December 7, 2022

UK study shows birth defect risk doubles with cousin marriages

A major study in the UK has found that the risk of birth defects doubles from 3% to 6% if the spouses are first cousins.

A major study in the UK has found that the risk of birth defects doubles from 3% to 6% if the spouses are first cousins.

The research was carried out in Bradford, a lower socio-economic area in northern England with large numbers of Pakistani immigrants. The health of 13,500 babies born at Bradford Royal Infirmary between 2007 and 2011 was tracked in a major longitudinal study. The results were published in The Lancet.

The greatest risk factor was found to be closely-related parents, not poverty or environmental factors. Among the Pakistanis, 77% of babies with birth defects were born to parents in consanguineous marriages.

However, geneticist and lead author Dr Eamonn Sheridan, from the University of Leeds, says: “It is important to note that the vast majority of babies born to couples who are blood relatives are absolutely fine, and whilst consanguineous marriage increases the risk of birth defect from 3% to 6%, the absolute risk is still small.”

Another researcher, Neil Small, described BIB as “the first study that has been able to explore all causes of congenital anomaly in a population where there are sufficient numbers in both consanguineous and non-consanguineous groups to come to reliable conclusions”.

It is estimated that more than a billion people worldwide live in communities where consanguineous marriage is commonplace.

The other major sub-group at risk for birth defects was white women over 34. The risk of bearing a child with a defect rises from 2% to 4% for them.

The results of the study were not news to geneticists, but they have to be treated with great sensitivity because of their potential for heightening cultural tensions. A local doctor, Mohammed Iqbal, said that the community would find the results helpful in making “more informed choices about choosing a partner and/or undertaking genetic screening before the birth of a child”.

Michael Cook
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birth defects
consanguinity
cousin marriages