<b>Conclusions</b>: In this CKD spectrum cohort, serum GRP was associated with CKD-MBD biochemical markers (KLb and FGF-23) much more strongly than with vascular phenotypes; its associations with vascular calcification burden and arterial stiffness were modest in multivariable modelling, supporting GRP as a marker of the CKD-MBD biochemical profile rather than a strong surrogate of vascular phenotype. This evidence concerns the gene FGF23 and Marchiafava-Bignami disease.