31 August 2010
Professor Emeritus, University of NottinghamAppeared in BioNews 573
Sometimes anticipation is worse than the reality. I was uncomfortable with advance information about Tazeen Ahmad's Dispatches programme, entitled: 'When Cousins Marry'. These included extracts talking about: 'the tragic consequences of first cousin marriage' that 'such marriages cause hundreds of children to be born with severe genetic defects, some so ill they die within five years', but that 'the dangers of the practice aren't being highlighted'.
But why am I criticising a campaign to reduce the incidence of severe autosomal recessive diseases? After all, I spent five years of my 40-year clinical career in medical genetics living in Oman - a Muslim country where over 50 per cent of marriages are consanguineous? Let's dig deeper!
First things first. I think Dispatches reporter Tazeen got the right balance between sensationalism, extremes of opinion and solid factual content. The programme began with heartrending personal footage of first cousins who had three children with mucolipidosis type-four, an incurable progressive severe autosomal recessive (AR) disorder. We were also introduced to young man with propionicacidaemia who had undergone a liver transplant at age 15 months and whose parents were cousins.
Reporter Tazeen spoke of her own mother's family in which five girls had died in childhood and three males were deaf (causes not given). She said that 'this tragedy was caused (sic) because my grandparents were first cousins'. The programme quoted data about the higher occurrence of congenital abnormalities in Birmingham where 50 per cent of British Pakistani families marry cousins.
The second part of the programme focused on attitudes to cousin marriage in communities like British Pakistanis in Birmingham. We visited a meeting of men who had married cousins and had healthy children. The benefits of the first cousin marriage (FCM) custom were raised, such as stronger family bonds - 'I know my daughter in law will look after me'. Other young adults in the Asian community, however, were much more critical of cousin marriage. The programme said cousin marriage was one of the ways young people were forced to accept parental marriage choices, with emotional blackmail used to clinch the deal.
At this point, the programme began to flick between politics and science. Professor Marcus Pembrey gave clear information about the genetics of AR disease. Then we returned to supporters of FCM who felt they were being targeted by Western societies for their cultural beliefs. MPs - the programme said - were hesitant to speak about the subject since it wasn't a vote winner.
The final part of the programme asked what could be done about cousin marriage. We saw a white British couple (first cousins once removed, i.e. they shared about six per cent of their genes) who had lost a child with severe AR disease, but later had two healthy children following genetic counselling. This genetic counselling could have been prenatal or PGD (preimplantation genetic diagnosis), but weren't told!
The programme highlighted the importance of encouraging individual, informed choice about cousin marriage. An impressive GP, whose Birmingham practice discouraged FCM but accepted individual choice, gave a clear account of the genetics of thalassaemia to a young woman from East Africa. I thought he had just the right approach and he correctly pointed out we can't test for all (AR) genetic disorders. An Imam at the Forest Gate mosque in London, his own family affected by genetic problems, preached about the need to follow accurate advice and emphasised people had a free choice about whether to marry a cousin.
The programme ended with the young man with propionicacidaemia getting muddled about first cousin marriage and his disease when he was at a follow-up clinic. The pleasant young doctor appeared to interrupt each time the patient started to explain something. The condition was getting worse and the doctor, noticing the mother was distressed, asked her - 'you all right?' before carrying on where he'd left off!
All of this seems fine so far so what was my problem? Well, my experiences in Oman seeing rare AR syndromes have made me desperate to spell out the true situation around autosomal recessive disease and how to tackle it. The primary causes of AR diseases are gene mutations arising in earlier generations. People are affected because they have inherited two copies of mutations in relevant genes - one from each parent. Given the presence of a mutation, cousin marriage increases the risk of abnormal children. But such consanguinity is a risk factor, not the primary cause. If we knew that a family did not have any AR mutations, the risk to the offspring of cousins would be very low. Knowing this takes some sting out of debating pros and cons of cousin marriage. It is fairly simple to teach the notion of damaging genetic changes, leading to an ancestor being a new carrier.
Now let's return to Tazeen's programme. She has increased awareness for many who watched or read her article in the Daily Mail online. But we need to move from awareness to understanding. Also, there are other issues to address. In Oman, for example, healthy siblings of a person with a known (AR) condition may find it difficult to marry outside their family. I was often told of their 'social problem': potential spouses were persuaded against the union by their own family due to the fear of genetic disease. To the siblings of an affected person, the only option may be to marry a cousin who would understand!