Because all the MECP2 mutations associated with RTT show decreased MeCP2 SUMOylation level and because Wnt6 mRNA level is dramatically reduced in MeCP2K412R sumo-mutant animals11, these observations suggest that deficiency in Wnt6 signaling and its downstream effectors may play a role in the pathogenesis of RTT. Here, MECP2 is linked to Rett syndrome.