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Inherited Disorders and Birth Defects

Cousin Marriage

12/22/2010

Question:

Sir, I want to marry my cousin. She is the daughter of my father`s sister. But the father of that girl doesn`t belong to our family. I want to know that is there any chances of repitition of reccesive genes in our children, as her father doesn`t belong to our family. Does she have a good reshuffle blood?

Answer:

Couples who are related by blood have a higher chance of having children with genetic diseases or birth defects. It is estimated that couples who are first cousins (3rd degree relatives) have about a 2-3% above the population risk, which is estimated to be about 3-4% of newborns.

If there is a specific genetic disorder in the family, then it would depend on what the disorder was and its specific type of inheritance pattern. 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 disorder, children from a first cousin mating would be at increased risk. The chance that both you and your first cousin carry a gene change (mutation that can cause a recessive genetic disease) is 1/16 and the chance that both of you would pass on that gene change (mutation) to a child at the same time is 1/64. This chance is based on the fact that both you and your cousin have common grandparents (your father’s and her mother’s parents) – it does not matter that her father is not related to your family.

The important thing is - you would need to know what medical or genetic problems are in your father’s and her mother’s side of the family. I would highly recommend that you talk to a geneticist or genetic counselor. They would be able to discuss your chances to have a child with a genetic disease based on your family history. They would also be able to talk to you about what options you have about preventing these problems. You can ask your doctor for a referral to a genetics clinic near you or you can locate one through the National Society of Genetic Counselors’ Resource Center website below.

Related Resources:

Find a Genetic Counselor - National Society of Genetic Counselors

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