Mick Hartley

As Matthew Syed reports, the dangers of birth defects has led to a ban on cousin marriages in Scandinavia:

A shift of potentially historic significance is under way, perhaps without many people noticing. Last week, after an official inquiry, Sweden moved to ban cousin marriage, following in the footsteps of Norway, which announced the same intention earlier this year.

The day after the Swedish announcement, Denmark did so too. In the United States, Tennessee banned cousin marriage in April, and other states lacking the edict have placed it under review.

Syed welcomes this from a cultural rather than a genetic point of view – decreasing tribalism – but it's the genetic factor which is surely the main issue here.

Pakistan is the country with the highest rate of consanguineous marriages, and the practice has come over here with immigration. A 2005 report, commissioned by MP 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. From that same period Dr Peter Corry, Consultant Paediatrician at Bradford Royal Infirmary, said his hospital saw so many recessive genetic illnesses that it had became a centre of excellence for the treatment of some of them. They'd identified about 140 different autosomal recessive disorders among local children: he estimated that a typical district would see 20 to 30.

There are indications that the rate of cousin marriages is decreasing. A BBC report from a year ago:

The number of people in Bradford's Pakistani community who have married a cousin has fallen sharply in the past 10 years, a study suggests. Higher educational attainment, new family dynamics and changes in immigration rules are thought to be possible reasons.

Juwayriya Ahmed married her cousin in 1988. The 52-year-old teacher says her children once asked her how she and their father met.

"I was laughing at them. I said I didn't really meet him. My parents took me to Pakistan and my dad said you're going to marry this person. And I sort of knew who he was, but the first time I met him properly was at the wedding," she says.

"My kids said that was disgusting. And then they told me, 'Don't you dare make us do anything like this.'"

Ten years ago researchers studying the health of more than 30,000 people in Bradford found that about 60% of babies in the Pakistani community had parents who were first or second cousins, but a new follow-up study of mothers in three inner-city wards finds the figure has dropped to 46%.

The original research also demonstrated that cousin marriage roughly doubled the risk of birth defects, though they remained rare, affecting 6% of children born to cousins.

"In just under a decade we've had a significant shift from cousin marriage being, in a sense, a majority activity to now being just about a minority activity," said Dr John Wright, chief investigator of the Born in Bradford research project.

"The effect will be fewer children with congenital anomalies."

It's in the right direction, but a drop from 60% to 46% is hardly a major shift.

Still, whether enforced by law or allowed to change as social customs change, it's at least welcome news that the subject's now being talked about.