AHR and obesity due to melanocortin 4 receptor deficiency: Of particular interest is the role of the aryl hydrocarbon receptor (AHR), which is bound and activated by a variety of POPs including coplanar polychlorinated biphenyls (PCBs) and halogenated aromatic hydrocarbons, in mediating the toxic effects of these compounds at high doses (Alaluusua and Lukinmaa 2006; Ren et al. 2011) and promoting obesity at low doses (Arsenescu et al. 2008; Howell and Mangum 2011).