Table 3.
Twin correlations and variance components estimated from the values of the lobar FA
| Twin correlations |
Percentage of variance estimated under the best model |
Percentage of variance estimated under the full model |
p(A) | p(C) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| MZ | DZ | a2 | c2 | e2 | a2 | c2 | e2 | |||
| Frontal-L | 0.45* (0.07, 0.72) | 0.01 (0, 0.28) | 55.0 (15.3, 100.0) | − | 45.0 (24.7, 85.2) | 55.0 (4.6, 100.0) | 0.0 (0, 32.2) | 45.0 (24.7, 85.2) | 0.04 | 1.0 |
| Frontal-R | 0.65* (0.34, 0.83) | 0.05 (0, 0.43) | 73.5 (37.0, 100.0) | − | 26.5 (14.7, 53.2) | 73.5 (30.0, 100.0) | 0.0 (0, 31.5) | 26.5 (14.7, 53.2) | 0.006 | 1.0 |
| Parietal-L | 0.79* (0.58, 0.90) | 0.02 (0, 0.41) | 84.8 (52.1, 100.0) | − | 15.2 (8.5, 31.4) | 84.8 (51.1, 100.0) | 0.0 (0, 25.7) | 15.2 (8.5, 31.4) | < 0.001 | 1.0 |
| Parietal-R | 0.80* (0.60, 0.91) | 0.12 (0, 0.49) | 84.3 (53.0, 100.0) | − | 15.7 (8.9, 31.2) | 84.3 (48.2, 100.0) | 0.0 (0, 33.4) | 15.7 (8.9, 31.2) | < 0.001 | 1.0 |
| Temporal-L | 0.74* (0.49, 0.88) | 0.56* (0.21, 0.78) | 83.0 (54.7, 100.0) | − | 17.0 (10.2, 31.1) | 43.9 (0, 100.0) | 38.8 (0, 96.3) | 17.3 (10.1, 33.4) | 0.06 | 0.19 |
| Temporal-R | 0.67* (0.37, 0.84) | 0.19 (0, 0.54) | 65.2 (34.8, 100.0) | − | 34.8 (21.1, 61.4) | 65.2 (0, 100.0) | 0.0 (0, 75.2) | 34.8 (21.1, 62.7) | 0.10 | 1.0 |
| Occipital-L | 0.65* (0.35, 0.83) | 0.03 (0, 0.42) | 75.6 (39.6, 100.0) | − | 24.4 (13.5, 49.4) | 75.6 (35.4, 100.0) | 0.0 (0, 28.8) | 24.4 (13.5, 49.4) | 0.003 | 1.0 |
| Occipital-R | 0.61* (0.28, 0.81) | 0.42* (0.03, 0.70) | 65.0 (35.2, 100.0) | − | 35.0 (21.4, 61.2) | 33.6 (0, 100.0) | 30.1 (0, 95.7) | 36.3 (21.5, 65.1) | 0.36 | 0.44 |
For each lobe, the average FA in white matter (defined as FA > 0.3) served as the observed variable for the ACE structural equation models. Values in parentheses indicate the 95% confidence interval, computed using the likelihood-based method (Neale and Miller, 1997). Statistical significance of the relative contributions to the total variance of the lobar FA by the genetic (A) and the shared environmental (C) factors is denoted by p(A) and p(C), presented in bold font if p(A) or p(C) < 0.05. Twin correlations were computed based on the analysis of variance for clustered measures, by comparing the between-group (each twin pair was treated as an individual group) variation and the total variation in values of the lobar FA (Ukoumunne, 2002).
*p < 0.05. L, Left; R, right.