It turns out that sex offending runs in families: Relatives of sex offenders are five times more likely to commit sex crimes, according to a new study published in the International Journal of Epidemiology.

Brothers and fathers of men who are sexual offenders, in particular, are more likely to also be convicted of sexual offences in comparison to men in the general population who have no ties to a sex criminal. Interestingly, it’s the genetic factors that create this link.

“Importantly, this does not imply that sons or brothers of sex offenders inevitably become offenders too,” Niklas Långström, professor of psychiatric epidemiology at Karolinksa Institute and lead author of the study, said in the press release. “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.”

Researchers from Oxford University and Karolinska Institute examined data on 21,566 men who had been convicted of sexual offences in Sweden between 1973 and 2009. They analyzed the chunk of brothers and fathers of convicted sex offenders who had committed offences themselves, then compared that to Swedish men from the general population. The results showed that 2.5 percent of the brothers and fathers of convicted sex offenders also happened to be sex offenders themselves — compared to the same 0.5 percent in the general population.

Forty percent of this is due to genetic factors, the authors claim, while another 58 percent of difference in risk seems to be due to “non-shared” environmental factors, like complications as a baby in the womb, head injuries, and childhood sexual abuse.

While genetics play a huge role in this, the authors note that this doesn’t necessarily mean that there’s a specific “sex offender gene.”

“We are definitely not saying that we have ‘found a gene for sexual offending’ or anything of the kind,” Professor Seena Fazel, an author of the study, said in the press release. “It tells us something about why if we take two sets of brothers, whose backgrounds might look identical, one set has a higher risk of sexual offending than the other — a large proportion of this difference is likely to be due to genetic factors.”

Fazel continues that in current procedures, genetic factors are rarely taken into account when making risk assessments of people at high risk of sexual offence. “Many of the families we are talking about may already be known to social services for other reasons […] if we can predict those at high risk of offending with greater accuracy, then it may be possible to shape these interventions and target education and preventative therapies where they could do the most good.”

The researchers hope to move their research to the next step by undertaking a large-scale study with biological samples — with the aim of looking for gene patterns that could make it easier to identify potential sex offenders before they commit crimes.

Source: Långström N, Babchishin K, Fazel S, Lichtenstein P, Frisell T. “Sexual offending runs in families: A 37-year nationwide study.” International Journal of Epidemiology. 2015.