The brothers of men convicted of sex offences are five times more likely than average to commit similar crimes, according to researchers

They also found that the sons of fathers with a criminal record for sex offending were nearly four times more likely to be convicted of such crimes. The biggest study of its kind suggests that sex offending could run in the family along the male genetic line. The findings show that 40% to 50% of the differences in risk between close relatives of offenders and men from the general population were genetically driven. Over the past few years a string of brothers have been convicted of child sex offences, including Mohammed Jumale and his brother Omar Jumale, who were part of a 13-strong gang that raped girls as young as 13-years old. Anjum Dogar, 31, and his brother Akhtar, 32 were jailed in 2013 for the abuse of six girls over the course of eight years in Oxford. The scientists studied data on all men convicted of sexual offences in Sweden between 1973 and 2009. Rates of sexual offending there are similar to those in Britain. Of the 21,566 offenders, nearly half had convictions for adult rape or child molesting. Other crimes included possession of child pornography, indecent exposure and sexual harassment. Evidence from half-brothers sharing either a mother or father and being raised in different family environments supported the idea that genetics played an important role in sexual offending. More than half of the difference in risk was linked to non-shared environmental factors including perinatal complications, head injuries and childhood sexual victimization that affect an individual but are not shared with other family members. Behavioral factors found in sex crimes, such as impulsive behavior, hypersexuality and sexual deviance, may be genetic-based drivers for the offences, said the researchers.