C4B and major depressive disorder: Notably, 75% of the WM tracts identified as significantly altered in MDD in our primary analysis remained detectable in this external dataset, including the CG, CH, Fmin, Fmaj, ILF, and SLF (|Cohen's d| > 0.21, P < 0.022, FDR q < 0.05, Fig. S11 and Table S12).