ACE model parameter estimates for concordant ASD and TD twin pairs*
| Parameter | ASD | TD | ASD | TD | ASD | TD | ||||
|---|---|---|---|---|---|---|---|---|---|---|
| a2 (95% CI) | p value | a2 (95% CI) | p value | c2 (95% CI) | p value | c2 (95% CI) | p value | e2 (95% CI) | e2 (95% CI) | |
| Cortical | ||||||||||
| ACC white matter volume | 0.97 (0.80 to 1.14) | < 0.001† | 0.42 (0.08 to 0.77) | 0.02† | x | x | x | x | 0.03 (−0.14 to 0.20) | 0.58 (0.23 to 0.92) |
| ACC grey matter area | 0.95 (0.79 to 1.10) | < 0.001† | — | — | x | x | x | x | 0.05 (−0.10 to 0.21) | — |
| ACC grey matter thickness | x | x | 0.77 (0.52 to 1.01) | < 0.001† | 0.44 (0.22 to 0.66) | < 0.001† | x | x | 0.56 (0.34 to 0.78) | 0.23 (−0.01 to 0.48) |
| OFC white matter volume | 0.65 (0.30 to 1.01) | < 0.001† | — | — | x | x | x | x | 0.35 (−0.01 to 0.70) | — |
| OFC grey matter area | 0.73 (0.40 to 1.06) | < 0.001† | — | — | x | x | x | x | 0.27 (−0.06 to 0.27) | — |
| OFC grey matter thickness | x | x | 0.56 (0.27 to 0.85) | < 0.001† | 0.60 (0.25 to 0.95) | < 0.001† | x | x | 0.40 (0.05 to 0.75) | 0.44 (0.15 to 0.73) |
| Striatal | ||||||||||
| Caudate grey matter volume | 0.89 (0.69 to 1.08) | < 0.001† | 0.64 (0.33 to 0.95) | < 0.001† | x | x | x | x | 0.11 (−0.08 to 0.21) | 0.36 (0.05 to 0.67) |
| Putamen grey matter volume | 0.81 (0.57 to 1.06) | < 0.001† | 0.75 (0.58 to 0.92) | < 0.001† | x | x | x | x | 0.19 (−0.06 to 0.43) | 0.25 (0.08 to 0.42) |
| Pallidum grey matter volume | 0.66 (0.32 to 1.00) | < 0.001† | 0.59 (0.31 to 0.86) | < 0.001† | x | x | x | x | 0.34 (0.00 to 0.68) | 0.41 (0.14 to 0.69) |
| Thalamic | ||||||||||
| Thalamus grey matter volume | — | — | 0.87 (0.70 to 1.05) | < 0.001† | x | x | x | x | — | 0.13 (−0.05 to 0.30) |
a2 = additive genetics; ACC = anterior cingulate cortex; ASD = autism-spectrum disorder; c2 = common or shared family environment; CI = confidence interval; e2 = unique or nonshared environment; TD = typically developing controls.
↵* We calculated ACE models for broad sense heritability separately for twin pairs in which both twins were diagnosed with ASD (monozygotic n = 30 twins/15 pairs; dizygotic n = 30 twins/15 pairs) or were TD controls (monozygotic n = 40 twins/20 pairs; dizygotic n = 28 twins/14 pairs), based on Falconer’s formula45 using a bootstrapping method to calculate estimates across 1000 repetitions. Twin pairs discordant for ASD were excluded. When A or C was nonsignificant in the model (x), we used a constrained AE or CE model. When model assumptions were violated, we did not generate model estimates, but the missing model parameters that would have been most appropriate based on intra-class correlation coefficients are indicated (—). Model parameters sum to 1, and E estimates were not tested for significance because they were based on the residual variation that had not yet been accounted for in the model.
↵† Significant model parameter at false discovery rate46 correction across the estimates in each column.