-An undergraduate student from New York
I can see why you might be concerned about your kids. We've all heard about what supposedly happens if cousins marry. A recent study, though, showed that while there is increased risk of some genetic disease, the risk is actually smaller than a lot of people might think.
The numbers from this study are pretty interesting. For unrelated people, the risk of having a child with a serious genetic problem is around 3 or 4 percent. In other words, 3 or 4 of every 100 babies have potential problems (seems high to me but that is what the report claims).
If first cousins have kids, that risk goes up by 2 or 3 percent. At first this almost doubling of the risk might seem scary. But many genetic advisers argue that the increase isn't big enough to discourage marriage between first cousins.
Why all the concern then? If we think about all of this genetically, we can begin to see where the worry might come from.
Remember, we all have two copies of each of our genes -- one from mom and one from dad. We also have on average around 5-10 disease genes each. So how come we all aren't wracked by genetic diseases?
Because most of these "bad" copies of genes are recessive. What recessive means is that you need both copies to be bad to get a disease -- a single good copy can save you.
If we all shared the same disease genes, then the likelihood of kids getting these diseases would be high. But we don't. Everyone has a different set of hidden disease genes so that the odds are against people each giving one of the same bad genes to their kids.
Now, the more closely related two people are, the more likely it is that they'll share the same set of hidden disease genes. People might have thought that first cousins were too closely related and so there would be a big increase in genetic diseases if cousins marry.
The data doesn't really show this. And if we think about it, it probably isn't surprising that the risk is small for first cousins.
There are lots of places in the Middle East, Africa and Asia where marriages between first cousins are encouraged. There is no rampant genetic disease in these places suggesting all along that the risk was low.
You may want to talk with a genetic counselor about the increased risks. They can help you decide whether the small increased risk is acceptable to you. You can find a genetic counselor near you at the link below.