Should countries introduce laws that would have made the first-cousin marriages of Darwin and Einstein illegal?
In many cultures, tradition favours marriage to someone within the extended family. Some European politicians claim that the children of immigrant populations with such traditions have an unacceptably high risk of genetic disorders and are calling for marriages between first cousins to be banned, as they are in most US states.
But geneticist Alan Bittles of Murdoch University in Perth, Western Australia, says education and genetic testing is the best way to minimise the risk.
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To estimate the risk, Bittle reviewed 48 studies from 11 countries. He found that infant mortality is only 1.2 per cent higher among the children of first cousins compared with children that have more distantly related parents. That is in line with a suggesting that first-cousin children are less than 3 per cent more likely to have birth defects.
However, the risk of genetic disease in a particular population may depend on how genetically diverse it is. Paediatrician Peter Corry of St Luke鈥檚 Hospital in Bradford, UK, estimates that among people in the city of Pakistani descent, 55 per cent of whom marry first cousins, the risk of a recessive genetic disorder 鈥� the type often due to related parents 鈥� is 10 to 15 times that in the general population. A 2004 study found that 13 out of every 1000 Asian children born in the area had recessive disorders. 鈥淏ut it is important to remember that there are lots of other, non-genetic reasons for illness and death in children,鈥� Corry says. 鈥淎nd even in places like Bradford most people, even cousins, have healthy children.鈥�
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