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Brothers and fathers of men convicted of sexual offences are up to five times more likely to be convicted of sexual offences than men in the general population, a new study shows. Genetic factors were found to make a substantial contribution to this increased risk with the shared family environment having a relatively small influence.

Sex offending genes more important than family environment

The study, by researchers from Oxford University (UK) and the Karolinska Institute (Sweden), used statistical methods to analyse data on all 21,566 men convicted of sexual offences in Sweden between 1973 and 2009.

The researchers looked at the share of sexual offences perpetrated by fathers and brothers of convicted male sex offenders and compared this to the proportion among Swedish men from the general population with similar age and family profiles. They found that around 2.5% of brothers or fathers of convicted sex offenders are themselves convicted of sexual offences. This compares to convicted sex offenders making up about 0.5% of men in the general population.

Having a brother convicted of a sexual offence led to five times the risk of a man being convicted of a sexual offence compared to a man whose brother had not been convicted of this type of crime. Meanwhile, being a father of a man convicted of a sexual offence led to almost four times the risk of being convicted of a sexual offence.

Statistical modelling suggests that around 40% of the difference in risk seen between brothers and fathers of convicted sexual offenders and brothers and fathers of those without such a conviction is due to genetic factors. Around 58% of the difference in risk appears linked to ‘non-shared’ environmental factors (such as perinatal complications, head injuries, childhood sexual victimisation, and peer group attitudes) that affect an individual but are not shared with other family members. Evidence on the difference in risk between maternal and paternal half-brothers (presumably reared in separate family environments) supports the idea that genetics makes a substantial contribution to increased risk.

A report of the research is published under open access in the International Journal of Epidemiology.*

‘Importantly, this does not imply that sons or brothers of sex offenders inevitably become offenders too. 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,’ said Niklas Långström, Professor of Psychiatric Epidemiology at Karolinska Institute and the study’s lead author.

‘We are definitely not saying that we have ‘found a gene for sexual offending’ or anything of the kind. What we have found is high quality evidence from a large population study that genetic factors have a substantial influence on an increased risk of being convicted of sexual offences,’ said Professor Seena Fazel of Oxford University’s Department of Psychiatry, an author of the paper. ‘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.

‘At the moment genetic factors are typically ignored when it comes to making risk assessments of those at high risk of sexual offending. We know that current tools are not very effective at predicting who might commit sexual offences and it could be that taking family risk into account would lead to more accurate predictions. Many of the families we are talking about may already be known to social services for other reasons, and 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,’ said Professor Fazel.

Any conviction for a sexual offence under the Swedish Penal Code over the 37 year period was counted as a sexual conviction. This included convictions for the rape of an adult (6,131 offenders), child molestation (4,465 offenders) as well as crimes such as possession of child pornography, indecent exposure, and sexual harassment. Rates of sexual offending in Sweden are largely similar to those reported in the UK, Europe, the USA and Canada. Whilst direct comparisons should be handled cautiously, the type of offences that lead to such convictions in Sweden, as well as its recording methods and reporting levels, are thought to make it broadly comparable to other European countries.

Professor Fazel said: ‘Our research was epidemiological but a logical next step would be to devise a large-scale study that included biological samples, and could include a wider set of outcomes and intermediaries. In this way it would be possible to look for patterns in genes that might contribute to a higher risk of problem sexual behaviours alongside environmental factors.’

For more information contact the Oxford University News Office on +44 (0)1865 283877 or email news.office@admin.ox.ac.uk


*A report of the research, entitled ‘Sexual offending runs in families: A 37-year nationwide study’, by Niklas Långström, Kelly M. Babchishin, Seena Fazel, Paul Lichtenstein & Thomas Frisell, is published in the International Journal of Epidemiology

 Press & Media Response

Study into gene link in sex attackers BBC News online, 09/04/2015

Men with a brother found guilty of a sex offence are up to five times more likely than average to commit a similar crime, a study suggests. Genetic factors had a ‘substantial influence’ on the risk of being convicted of a sex offence, it found. The study analysed data from 21,566 men convicted of sex offences in Sweden between 1973 and 2009. The study – by researchers from Oxford University and the Karolinska Institute, in Sweden - looked at the proportion of sexual offences carried out by sons and brothers of convicted male sex offenders. The authors then compared the data with the criminal records of men from the general Swedish population with similar age and family profiles. It found around 2.5% of brothers of convicted sex offenders were themselves convicted of sexual offences - compared with 0.5% of men in the general population. Genetic factors were found to have a ‘substantial influence on an increased risk of being convicted of sexual offences’, Professor Seena Fazel, one of the co-authors, said. ‘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,’ he said. The analysis could help authorities target potential offenders, Professor Fazel said, adding: ‘At the moment genetic factors are typically ignored when it comes to making risk assessments of those at high risk of sexual offending.’

