Close relatives of men convicted of sexual offenses commit similar offenses themselves more frequently than comparison subjects, according to a recent study.

Researchers from Sweden's Karolinska Institutet and Oxford University believe this is due to genetic factors rather than shared family environment. The study includes all men convicted of sex crime in Sweden during 37 years.

"Importantly, this does not imply that sons or brothers of sex offenders inevitably become offenders too", Niklas Langstrom, lead author of the study, said in a statement. "But although sex crime convictions are relatively few overall, our study shows that the family risk increase is substantial. Preventive treatment for families at risk could possibly reduce the number of future victims."

For the study, researchers collected and analyzed data from nearly 22,000 men convicted for sex offences in Sweden between 1973 and 2009. 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.

The findings suggest that 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 equivalent figure for men in the general population is about 0.5 percent. Using a well-established statistical calculation model, the researchers also analyzed 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 said. "Such factors could include emotional lability and aggression, pro-criminal thinking, deviant sexual preferences and preoccupation with sex."

Self-reported sexual victimization rates in Sweden are largely similar to those in other Western and central European nations, Canada and the United States.

Researchers said other cross-national comparisons of police-reported offenses should be done cautiously because of differences in legal definitions, methods of offence counting and recording, and low and varying reporting rates of sexual violence to the police.

The findings are detailed in the International Journal of Epidemiology.