**Question:** An 8-year-old boy presents with periorbital edema and throbbing headaches. His parents report that the boy had a "strep throat" 2 weeks ago. Urinalysis shows 3+ hematuria. A renal biopsy shows hypercellular glomeruli, and electron microscopic examination of glomeruli discloses subepithelial "humps." Which of the following best explains the pathogenesis of glomerulonephritis in this patient?

A. Membranous nephropathy
B. Membranoproliferative glomerulonephritis
C. IgA nephropathy
D. Minimal change disease

**Correct Answer:**

**Core Concept:** Glomerulonephritis refers to a group of kidney diseases characterized by inflammation of the glomeruli, which are the smallest blood vessels in the kidneys responsible for filtering blood. In this question, we are provided with specific clinical signs and laboratory findings that help narrow down the diagnosis.

**Why the Correct Answer is Right:**

The correct answer is **B** Membranoproliferative glomerulonephritis. The key clue here is the electron microscopic examination of glomeruli disclosing subepithelial "humps." Membranoproliferative glomerulonephritis is a type of glomerulonephritis characterized by the presence of subepithelial immune deposits, leading to proteinuria, hematuria, and hypertension. These deposits cause a thickening of the glomerular basement membrane (GBM), leading to the subepithelial "humps" observed in the electron microscopic examination.

**Why Each Wrong Option is Incorrect:**

A. Membranous nephropathy: Membranous nephropathy is characterized by subepithelial immune deposits but lacks the thickening of the GBM seen in membranoproliferative glomerulonephritis. Membranous nephropathy usually presents with more severe symptoms, such as hypertension and proteinuria, and is less commonly associated with hypertension.

C. IgA nephropathy: IgA nephropathy is characterized by immune deposits made of IgA immunoglobulins, not subepithelial humps. It typically presents with microscopic hematuria, proteinuria, and hypertension. IgA nephropathy is more common in certain ethnic groups, especially those of African, Asian, and Mediterranean descent.

D. Minimal change disease: Minimal change disease is characterized by the absence of immune deposits and is more commonly observed in children and young adults. It presents with nephrotic syndrome, hypoalbuminuria, and edema. Minimal change disease does not typically cause hypertension.

**Clinical Pearl:**

Subepithelial immune deposits are a hallmark of Membranoproliferative glomerulonephritis. In this case, the presence of subepithelial immune deposits and hypertension are key features that lead to the diagnosis of Membranoproliferative glomerulonephritis. The correct diagnosis is essential for proper management and treatment of the patient. The correct diagnosis enables the clinician to choose targeted therapy such as steroids, cyclophosphamide, or other immunosupp