Relatively speaking, it’s OK to be kissing cousins
Thirty states ban them, society frowns upon them, comedians make fun of them, but the genetic consequences of first cousins marrying each other are not as severe as commonly thought, say UW genetics experts.
The general public believes offspring from such marriages are doomed to have genetic flaws such as mental retardation. “Because of widespread misconceptions about the actual level of risk to offspring, some of these pregnancies are terminated and other couples suffer a lot of needless anxiety,” says UW Genetic Medicine Clinic Manager Robin Bennett.
Bennett is the lead author of a paper published in the April issue of the Journal of Genetic Counseling that estimates the risk is quite low.
In a review of research results, the authors looked for the additional risk of significant birth defects (mental retardation or genetic disorders) rising from these unions. Although they emphasize that it is not possible to come up with one number for all populations, the authors estimate the additional risk ranges from 1.7 to 2.8 percent for first cousin unions. The paper’s senior author is Arno Motulsky, professor emeritus of medicine and genome sciences at the UW and a pioneer in medical genetics studies.
A task force from the National Society of Genetic Counselors has provided guidelines for counseling such couples. The consensus of the task force “is that beyond a thorough medical family history with follow-up of significant findings, no additional preconception screening is recommended for consanguineous (blood-sharing) couples.” They should, of course, be offered genetic screening tests that would routinely be offered to other couples of their ethnic group.
Doctors are seeing more cousin unions as a result of the rise in the immigrant population coming from Africa and the Middle East. In some of these societies, the authors note, cousin marriages are preferred and quite common. But because of the stigma, many such unions are kept secret. Better information and appropriate guidelines are especially needed by physicians and genetic counselors who work with these groups, the authors note.