RESUMEN
Rett syndrome (RS) is a neurodevelopmental disorder, preferentially found in females and specifically involving the functions on which intelligence and its expression depend - learning, hand use and speech - leaving many others intact. Mutations have been identified at Xq28 on the MECP2 gene (methyl-CpG 2), which selectively silences the expression of other genes whose location is still unknown. This is a study on clinical, diagnostic and epidemiological aspects of RS in a Brazilian sample. It included 33 female patients with chronic encephalopathy without known etiology. RS was diagnosed in 24 patients (72.7 percent): 17 (70.8 percent) had classical RS; 5 (20.8 percent), atypical RS and 2 (8.4 percent), potential RS. In 9 girls clinical data and/or laboratory studies excluded diagnosis of RS. Among the atypical RS patients, 4 were form fruste and one, congenital form. Among the girls with other encephalopathies, cerebral malformation was the most frequent finding