Nephronophthisis (1 NPHP1, 1 NPHP4, and 1 TTC21B found in our study) may also be a differential diagnosis of ADTKD in young adults; however usually, autosomal recessive inheritance distinguishes it from ADTKD.1 This evidence concerns the gene TTC21B and autosomal dominant medullary cystic kidney disease with or without hyperuricemia.