Background: While parental consanguinity is known to increase the risk of birth defects in offspring, it is hard to quantify this risk in populations where consanguinity is prevalent.
Methods: To support ongoing studies of cancer and of psychiatric disease, we studied relationships of consanguinity to 1,053 major birth defects in 29,815 offspring, born in 1964-1976. To adjust for confounding variables (geographic origin, social class and hospital), we constructed logistic regression models, using GEE to take into account correlations between sibs. Odds ratios (ORs) and 95% confidence limits were estimated in comparison to a reference group of offspring with grandfathers born in different countries.
Results: With 10.1% of offspring having consanguineous parents, the adjusted OR for major birth defect was 1.41 (1.12-1.74). Offspring of marriages between uncles-nieces, first cousins and more distant relatives showed adjusted ORs of 2.36 (0.98-5.68), 1.59 (1.22-2.07) and 1.20 (0.89-1.59) respectively. For descendents of grandfathers born in the same country, but not known to be related, the OR was 1.05 (0.91-1.21); these showed increased risk associated with ancestries in Western Asia (1.27, 1.04-1.55, p < 0.02) or Europe (1.13, 0.79-1.80).
Conclusions: A strong association of consanguinity with poverty and low education points to the need to avoid exposure to environmental hazards in these families.
Copyright 2008 S. Karger AG, Basel.