CUBN-AMN pathway loss in chronic benign proteinuria

This case demonstrates that persistent isolated proteinuria, maintained for over a decade with entirely normal serum albumin and kidney function, can be the hallmark of a renal-limited cubilin-amnionless (CUBN-AMN) pathway defect rather than a primary podocytopathy. The patient’s clinical journey began in infancy, when proteinuria was incidentally detected (Figure 1a). Initial urine protein-to-creatinine ratios were approximately 230 mg/mmol (approximately 2 g/g Cr), subsequently stabilizing between 55 and 110 mg/mmol (between 0.5 and 1.0 g/g Cr).