Insulin-like growth factor 2 (Igf2), which is one of the best known epigenetically imprinted genes, and a key intra-ovarian regulator of follicular development and steroidogenesis [14, 15], is associated with greater body weight, obesity [16, 17], and polycystic ovary syndrome [18, 19]. The gene discussed is IGF2; the disease is obesity due to melanocortin 4 receptor deficiency.