Cystatin C (CST3) is highly expressed in mature human astrocytes (Bachoo et al, 2004; Zhang et al, 2016) and is induced in Alzheimer's disease and epilepsy (Steinhoff et al, 2001; Pirttilä et al, 2005; Gauthier et al, 2011), raising the possibility that astrocyte‐like glioma cells may be responding to the same cues or stresses that reactive astrocytes encounter in these disorders. Here, CST3 is linked to early-onset autosomal dominant Alzheimer disease.