The late infantile regression period (stages I and II) was analyzed retrospectively in 91 girls and women at the Department of Pediatrics, University of Goteborg and Pediatric Clinic, Ostersund Hospital, Sweden. The median age at onset of developmental stagnation (stage I) was 11 months, and loss of acquired skills (stage II) began at 19 months and lasted for 19 months. The onset of regression was distinct in 43%, dramatic in 16%, and insidious in 41%. The first observed signs of disease were delay in reaching expected gross motor milestones, dissociation of motor development, and disequilibrium. A triad of manifestations characterized the deterioration or loss of acquired skills: contact/communication, hand use/skill, babble/words. End of regression occurred at mean age 2.5 years. The girls gradually became more alert and showed an interest to act and interact. Handedness showed a preference for the left hand compared to the right, and was associated with spike activity in the left central leads in the EEG in 13 of 20 girls. 
COMMENT. This further delineation of the stages of Rett syndrome may help in the diagnosis and pathophysiology of the disorder. In a study involving the analysis of beta-endorphin, as well as lactate, pyruvate and metabolites of norepinephrine, dopamine and serotonin in CSF from 12 girls with Rett’s syndrome, the most consistent and significant difference from a control group was the elevation of beta-endorphin immunoreactivity in the CSF. Myer EC et al. from the Department of Child Neurology, Medical College of Virginia, Richmond VA found increased levels of beta-endorphin immuno-reactivity in lumbar CSF in 90% of 158 Rett syndrome patients . The authors note that the symptoms of Rett syndrome are similar to the effects of centrally administered beta-endorphin or other opioids in experimental animals.