PTH and Marchiafava-Bignami disease: We now know that at least very low or very high levels of PTH (i.e., less than 2X or more than 9X the upper normal limit for the used assay) are associated with low or high-turnover bone disease (ABD or osteitis fibrosa, respectively) in dialysis patients; both extremes increase not only the risk of fractures but also mortality by different means (Kidney Disease: Improving Global Outcomes KDIGO CKD-MBD Update Work Group, 2017; Kidney Disease: Improving Global Outcomes KDIGOCKD–MBD Work Group, 2009; Torregrosa et al., 2022).