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Inherited Disorders and Birth Defects

First Cousins Marriage



Me and my first cousin want to be engaged and get married. My parents are first cousins and his parents are first cousins too.

The family is afraid from having a big risk because both our parents are relatives. They are worried about our future kids and afraid about having genetic diseases.

We want to know more about our case in details. And what are the available tests (if any) that might show the real risk and help us to take our decision.


The answer to your question really depends on your family history and whether or not there are any genetic disorders or birth defects in your families. In order to do any testing, you need to know what genetic diseases to look for.

In general, when you do not know about any genetic problems or birth defects, consanguinity (related by blood) appears to cause some increase in the rate of birth defects. The risk is about 3%. This risk is about double the general population risk for having a child with a birth defect or death in early childhood.

If there is a specific genetic condition in the family, then the chance that you would have a child with the condition depends on what the disorder is and how it is inherited. First cousins have a higher chance of sharing the same genes - and since most people carry at least a couple of recessive genes that could lead to a genetic disease, children from a first cousin mating would be at some increased risk.

Again, you would need to have some idea of what to look for if you want to have genetic testing. While there hundreds of genetic tests that could be done, it would not be possible to do them all (and extremely expensive).

I would recommend that you and your cousin talk to your mothers about what diseases run in your families. If there are some, then I would recommend that you talk to a genetic counselor or geneticist to review your family histories in detail. Then you would have specific information. You can ask to your doctor for a referral or contact the National Society of Genetic Counselors at the website below to find a genetics center near you.

Related Resources:

National Society of Genetic Counselors Resource Center

For more information:

Go to the Inherited Disorders and Birth Defects health topic, where you can:

Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University