As shown in Table 3 and Figure 2, the ROC curve analysis of high-grade liver steatosis in obese and overweight children revealed that γ-GT ≥ 21.50 U/L, FGF-21 ≥ 106.10 pg/mL, TG ≥ 77.00 mg/dL, and BMI ≥ 25.83 kg/m2 were significant predictors with optimal AUROC (0.732–0.840) and good sensitivity (82.5–90.24%); nevertheless, the specificity was relatively lower (50.0–70.50%). This evidence concerns the gene FGF21 and fatty liver disease.