effects62. SNPs in and around the MHC locus reached genome-wide significance for BD for the first time. However, unlike in schizophrenia, we found no influence of C4 structural alleles or gene expression63. Rather the association was driven by variation outside the classical MHC locus, with the index SNP (rs13195402) being a missense variant in BTN2A1, a brain-expressed gene64 encoding a plasma membrane protein.
