Idiopathic Calcium Nephrolithiasis: A Review of Pathogenic Mechanisms in the Light of Genetic Studies

Endoscopy observations suggested that precipitation of calcium-oxalate on the Randall's plaque at the papilla surface may cause idiopathic calcium-oxalate stones. The Randall's plaque is a hydroxyapatite deposit in the interstitium of the kidney medulla, which resembles a soft tissue calcification. Conversely, calcium-phosphate stones may develop from crystalline deposits located at the tip of the Bellini duct. Polymorphisms of eleven genes have been associated with stones in genome-wide association studies and replicated candidate-gene association studies: VDR, SLC34A1, SLC34A4, CLDN14, and CaSR genes coding for proteins regulating tubular phosphate and calcium reabsorption; CaSR, MGP, OPN, PLAU, and UMOD genes coding for proteins preventing calcium salt precipitation; AQP1 gene coding for a water channel in the proximal tubule. The renal activity of the last gene, DGKH, is unknown. Polymorphisms in these genes may predispose to calcium-oxalate and -phosphate stones by increasing the risk of calcium-phosphate precipitation in the tubular fluid. Key Messages: Genetic findings suggest that tubular fluid supersaturation with respect to calcium and phosphate predisposes to calcium-oxalate stones by triggering cellular mechanisms that lead to the Randall's plaque formation.