This is particularly pertinent for group 1 (Gp1) mGluRs because abnormal Gp1 mGluR signaling is frequently observed in neurodevelopmental and cognitive disorders such as fragile X syndrome (FXS), autism spectrum disorders (ASDs), and Alzheimer’s disease (Bear et al., 2004; Kleijer et al., 2014; Kumar et al., 2015), where synaptic strength or number is dysregulated. The gene discussed is GTPBP1; the disease is early-onset autosomal dominant Alzheimer disease.