[Rett syndrome. A well defined but mysterious encephalopathy]

The Rett syndrome is characterized by a progressive development of loss of intellectual functions and of motricity, including abnormal stereotypic hand movements and reduction of the motor skill. This syndrome is exclusively observed in girls. Its typical evolution is characterized by a normal initial development (until 6 to 18 months after birth) followed by a progressive installation of the clinical signs in 4 steps. There is currently no biological marker for the Rett syndrome and therefore the diagnosis is only based on clinical criteria. The most common erroneous diagnosis is infantile autism. In this review, the current status of clinical, genetic and pathogenetic knowledge of the Rett syndrome is presented.