The histopathologic findings of three sural nerve biopsies and one muscle biopsy from three patients with Rett syndrome are described from the Department of Pediatrics, National Sanatorium Yakumo Hospital, Yakumo, Hokkaido, Japan. The biopsies demonstrated mitochondrial changes in the cytoplasm of Schwann cells, occasional onion bulb formations, and mitochondrial alterations in myelinated axons with reduction in the number of large myelinated fibers. The muscle showed small dark angulated fibers with NADH-TR staining and dumbbel 1-shaped mitochondria. 
COMMENT. These findings suggest peripheral nerve involvement and mitochondrial abnormalities in Rett syndrome. An additional article describes cerebellar pathology at autopsy of five patients with Rett syndrome . Patients ranged in age from 7 to 30 years. All had reduced brain weights with small cerebella. There was loss of Purkinje cells, atrophy, astrocytic gliosis of molecular and granular cell layers, and gliosis and loss of myelin in the white matter. The cerebellar atrophy was greater in two patients treated with phenytoin. The pathology of Rett syndrome appears to involve the cerebellum, cerebral hemispheres, basal ganglia, especially substantia nigra, spinal cord, peripheral nerve, and muscle.