MAPT and Alzheimer disease: It has been suggested that circPCCA was decreased in the CSF of AD patients, and Li et al. (2020a) speculated that circPCCA might competitively bind to miR-138–5p to inhibit its induction of glycogen synthase kinase-3β activation and facilitate tau phosphorylation; therefore, circPCCA’s low expression was involved in exacerbating AD severity (Wang et al., 2015).