This study will characterize the pathophysiology and course of glomerular injury in patients with various glomerulopathies. The investigators hypothesize that alterations in the glomerular capillary wall (GCW) pore-size structure (loss of pore density and changes in pore size distribution) are the ultimate cause of hypofiltration and proteinuria, and that progressive azotemia is the result of progressive injury to the GCW itself.