KL and secondary hyperparathyroidism: Klotho deficiency exacerbates CKD-MBD by impairing phosphate regulation, disrupting vitamin D signalling, and promoting secondary hyperparathyroidism, which initially compensates for diminished calcitriol but eventually fails in CKD stages 4-5, resulting in uncontrolled hyperphosphatemia, severe secondary hyperparathyroidism, calcitriol deficiency, accelerated vascular calcification, and increased morbidity and mortality [10,11].