Rett syndrome is caused by mutations in X-linked MECP2, encoding methyl-CpG-binding protein 2. Research highlights include trends in diagnosis, clinical phenotypes of males with MECP2 mutations, multidisciplinary approaches to understanding MECP2-related disorders, revised diagnostic criteria, and advancements in clinical trial readiness for therapeutic development. Studies also focus on genotype-phenotype relationships, mutation severity, and the development of evaluation tools and treatment trials for Rett syndrome.