The CKD-FIX Study (randomized Controlled trial of slowing of Kidney Disease progression From the Inhibition of Xanthine oxidase), enrolling a total of 363 patients with stage 3 or 4 CKD, concluded that allopurinol did not appear to effectively alter the progression of renal insufficiency during a 2-year follow-up (42). This evidence concerns the gene XDH and Renal insufficiency.