MC4R and fatty liver disease: Mc4r-KO F/F mice at 16 to 19 weeks of age (Figure 6A) had a BW similar to that of 10- to 12-week-old ob/ob F/F mice (Figure 2A) and manifested overt hepatic steatosis accompanied by liver dysfunction — as assessed on the basis of the gross appearance and weight of the liver, Oil Red O staining of liver sections, hepatic lipid content, plasma transaminase levels, and hepatic expression of genes related to ER stress, inflammation, and apoptosis—compared with F/F mice (Figure 6, B–G).