Awareness of Rett syndrome (RS) among clinicians in English-speaking countries was prompted by a publication by Hagberg et al. ( 1983 ) – almost two decades after the condition was described by Andreas Rett in Vienna (Rett 1966 ). Much was therefore already known about its clinical and pathological characteristics before the discovery by Amir et al. ( 1999 ) that the syndrome results from mutations in the MECP2 gene, located at Xq28 . This discovery has led to a further rapid increase in understanding of the pathogenesis of the disorder. It is now apparent that mutations within the coding region of MECP2 are responsible for more than three quarters of cases with classic (typical) features of RS and close to half of those with atypical features, including some males (Shahbazian & Zoghbi 2002 ). Mice have been developed with equivalent mutations on the corresponding gene Mecp2 (Guy et al. 2001 ; Chen et al. 2001 ) and there are new insights into the disturbed cellular processes responsible for this severe neurodevelopmental disorder, to the extent that testable hypotheses about therapeutic interventions are emerging.