Treatment of ob/ob mice with physiological doses of leptin (to match WT serum levels) reverses insulin resistance (Pelleymounter et al., 1995), as it does in lipodystrophic mice and humans (Petersen et al., 2002; Shimomura et al., 1999), suggesting this could be the mechanism of action of muscle mass accretion with leptin treatment. The gene discussed is LEP; the disease is Insulin resistance.