Most people who develop Alzheimer's disease do not have a history of the disease in their families. But a family history of Alzheimer's disease (one or more members of a family have had the disease) does increase other family members' risk of developing Alzheimer's.
Some people who have the gene for apolipoprotein E-4 (ApoE-4) may be more likely to develop the disease, but the presence of this gene does not predict with certainty whether a person will have Alzheimer's disease. Many people who have the ApoE-4 gene do not get Alzheimer's disease, and many people who do not have the gene still develop the disease.
In some families with a history of Alzheimer's disease (less than 5% of cases), the disease has been linked to defects in specific genes. There is a 50% risk that these genes will be passed on. A person who inherits the genetic defect will almost always develop Alzheimer's disease. This rare form of the disease is called autosomal dominant Alzheimer's. Because it tends to develop earlier in life than is typical, often by age 50, it is also referred to as early-onset Alzheimer's disease.
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