LIKE many young women from Muslim families, Bushra Ali might easily have married one of her cousins. When she looks at Asim, her healthy seven-year-old son, she is thankful that she chose a husband unrelated to her family.

Had she married a cousin, her children would have been at high risk of suffering from the hereditary disorder that has already afflicted many family members. The condition, a form of histiocytosis, causes deafness and deforms the bones. It is carried by her father's side of the family.

'My paternal grandmother and my dad's brother both died from it,' she says. 'And my sister has had it from the age of three. She could never run or play like other children.'

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Genetic counsellors have told Mrs Ali, 28, that although she is a carrier of the defective gene that causes the disorder, her children will be unlikely to suffer from it. Some of the cousins in her family who did marry each other have been less fortunate: where both mother and father are carriers, the baby is at high risk of developing the condition. 'Some of their children have been diagnosed with this disease, including a little baby of eight months back home in Pakistan.'

Mrs Ali, 28, wants to help publicise the risks of genetic diseases among the offspring of couples who are cousins - especially in the Pakistani community, among whom such marriages are common. She says: 'Many people in this country from Pakistan are from quite a poor background and have not had much of an education, so they may not realise that a child is suffering from a genetic disorder or that it can be dangerous to marry a cousin, because you share some of the same genes.'

Mrs Ali's concern is shared by researchers in her home town of Birmingham, who say there is evidence that cousin marriages among Pakistani people living in Britain are resulting in high rates of chronic disability among their children.

Dr Sarah Bundey, clinical geneticist at Birmingham Maternity Hospital, says: 'There have been many rumours that cousin marriages were the cause of excess problems in Pakistani children, but this has never been carefully documented.

'But a study that we have recently completed has shown what paediatricians in Birmingham have suspected: that there is a tremendous excess of chronic handicapping conditions in the offspring of Pakistani married couples who are cousins.'

Worldwide, marriage between cousins is common. Muslims often marry cousins, taking their lead from the prophet Mohamed, who married a cousin.

Cousin marriages among the white population of Britain account for about one in every 200 couples. But in people of Pakistani origin, about two in every three marriages are between first cousins.

Birmingham has the second-largest Pakistani community in the UK, and anecdotal reports have long suggested that this community suffers higher- than-average rates of chronic disability. There were, for example, said to be far more pupils of Pakistani origin at schools for severely handicapped children than would be expected.

Dr Bundey and her colleagues interviewed almost 5,000 mothers who gave birth in Birmingham on weekdays during 1986 and 1987. The researchers kept a check on the health of the babies until they reached the age of five. Information was collected on the ethnic group and religion of both parents, whether they were cousins, and whether there had been earlier cousin marriages among their parents and grandparents.

The first results to be analysed were those on deaths late in pregnancy and in the first week of life. Dr Bundey found that 15 to 16 in every 1,000 infants of Pakistani origin suffered lethal malformations - more than double the expected rate. About half were due to a genetic recessive disorder - one caused by the inheritance of two copies of an abnormal gene, one from each parent. In each of these cases, the parents were cousins.

Dr Bundey's most recent results, which are being published later this year in the European Journal of Human Genetics, examine death and serious illness after the first month and during the first five years of life. She found a 'significant excess' of chronic illnesses and disabilities in the offspring of Pakistani couples who were cousins. For them, the risk of a child dying or developing a chronic disease in the first five years of life was more than 10 per cent - compared with 3 per cent for Pakistani couples who were not related.

Geneticists normally advise white couples in the UK who are cousins that the risk of disability or death among their offspring is one in 20. The higher risk among those of Pakistani origin, Dr Bundey believes, is the long history of intermarrying in those families. 'The reason seems to be that there have often been cousin marriages in previous generations.'

Most of the problems among these children are caused by recessive genetic disorders. The genetic disease thalassaemia, a blood disorder causing life-threatening anaemia, is an example of a recessively inherited disease that is prevalent among certain ethnic groups, including those from South-east Asia.

Many people carry one copy of the abnormal gene for thalassaemia, but they do not develop the disease because the dominant healthy gene, inherited from the other parent, overrides the recessive, abnormal one. If, however, two people who each have one copy of the abnormal gene for thalassaemia have children together, each child will have a one in four chance of inheriting two copies of the faulty gene - and suffering from the disease.

One of the most common disorders found among the offspring of cousin couples was a genetic form of severe mental retardation. Overall, Dr Bundey found that 48 per cent of serious problems in Pakistani children were due to 'certain, probable or possible recessive diseases'. This figure compares to just 3.6 per cent for all other ethnic groups combined.

Dr Bundey has calculated that if people of Pakistani origin ceased to marry relations, the incidence of deaths and serious illnesses among young children would drop by 60 per cent within the space of a generation. The first step towards this, she believes, would be better uptake of genetic counselling by those in the Pakistani community who may be at risk. 'Counselling should be available before conception, as well as in the antenatal clinic and when a child develops a problem that may have a genetic cause,' she argues.

Women thought to be at risk should be offered careful examinations in pregnancy with the option of termination if a serious defect is found. Children should also be followed up carefully to detect any problems as soon as possible.

But Dr Bundey also points out that genetic counselling has to be carried out sensitively. To many in the Pakistani community, she says, 'Marrying a cousin is very important socially and culturally, particularly for those who are in a strange country.' Her study also showed that many families in which there have been first-cousin marriages have had no problems among their children. Understandably, she says, 'they find it hard to accept that there may be a high risk and you can sympathise with that view.'

She recommends that families should think about planning marriages between second cousins rather than between first cousins in future, as this would reduce any risk of genetic disease by a factor of four.

Dr Wagiha Syeda, a community paediatrician in Birmingham who assists Dr Bundey with genetic counselling, recognises that the information conveyed can sometimes be unpalatable to families. In one family, she says, several children had already been severely affected by a disabling hereditary disorder, yet the parents were planning on their daughter marrying her first cousin. 'We have to give our advice very gently. We don't want to injure family relationships. We just want to give the facts so people can make up their own minds.'

She is pleased that many girls from Pakistani families are now seeking genetic advice - even without parental consent - before they get married.

Many doctors also need better information about the risks of cousin marriages. The Health Promotion Research Trust, which funded Dr Bundey's work, has produced a leaflet explaining her findings for GPs in Birmingham; there are also plans for leaflets to be distributed in Birmingham hospital outpatient departments. In addition, Dr Bundey hopes that the local health authority will provide funds for a Muslim genetic counsellor to visit families in their own homes.

Dr Hussein Maqbool, consultant in public health medicine in Birmingham, agrees that education about the risks has to be tackled sensitively, perhaps first by contacting community leaders. 'People have been reluctant to bring up this issue. We need to involve the community themselves so that they don't feel threatened or under attack because of their cultural practices.'

(Photograph omitted)