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.