GPM6A and major depressive disorder: In addition, a subgroup of patients with schizophrenia who also suffer from depression turned out to be useful for searching for genetic associations, including the following candidate genes: the GRIN1 gene encoding the N-methyl-d-aspartate receptor (NMDAR) subunit; the GPM6A gene encoding a glycoprotein modulating stress in the hippocampus [42,43,44].