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Inherited Disorders and Birth Defects

Sterility issue



Is there a sterility issue for a man if his mother and father were first cousins? In this particular case the grandmothers of the man had different fathers but the same mother so does that factor in?


Not necessarily. There are many reasons for a man to be sterile. For example, having some diseases such as diabetes may cause sterility in men. If there are abnormalities in the Y-chromosome (this would be inherited from the man’s father) or having the wrong number of sex chromosomes can cause sterility. Sterility can be caused from a blockage in the tubes that carry sperm (then the person has to find out what caused the blockage – an infection or disease or treatment for some diseases such as cancer – the cancer treatments such as radiation or chemotherapy can lead to sterility). The first thing the person should do is be seen by a urologist or doctor who specializes in infertility to look for the cause of the why the person is infertile.

In the situation that you describe, because the grandmothers are half-siblings (they have the same mother, but different fathers), then the man’s parents are half-first cousins. So while they do share some of the same genes, they share fewer genes in common than if they were full first cousins. If the reason for the sterility was due to a genetic disease, then there is a possibility that having parents who are half-first cousins may mean the man’s parents both carry a gene that is related to a disease that has sterility as one of its problems.

It would be important that the man give the doctor the information about how his parents are related so that the doctor can take this into consideration when evaluating the person for sterility.

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Response by:

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