A study in Mexico City, at a similar elevation (2300 m vs. 1350 m for Ulaanbaatar) reported that for healthy, normal-weight 11 ± 3 year-olds, exposure to PM2.5 concentrations near 20 μg/m3, together with elevated ozone levels, are “associated with 12 h fasting hyperleptinemia, altered appetite-regulating peptides, vitamin D deficiency, and increases in ET-1 in clinically healthy children. The gene discussed is EDN1; the disease is vitamin D deficiency.