Congenital birth defects risk almost doubles in children whose parents are first cousins, even though the rate of such abnormalities remains rather low.
A recently published British study Born in Bradford (“BiB”), considered the biggest study of its kind, looked at more than 11 thousand children from a traditional Pakistani community in the city of Bradford, Northern England starting 2007 and through 2011.
More than one billion people around the world live in societies where intermarriage between blood relatives is accepted or even compelled.The Pakistani community of Bradford has remained traditional, therefore marriages between blood-related individuals are still common.
During the study, scientists calculated the overall rate of birth defects in the children of Bradford - which included predominantly Pakistani and white British mothers, and also other ethnic minorities - was approximately 3%, nearly double the national rate of around 1.7%.
The so called consanguineous parents accounted for more than 30 % of congenital abnormalities in children that varied from minor anatomic problems such as extra toes or fingers to graver life-threatening defects such as spine, brain, heart and vascular development failings.
They also found that among the Pakistani group, 77% of offspring with birth abnormalities were born to parents who were blood relatives.
Neil Small, a professor of Health Research at the University of Bradford said he hoped the strong evidence provided by the study would prove effective in promoting awareness among the closed communities worldwide that sanction cousin marriages including Kurdish, Romany, Amish, and others.
"At the heart of all this are children who are born with often very distressing illnesses that can create both misery in themselves and anguish in the families," he said.
"Many of these things are preventable and we hope that what our study does is contribute to a debate that means in the future, some of them will be."
"Whilst consanguineous marriage increases the risk of birth defect in offspring from 3 percent to 6 percent, the absolute risk is still small," said Eamonn Sheridan, a senior lecturer in clinical genetics at the University of Leeds who co-led the study and presented its results at a briefing in London.
He continued that it still meant that 96 percent of blood-relative couples were likely to have children with no birth defects: "It's important to note that the vast majority of babies born to couples who are blood relatives are absolutely fine."
Hamish Spencer, a professor of zoology at New Zealand's University of Otago who has studied consanguineous marriage before, said they were important because there are significant public health consequences in places with higher rates of birth defects.
"Awareness of the risks to the children of cousin marriage needs to be increased but in a culturally sensitive way," he said in an emailed comment.
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