Quiz page December 2013: Hypoplastic nails, bowed elbows, and nephrotic syndrome. Nail-patella syndrome

A 13-year-old boy with generalized body swelling, reduced urine output, and nephrotic-range proteinuria was referred for evaluation. He previously had received 6 weeks of treatment with prednisolone, 60 mg/m² per day without a response. He was the first-born child of nonconsanguinous parents, and there was no family history of kidney disease. Physical examination findings were remarkable for finger and toenail hypoplasia, “swan neck” deformity of the fingers (Fig 1A), and bilateral fixed flexion deformity of the elbows.