Heritability estimates for mean volumes of each of the eight structures in this study were calculated using structural equation modelling in OpenMx39. Twin modelling was performed controlling for age and sex differences on a large sample (n = 1,030) of healthy adolescent and young adult twins (148 monozygotic and 202 dizygotic pairs) and their siblings from the Queensland Twin Imaging (QTIM) study. Subsequently, a multivariate analysis showed that common environmental factors (C) could be dropped from the model without a significant reduction in the goodness-of-fit (Δχ236 = 29.81; P = 0.76). Heritability (h2) was significantly different from zero for all eight brain measures: putamen (h2 = 0.89; 95% confidence interval 0.85–0.92), thalamus (h2 = 0.88; 0.85–0.92), ICV (h2 = 0.88; 0.84–0.90), hippocampus (h2 = 0.79; 0.74–0.83), caudate nucleus (h2 = 0.78; 0.75–0.82), pallidum (h2 = 0.75; 0.72–0.78), nucleus accumbens (h2 = 0.49; 0.45–0.55), amygdala (h2 = 0.43; 0.39, 0.48) (Extended Data Fig. 11a).
