[Clinical phenotypes of classic Rett syndrome]

Rett syndrome (RS) is a progressive neurological disorder that is diagnosed by essential, supportive and exclusion clinical criteria, and development takes place in four stages. It has been shown to be caused by de novo mutations of a gene located in the long arm of the dominant X chromosome that codes for the methyl CpG binding protein (MECP2). It has been observed that girls with classic RS (CRS) present distinguishing nuances with respect to the age of onset of the different criteria and as regards the progression of the disorder. Taking the ability or failure to walk as a reference, we have established three phenotypes.

Phenotype I. Ambulant CRS, which corresponds to a permanent stage III, or a stage III that lasts a long time before going into stage IV. The loss of the ability to use the hands in a purposeful way takes place at the age of 25.6 months, social withdrawal at 25.4 months, language impairment at 20 months, stereotypic hand movements at 22.8 months and signs of spasticity appear around the age of 8-10 years. Phenotype II. Ambulant CRS. Transitory, which corresponds to an early stage IV-A. The first signs of abnormality appear around the age of 9-10 months. This is followed by the loss of the purposeful use of the hands towards the age of 23.4 months, social withdrawal around 21.4 months, language impairment at 20 months, stereotypic hand movements at 25.2 months and scoliosis, neuromotor disorders and trophic and vasomotor disorders at the age of 4-5 years. Phenotype III. Non ambulant CRS, which corresponds to stage IV-B. It begins with hypotonia towards the age of 5-6 months, loss of voluntary grasping at 17.8 months, social withdrawal at 18 months, language impairment at the age of 12 months, stereotypic hand movements at 13 months and early onset of motor, trophic and vasomotor disorders. Genetic studies were conducted in 12 girls and MECP2 gene mutations were found in 10 of them, belonging to the three different phenotypes.

We have established three phenotypes in RS according to the ability to walk. If walking is not achieved or the ability is lost early on, speech loss, social withdrawal and the onset of stereotypic movements, motor, trophic and vasomotor disorders all progress more quickly. Mutations in the MECP2 gene have been found in the three phenotypes. In 16.6% the genotype was normal. Greater accuracy is required in the definition of cases of CRS in order to establish phenotype genotype correlations.