Morphological study of neocortical areas in Rett syndrome

Various neocortical areas from four females aged 16-24 years with Rett syndrome (RS) were investigated and compared with brains of therapy-resistant partial epilepsy (TRPE) patients (18-25 years), infantile autism (IA), and control brains (24 and 58 years). The cytoarchitecture of area 10 (frontal), area 21 (temporal), area 4 (primary motor cortex), and area 17 (primary visual cortex) was studied by the combined Klüver-Barrera (luxol fast blue and cresyl violet) standard procedure. Autofluorescence of lipofuscin, immunofluorescence of synaptic vesicle proteins [synaptophysin (p38)] and lectin-stained (Wisteria floribunda agglutinin) perineuronal nets (PNs) were studied in the cortices using dual-channel confocal laser scanning microscopy. The brains of RS females show various types of morphological/cytoarchitectonical abnormalities of single pyramidal neurons in layers II-III, and V-VII of different cortical areas. The abnormalities include mild losses of pyramidal neurons, more pronounced in layers II and III than in layers V and VII, and more evident in frontal and temporal areas than in the visual cortex. Microdysgenesis, including abnormalities due to neuronal migration disorders, was not found in RS, in contrast to the observations in TRPE patients, strongly indicating that RS is not a neuronal migration disorder. Lipofuscin distribution was normal but amounts were lower in RS cases than in control and TRPE brains. PNs were less expressed in cortices of the IA case but were clearly overexpressed in the motor cortex of RS. Quantitative analysis of p38 showed a decrease in the area occupied by p38 immunoreactivity by 20-40% in RS compared with controls. It is concluded that RS could best be explained by a postnatal synaptogenic developmental deficiency; the basic defect, however, is still completely unknown.