Marriage between first cousins could double the risk of any offspring having a birth defect, researchers say.
In a large multi-ethnic study performed in Bradford in the UK, scientists sought to investigate why congenital anomalies were more common in babies born to Pakistani mothers in England and Wales than to white British mothers. The study found that nearly one third (31 percent) of these cases could be attributed to cousin marriage in the Pakistani community.
But Dr Eamonn Sheridan, from the University of Leeds, the study's lead author, added: 'It is important to note that the absolute increase in risk is small (from three percent to six percent), meaning that only a small minority of babies born to couples who are blood relatives [...] will develop a congenital anomaly'.
The study also reported a similar increase in risk in white British women over the age of 34, whose likelihood of having a child with a birth defect doubled from two to four percent. Other factors such as social deprivation, smoking or alcohol consumption were not significant.
Consanguineous marriages are an established tradition in many cultures, with over a billion people in the world living in countries where such marriages are customary. In Bradford over 60 percent of the Pakistani mothers in the study were married to a blood relative.
This cultural aspect to consanguineous marriage has made the subject highly sensitive and some previous studies have caused controversy. However, speaking to the Guardian, Dr Sheridan said there had been strong community involvement in the study, and that 'the community has not been surprised by the findings'.
The Born in Bradford study, which was published in The Lancet, follows the health of 13,500 babies born in Bradford Royal Infirmary between 2007 and 2011. It the largest study of its kind in the UK to date.
Professor Neil Small of the University of Bradford, a co-author of the paper, said: 'We hope this research will be used to enhance the knowledge of Bradford's health professionals, help individuals to make informed choices and support family centred genetic counselling services'.
Nonetheless, speaking to the Independent, Dr Rafaqut Rashid, a Bradford GP, pointed out that patients often recognise social benefits to cousin marriages such as extended families, social stability and marital stability.
'Patients should be given an informed choice', he said. 'We don't want to force anything on [them]'.