There Has Been a Growing Interest in Ethnic and Racial Diversity in Relation to Sleep Pa- Rameters. the Study of Differences in Sleep

1221 THERE HAS BEEN A GROWING INTEREST IN ETHNIC AND RACIAL DIVERSITY IN RELATION TO SLEEP PARAMETERS. THE STUDY OF DIFFERENCES IN SLEEP between racial groups may lead to an increased understanding of genetic and environmental contributions to sleep physiology and its disorders. Numerous studies of sleep have examined differences in sleep parameters and sleep related symptoms by gender and age, but not nearly as many have focused on racial differences. Nonetheless, several studies have demonstrated racial differences in relation to sleep variables. Differences in sleep habits1 as well as a higher prevalence of sleep disordered breathing (SDB) in African Americans compared to Caucasians2-4 has been reported. The heterogeneity of restless leg syndrome (RLS) prevalence estimates (0.1% to 13%) across countries with varying ethnic and racial distributions5-10 has led to studies investigating potential racial differences in this disorder. In one population-based survey in the United States, the prevalence of RLS was estimated at approximately 4% in both African Americans and Caucasians.11 In a study of older hemodialysis patients, Kutner and Bliwise found a lower prevalence of restless leg symptoms in African American patients12 and in a follow-up analysis reported reduced periodic limb movements during sleep (PLMS) in the African American sample.13 Thus, the influence of racial differences in RLS and/or PLMS is not well defined. Despite the wealth of data available on the prevalence of RLS among individuals of varying ethnic and racial backgrounds, few studies have examined potential racial differences in the closely related occurrence of PLMS. The term for periodic limb movements during sleep, originally called nocturnal myoclonus, was defined as a phenomenon characterized by repetitive flexions and extensions involving the toes, ankles, and occasionally the knee and hip. These frequent movements occur in one or both legs during sleep, and often produce brief arousals and, in some cases, full awakenings from sleep.14 Periodic limb movement disorder (PLMD) is defined by the International Classification of Sleep Disorders (ICSD) as periodic leg moveRacial DiffeRences in PeRioDic limb movements