Six years after the law passing, Qatar has started mandatory premarital screenings this week, mainly to alert couples who may be related, of any potential health risks for their future offspring. About half of all marriages across Gulf nations are between cousins, and their frequency is increasing, according to a recent study in the Asian Pacific Journal of Cancer Prevention. At 54 per cent, the rate of cousin marriage appears highest in Qatar, and has increased nearly 30 per cent from the previous generation.

On its own, marriage between cousins, or consanguinity, is not necessarily problematic. But many debilitating genetic disorders – including sickle cell anaemia, cystic fibrosis, spinal muscular atrophy, mental retardation, epilepsy and Down syndrome – can be up to 20 times more frequent among populations in which cousin marriages are common.

“It is certainly a problem,” said Dr Ahmad Teeb. A genetics and paediatrics professor at the Weill Cornell Medical College of Qatar, he has been researching Arab genetic disorders for more than 25 years and contributed to the recent study. “The issue here is not the cousin marriage, the issue here is to avoid the disease,” Dr Teebi said. “However, virtually none of us is free from carrying some bad genes, and when you are cousins the likelihood of you are carrying the same bad gene is higher.”

Marriage between second cousins or more distant relations has very little impact on the passing down of genetic disorders. Yet the children of first cousins, who share 12.5 per cent of their genes, are nearly twice as likely as the general population to contract a disorder. And within populations that intermarry regularly over generations, the coincidence of disorders can increase exponentially. “If certain disorders are more common in a population,” said Dr Teebi, “the likelihood of its occurrence can be many times increased.” In the Gulf, most cousin marriages are between first cousins.

A report by the Dubai-based Centre for Arab Genomic Studies (CAGS) in September found that a handful of genetic diseases – the blood disorder; thalassaemia, diabetes and Down syndrome among them – have reached epidemic levels (more than 100 cases per 100,000) in several Gulf countries. The report also found that Arabs have one of the world’s highest rates of genetic disorders, nearly two-thirds of which are linked to consanguinity...