Circulating niacin concentration was inversely correlated with BMI (p < 0.0001, Figure 2A) and the lowest levels were observed in individuals affected by obesity and carrying the PNPLA3 CG/GG mutation thus confirming the results obtained in the Discovery cohort (p = 0.0001 at ANOVA, adj p < 0.05 vs PNPLA3 CC with either BMI < 30 or BMI ≥ 30; adj p < 0.01 vs PNPLA3 CG/GG with BMI < 30, Figure 2B). This evidence concerns the gene PNPLA3 and obesity due to melanocortin 4 receptor deficiency.