Do teenagers have 'genetically weak' sperm?

Teenage boys already have plenty to worry about: spots, girls and the size of their "thing", as Adrian Mole might have put it. Does the problem of having "genetically weak" adolescent sperm really need to be added to this list?

Scientists at the University of Cambridge have suggested this is the case after carrying out a study involving more than 24,000 parents and their children. The analysis focused on tiny genetic differences between parents and children, which are assumed to be caused by copying errors in the egg or sperm cells.

The study shows that, on average, fathers pass on at least six times as many of these mutations to their children as mothers. This suggests sperm DNA is a less faithful replication of the father's genetic sequence, probably because sperm cells have undergone more divisions than the female egg cell by the time that conception occurs. The more striking claim - and the one that got most attention - is that the error rate in the sperm cells of teenage boys is about 30 per cent higher than that for young men. The researchers say higher levels of mutations in teenage sperm could explain "why the children of teenage fathers have a higher risk for disorders such as autism, schizophrenia and spina bifida".

The author of the paper, Peter Forster, said: "Children of 15-year-old boys have about 30 per cent more mutations than children of young men. It's a J-shaped distribution".

This probably translated to a risk of birth defects of about 2 per cent for teenage boys, compared with an average risk of 1.5 per cent, he said.