BACKGROUND: Sexual crime is an important public health concern. The possible
causes of sexual aggression, however, remain uncertain. METHODS: We examined
familial aggregation and the contribution of genetic and environmental factors to
sexual crime by linking longitudinal, nationwide Swedish crime and
multigenerational family registers. We included all men convicted of any sexual
offence (N = 21,566), specifically rape of an adult (N = 6131) and child
molestation (N = 4465), from 1973 to 2009. Sexual crime rates among fathers and
brothers of sexual offenders were compared with corresponding rates in fathers
and brothers of age-matched population control men without sexual crime
convictions. We also modelled the relative influence of genetic and environmental
factors to the liability of sexual offending. RESULTS: We found strong familial
aggregation of sexual crime [odds ratio (OR) = 5.1, 95% confidence interval (CI)
= 4.5-5.9] among full brothers of convicted sexual offenders. Familial
aggregation was lower in father-son dyads (OR = 3.7, 95% CI = 3.2-4.4) among
paternal half-brothers (OR = 2.1, 95% CI = 1.5-2.9) and maternal half-brothers
(OR = 1.7, 95% CI = 1.2-2.4). Statistical modelling of the strength and patterns
of familial aggregation suggested that genetic factors (40%) and non-shared
environmental factors (58%) explained the liability to offend sexually more than
shared environmental influences (2%). Further, genetic effects tended to be
weaker for rape of an adult (19%) than for child molestation (46%). CONCLUSIONS:
We report strong evidence of familial clustering of sexual offending, primarily
accounted for by genes rather than shared environmental influences. Future
research should possibly test the effectiveness of selective prevention efforts
for male first-degree relatives of sexually aggressive individuals, and consider
familial risk in sexual violence risk assessment.The Swedish Prison and Probation Service R&DThe Swedish Research CouncilThe Wellcome TrustThe CIHR Banting fellowship programPublishe
