How Safe Is It to Date a Cousin?

A woman wrote to Henry Louis Gates Jr. to ask his advice on dating a distant cousin.  In his answer he also addresses first cousin relationships:

For instance, as of 2012, first-cousin marriages were illegal in 25 American states and restricted in six others (e.g., allowable among people who are both over the age of 50, and presumably unable to reproduce).

Occasionally on my genealogy TV series on PBS, Finding Your Roots, guests have found unexpected cousin marriages in their family trees. [A]ction star Michelle Rodriguez learned that her Puerto Rican forebears preferred to marry first cousins in order to preserve a high degree of European ancestry (and lighter complexions) in their offspring.

Cousin marriage figured into the life of Henrietta Lacks, the black woman whose cancer cells were taken in 1951 without her knowledge and later used in the development of many medical breakthroughs. Lacks, whose life will be depicted this month in an HBO film starring Oprah Winfrey, had a child at age 14 by her first cousin David “Day” Lacks, whom she later married.

As for your situation, we asked genetic counselor and DNA consultant Brianne E. Kirkpatrick to weigh in. She told us the following in an email:

First cousins share a small amount of DNA inherited from a set of grandparents that they have in common. It is possible the shared DNA might happen to contain the same marker for a genetic condition, thus cousin couples can have a higher chance of pregnancy loss or a child born with special health needs.

The baseline chance for a birth defect or other special health needs in any child is around 2-3 percent. Having parents who are first cousins bumps that risk to 4-6 percent.