Sleep apnea is a common condition that affects 4 percent of middle-aged males and 2 percent of middle-aged females. There is recent evidence that there is a genetic influence because first degree relatives of patients with this disorder have an increased risk of having obstructive sleep apnea. The basis for this increased familial risk is undefined. The investigators postulated that there were three specific intermediate traits, each of which reduced upper airway size, thereby increasing the risk of sleep apnea. These intermediate traits included: a) particular distribution of fat in the neck; b) craniofacial structure; and c) size of critical soft tissues in the airway (soft palate, tongue, lateral pharyngeal walls). All of these risk factors could be assessed quantitatively using advanced magnetic resonance imaging and novel volumetric image analysis techniques that had been developed..