SLC1A4 and schizophrenia: Studies have reported low serum D-serum levels in people with schizophrenia, however (see Cho et al., 2016 for a meta-analysis of 20 studies [52]), and although studies have failed to identify a genetic association between SLC1A4 and schizophrenia, SLC1A4 was identified as a gene with dysregulated expression in the cortical brains of individuals affected with schizophrenia [53], suggesting that it may be involved in disease pathogenesis but acts downstream of causative genes.