Renal System MCAT Practice Question
A 6-year-old boy presents with sudden onset of periorbital edema, abdominal distension, and foamy urine. His mother reports he had a upper respiratory infection 2 weeks ago. Physical examination reveals 3+ lower extremity edema and blood pressure of 128/82 mmHg (95th percentile for age). Laboratory studies show: serum albumin 1.8 g/dL (normal 3.5-5.0), total serum protein 4.2 g/dL, urinalysis with 4+ proteinuria and urinary protein excretion of 5.2 g/day. Serum creatinine and complement levels are normal. Renal biopsy with electron microscopy shows diffuse effacement of visceral epithelial cell (podocyte) foot processes with intact basement membrane and normal glomeruli on light microscopy. Which of the following best explains the proteinuria and nephrotic syndrome in this patient?
Answer choices
- ADisruption of the glomerular basement membrane with loss of the charge barrier
- BDysfunction of slit diaphragm proteins (nephrin and podocin) causing loss of the size barrierCorrect answer
- CIncreased glomerular capillary permeability due to fenestral widening
- DMesangial proliferation with expansion of the extracellular matrix
- EIgA immune complex deposition along the glomerular basement membrane
- FEndothelial injury with resultant thrombotic microangiopathy
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