Introduction: there are several clinical phenotypes related to mutations in MECP2 gene, being Rett syndrome in females the most frequent in its classical and variants forms, and syndromes in males going from encephalopathy to mental disability.

Objective: to establish the clinical phenotype and evolution of patients with mutations in MECP2 gene and to describe its relation to the phenotype.

Materials and methods: descriptive and retrospective study of patients with mutations in MECP2 gene controlled in our Service between 2005-2009.  Cases with positive mutations are studied from the protocol applied to girls with Rett syndrome phenotype.

Results and discussion: 11 girls with Rett syndrome phenotype, 9 classical forms and 2 variants.  The 9 girls with the classical form had normal initial development, regression between 6 to 18 months, stereotypies emergence, 7 lost hand propositivity, 6 had epilepsy, 7 acquired microcephaly, 4 achieved gait and none had language.  6 patients had frequent mutations R255X, R168X y R306C with similar clinical severity.  The 2 patients with variant forms had normal development until 3 years old, slow progression of language, normocephaly, epilepsy, late stereotypies, preserved gait, with R294X and TRUNC293 mutations.

Conclusion: phenotypes of MECP2 gene mutations manifest as usually is described in females with Rett syndrome.  Most are classical forms, with the exceptional gait achievement as highlight.  The most frecuent mutation is R255X and the severity of the phenotype is not related with a mutation in particular.