For the dACC/MCC rCMRglu ROI, the PTSD main effect yielded F1,31.2 = 18.0, P <.001. The following covariates were screened as potential confounders of this result by examining their association with the dependent measure using a screening threshold of P < .2: weeks born premature, birth weight, age, total score on the Childhood Trauma Questionnaire, education, Beck Depression Inventory score, MAST score, Positive and Negative Affect Schedule scores, and severity of combat exposure (in the exposed twin). Only combat severity met this threshold. Adjusted for combat severity, the PTSD main effect yielded F1,30.4 = 7.8, P = .009. Parallel analyses in combat-exposed participants alone indicated that only birth weight and combat severity were potential confounders. Unadjusted, the PTSD main effect yielded F1,31 = 11.5, P = .002 (adjusted for birth weight, F1,27 = 9.2, P = .005; adjusted for combat severity, F1,30 = 5.0, P = .03). Parallel analyses in participants not exposed to combat alone indicated that only MAST score and combat severity were potential confounders. Unadjusted, the PTSD main effect yielded F1,31 = 28.2, P < .001 (adjusted for MAST score, F1,27 = 28.2, P < .001; adjusted for combat severity, F1,30 = 10.1, P = .004).