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Dr Essi Viding, Social Genetic and Developmental Psychiatry Centre, P080, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, UK. Email: [email protected]
Declaration of interest
None. Funding detailed in Acknowledgements.
One delineator of heterogeneity within children with early-onset antisocial behaviour is a callous and unemotional disposition (Frick & Morris, 2004; Lynam & Gudonis, 2005). This designates a subgroup of children/youths with a more-severe, aggressive and stable pattern of antisocial behaviour and a specific neurocognitive profile indicative of defects in affect processing (Lynam & Gudonis, 2005;Blair, 2006). These are all markers that could be considered precursors of adult psychopathy and as such warrant careful study. We recently conducted the first twin study of callous–unemotional traits and conduct problems in childhood. High levels of callous traits were found to be under strong genetic influence (Viding et al, 2005). This finding was consistent with behavioural genetic studies of psychopathic personality in youth and adults (Bloningen et al, 2003; Taylor et al, 2003; Larsson et al, 2006). Furthermore, when twins with conduct problems were divided according to the presence of callous traits, a strong genetic influence on conduct problems was found.
These results provide strong support for the use of callous–unemotional traits to designate children with early-onset conduct problems who may have distinct causal processes leading to their antisocial behaviour. The present study expanded on these findings by examining the extent of genetic and environmental influences on the relationship between these two important dimensions in 7-year-old twins. Extremes in combination could be highly heritable simply because individual differences across the continuum are highly heritable, even if they are genetically uncorrelated. If common genes are important mediators of the relationship, molecular genetic analyses should focus on finding the common genes that mediate the risk.
Two twin studies to date have addressed the extent of overlap in the genetic influences on callous–unemotional traits and antisocial behaviour/lifestyle (Taylor et al, 2003; Larsson et al, 2006). In both studies the genetic influences on the two domains showed substantial overlap, although independent genetic influences were also observed. Both studies were conducted on youths and young adults only, some of whom may have had a childhood onset to their antisocial behaviour. In addition, neither study focused on extreme of...