BANNING marriages between cousins would be "pointless" despite the increased risks of inherited illness, the world leading expert on the issue warned yesterday.
Professor Alan Bittles said it would not eliminate genetic diseases and ignored the social and economic benefits of unions between related people.
Concerns over marriages which are consanguineous – between second cousins or closer – have been raised in Bradford, which has significantly increased levels of genetic illness particularly in the Asian community, prompting some calls for an end to the tradition.
Bradford paediatrician Peter Corry, who yesterday joined Prof Bittles at a briefing in London by the Royal Society of Medicine to mark 100 years of medical genetics, said more than 150 genetic conditions in children had been pinpointed in the city compared to around 30 in an average population.
They ranged from relatively minor skin disorders to life-limiting illnesses and affect up to 1,000 youngsters. Some were among only a small number discovered in the world.
Around 70 youngsters have terminal disorders which lead to dementia-type illnesses – eight per cent of the total in the UK.
Early evidence of family trees from the pioneering Born in Bradford study, which is tracing the lives of thousands of babies born in the city over the next 20 years, showed about 70 per cent of marriages among couples of Pakistani origin were consanguineous.
Prof Bittles, director of the Centre for Human Genetics in Perth, Australia, said more than one billion people lived in countries where 20-50 per cent of marriages were between cousins. Muslim, Buddhist, Christian, Hindu and Jewish communities permit the unions.
He said: "Stopping cousin marriage makes no sense and is bad science because it will not eliminate genetic disease. Calls for the abandonment of such well-established marriage customs are pointless. A more realistic and workable approach is to concentrate on identifying the families in which specific genetic diseases occur, complemented by focused and culture-sensitive genetic counselling and premarital carrier testing."
He said unions between relatives were undertaken primarily for social and economic reasons so the balance between the social advantages and potential health problems varied around the world.
A large majority of offspring born to related couples were healthy. But studies showed infant mortality was on average 1.2 per cent higher in children of first cousins. Ill-health was more common, with elevated risks of deafness and otherwise rare genetic disorders.
Dr Corry, of the child development centre at St Luke's Hospital, said: "These genetic variations are more common in Bradford although individually they are still pretty rare when you consider there is a big population of 100,000 children.
"There are links between cousins and marriage and the increased risk of disorders but most people have healthy kids."
He said genetic counselling for couples at risk of children suffering from disorders had improved significantly and there was also more awareness in the community. "Every time we discover a new gene that is useful for our patients because people can be given better genetic counselling," he said.
He said inter-marriage was not a modern phenomenon. It had been common until relatively recently in Britain. In remote areas in Yorkshire, even if people had not married relatives, in the past they married the "boy next door".