16 September 2009

Genetic testing

Disclosure of APOE genetic status
Dementia News (Alzheimer’s Australia): 4 September 2009
One of the genes that humans carry is the apolipoprotein E (APOE) gene. There are different forms of this gene, one of which is a risk factor for developing Alzheimer's disease. This particular variation is known as APOE ε4. But, having the APOE ε4 variation does not mean that the carrier will definitely develop Alzheimer’s disease. Many people who do not have the APOE ε4 variation develop Alzheimer’s and many people with Alzheimer’s do not have the APOE ε4 variation. For this reason, and probably because knowing that one has the APOE ε4 variation might lead to unnecessary anxiety, testing for the gene has been discouraged.

Researchers from the Boston University School of Medicine examined the effect of disclosing this genetic information. They randomly assigned 162 people without any symptoms of dementia, but who had a parent with Alzheimer’s disease, into two groups. Participants in one group were told whether or not they carried the APOE ε4 genetic variation; this information was withheld from participants in the other group. Participants were given follow-up investigations for symptoms of anxiety, depression, and test-related distress at six weeks, six months, and one year after the genetic test results had either been either given or withheld.

No significant differences were found between the disclosure and nondisclosure groups in changes in measures of anxiety, depression, or testrelated distress. The researchers also found no significant differences between the nondisclosure group and a subgroup of participants in the disclosure group who had been told that they were carrying the APOE ε4 genetic variation.

But, within the disclosure group, participants who had the APOE ε4 gene variation had significantly higher levels of test-related distress than did those who did not have the APOE ε4 gene variation.

In terms of clinically meaningful changes in psychological outcomes, there was an even distribution of people amongst the disclosure and nondisclosure groups, and amongst those with the APOE ε4 gene variation and those without. Participants who had high scores for anxiety and depression before testing showed similarly high levels of emotional distress after being told their APOE ε4 status.

In summary, adult children who were given their APOE ε4 status did not suffer any significant short-term psychological harm. Participants who learnt that they were APOE ε4-negative had reduced test-related distress than those who were APOE ε4-positive, and those with high levels of emotional distress before undergoing genetic testing were likely to have emotional difficulties after disclosure of their test results. It is important to bear in mind that this study had certain limitations. One of these was that only one genetic variation was studied. Another was that the study population was selective, that is, all participants had a similar ancestry and a known family history of Alzheimer’s disease. Those considering finding out their APOE ε4 status need to bear in mind that being APOE ε4-positive is only one of many risk factors for developing Alzheimer’s disease; many people with Alzheimer’s disease are APOE ε4- negative. Furthermore, there is no medical benefit in having this information.

Reference: Green RC, Roberts JS, Cupples LA, Relkin NR, Whitehouse PJ, Brown T, Eckert SL, Butson M, Sadovnick AD, Quaid KA, Chen C, Cook-Deegan R, and Farrer LA. 2009. Disclosure of APOE genotype for risk of Alzheimer's disease. New England Journal of Medicine 2009; 361:245-254.

See related Alzheimer's News story: Disclosure of results of genetic testing

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