Retrophin (RTRX) shares have surged after the company announced positive results in a Phase 2 clinical trial, DUET, evaluating sparsentan (RE-021) for the treatment of focal segmental glomerulosclerosis, a rare kidney disorder that leads to end-stage renal disease. The study met its primary endpoint of a statistically valid reduction (more than two-fold) in proteinuria (protein in urine) compared to irbesartan after an eight-week treatment period. Specifically, patients treated with 200, 400 and 800 mg/day of sparsentan (n=64) showed a mean reduction of proteinuria from baseline of 44.8% after eight weeks of treatment compared to 18% for those (n=32) receiving 300 mg/day of irbesartan (p=0.006). The 400 mg and 800 mg sparsentan cohorts also showed superiority to 300 mg of irbesartan, 47.4% vs. 19.0% (p=0.011).