Locomotor hyperactivity in Mmp‐9 heterozygous mice, which have lower levels of Mmp‐9 expression in the brain, together with decreased MMP‐9 activity for the “risk” MMP‐9_C variant supports the previously postulated connections between MMP‐9 activity, glutamate signaling, and schizophrenia (Lepeta & Kaczmarek, 2015). The gene discussed is MMP9; the disease is schizophrenia.