Cousin marriage doubles the risk of passing on recessive genes
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The tradition of marrying a cousin is becoming more entrenched among British-born Pakistanis living in Bradford than it was a generation ago, writes Winifred Robinson. This has been the surprise finding of the
Born in Bradford research project
. It's a huge long-term study of 14,000 mothers and babies in the city, the largest ever undertaken in the UK. Half of the families in the project are Asian. Cousin marriage has important implications for health because marrying a cousin increases the risks of passing on genetic disorders. Bradford has three times the national rate among children for disabilities including deafness and blindness. Globally, cousin marriage is practised by an estimated billion people, according to Professor John Wright, who is leading the Born in Bradford research project. It yields considerable social benefits - particularly in ethnic groups, where it is traditional for women to live with their in-laws. "People marry cousins because it means you are coming into a family where everybody loves you," Professor Wright says, "and there are economic benefits of keeping land or other assets in the family".
Most of the people of Asian origin in Bradford come from the rural villages of Mirpur in Pakistan. Families in Bradford are still arranging marriages and choosing brides and grooms among their extended family back home - one in four children in the study had a parent brought over for marriage. The problem with cousin marriage is that it doubles the risk of passing on the recessive genes that lead to abnormalities. Cystic fibrosis is the one we all know about, where two healthy parents carry a recessive gene for the condition. "If a cousin has a genetic variant that causes a disease and marries a cousin with the same genetic variant, then there is a one in four chance that the children will have that disease," Professor Wright explains. On the face of it the risk is not great - a 4% risk of having a child with an abnormality if you marry a cousin, compared with 2% among the general population. But with repeated cousin marriage, the risks stack up in families with sometimes devastating results. We met Ruba who is 23. She has two children Alishbah, aged two and Hassam, aged four. Ruba was 18 when she married her second cousin. Her children have I-cell disease, a rare disorder which has prevented them growing and developing as they should, from the start. "It was a real shock to me when he was diagnosed," she says, "I didn't even know what it was, we've nearly all been married to cousins in our family and we didn't know this condition existed. I was looking at him thinking he's still my son and whatever he's got I'm going to love him.
Globally, cousin marriage is practised by an estimated billion people
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"He's delayed in development mentally and physically, he can't walk or sit up on his own. He is prone to chest infections and all his bones are abnormal, they're not the right shape. He's got narrow air ways and so it's difficult for him to breathe and he's on oxygen at night - last night I had to get up three times for my daughter and nearly every hour for my son. It's getting harder and harder to look after both of them." Ruba has been told her children's life expectancy is short - seven to eight years. She met another woman in Bradford with a son who died at nine months from the same disease… there was another child born with the condition when her daughter was born. The Born in Bradford researchers are determined that theirs should be an applied health research study with results leading to better services. "Everything we do gets translated into practice so that our work on congenital anomalies has led to a city register for these children and also a Yorkshire register," Professor Wright insists. Professionals working with couples like Ruba and her husband hope that in the future they wlll be able to provide better genetic screening and advice for couples who want it.
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