One study suggested that in the absence of glutamic acid at the 74th position of the mature protein encoded by the major histocompatibility complex, Class II, DR Beta 1(HLA-DRB1) gene, the amino acid methionine at the 99th position of HLA-C may contribute to individuals’ susceptibility to schizophrenia, in which the glutamic acid in HLA-DRB1 has a protective function against the disease (Seshasubramanian et al., 2020). This evidence concerns the gene HLA-C and schizophrenia.