Genetics in Alzheimer’s Disease

Is Alzheimer’s inherited? In this video, John Hardy, Ph.D., of the National Institute on Aging, explains how genes cause disease, the difference between deterministic and risk genes, and which genes of each type are implicated in early-onset and late-onset Alzheimer’s.

Risk genes increase the likelihood of developing a disease, but do not guarantee it will happen. Scientists have so far identified several risk genes implicated in Alzheimer’s disease. The risk gene with the strongest influence is called apolipoprotein E-e4 (APOE-e4). Scientists estimate this gene may be a factor in 20 to 25 percent of Alzheimer’s cases.

Deterministic genes directly cause a disease, guaranteeing that anyone who inherits them will develop the disorder. Scientists have discovered variations that directly cause Alzheimer’s disease in the genes coding three proteins: amyloid precursor protein (APP), presenilin-1 (PS-1) and presenilin-2 (PS-2). When Alzheimer’s is caused by these deterministic variations, it is called “familial Alzheimer’s disease,” and many family members in multiple generations are affected. Symptoms nearly always develop before age 60, and may appear as early as a person’s 30s or 40s. Deterministic Alzheimer’s variations have been found in only a few hundred extended families worldwide. True familial Alzheimer’s accounts for less than 5 percent of cases.

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