1 in 25 men in dark as they raise others' children

One father in 25 could unknowingly be bringing up a child who is not his own, says new research that suggests a rise in genetic testing has opened a Pandora's box of sexual secrets and lies. Genetic testing for diseases in families is growing and can reveal a child's real paternity, leaving doctors to decide how much to disclose to the family.

One of the authors of the study, Prof Mark Bellis, of the centre for public health at Liverpool John Moores University, said: "Twenty years ago doctors would have tended not to tell when they came across this information unless it was important for the health of the child. "But advances in genetics mean that there is now more pressure for a child to know who his or her biological parents are." The study found that the general rate of what Prof Bellis calls "paternal discrepancy" across western populations was usually given as about 10 per cent. But his work, based on studies between 1950 and last year, which gave proof of paternity through blood or DNA testing, found rates as low as one per cent and as high as 30 per cent, with a median of four per cent.