Studies in the genetics of sleep apnea-surveillance on familial aggregation of the disorder and its causes

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1. We reported a family in which 6 of 29 members were affected with sleep apena syn-drome (SAS). The two affected members with severe obesity had suffered from excessive daytime sleepiness, while the other four affected members without obesity showed no clinical symptoms. The respiratory chemoreceptor function of the affected members were normal regardless of the severity of SAS.On the findings of upper airway MRI,all the affected members showed the velopharyngeal obstruction during sleep apneic episodes.2.1) We performed an epidemiological surerillance of SAS among the first degree relatives (n=889) of the index SAS patients (n=141). The prevalence rate of the disorder was four times greater in the first degree relatives compared with the control subjects.2) The onset age of the disorder were youger in the familial aggregated SAS cases compared with the solitary occurred cases. This phenomenon was thought to be related with the genetical acceleration of the occurrence of the disorder. However, clinical symptoms were less frequent in the affected first degree relatives compared with the index cases.3) In the affected first degree relatives, body mass index was significantly smaller than the index cases and solitary occurred cases.4) On the findings of cephalogram, the index cases and the affected fiest degree relatives showed the similar mild carniofacial abnormalites. In addtion, upper airway MRI findings during apneic epsodes showed that obstructed area concentrated to velopharynx both in the index cases and the affected first degree relatives.3. Judged from the above results, we speculated that similarities of craniofacial abnormality leading to the velopharyngeal obstruction was the dominant cause of the familial aggregated occurrence of SAS and that obesity might contribute to the aggravating process.