MAPT and chronic kidney disease: Finally, both Aβ42 and Aβ40 seemed to be influenced by kidney impairment,8 although we did not observe an association when considering the ratio of the 2 biomarkers instead—which is in line with previous works.8,9,18 Similarly, a previous study33 found that plasma ratios of phosphorylated-to-unphosphorylated tau were less strongly associated with CKD than p-tau forms alone.