Finally, comparison of the major depression loci with 108 loci for schizophrenia19 identified six shared loci. Many SNPs in the extended MHC region are strongly associated with schizophrenia, but implication of the MHC region is novel for major depression. Another example is TCF4 (transcription factor 4) which is strongly associated with schizophrenia but not previously with MDD. TCF4 is essential for normal brain development, and rare mutations in TCF4 cause Pitt–Hopkins syndrome which includes autistic features41. GRS calculated from the schizophrenia GWA results explained 0.8% of the variance in liability of MDD (Fig. 2c).
