23 Sleep and Hypnosis, 12:1-2, 2010 INTRODUCTION O bstructive sleep apnea (OSA) is defined specifically as the occurrence of repetitive episodes of complete or partial obstruction of the upper airway during sleep, usually in association with loud snoring and daytime sleepiness. Such episodes are often associated with arousals, sleep fragmentation, intermittent hypoxaemia and hypercapnia, and nocturnal hypertension (1,2). Associated nocturnal symptoms include restlessness, excessive salivation and sweating, nocturia, and gastro- esophageal reflux. The patient frequently wakes in the morning with a headache and dry mouth or throat. OSA is now recognized to occur commonly, affecting 2 to 3% of children, (3) 2% to 4% of middle-aged adults, (4) and 10% of the elderly population. Among people over 55 years of age, 30 to 60% meet the polysomnographic diagnostic criterion of an apnea-hypopnea index (AHI) of ≥5 (3). The association of OSA with several chronic health conditions, particularly obesity, hypertension, diabetes, and cardiovascular diseases, (5,6,7) has underscored the broad public health importance of this condition. Obstructive Sleep Apnea and Genes Surya Kant, M.D., Harshita Gupta, M.Sc., S.M.Natu, Ph.D, Pooran Chand, M.D.S, and Saumendra Vikram Singh, M.D.S Obstructive sleep apnea (OSA) is a disorder in which complete or partial obstruction of the airway during sleep causes loud snoring, oxyhemoglobin desaturation, and frequent arousals. As a result, affected persons have unrestful sleep and excessive daytime sleepiness. Potential genetic interaction between obesity and OSA phenotypes is one in which a particular polymorphism leads to both obesity and OSA through independent mechanisms. Reductions in serotoninergic activity, by increasing appetite, could promote obesity and by lowering muscle tone in the upper airway, promote OSA. Presence of the arginine 64 allele of the ß3-adrenergic receptor gene does not increase the risk of OSA syndrome, but is associated with the development of obesity in those patients who suffer OSA syndrome. Both shared and unshared genetic factors underlying susceptibility to OSA and obesity, and the genetic determinants of obesity in this population may be modulated by apnea severity. Other genetic loci reviewed likely interact with obesity to influence development of OSA in a gene-by-environment type of effect. Conversely, environmental stressors, such as intermittent hypoxia and sleep fragmentation produced by OSA, may interact with obesity susceptibility genes to modulate the importance that these loci have on defining obesity-related traits. (Sleep and Hypnosis 2010;12(1-2):23-34) Key words: Obstructive sleep apnea, excessive daytime sleepiness, phenotypes, genetic loci. REVIEW ARTICLE From Department of Pulmonary Medicine (Drs. Kant and Gupta), Department of Pathology (Dr. Natu), and Department of Prosthodontics (Drs. Singh and Chand), C. S. M. Medical University (Erstwhile King George Medical College), U. P., Lucknow, India Address reprint requests to: Surya Kant, M.D. (Gold Medalist), FCCP (USA), FIMSA, FNCCP, FCAI, FICS, FIAB, Department of Pulmonary Medicine, C. S. M. Medical University (Erstwhile King George Medical College), U. P., Lucknow Tel: + 91-522-2255167 Fax No: - 0522-2255167 Email: - dr.kantskt@rediffmail.com Accepted September 10, 2010