Genetic testing can reveal proclivity for Alzheimer's

ON CALL

September 28, 1993|By Dr. Simeon Margolis | Dr. Simeon Margolis,Contributing Writer

Q: I am concerned that I may acquire Alzheimer's disease because both my father and his brother developed the disease when they were in their 80s. Is there any test that can determine my risk for Alzheimer's disease?

A: Recent research has offered a promising new way to estimate the likelihood of developing Alzheimer's disease in families in which the disorder has a late onset (begins after the age of 65). The method is based on the inheritance of a cholesterol-carrying protein called apoprotein E (apoE), that is coincidentally liked to Alzheimer's disease.

There are three genetic variants of apoE, referred as E2, E3 and E4, each coding for a lightly different protein. Every individual inherits two copies of the apoE gene. For example, people who have two genes for E3 will make only the E3 form of the apoprotein, while those who have one gene for E3 and one for E4 will manufacture both the E3 and E4 variants of the apoprotein. Most common is the 3/3 genotype which occurs in about 60 percent of the population.

A study of 42 families with late onset Alzheimer's disease found that the disorder occurred more often in those who had inherited at least one copy of the E4 variant.

The likelihood of developing Alzheimer's disease by age 75 in members of these families was 20 percent in those with no copies of E4, 45 percent in those with one copy, and 90 percent when two copies of E4 were present.

It is not yet clear whether the E4 protein itself causes Alzheimer's disease or if it's just a case in which the E4 gene is closely linked to the gene for another protein that actually produces Alzheimer's disease.

But before you have the test, you should decide whether such information would be helpful or harmful to you.

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