The glomerular basement membrane abnormality in Alport's syndrome.

The characteristic electron microscopic abnormality in Alport's syndrome is thickening of the glomerular basement membrane with splitting and lamellation of the lamina densa. It is commonly accompanied by severe attenuation of the basement membrane and sometimes by disruption of capillary walls. The ultrastructural abnormality is secondary to a more basic defect in the chemical structure of the glomerular basement membrane. Clues to chemical abnormalities have come from immunochemical studies, which suggest a lack of or alteration in that part of the noncollagenous portion of type 4 collagen related to Goodpasture antigen. Variability in the results of immunochemical studies suggest biochemical heterogeneity that still needs to be correlated with the known evidence of genetic heterogeneity in Alport's syndrome.