the potential of GWAS in OUD research will necessitate organized sample collection and meta-analyses of existing data sets. An additional lesson from other disorders is the “missing heritability” problem in which even appropriately powered GWAS are unable to explain all of the calculated heritability of the phenotype. The OUD field will eventually need to move outside of common variants and explore other relevant sources of variation, including rare variants, gene × environment effects, gene-gene interactions, and epigenetics.
