Close male relatives of men convicted of sexual offences are more likely to commit the same types of crimes, Swedish scientists have found. This is due to genetic factors rather than shared family environment, says the team from Sweden's Karolinska Institutet and Oxford University.
"Importantly, this does not imply that sons or brothers of sex offenders inevitably become offenders too," said lead author Niklas Langstrom from Karolinska Institutet.
"But although sex crime convictions are relatively few overall, our study shows that the family risk increase is substantial," Langstrom said.
The results suggested familial clustering of sex offenders, about 2.5 percent of brothers or sons of convicted sex crime offenders are themselves convicted for sex crimes.
The research included all 21,566 men convicted between 1973 and 2009 for sex offences in Sweden -- for example rape of an adult (6,131 offenders) and child molestation (4,465 offenders).
The researchers looked at the share of sex crimes perpetrated by fathers and brothers of convicted male sex offenders and compared this to the proportion among comparison men from the general population with similar age and family relationships.
"Preventive treatment for families at risk could possibly reduce the number of future victims," Langstrom said.
Using a well-established statistical calculation model, the researchers also analysed the importance of genetic and environmental factors for the risk of being convicted of sexual abuse.
"We found that sex crimes mainly depended on genetic factors and environmental factors that family members do not share with one another, corresponding to about 40 percent and 58 percent, respectively," Langstrom explained.
"Such factors could include emotional liability and aggression, pro-criminal thinking, deviant sexual preferences and preoccupation with sex," the researcher said.
The report was published in the International Journal of Epidemiology.
