What genetic risks are associated with marriage between close relatives?
Last reviewed:
Direct answer
Close relatives are more likely to carry the same rare recessive variant inherited from a shared ancestor. If both partners carry a disease-causing variant in the same gene, each pregnancy may have a 25% chance of an affected child for a typical autosomal-recessive condition. Reviews estimate that first-cousin couples have an additional absolute risk of major congenital or genetic problems of roughly 2–3 percentage points above the background risk. The exact risk depends on family history, degree of relationship and the specific variants involved.
+2–3 pointsapproximate additional absolute risk reported for first-cousin couples
Sources used
Genetic Counseling and Screening of Consanguineous Couples and Their Offspring
Journal of Genetic Counseling
Practice resource explaining recurrence risk, family history and counseling for related couples.View sourceConsanguinity and reproductive health among Arabs
Reproductive Health, PubMed Central
Peer-reviewed review summarizing the additional absolute risk associated with first-cousin unions.View source