COPD USMLE Step 1 Practice Question
A 6-year-old boy presents with failure to thrive, recurrent sinopulmonary infections, and bulky, foul-smelling stools despite adequate caloric intake. Vital signs show HR 110/min, RR 28/min, SpO2 92% on room air, and temperature 37.2°C. Chest X-ray reveals hyperinflation with bronchial wall thickening. Fecal fat is elevated at 8 g/day. He denies recent antibiotic use. Genetic analysis confirms the most common cystic fibrosis mutation. Which molecular defect does this mutation cause?
Answer choices
- ADefective receptor tyrosine kinase signaling
- BMisfolding with impaired protein trafficking to the cell surfaceCorrect answer
- CReduced synthesis of surfactant phospholipids
- DPremature truncation of a mitochondrial membrane protein
- EAbnormal collagen cross linking in the extracellular matrix
- FLoss of zinc finger domains resulting in impaired transcriptional regulation
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