Two G protein–coupled receptors for cysLTs have been characterized and designated as cysteinyl leukotriene receptor 1 (CysLT1) and cysteinyl leukotriene receptor 2 (CysLT2).13,14 CysLT1 mediates bronchoconstriction and proinflammatory effects, including activation and migration of leukocytes.15,16 CysLT1 antagonists, including montelukast, are approved for clinical use in patients with asthma and allergic rhinitis. The gene discussed is CYSLTR2; the disease is asthma.