Inaccurate information, rather than genetic conditions, may pose a greater threat to cousins who want to have children together. It is generally believed that serious genetic disorders are common among children of first cousins. Data published in the April issue of the Journal of Genetic Counseling show that such risks, while real, are relatively small.
A task force assembled by the National Society of Genetic Counselors (NSGC) that included genetic counselors, physicians and epidemiologists together then published guidelines for advising cousin couples after evaluating the risks and reviewing the data from six major studies from 1965 to August 2000. What the authors were looking for was the additional risk of significant birth defects (including mental retardation or genetic disorders) as compared to the 3 to 4 percent risk faced by the general population of couples. Although it's not possible to come up with one number for all populations of consanguineous couples, the authors estimate the additional risk of deleterious genetic conditions range from 1.7 to 2.8 percent for first cousin unions.
The actual total risk for a child of such couples is around 6 percent. This means that there is a high likelihood (94 percent) that the child will be healthy. Due to widespread misconceptions about the actual level of risk to offspring, some of these pregnancies are terminated and other couples suffer needless anxiety. In 30 states, including the WWAMI states Washington, Wyoming, Montana and Idaho, it is illegal for cousins to marry.
Robin Bennett, genetic counselor and manager of the UW Medical Genetics Clinic, is lead author of the paper and president-elect of the National Society of Genetic Counselors. Arno Motulsky, professor emeritus of medicine and genome sciences, is the senior author.