Furthermore, two recent randomized studies in patients with type 1 diabetes (Preventing Early Renal Loss in Diabetes trial: PERL trial) and those with CKD stage 3 to 4 (Controlled Trial of Slowing of Kidney Disease Progression from the Inhibition of Xanthine Oxidase trial: CKD-FIX trial) reported that there were no clinically meaningful benefits of allopurinol on renal outcomes [9,10]. This evidence concerns the gene XDH and chronic kidney disease.