We herein provide the first evidence in CKD patients that: 1) the serum soluble Klotho level is significantly correlated with markers of CKD-MBD, including the levels of PTH, 1,25D and FEPi; 2) decreased levels of serum Klotho are significantly associated with signs of vascular dysfunction such as pronounced arterial stiffness evaluated by baPWV; and 3) in a multivariate analysis, the serum Klotho level was found to be an independent determinant of marked arterial stiffness, which has been reported to be associated with increased cardiovascular mortality and morbidity. This evidence concerns the gene KL and Marchiafava-Bignami disease.