The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor essential for a variety of cellular functions; for example, this receptor is involved in xenobiotic sensing [7], normal physiological functions (such as liver development [8,9], immune response [10,11], and hematopoietic stem cell differentiation [12]), and many diseases (such as breast and other cancers [13,14,15], cardiac disorders [16,17], respiratory disorders [18,19], metabolic disorders [20,21], and macular degeneration [22,23]). This evidence concerns the gene AHR and respiratory system disorder.