We recently reported that PM2.5 exposure was associated with endothelial cell dysfunction in patients with type 2 diabetes and that factors such as obesity and an elevated HbA1c level, as well as deficient antioxidant gene capability (GSTM1 null), enhanced this deleterious association (Schneider et al. 2008). The gene discussed is GSTM1; the disease is obesity due to melanocortin 4 receptor deficiency.