GRIK4 and schizophrenia: After resequencing 516 unrelated patients with schizophrenia, 44 protein-altering variants were identified, including 12 in the GRIK1, 5 in the GRIK2, 7 in the GRIK3, 13 in the GRIK4, and 7 in the GRIK5 (Table 1, Supplementary Figure S1).