Cousin marriage: A cause for concern?

Over a billion people worldwide live in regions where 20-50 per cent of marriages are consanguineous, and first-cousin unions are especially popular. Discussion of this phenomenon is confused by the fact that its causes are social and economic, while its outcomes tend to be measured in terms of child health. International variations in infant mortality, and varying genetic factors within given communities, make it difficult to attribute health problems to cousin marriages with any degree of accuracy. But this hasn't prevented government minister Phil Woolas from arguing that cousin marriages among immigrants are contributing to a surge of birth defects in the UK.

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:

• genetics infrastructure that responds to family need in a multiethnic context;

• training for health professionals;

• community engagement programmes - increase public understanding of genetics;

• communication tools to facilitate communication between families and health professionals;

• adequate health service resources.

After the talks, a diverse audience of some 120 delegates made for an extremely interesting and informed debate.

Given the long tradition of cousin marriages among many cultures worldwide, one audience member questioned whether there were any advantages to such practices. Walji said that in his experience, many individuals will consider revising their choice of marriage partner in light of information about the risks of cousin marriage, so he felt that it was difficult to say whether such marriages are beneficial or not, even if superficially they appear to be successful. Darr felt that, given the widespread availability of genetic screening services to couples in the UK which can now detect 40 per cent of disorders, it was unnecessary to advise cousins not to marry.

She felt that the low uptake of these services was partly due to the insensitive way in which the debate has been handled by the media and politicians, who she said are too preoccupied with the notion of a ban to realise that there are other alternatives that warrant consideration.

Another question from the floor related to the affect of cousin marriages on polygenic traits - those which result from both genetic and environmental factors. In his reply, Bittles confirmed that many experts, himself included, do believe that cousin marriages have an impact on such traits, but that it is very difficult to obtain sufficient data to analyse any such trend due to the complex variety of factors in play.

House of Lords cross-bencher Baroness Ruth Deech said that she was 'shocked' to hear that experts felt any increase in birth defects was acceptable, no matter how small a percentage of the population, and advocated a national campaign on the scale of anti-smoking or the dangers of Down syndrome in older mothers, in order to try and encourage carrier testing before marriage.

Professor Pembrey, stepping out of his role as chair for a moment to give his perspective as a clinical geneticist, speculated that the delivery of a comprehensive national screening programme like this may present a considerable challenge given that new tests may need to be tailor made for each rare genetic condition. However, Darr felt that the close-knit nature of families with a long tradition of cousin marriages might help to ease pressure on genetic services, because they are more likely to be in touch with other living relatives who may be at risk from the same mutation.

As the debate drew to a close, the speakers were asked to each deliver a 'take home message', summarising their views:

• Darr said that we as a society need to stop focusing on social engineering and accept cousin marriage as a social reality. Only then can we deliver adequate genetic services to those who need them most, she said.

• Walji highlighted the need for a national drive to raise awareness and understanding about genetics among GPs in order that they can deliver this information to the communities they serve.

• Bittles agreed that cousin marriage should be viewed as a feature of the current social context, concluding that attempting to ban such practices, which have enjoyed a long tradition in Britain and which were even thought romantic at one time, would be both unnecessary and ineffective.