MECP2 and long QT syndrome 3: Previously, we showed that cardiomyocytes isolated from mice deficient in Mecp2 have an abnormal Na+ current (McCauley et al., 2011) similar to a LQT3 phenotype (Fabritz et al., 2010), and that a single dose of phenytoin prior to PES prevents induction of arrhythmias in male Mecp2Null/Y mice (McCauley et al., 2011).