Three children with Rett syndrome and normal muscle mitochondrial structure but abnormalities in mitochondrial respiratory chain enzymes are reported from the Departments of Neurology and Pediatrics, Loyola University, Stritch School of Medicine, Maywood, IL. The children, all girls, were three, four, and 13 years of age. The 13 year old had normal development until 15 months of age when she stopped talking and developed an abnormal gait and loss of hand use. At six years of age, self-injurious behavior and head hitting developed and at age nine years, she had atonic and clonic seizures. Her behavior was autistic and hyperactive. Hand wringing and mouthing were constant while awake. The head circumference was 49 cm (below the 2nd percentile). There were low levels of cytochrome c-oxidase and succinate cytochrome c reductase in all cases. Muscle morphology by light and electron microscopy was normal. 
COMMENT. Mitochondrial alterations in muscle, including distention, vacuolation, and membranous changes, have been described in children with Rett syndrome. (See Ped Neur Briefs Sept 1989).