A 16-year-old girl has nephrotic-range proteinuria and hypertension. Biopsy light microscopy shows a membranoproliferative pattern. Immunofluorescence reveals C3 deposition only, with no immunoglobulin, and serum C3 is persistently low with normal C4. Genetic testing shows a factor H mutation. The most likely diagnosis is:

• A Post-streptococcal glomerulonephritis
• B Lupus nephritis class IV
• C C3 glomerulopathy (dense deposit disease) ✓
• D Mixed cryoglobulinaemia

Explanation

Isolated B3 staining without immunoglobulin, persistent isolated low B3, and alternative pathway dysregulation define B3 glomerulopathy, of which dense deposit disease is the classic form. It results from uncontrolled activation of the alternative complement pathway due to autoantibodies (B3 nephritic factors) or regulatory mutations such as factor H deficiency. Post-infectious GN resolves within weeks with falling B3 recovery, while lupus and cryoglobulinaemia show full-house or IgG-dominant immunoglobulin deposits.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.