Genetic and environmental aetiology of the dimensions of Callous-Unemotional traits

Background. A Callous-Unemotional trait specifier (termed ‘Limited Prosocial Emotions’) was added to the diagnosis of conduct disorder in DSM-5. The Inventory of Callous-Unemotional Traits (ICU) is a comprehensive measure of these traits assessing three distinct, yet correlated dimensions – Callousness, Uncaring, and Unemotional – all thought to reflect the general Callous-Unemotional construct. The present study was the first to examine the degree to which the aetiology of these dimensions is shared v. independent. Method. Parent-reported ICU data from 5092 16-year-old twin pairs from the Twins Early Development Study were subjected to confirmatory factor analysis. Multivariate genetic modelling was applied to the best-fitting structure. Results. A general-specific structure, retaining a general factor and two uncorrelated specific factors (Callousness-Uncaring, Unemotional), provided the best fit to the data. The general factor was substantially heritable (h2 = 0.58, 95 % CI 0.51–0.65). Unusually, shared environmental influences were also important in accounting for this general factor (c2 = 0.26, 95 % CI 0.22–0.31), in addition to non-shared environmental influences. The Unemotional dimension appeared phenotypically and genetically distinct as shown by the substantial loadings of unemotional items on a separate dimen-sion and a low genetic correlation between Unemotional and Callousness-Uncaring. Conclusions. A general factor, indicative of a shared phenotypic structure across the dimensions of the ICU was under substantial common genetic and more modest shared environment influences. Our findings also suggest that the rele-vance of the Unemotional dimension as part of a comprehensive assessment of CU traits should be investigated further