COL4A1 and Polyuria: Despite the low blood pressure and increased sodium reabsorption, a metabolic cage study revealed polyuria in mutant animals, with Col4a1+/Raw mice displaying a ∼1.8-fold increase in daily urine production (Fig. 2A) and a ∼1.7-fold increase in urine flow rate as measured by in vivo renal clearance assays (Fig. 2B), further confirming the tubular disease.