Atypical Atypical <scp>MECP2</scp> ‐Related Rett Syndrome Presenting with Movement Disorders‐ Predominating Phenotype

BACKGROUND: Rett syndrome (RTT) is an X-linked neurodevelopmental disorder characterized by a typical natural history, including early stagnation, rapid regression, a pseudostationary phase, and late motor deterioration. Seizures, autistic features, breathing abnormalities, stereotypies, and various movement disorders are often present. Currently, the diagnosis of atypical RTT requires a period of regression and fulfillment of at least two main criteria, and at least five of 11 supportive criteria. CASES: We describe five patients (aged 20-61 years), unexpectedly diagnosed with RTT, exhibiting a movement-disorder-predominant phenotype, most commonly dystonia. These patients lacked the typical natural course of RTT and, in most cases, showed preserved social functioning and an essentially normal life. As none of the patients fulfilled the diagnostic criteria for either typical or atypical RTT, we have labeled them as "atypical atypical" RTT. CONCLUSIONS: We recommend a revision of the current diagnostic criteria for RTT to include also more atypical presentations.