Renal System MCAT Practice Question
A 6-year-old boy presents to the pediatric clinic with periorbital edema and his mother reports his urine appears "foamy." Vital signs show BP 110/68 mmHg (normal for age). Laboratory studies reveal serum albumin 2.1 g/dL (normal 3.5-5.0), total urine protein 4.2 g/day, serum creatinine 0.7 mg/dL, and lipid panel showing total cholesterol 285 mg/dL. Serum complement levels are normal. Light microscopy of a kidney biopsy shows glomeruli that appear normal, but electron microscopy reveals diffuse fusion of podocyte foot processes with no immune complex deposits. Which of the following structural defects best explains the proteinuria in this patient?
Answer choices
- ALoss of heparan sulfate proteoglycans in the glomerular basement membrane
- BMutation in genes encoding slit diaphragm proteins such as nephrin and podocinCorrect answer
- CThickening and splitting of the glomerular basement membrane creating a "basket-weave" appearance
- DDisruption of the fenestrated endothelium of the glomerular capillaries
- EIgA immune complex deposition in the mesangium and capillary walls
- FProliferation of mesangial cells reducing the glomerular filtration surface area
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