Electron-dense lipidic capillary deposits in Rett syndrome.

Conjunctival, muscle, and peripheral artery biopsies were examined by light and electron microscopy in a patient with clinically diagnosed Rett syndrome. In capillaries, amorphous and membranous electron-dense deposits were observed (a) endoluminally attached to endothelial cell membranes, (b) within junctional clefts of adjacent endothelial cells, and (c) at abluminal sites of endothelial cells. In addition, electron-dense deposits lay isolated or inside multivesicular bodies in endothelial cells and pericytes. These findings have not been reported before in Rett syndrome. They were not seen in age-matched normal or pathological control cases and are suggested to indicate deposition of an as yet unknown lipidic plasma component possibly in association with impairment of the blood-tissue barrier.