CST3 and Alzheimer disease: Specifically, in patients with AD, cystatin C levels in CSF were found to be reduced, compared to individuals without dementia (Simonsen et al., 2007; Hansson et al., 2009; Zhong et al., 2013), and CSF cystatin C levels were positively correlated with tau and Aβ levels (Sundelöf et al., 2010; Zhong et al., 2013).