IgA Nephropathy (Berger Disease)

IgA nephropathy (Berger disease) is the most common primary glomerulonephritis worldwide, and it's a high-yield topic on USMLE Step 1 for good reason — it sits right at the intersection of several easily confused concepts. The core pathophysiology is aberrant IgA1 glycosylation leading to immune complex formation and mesangial deposition. The classic presentation is a young male with episodic gross hematuria occurring concurrent with a URI or GI illness — not after it. That timing distinction is the single most tested and most commonly blown detail on this topic.

Step 1 tests IgA nephropathy from three main angles: recognizing the clinical presentation and distinguishing it from PSGN, identifying the biopsy findings (specifically the immunofluorescence pattern), and understanding the long-term prognosis. Questions often use clinical vignettes where you have to pick the correct diagnosis from a set that includes PSGN, IgA vasculitis, and IgA nephropathy — all of which can involve hematuria after an infection. The exam also tests whether you know the IF staining pattern and what it means diagnostically.

The tricky part is that IgA nephropathy superficially resembles PSGN — both involve young patients, both involve infections, both cause hematuria. But the differences are critical: timing (concurrent vs. 1–3 weeks later), immunofluorescence (IgA mesangial vs. IgG/IgM/C3 subepithelial 'lumpy-bumpy'), and prognosis (potentially progressive vs. usually self-limited). Students who don't nail these distinctions will consistently miss questions on both diseases.