LEP and hypogonadism: Mice lacking leptin (ob/ob, Lep gene) or leptin receptor (db/db, Lepr gene) are obese, infertile, and have hypogonadism, among other disturbances (Barash et al., 1996; Chehab et al., 1996; Casanueva and Dieguez, 1999; Elias and Purohit, 2013).