Rett Syndrome (RTT) is an X chromosome-linked progressive neurodevelopmental disorder caused by loss-of-function mutations in the MECP2 (methyl CpG-binding protein 2) gene (Amir et al., 1999; Cheadle et al., 2000; Ip et al., 2018). This evidence concerns the gene MECP2 and atypical Rett syndrome.