Question 191

Question:

A 7-month-old infant is brought to the physician’s office because of poor weight gain despite large food intake. He has had two episodes of pneumonia and has frequent bulky stools. He coughs frequently. X-rays of the lungs show increased markings and hyperinflation. Trypsin is absent in a fresh stool sample, and the fat content is increased. Which of the following is the most likely cause of this infant’s disorder?

Correct Answer: B.  Defective ion transport at epithelial surfaces

This infant has the clinical presentation of cystic fibrosis, which is due to defective ion transport at epithelial surfaces (choice B). This is an autosomal recessive disease due to a mutation in the chloride transporter, cystic fibrosis transmembrane conductance regulator (CFTR). Patients present with meconium ileus, deficiencies of pancreatic enzymes, pulmonary obstruction, frequent pulmonary infection, bronchiectasis, cor pulmonale, and respiratory failure. Other findings include liver cirrhosis, infertility, and elevated NaCl concentrations in sweat.
This is not due to an autoimmune disorder (choice A), disaccharidase deficiency (choice C), inability to synthesize apolipoprotein B (choice D), or villous atrophy of the jejunum (choice E).