CST-C is encoded by the CST3 gene, considered to be a “risk” gene for AD (Bertram et al., 2007; Wang et al., 2021) with altered levels of this cystatin reported in both CSF and blood of AD individuals (Zhong et al., 2013; Wang et al., 2017; Chen et al., 2022). This evidence concerns the gene CST4 and Alzheimer disease.