1. Division of Pulmonary, Sleep and Critical Care Medicine, Department of Internal Medicine, Korea University Ansan Hospital, Korea University College of Medicine, Ansan, Korea.
2. Department of Otorhinolaryngology-Head and Neck Surgery, Korea University Ansan Hospital, Korea University College of Medicine, Ansan, Korea.
3. Institute of Human Genomic Study, Korea University Ansan Hospital, Korea University College of Medicine, Ansan, Korea.
4. Department of Sleep Medicine, Shiga University of Medical Science, Otsu, Japan.