The risk of having a child born with certain congenital problems may increase with the father's age, US and Danish researchers say. In a study of over 70,000 births, published online in the journal Human Reproduction, they report that the risk of Down syndrome and other conditions begins to increase in children fathered by men aged over 35. The results could be due to genetic mutations in sperm caused by biological or environmental factors, the researchers say.
It is known that the rate of genetic errors in a man's sperm-producing cells increases with age, and previous research has suggested a link between increased paternal age and certain genetic conditions. However, the strong association between older mothers and a raised risk of conditions such as Down syndrome has hampered efforts to investigate the impact of paternal age. In the latest study, the team looked at data from 71,937 firstborn babies born in Denmark between 1980 and 1996. All had mothers aged between 20-29 years, to reduce the potentially confounding effects of increased maternal age.
The researchers found that there was no overall increased risk of birth defects related to increasing paternal age. However, they did find a link between older fathers and a raised risk of certain conditions - including Down syndrome and some syndromes involving multiple body systems or limb malformations. Compared to younger men aged between 20-29 years, the incidence of Down syndrome increased by 15 per cent in men aged over 35, rising to 30-40 per cent in fathers over 40. In men over 50, the risk was around three times higher that of younger men.
Previous research has shown that 5-9 per cent of Down syndrome cases are caused by a chromosome abnormality (an extra copy of chromosome 21) inherited from the father. The scientists say their results suggest that a high paternal age - as well as a high maternal age - could be 'an indication for screening'. They conclude that 'advanced paternal age may be associated with an increased occurrence of some specific malformations, including Down syndrome'.