A few studies have reported lower prefrontal mGluR5 levels in patients with major depressive disorder (MDD) compared with healthy controls (Deschwanden et al., 2011; Esterlis et al., 2017), whereas other studies have reported comparable or even higher levels of prefrontal mGluR5 (DeLorenzo et al., 2015; Gray et al., 2015). The gene discussed is GRM5; the disease is major depressive disorder.