Is cousin marriage a legitimate cause for concern? If not, then why does it attract so much attention? If so, then what should be done about it? These were some of the questions addressed at a debate organised by the Progress Educational Trust at Clifford Chance, in East London, on Thursday 29th May.
The debate was chaired by Marcus Pembrey, Emeritus Professor of Genetics at the Institute of Child Health and Chairman of the Progress Educational Trust, who welcomed three expert speakers: Professor Alan Bittles, one of the leading experts in this area and a population geneticist at the Centre for Comparative Genomics, Dr Mohamed Walji, who has been a General Practitioner in inner Birmingham since 1983, and Dr Aamra Darr, a medical sociologist and Senior Research Fellow at Bradford University.
Professor Bittles opened the discussion by reminding the audience of the reality that all humans are related to some extent and that, although harmful mutations arise naturally in the genome, nature has several very good mechanisms for reducing their impact on health. For example, 50 per cent of women miscarry, despite being in peak fertility, owing to genetic abnormalities in their unborn child which are incompatible with life. Furthermore, the vast majority of such abnormalities are recessive and may therefore be passed through several generations before an affected child is born. Bittles emphasised that even when two carriers of the same recessive condition reproduce, each child they have has a 75 per cent chance of being unaffected.
He went on to explain that only those genetic conditions which are rare among the general population are more likely among cousin marriages. Those which are relatively common among the population, such as cystic fibrosis, the gene for which is carried by one in eight Europeans, or thalassaemia, carried by one in seven people of Asian origin, are no more likely to result from consanguineous marriages than from unrelated ones, he said.
Bittles believes that the media's alleged 'doubling of the death rates' among children born to consanguineous parents is irresponsible and alarmist when data shows that only a relatively small number of children are affected. In terms of birth defects, he says the risks rise from about two per cent in the general population to four per cent when parents are closely related. Given the relatively small number of cases in which problems occur, Bittles supported better genetic screening services for those affected over any kind of ban or limit on first cousin marriages.
Next to speak was Dr Walji, who was resolute that the effects of cousin marriages are extremely serious and something that he sees in his clinic on a regular basis. Walji described the 'heartache' and 'anguish' felt by those couples who give birth to affected children, many of which he said were previously unaware that consanguineous marriage put them at any increased risk. Anecdotally, he said that the incidence of infant death and mortality was on the increase among his patients, a trend which he felt could only be explained by the high incidence of cousin marriage among the local community, a large proportion of which are Muslim.
Walji considered it his duty as a doctor to raise awareness of the dangers of cousin marriages among these communities and, where possible, to discourage this practice in order to prevent affected children being born 'unnecessarily'. A wide variety of studies have tried to quantify the impact of cousin marriages on health, he reported, but among these results vary widely, highlighting the urgent need for robust data on which sound clinical advice can be given.
Following the introduction of a screening programme in his local mosque which advises against marriage between carriers, Walji said that he had witnessed the incidence of birth defects diminish markedly, suggesting that increased GP awareness and accessible genetic screening programmes are the key to reducing the incidence of genetic conditions among cousin marriages.
Last to speak was Aamra Darr, who is currently undertaking research into the societal aspects of consanguineous marriage and its relevance to genetic service delivery in multiethnic populations. Darr firmly believes that there are steps that can be taken to reduce the risk of birth defects, including avoiding cousin marriage and accessing genetic screening or prenatal testing, but that people need the opportunity to make informed choices about which risks they want to take and which they want to avoid.
Her studies have highlighted a huge deficit in the understanding of recessive inheritance among Muslim and Asian families, often those who are most at risk. She felt that it was unhelpful to think of risk of inheriting genetic disorders in terms of populations, when the individual's risk can vary so wildly, highlighting the need for robust genetic services capable of carrying out accurate risk assessment.
Darr said that, like the increased risk of Down syndrome in older mothers, we can only reduce any risks associated with cousin marriage if we accept it as a 'social reality', thereby adopting a strategy which aims to promote increased awareness of the risks and understanding of the causes, rather than imposing a complete ban, which could easily be misconstrued as an act of discrimination.
Specifically, she felt that the following measures were necessary to enable at-risk couples to make informed reproductive choices: 0
