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Thank you for the quick response. How much greater of a risk is it? And should such a union be considered provided that the family tree does not present any specific genetic diseases. Thanks again.
17 أغسطس 2014
رأي ثانوي

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د. Rania Mousa الطب العام
In most cases, a person suffers from a genetic defect because they have inherited two copies of a defective allele for a particular gene (aka, they are homozygous for that allele). With two defective copies, the gene is not properly expressed, and an abnormality develops. People who have only one defective copy (allele) of a particular gene are said to be carriers for the particular defect that results when you inherit two copies. Now, it just so happens that each of us is a carrier of some sort of defective allele. We each have about 30,000 genes, and on average it is thought that each of us has about 5-10 defective alleles that we can pass on to the next generation. So, when we think about the increased risk of genetic defects due to inbreeding, we need to look at the chances of inheriting a particular defective allele.

Marriage between first cousins more than doubles the chance of having a baby with potentially life-threatening birth defects

So, overall I would not expect to see a tremendous increase in the risk of genetic defects in the offspring of so-called double cousins when compared to the offspring of first cousins. The empirical evidence suggests that the increased risk for first cousin matings is about 2x that of the general population, and since the offspring of so-called double cousins have twice as many defective alleles to consider, I would predict that their risk would be elevated by a comparable degree.

of course if the family tree has certain defects then the risk is bigger ,in the above ratings we are asuming risks concerning normal healthy family members and carriers of certain defects that pass them to other generation and thus having defects means they are passing the two alleles to the offsprings and hence more risk percentage .
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