At the criterion level, ASPD CD had equally strong genetic and environmental longitudinal effects (χ2 < 0.001, d.f. = 1, p = 0.999), whereas these differed for BPD 4 (χ2 = 5.39, d.f. = 1, p = 0.020), the environmental component being negligible in the latter case (Figure 1c). While the AE models made use of all the twin data, they neglected possible non-additive genetic effects. Therefore, we re-examined the possibility of genetic confounding by studying within-twin-pair effects in the genetically identical MZ twins. Qualitatively similar conclusions were recovered, indicating that the findings were robust with respect to the assumptions on additivity of genetic effects and threshold-liability model (Figure 1d). The “ASPD 1” criterion that emerged in the sensitivity analysis without BPD 4 shared characteristics from both BPD 4 and ASPD CD (Supplement, section 3).
