An infant is brought in by his mother, who says that his skin tastes salty. With time this patient’s pancreas is expected to undergo progressive fibrosis with atrophy of the exocrine glands and cystic dilation of the ducts. The basic abnormality in this infant involves
Correct Answer: Decreased glycosylated chloride channel
Description: Cystic fibrosis (CF) is one of the most common lethal genetic diseases that affects white populations (1/2000). The primary abnormality in patients with cystic fibrosis involves the epithelial transpo of chloride. Normally, binding of a ligand to a membrane surface receptor activates adenyl cyclase, which leads to increased intracellular cAMP. This in turn activates protein kinase A, which phosphorylates the cystic fibrosis transmembrane conductance regulator (CFTR), causing it to open and release chloride ions. Sodium ions and water then follow the chloride ions to maintain the normal viscosity of mucus. The most common abnormality in patients with CF involves decreased glycosylation of the CFTR, which then does not become incorporated into the cell membrane. A lack of chloride channels then causes decreased chloride, sodium, and water secretion, all of which together results in a very thick mucus (the other name of CF is mucoviscidosis). These thick mucus plugs can block the pancreatic ducts, causing fibrosis and cystic dilation of the ducts (hence the name cystic fibrosis). Decreased excretion of pancreatic lipase leads to malabsorption of fat and steatorrhea, which may lead to deficiency of fat-soluble vitamins. Thick mucus may also cause intestinal obstruction in neonates, a condition called meconium ileus. Abnormal mucus in the pulmonary tree leads to atelectasis, fibrosis, bronchiectasis, and recurrent pulmonary infections, especially with Staphylococcus aureus and Pseudomonas species. Obstruction of the vas deferens and seminal vesicles in males leads to sterility, while obstruction of the bile duct produces jaundice. This child's skin tasted salty because of increased sweat electrolytes, the result of decreased reabsorption of electrolytes from the lumina of sweat ducts Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition
Category:
Pathology
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