MECP2 and atypical Rett syndrome: Rett syndrome is caused by loss of MeCP2 function and is associated with an increase in respiratory pattern irregularity characterized by periods of forceful breathing (hyperventilation), breathing pauses, and abnormal cardiorespiratory coupling, as well as increased mean respiratory frequency (Weese-Mayer et al., 2006; Katz et al., 2012).