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How does the health risk for children of first cousins compare with the risk for children of unrelated parents?

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consanguinity (Left) Absence of inbreeding: horizontal lines connect mates, vertical lines connect parents with their child; (right) an inbreeding loop: horizontal bar at top of loop connects brother and sister, all other lines and bars as above

Research indicates that children born to first cousins face a higher risk of adverse health outcomes compared to children of unrelated parents. Specifically, the mortality rate for offspring of first-cousin marriages is approximately 3.5 to 4.5 percent higher than that of nonconsanguineous progeny. Additionally, these children experience a 2 to 3 percent increase in the risk of birth defects.1

While these statistics highlight a measurable genetic impact, it is important to note that the overall influence of inbreeding is often limited in populations where such unions are rare. Furthermore, researchers emphasize that nongenetic factors—such as sociodemographic circumstances and maternal age—are major contributors to these health outcomes, rather than genetics alone. Understanding these risks is essential for informed reproductive health decisions, as genetic disease can become a more significant factor in communities where consanguineous marriage is a common cultural practice.1