GRM3 and early-onset autosomal dominant Alzheimer disease: GRM3 has been strongly validated by multiple groups as a GWAS risk gene for schizophrenia, and a reduction in GRM3-expressing dendritic spines has been observed in Alzheimer’s disease and aging (Saini et al., 2017; Morrison and Baxter, 2012; Sartorius et al., 2008; Harrison et al., 2008; Egan et al., 2004).