Table 1. Cross-twin within-trait and cross-trait correlations, stratified by zygosity and gender.
Cross-trait correlations are below the diagonals; within-trait correlations are on the diagonals. Abbreviations: CU = callous-unemotional; SI = Social interaction; SC = Social communication.
| Monozygotic Males | CU, Twin 1 | SI, Twin 1 | SC, Twin 1 |
| CU, Twin 2 | .68 (.65 - .70) | - | - |
| SI, Twin 2 | .24 (.20 - .27) | .76 (.73 - .78) | - |
| SC, Twin 2 | .23 (.20 - .27) | .26 (.23 - .29) | .81 (.79 - .82) |
| Dizygotic Males | CU, Twin 1 | SI, Twin 1 | SC, Twin 1 |
| CU, Twin 2 | .34 (.29 - .39) | - | - |
| SI, Twin 2 | .07 (.03 - .11) | .30 (.24 - .35) | - |
| SC, Twin 2 | .10 (.06 - .15) | .06 (.01 - .10) | .41 (.35 - .45) |
| Monozygotic Females | CU, Twin 1 | SI, Twin 1 | SC, Twin 1 |
| CU, Twin 2 | .64 (.61 - .67) | - | - |
| SI, Twin 2 | .17 (.14 - .21) | .70 (.68 - .73) | - |
| SC, Twin 2 | .16 (.13 - .20) | .18 (.15 - .22) | .80 (.78 - .82) |
| Dizygotic Females | CU, Twin 1 | SI, Twin 1 | SC, Twin 1 |
| CU, Twin 2 | .31 (.27 - .35) | - | - |
| SI, Twin 2 | .07 (.03 - .12) | .34 (.29 - .39) | - |
| SC, Twin 2 | .12 (.08 - .16) | .10 (.06 - .14) | .50 (.46 - .54) |
| Dizygotic opposite-sex | CU, Twin 1 | SI, Twin 1 | SC, Twin 1 |
| CU, Twin 2 | .44 (.39 - .48) | - | - |
| SI, Twin 2 | .09 (.05 - .13) | .29 (.23 - .34) | - |
| SC, Twin 2 | .13 (.09 - .16) | .11 (.07 - .15) | .46 (.41 - .50) |
Key points
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-Difficulties in appropriate social interaction are characteristic of both children with autism spectrum disorders and children with callous-unemotional traits.
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-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.
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-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.
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-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.