Cross-twin within-trait and cross-trait correlations, stratified by zygosity and gender.

Key points -Difficulties in appropriate social interaction are characteristic of both children with autism spectrum disorders and children with callous-unemotional traits.-Experimental studies suggest that the nature of atypical social cognition that characterises these two profiles is not identical. However, ‘empathizing’ difficulties have been reported in both groups.-Our findings indicate that both social and communication impairments and callous-unemotional traits show modest phenotypic overlap. Aetiological influences accounting for individual differences on each domain were predominantly independent.-Although both children with high levels of ASD traits and children with high levels of callous-unemotional traits exhibit difficulties in appropriate social behaviour, the underlying drivers of these impairments are predominantly distinct.-Difficulties in appropriate social interaction are characteristic of both children with autism spectrum disorders and children with callous-unemotional traits.-Experimental studies suggest that the nature of atypical social cognition that characterises these two profiles is not identical. However, ‘empathizing’ difficulties have been reported in both groups.-Our findings indicate that both social and communication impairments and callous-unemotional traits show modest phenotypic overlap. Aetiological influences accounting for individual differences on each domain were predominantly independent.-Although both children with high levels of ASD traits and children with high levels of callous-unemotional traits exhibit difficulties in appropriate social behaviour, the underlying drivers of these impairments are predominantly distinct.Cross-trait correlations are below the diagonals; within-trait correlations are on the diagonals. Abbreviations: CU = callous-unemotional; SI = Social interaction; SC = Social communication.