Mesangial proliferative glomerulonephritis with irregular intramembranous deposits. Another variant of hypocoplementemic nephritis.

Two patients with a persistent mesangial proliferative glomerulonephritis and reduced serum C3 levels have been followed for six and 10 years. Both have had a mild course with normal renal function and spontaneous morphologic improvement. Levels of the fourth component (C4) and second component (C2) of complement, and properdin factor B have been normal; the third component (C3) of complement nephritic factor has not been detected. Ultrastructurally, irregular intramembranous electron-dense deposits are present, primarily within the lamina densa. These deposits are separated by varying lengths of normal-appearing glomerular basement membrane. Intramembranous and subendothelial electron-lucent areas, containing vesicles, are also seen. Subendothelial deposits, mesangial interposition, splitting of the glomerular basement membrane and ribbon-like intramembranous deposits are not found. The disease in these patients was clinically indistinguishable at onset from mrmbranoproliferative glomerulonephritis (MPGN). The possibility of a variant with mild clinical course, no progression and spontaneous morphologic improvement is important in planning and assessing treatment programs in this disease group.