MEN over 40 have an increased risk of fathering a baby with Down鈥檚 syndrome, according to French researchers. The risk of having a Down鈥檚 baby is known to increase with the age of the mother, but a link with the father鈥檚 age has never been proven.
Researchers at INSERM, France鈥檚 national medical research agency, studied 11 535 pregnancies resulting from artificial inseminations carried out at 22 fertility clinics across France. They divided the pregnancies into three groups according to the age of the sperm donor, and then calculated the percentage of Down鈥檚 babies born in each group. The preliminary results, which are unpublished, show that 0.14 per cent of the children born to fathers under 35 had Down鈥檚 syndrome, compared with 0.23 per cent of babies born to men aged between 35 and 39, and 0.41 per cent born to men over 39 鈥� an almost threefold increase over those in the youngest age group.
Paul Jalbert, who coordinated the research at the Centres for the Study and Conservation of Human Eggs and Sperm (CECOS), says that the age of mothers can be discounted. In most pregnancies both parents are of a similar age. In such cases, any additional risk of having a Down鈥檚 baby associated with the father鈥檚 increased age is masked by the known risk due to increasing maternal age. Because the ages of the mothers were similar in each of the three donor groups in the CECOS study, it can be assumed that the father鈥檚 age is the main variable, says Jalbert.
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He warns, however, that the results must be interpreted cautiously because of the small number of Down鈥檚 cases in the study: 25 in all. 鈥淭he study needs to be taken further using techniques which would show whether the origin of the Down鈥檚 syndrome was maternal or paternal,鈥� he says. People with Down鈥檚 syndrome have three copies of chromosome 21 instead of two. By comparing the extra chromosome with those of the parents, says Jalbert, it is possible to find out who the extra copy came from.
CECOS has decided not to accept sperm from men over 45. Jalbert says this is because of mounting evidence that some genetic diseases such as achondroplasia 鈥� a form of dwarfism 鈥� are more common among children fathered by older men. But the maximum age will not be lowered in the light of the new findings until the results are confirmed. CECOS has another 10 000 cases to analyse.
Howard Cuckle, professor of reproductive epidemiology at the University of Leeds Medical School, says that the consensus of opinion up to now has been that the age of the father has no effect on the incidence of Down鈥檚 syndrome. 鈥淏ut these results show a clear trend,鈥� he says. 鈥淚t鈥檚 a first step.鈥