A 15-year-old boy presents with rough, corrugated plaques on his hands, wrist, feet, and ankles. The presentation appeared shortly after birth and has worsened over the years. The soles of his feet, as well as his face, abdomen, and palms, remain unaffected. He is otherwise well. What’s the cause of this striking skin abnormality? Learn more about this case and join the conversation on Figure 1.