Graziano PA, et al. - In the present study, the researchers sought to investigate differences in the white matter microstructure in the uncinate fasciculus (UF) and other major fiber tracks between young typically developing (TD) children and those with a disruptive behavior disorder (DBD), as well as whether individual differences in these white matter tracts relate to co-occurring conduct problems (CP) and callous-unemotional (CU) behaviors within the DBD group. The sample consisted of 198 young children (69% boys, M _age = 5.66 years; 80% Latinx; 48.5% TD). A combination of teacher and parent ratings was used to assess CU behaviors and CP. Even after accounting for whole brain FA, gender, movement, parental income, and IQ, children in the DBD group had reduced FA on four out of the five fiber tracks studied (except for cingulum and right ILF) compared with TD children. Even in very young children, changes in the white matter microstructure within bilateral UF and left IFOF may be biomarkers of CU behaviors.