Scanning electron microscopic study of normal human glomerulogenesis and of fetal glomeruli in congenital nephrotic syndrome of the Finnish type

Kidneys from 5 normal fetuses and 3 with congenital nephrotic syndrome gestational age of 13 to 24 weeks, were studied under a scanning electron microscope. Differentiation of the visceral epithelial cells was observed in normally developing glomeruli. The originally cuboidal, smooth epithelial cells first flattened and acquired cytoplasmic buds on the cell margin. The buds gradually grew longer and branched out to form regular interdigitating foot processes. In the most mature glomeruli the majority of the visceral epithelial cells were trabeculated and the cytoplasmic processes were tightly wound around the glomerular capillaries. In the glomeruli of specimens from fetuses with congenital nephrotic syndrome the epithelial differentiation was different. The individual epithelial cells varied in size and shape and formed irregular cell groups. The cytoplasmic processes of visceral epithelial cells were shortened and flattened. Also, there was a marked loss of interdigitation of adjacent processes. The findings confirm previous transmission electron microscopic observations of pathological foot processes in glomeruli of fetuses with congenital nephrotic syndrome and show that the differentiation of the visceral epithelial cells is abnormal prior to the formation of the final interdigitating processes.