KL and chronic kidney disease: Decreased Kl expression, lower klotho levels in kidney tissue, and lower circulating levels of soluble klotho have been identified in animal models of CKD, suggesting the implication of klotho deficiency in CKD (Chen et al., 2013; Gołembiewska et al., 2016) and in aging-related disorders when its promoter is aberrantly methylated (Kuro-O et al., 1997).