A serum leptin level of approximately 2 μg/L predicts both AN and a lifetime history of secondary amenorrhea in underweight females and also largely separates patients with AN from those with bulimia nervosa (Kopp et al., 1998; Föcker et al., 2011), indicating that serum leptin can be used to screen for AN or serve as a diagnostic marker (Hebebrand and Bulik, 2011). The gene discussed is LEP; the disease is amenorrhea.