If cousin couples happen to be carrying known genetic diseases, the risks faced by their offspring can jump.Experts say 1 out of 4 such children will have some sort of disorder.Women in their forties are not made to feel guilty about having babies and the same should apply to cousins who want to marry, said Professor Diane Paul of the University of Massachusetts in Boston and Professor Hamish Spencer of the University of Otago in Dunedin, New Zealand.
The risk of giving birth to babies with genetic defects as a result of marriages between first cousins is no greater than that run by women over 40 who become pregnant, according to two scientists who call for the taboo on first-cousin families to be lifted.
Most states in America have either outlawed or restricted the practice, as has China, Taiwan and both North and South Korea.
Professor Spencer, an evolutionary zoologist, said these laws should be repealed, especially in America, where he said they were drafted in a way that discriminated against the rural poor and immigrants: "Neither the scientific nor social assumptions behind such legislation stand up to close scrutiny.
"A lot of arranged marriages are with first cousins, and that produces lots of genetic problems in terms of disability [in children]," Mr Woolas said.
Peter Corry of St Luke's Hospital in Bradford estimates that among people of Pakistani descent in the city, 55 per cent of whom marry first cousins, the risk of recessive genetic disorders – the type due to related parents – is between 10 and 15 times higher than in the general population.