Friday, November 18, 2005

British Pakistanis' 2nd Cousin Marriage Birth Defect Rates

British officials want to stop cousin marriages because birth defect rates appear to be about ten times higher than for more distantly related married couples:


Marriages between cousins should be banned after research showed alarming rates in defective births among Asian communities in Britain, a Labour MP said last night.

The report, commissioned by Ann Cryer, revealed that the Pakistani community accounted for 30 per cent of all births with recessive disorders, despite representing 3.4 per cent of the birth rate nationwide.

“We address problems of smoking, drinking, obesity and we say it’s a public health issue, therefore we have to get involved with persuading people to adopt a different lifestyle,” the MP for Keighley, Bradford, told BBC2’s Newsnight programme last night.

“I think this should be applied to the Asian community. They must look outside the family for husbands and wives for their young people.”

It is estimated that more than 55 per cent of British Pakistanis are married to first cousins, resulting in an increasing rate of genetic defects and high rates of infant mortality. The likelihood of unrelated couples having the same variant genes that cause recessive disorders are estimated to be 100-1. Between first cousins, the odds increase to as much as one in eight.

In Bradford, more than three quarters of all Pakistani marriages are believed to be between first cousins. The city’s Royal Infirmary Hospital has identified more than 140 different recessive disorders among local children, compared with the usual 20-30.

The findings were expected to be condemned by the Asian community, in which many see the tradition of marriages between first cousins as culturally fundamental.

“You have an understanding, you have the same family history,” said Neila Butt, who has had two children with her husband, Farooq, her first cousin. “It’s just a nicer emotional feel.”

Somthing to keep in mind is that these birth defect rates are the result, most likely, of repeated generations of first-cousin marriages, where the gene pool keeps getting more and more concentrated due to generation after generation of inbreeding. This is very interesting because the number typically reported is that first-cousin marriages result in birthdefects about double the rate for non-related couples. But that rate is derived in cultures where first cousin marriages are very rare and where the culture has no tradition of encouraging first cousin marriages. Consequently, that rate reflects what happens when you get a first-cousin couple coming from a background in which there had been no previous incest, presumably, in previous generations. Here we have about 10 times the rate in a situation where there is repeated first-cousin marriages over and over, generation after generation. Clearly, things get worse and worse.

On the other hand, it's surprising in some way that the bith defect rates aren't even higher. I would like to be able to compare miscarriage rates. It is known that human bodies will spontaneously miscarry many defective fetuses. Perhaps the rates aren't even higher because so many fetuses never make it to full term to be counted in the official stats on birth defects. You have to be born after all to have a birth defect. Pity the many who never make it even that far.