A 24-year-old male from rural Maharashtra presents with progressive tremor, dysarthria, and behavioral changes over 6 months. On examination, slit-lamp examination reveals golden-brown rings at the periphery of the cornea in the Descemet membrane, as marked **D** in the diagram. His serum ceruloplasmin is 12 mg/dL (normal >20 mg/dL) and 24-hour urine copper is 180 mcg/24h. Which of the following is the PRIMARY pathophysiologic mechanism responsible for the deposition of copper in the structure marked **D**?

Explanation

## Why Option 1 is right The Kayser-Fleischer ring (marked **D**) is a pathognomonic sign of Wilson disease caused by copper deposition in the Descemet membrane of the cornea. The underlying mechanism is a mutation in ATP7B (chromosome 13), the hepatic copper transporter responsible for biliary copper excretion. When ATP7B is defective, the liver cannot excrete copper into bile, leading to progressive hepatic copper accumulation. Once the liver's storage capacity is saturated, excess copper spills into the systemic circulation and deposits in extrahepatic tissues, including the cornea (Kayser-Fleischer rings), basal ganglia (neurologic manifestations), and other organs. This patient's low ceruloplasmin, elevated 24-hour urine copper, and clinical presentation (neurologic Wilson disease) are consistent with this mechanism. The presence of Kayser-Fleischer rings indicates systemic copper overflow from hepatic saturation—the hallmark of Wilson disease pathophysiology (Harper 32e Ch 50; Harrison 21e Ch 415). ## Why each distractor is wrong - **Option 2**: Corneal epithelial cells are not primarily affected in Wilson disease. The copper deposition occurs in Descemet membrane (a basement membrane structure), not due to local corneal cell mutations. Wilson disease is a systemic metabolic disorder of hepatic copper handling, not a primary corneal disorder. - **Option 3**: Intestinal copper absorption is not increased in Wilson disease. Rather, the problem is impaired hepatic excretion. Ceruloplasmin is a plasma copper carrier and acute-phase reactant, not a primary regulator of intestinal copper absorption. Low ceruloplasmin is a consequence of copper accumulation and liver dysfunction, not a cause of increased absorption. - **Option 4**: Renal tubular reabsorption defects do occur in Wilson disease (Fanconi syndrome), but this is a secondary manifestation of systemic copper toxicity, not the primary mechanism of corneal copper deposition. Copper reaches the cornea via systemic circulation after hepatic spillover, not via selective renal dysfunction. **High-Yield:** Kayser-Fleischer rings = copper in Descemet membrane = pathognomonic for Wilson disease = result of ATP7B-mediated impaired biliary excretion → hepatic saturation → systemic spillover. Present in >95% with neurologic Wilson, ~50% with hepatic-only disease. [cite: Harper 32e Ch 50; Harrison 21e Ch 415]