To deepen whether the I148M variant may influence niacin metabolism, we evaluated the hepatic NAD biosynthesis and we found that NAPRT1, involved in the canonical NAD pathway, was reduced in subjects with the PNPLA3 G risk allele independently of steatosis grade, mirroring the low serum niacin levels observed in both Discovery and Validation cohorts. The gene discussed is PNPLA3; the disease is steatosis.