samples of 500,000 cases and controls (i.e., total N = 1,000,000), identified risk variants will account for 60% of the SNP-based heritability for SCZ and BIP, and only 10% of the SNP-based heritability for MDD (Holland et al., 2019). Identifying risk variants for MDD is especially difficult as this reflects a disorder that is both highly polygenic and less heritable, which is to say that there are a relatively large number of risk variants with particularly small effect to uncover. This indicates that cross-disorder genomic efforts in the near future should look beyond solely identifying additional pleiotropic loci as this will likely only capture a portion of the overarching biological picture. With that said, efforts to include more sophisticated phenotypes and explicitly consider the role of the environment are both within reach and likely to add considerable nuance to our current understanding.
