Table 2.
Generalized additive mixed-effects models examining group and age-related changes in DTI metrics
| Longitudinal DTI changes | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Group | Age spline | Age X group spline | ||||||||
| Mean | Estimate a | P -value | EDF | F | P -value | EDF | F | P -value | ICC | |
| Genu FA | ||||||||||
| ASD and TDC | 0.62 | −3.12% | 0.048 | 3.45 | 3.99 | 0.006 | 4.67 | 2.25 | 0.05 | 89.7% |
| ASD | 0.61 | - | - | 4.31 | 2.11 | 0.075 | - | - | - | |
| TDC | 0.63 | - | - | 5.26 | 5.02 | 0.0002 | - | - | - | |
| Body FA | ||||||||||
| ASD and TDC | 0.61 | −2.40% | 0.001 | 3.99 | 8.95 | **** | 6.33 | 2.41 | 0.02 | 88.3% |
| ASD | 0.61 | - | - | 6.59 | 3.46 | 0.002 | - | - | - | |
| TDC | 0.62 | - | - | 4.25 | 15.64 | **** | - | - | - | |
| Splenium FA | ||||||||||
| ASD and TDC | 0.69 | −2.27% | 0.04 | 5.91 | 9.66 | **** | 1.00 | 0.19 | 0.66 | 81.1% |
| ASD | 0.69 | - | - | 6.65 | 6.89 | **** | - | - | - | |
| TDC | 0.7 | - | - | 3.67 | 11.54 | **** | - | - | - | |
| Genu MD | ||||||||||
| ASD and TDC | 0.76 | 1.63% | 0.46 | 3.60 | 8.06 | **** | 1.00 | 0.07 | 0.78 | 85.9% |
| ASD | 0.76 | - | - | 3.04 | 5.20 | 0.002 | - | - | - | |
| TDC | 0.75 | - | - | 4.87 | 7.06 | **** | - | - | - | |
| Body MD | ||||||||||
| ASD and TDC | 0.79 | 1.90% | 0.23 | 3.49 | 6.39 | 0.0002 | 1.30 | 0.06 | 0.86 | 82.4% |
| ASD | 0.79 | - | - | 3.57 | 6.39 | 0.0002 | - | - | - | |
| TDC | 0.78 | - | - | 3.06 | 12.13 | **** | - | - | - | |
| Splenium MD | ||||||||||
| ASD and TDC | 0.77 | 1.89% | 0.001 | 1.81 | 0.53 | 0.57 | 4.63 | 5.62 | **** | 83.0% |
| ASD | 0.78 | - | - | 4.58 | 8.25 | **** | - | - | - | |
| TDC | 0.76 | - | - | 2.96 | 1.63 | 0.18 | - | - | - | |
| Genu RD | ||||||||||
| ASD and TDC | 0.37 | 5.89% | 0.23 | 3.52 | 3.91 | 0.006 | 3.38 | 1.50 | 0.21 | 87.8% |
| ASD | 0.38 | - | - | 3.80 | 2.75 | 0.03 | - | - | - | |
| TDC | 0.36 | - | - | 4.87 | 5.89 | 0.00007 | - | - | - | |
| Body RD | ||||||||||
| ASD and TDC | 0.4 | 5.33% | 0.08 | 3.89 | 7.46 | 0.00001 | 4.93 | 1.47 | 0.20 | 91.7% |
| ASD | 0.4 | - | - | 5.05 | 4.11 | 0.001 | - | - | - | |
| TDC | 0.38 | - | - | 4.00 | 15.00 | **** | - | - | - | |
| Splenium RD | ||||||||||
| ASD and TDC | 0.32 | 7.54% | 0.01 | 4.72 | 7.92 | **** | 1.00 | 0.70 | 0.40 | 86.6% |
| ASD | 0.33 | - | - | 5.89 | 5.55 | **** | - | - | - | |
| TDC | 0.31 | - | - | 3.34 | 8.66 | **** | - | - | - | |
| Genu AD | ||||||||||
| ASD and TDC | 1.38 | −0.28% | 0.60 | 3.99 | 5.53 | 0.0002 | 1.00 | 0.06 | 0.81 | 85.9% |
| ASD | 1.38 | - | - | 3.10 | 6.10 | 0.0004 | - | - | - | |
| TDC | 1.39 | - | - | 1.87 | 8.58 | 0.0005 | - | - | - | |
| Body AD | ||||||||||
| 1.48 | −0.005% | 0.08 | 1.00 | 4.22 | 0.04 | 2.19 | 2.01 | 0.13 | 56.6% | |
| 1.48 | - | - | 1.93 | 9.72 | 0.0001 | - | - | - | ||
| 1.48 | - | - | 2.66 | 3.25 | 0.03 | - | - | - | ||
| Splenium AD | ||||||||||
| 1.55 | 0.35% | 0.03 | 1.67 | 0.37 | 0.65 | 3.55 | 1.87 | 0.12 | 80.0% | |
| 1.55 | - | - | 3.47 | 2.64 | 0.04 | - | - | - | ||
| 1.54 | - | - | 3.70 | 1.64 | 0.17 | - | - | - | ||
aFor the parametric group differences, the estimate is reported as the percent deviation in the ASD group compared to the TDC group with the corresponding P-value. For the age spline and the age-by-group splines, the estimated degrees of freedom (EDF), F-value, and P-values are reported. ****P-value <0.00005. AD, axial diffusivity; ASD, autism spectrum disorder; EDF, estimated degrees of freedom to assess smooth spline complexity; ICC, intra-class correlation coefficient; FA, fractional anisotropy; MD, mean diffusivity; RD, radial diffusivity; TDC, typically developing controls.