Teenage fathers are more likely to have children with birth defects than men who are in their twenties, a new study has found.
The University of Cambridge study on 24,000 parents and their children found that sperm cells of teenage fathers had 30 per cent higher rates of DNA mutation - increasing the risk of birth defects - compared with those of men in their twenties.
Until now, it had been assumed that DNA mutation in germ cells increases with age, as more cells divide.
Scientists said that the "unexpected" findings would force "textbooks to be rewritten" but said it was not clear why teenage male germ cells are likely to accumulate more DNA errors, which can cause inherited diseases.
Mutations that occur in germ cells - which create sperm or eggs - can cause changes affecting offspring.
The study found the germ cells of adolescent boys have more than six times the rate of DNA mutations as the equivalent egg cells in adolescent girls - and that the number of mutations passed down to children of teenage fathers was higher as a result.
The study compared fathers of different ages. It found that sperm cells in teenagers had approximately 30 per cent higher rates of DNA mutation than those of young men in their twenties, 'The Telegraph' reported.
The study found the levels of DNA mutation in the sperm cells of teenage boys were similar to those of men aged in their late thirties and forties, where the ageing process would be expected to result in an increased the risk of genetic flaws.
Researchers said the findings could explain why the children of younger fathers have been found to have a higher risk of disorders such as autism, schizophrenia and spina bifida, which have some genetic links.
They stressed that the absolute chance of having children with abnormalities remains low for fathers in their teens or forties, with an overall risk of around 2 per cent.
The study found that male germ cells go through around 150 cell divisions by puberty compared to the 22 cell divisions experienced by female germ cells.
Until now, it had been thought that male germ cells had undergone 30 divisions by puberty.
The study was published in the journal Proceedings of the Royal Society B.
