LEP and obesity due to melanocortin 4 receptor deficiency: In leptin-deficient ob/ob and ObR-deficient db/db mice, colon tumor growth was inhibited, although the animals exhibited severe obesity [226]; moreover, in leptin-deficient ob/ob mice, the presence of abnormally dense mucus-filled goblet cells suggested the possible involvement of leptin in tissue injury and/or mucosal defense mechanisms.