This report contributes important new data about the nature of MDD.33 Unlike a large number of other GWAS that provide precious etiological clues, our analyses are more informative about what MDD is not. The path to progress is likely to be more difficult for MDD, but there are a number of rational next steps. We have offered some ideas about how progress might be achieved. The PGC is conducting GWAS metaanalyses across ADHD, autism, BIP, MDD and schizophrenia, and these very large analyses could identify genetic variants that predispose or protect to psychiatric disorders in general, and thus provide key initial findings that could be used to disentangle the etiology of MDD. Analysis of copy number variation has provided important leads for autism and schizophrenia, and might prove informative for MDD.
