The case-control study identified the structural risk factors for sleep apnea. The study was complemented by studies in siblings of the patients and controls in order to identify those traits that demonstrated family aggregation not explained by shared environmental factors. The investigators believed that these structural risk factors would interact to increase the risk of sleep apnea. The elucidation of upper airway structural risk factors should provide the basis for developing new, more effective techniques for screening patients for sleep apnea and provide the basis for performing future DNA analyses aimed at identifying the genetic loci for these risk factors.