• Electron photomicrograph showing several capillary loops.

• A number of the capillary loops show two basement membranes (arrowhead).

• The external capillary basement membrane is the original native basement membrane.

• The internal capillary basement membrane is a newly formed basement membrane.

• Between the two basement membranes is cytoplasm of mesangial cells that have extended beyond the confines of the mesangium.

• The newly formed internal basement membrane is a product of the mesangial cell and the endothelial cell.

•Membranoproliferative glomerulonephritis type I is more a morphologic pattern of injury that a single disease.

•Membranoproliferative glomerulonephritis type I can be a manifestation of lupus nephritis and hepatitis C/cryoglobulinemia.

•Many cases are idiopathic.

•Membranoproliferative glomerulonephritis type I is an immune complex mediated disorder.

•Immune complexes are deposited in the mesangium and subendothelial spaces.

•Mesangial cells proliferate in response to the immune complex deposition and extend beyond the confines of the mesangium to mesangialize the capillary loops.

•A second internal basement membrane is formed by the mesangial cell and the undermined endothelial cells.

•Idiopathic membranoproliferative glomerulonephritis type I tend to be seen in older children and in adults. There is no sex predilection.

•Some cases of membranoproliferative glomerulonephritis type I are due to lupus nephritis.

•Some cases of membranoproliferative glomerulonephritis type I are due to hepatitis C/cryoglobulinemia.

•The condition of sickle cell anemia can produce a membranoproliferative type glomerular injury.

•Patients with membranoproliferative glomerulonephritis type I manifest heavy proteinuria (3.5 gm or more per 24 hours) and the consequence of protein loss (hypoalbuminemia, hyperlipidemia, edema).

•Not infrequently there is a nephritic component with red cells and red cell casts in the urine sediment along with renal insufficiency and hypertension.

•The kidneys in membranoproliferative glomerulonephritis type I show no particular gross abnormalities that reflect the pathologic process.

•In severe and particularly active cases of membranoproliferative glomerulonephritis, the cut surface of the renal cortex may show a petechial or flea-bitten appearance due to the activity in the glomeruli.

•The disease process is diffuse meaning that all glomeruli are affected.

•The glomerular tufts are globally hypercellular usually to a marked degree.

•The cellularity is endocapillary meaning that the proliferation of cells is within the tuft and not in the urinary space.

•There is lobular accentuation and individual segments can be appreciated.

•On the PAM silver stain for basement membranes, the capillary loops show a double contour or tram-track appearance.

•Idiopathic forms of membranoproliferative glomerulonephritis type I usually show granular mesangial and capillary loop fluorescence for IgG and C3.

•Electron microsocpy shows mesangial and subendothelial immune complex type dense deposits, mesangialization of most capillary loops and formation of a new basement membrane internal to the native glomerular basement membrane.

• Cotran RS, Kumar V, Robbins SL: Robbins Pathologic Basis of Disease. 5th ed. Philadelphia, W.B. Saunders, 1994, pp.

•Rose B. Renal Pathophysiology the essentials. Baltimore: Williams and Wilkins. 1994. Ch. 9. diseases.

• Current literature from PubMed at National Library of Medicine