The ROC curve analysis of eIF2B GEF activity performed towards differential diagnosis between eIF2B-related (n = 63) and eIF2B-unrelated (n = 38) leukodystrophy patients lead to a pathognomonic threshold “≤77.5% of GEF activity”, achieving 100% specificity (95% CL = 90.7–100%) and 88.9% sensitivity (95% CL = 78.4–95.4%), with an almost perfect discrimination (AUC = 0.96±0.024, p<0.0001) (Figure 3). Here, EIF2B1 is linked to leukodystrophy.