
Figure One. A family tree of an inherited, late-onset Alzheimer's disease
Inherited, late-onset Alzheimer's disease Every row represents a new generation. Boxes are men; circles are women. Diagonal line through the circle or square means that the person has died. An open (white) circle or box shows no disease. A shaded circle or box means that the person has/had Alzheimer's disease).
Looking at Figure 1, A, B and C are all siblings in their early to mid 50s. Their father has just been diagnosed with Alzheimer's disease at the age of 80. His sister also had Alzheimer's disease, as did their father (the grandfather of A, B and C), their father's sister and their father's mother (the great grandmother of A, B and C). For each of the siblings A, B, or C that lives to age 80, their individual risk for late-onset Alzheimer's disease is about one in two.
For most people, however, there is no more than one person affected in each generation. So for example, an 80-year-old man who is diagnosed with Alzheimer's disease, who had no brothers or sisters affected, would not have an inherited form of the disease. However, the risk to any of his children would be about double the average risk. In this part of the Western world, the average risk is about 10%, so the risk if one parent is affected is about 20%. An example of a family tree with this level of increased risk is shown in Figure 2.
Figure Two. The risk associated with sporadic , late-onset Alzheimer's disease.
Sporadic, late-onset Alzheimer's disease Every row represents a new generation. Boxes are men; circles are women. A diagonal line through the circle or square means that the person has died. An open (white) circle or box shows no disease. A shaded circle or box means that the person has/had Alzheimer's disease.
In this example, A, B, C and D are the adult off-spring in their mid to late 50s, of a father who was just diagnosed with Alzheimer's disease in his 80s. The only other people affected in the family are his aunt (who is not a first degree relative) and his sister-in-law (who is not a blood relation). The risk to A, B, C and D is increased for each of them from the usual population risk (1 in 10) to about twice that (1 in 5).
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About Dementia > Alzheimer's Disease > Prevention