Sex crimes may run in a family's male genes Daily Mail, 09/04/2015, p.20, Jenny Hope

The brothers of men convicted of sex offences are five times more likely than average to commit similar crimes, according to researchers from Oxford University and the Karolinska Institute. The biggest study of its kind suggests sex offending could run in the family along the male genetic line. The findings show that 40 to 50 per cent of the differences in risk between close relatives of offenders and men from the general population were genetically driven. But the researchers stressed that this did not mean a man with a brother or father convicted of rape would inevitably follow in their footsteps. Lead scientist Professor Niklas Langstrom, from the Karolinska Institute in Sweden, said: ‘It’s important to remember that it’s nothing mystic. ‘Of course you don’t inherit in some kind of automatised robotic way so that you will grow up to be a sexual offender.’ In terms of absolute risk, being closely related to an offender only led to a small increase in the chances of committing a sexual crime. Just 2.5 per cent of brothers of sex offenders were convicted of similar crimes, compared with 0.5 per cent of men in the general population, according to the study reported in the International Journal of Epidemiology. Co-author Professor Seena Fazel, from Oxford University, said: ‘We are definitely not saying that we have found a gene for sexual offending What we have found is high-quality evidence from a large population study that genetic factors have a substantial influence.’ The findings may point the way towards providing better social help to at-risk families, many of which were already known to social services, said the authors.

Radio: Today, BBC Radio 4

09/04/2015, 7:50

The brothers and fathers of men convicted of sex offenders are up to five times more likely to be convicted of a similar crime, and genetic make-up may be the key, a new study suggests. Study author Professor Seena Fazel of Oxford University is interviewed: ‘…we thought the genetic contribution probably contributes between 30 to 50 percent of the risk, and we did that by using different ways of modelling the family pedigree, so for instance if you take a family where you have a half-brother growing up in the same family as a full brother we found quite a large difference in risk of sexual offending. They are growing up in the same environment and yet the only difference between them is a genetic difference of around 25%... there may also be something specific to sexual offending and that might also be genetically determined, for instance hypersexuality and not being able to figure out boundaries in relationships… prevention is key here… if there are high risk families already receiving services from child and family services…it might be that these families can receive other interventions around normal relationships…’

Also:

Sex crime is ‘genetically influenced’, finds biggest study yet The Independent, 09/04/2015, p.1, Steve Connor

Risk of sex offending linked to genetic factors, study finds The Guardian online, 09/032015, Hannah Devlin

Sex offenders' brothers five times more likely to commit rape or assault Daily Telegraph, 09/04/2015, p.11, Sarah Knapton

Sex Offenders Could Be 'Influenced' By Genes Sky News online, 09/04/2015, Thomas Moore

Sex offending runs in the family, warn scientists i (The paper for today), 09/04/2015, p.11, Steve Connor

Sex offender tendencies are genetic The Times, 09/04/2015, p.17, Oliver Moody

The rape gene The Sun, 09/04/2015, p.17, Nick McDermott

Radio: Wake up to Money, BBC Radio 5 09/04/2015, 05:15

TV: Breakfast, BBC One 09/04/2015, 06:34

 and more Press & Media Responses

Relatives of Rapists More Likely to Offend, Finds Study Newsweek (USA), 09/04/2015, Conor Gaffey

Male relatives of sexual offenders are up to five times more likely to commit similar offences, researchers have found. The Swedish-led study also revealed that genetic factors explain around 40% of the liability to commit sexual crimes, rising to 46% in the case of child sexual offences specifically. Among brothers and fathers of sexual offenders, 2.5% went on to offend themselves, compared to 0.5% of unrelated males. Co-author Seena Fazel, professor of forensic psychiatry at the University of Oxford, believes that the findings should lead to preventative intervention with families of sexual offenders. ‘These type of offences do run in families,’ says Fazel. ‘This doesn’t mean in any way that it’s inevitable these brothers are going to offend but there is an increased risk.’ Fazel suggests that if social services are already working with high-risk families, those services may wish to ‘optimise’ by offering advice on relationship management and impulse control to relatives.

