ID of unknown etiology. Results: We describe the evolution of the phenotype in adults with EHMT1, TCF4, MECP2, CDKL5, and SCN1A mutations and 22qter deletions and also provide an overview of previously published adult cases with similar diagnoses. Conclusion: These data are highly valuable in adequate management and follow-up of patients with Angelman-and Rett-like syndromes and accurate counseling of their family members. Furthermore, they will contribute to recognition of these syndromes in previously undiagnosed adult patients.