CST3 and early-onset autosomal dominant Alzheimer disease: Cystatin C is highly expressed in the brain and cerebrospinal fluid (CSF) (Löfberg and Grubb, 1979), and it is indicated to play many roles in the risk and pathobiology for Alzheimer's disease (AD) (Taupin et al., 2000; Palmer et al., 2001; Gauthier et al., 2011).