Also:

Radio: Newshour, BBC World Service Radio 09/04/2015, 14:24
A new study, conducted by researchers from Oxford University and the Karolinska Institute in Sweden, suggests genetic factors may play a role in determining how likely someone is to commit sexual offences. Seena Fazel, report co-author and Professor of Forensic Psychiatry at the University of Oxford is interviewed.
(Around 18:38 on the clock)

Radio: Newsdrive, BBC Radio Scotland  09/04/2015, 16:41 and 16:47
Professor Seena Fazel is interviewed.

Radio: Morning Reports, BBC Radio 5 Live 09/04/2015, 05:02

Genetics can make people more likely to commit sex offenses, study says CNN (USA), 09/04/2015, Don Melvin

Radio: The Morning News, LBC 97.3 09/04/2015, 06:41
Professor Seena Fazel is interviewed.

Sex crimes influenced by genes in families: Study Times of India, 10/04/2015, via IANS

Sex offences could be in the genes Brisbane Courier-Mail (Australia), 09/04/2015

Sex offences could be in the genes Daily Telegraph (Australia), 09/04/2015

Will DNA link to sex-offending let paedophiles and rapists off the hook? Daily Express online, 09/04/2015, Rebecca Perring

Your genes may determine whether you're a sex attacker, study claims The Mirror online, 09/04/2015, John von Radowitz

Radio: Drivetime - BBC London 94.9 FM 09/04/2015, 18:50

Sex offences may run in a family’s DNA Oxford Mail, 10/04/2015, p. 18

Radio: Nick Ferrari, LBC 97.3 09/04/2015, 07:02

Radio: Breakfast, BBC Radio Oxford 09/04/2015, 06:02, 06:17, 06:35, 06:48, 07:02, 7:09, 7:16, 07:36, 07:48, 8:02, 08:12, 08:16, 08:32 and 08:50
Professor Seena Fazel is interviewed.

Radio: Drivetime, BBC Radio Oxford  09/04/2015, 17:00, 17:06, 17:18, 17:31 and 17:46

Even more press & media responses:

We can identify men at risk of committing sex crimes, but will we help them? The Guardian, 11/04/2015, p.31, Deborah Orr

Comment piece following the publication of research from the University of Oxford and the Karolinska Institute in Sweden which analysed data about 21,566 sex offenders and found that the brothers of men convicted of sex crimes are five times more likely to commit a sexual assault than an average man. Half-brothers were much less likely to carry out attacks than full brothers, even if they were brought up in the same household.
The author comments: ‘The study’s conclusion is that around 40% of the risk of committing a sex crime is genetic. The scientists are at pains to emphasise that their findings do not imply that it is inevitable that some men will carry out sex attacks, or that they will not be responsible for their actions if they do. They understand all too well how wary society is of evidence that seems to offer people excuses for their aberrant, abusive or cruel behaviour. Those who conducted the study speak instead of targeted psychological support for men at risk of sex offending.’

Also:
Can our DNA turn us into criminals? The Telegraph online, 10/04/2015, Neil Levy

Neil Levy, deputy director at the Oxford Centre for Neuroethics, comments on new research indicating that there is a substantial genetic component to the risk of sexual offending. It shows that sons and brothers of sex offenders are far more likely to be sex offenders themselves than the general population and half-brothers – who share a home with sexual offenders but not their genes – are much less likely to become sex offenders than full brothers: ‘This research is both fascinating and important. But beware, several complex questions need be answered to grasp its full significance… It doesn’t show, for example, that there is a “sex offending gene” that can be isolated, or that we could screen for risk of sexual offending by conducting genetic tests… it doesn’t show that sex offenders are less blameworthy or less responsible for their actions. The scientists who conducted the research have tried to tackle some of these misunderstandings straight away, warning that instead of discovering a “gene for sexual offending”, what they had actually done is shown that genes themselves make a significant contribution (explaining around 40 per cent of the increased risk of offending)… it is very unlikely that there is a single gene for sex offending… The genes that contribute to sex offending are likely to be multiple, and many of them are probably gene variants that are innocuous or even beneficial in other contexts… We are not automata, under the control of our genes. Quite the reverse; the findings of this study may in fact help us increase our control over our destinies...’