Both the original Traj18−/− (10) and the Cd1d−/− (12–14) mice have been used by many different research groups to study the role of iNKT cells and/or type II NKT cells in obesity-related pathologies in high fat diet (HFD)-induced obesity models. The gene discussed is CD1D; the disease is obesity due to melanocortin 4 receptor deficiency.