Even as genomics has rapidly expanded there are certain traits, namely those that are more intensive to measure, that are unlikely to reach sufficient sample sizes for GWAS in the near future. In these instances, polygenic risk score (PRS) analyses may prove informative in associating genetic risk for a given psychiatric disorder to these more nuanced outcomes. PRS analyses utilize genome-wide summary statistics from an independent sample to construct individual participants’ risk scores based on their measured genotypes (Wray et al., 2014). Constructing a PRS is similar to scoring a questionnaire, where the summary statistics reflect the scoring key, and the participant genotypes their responses on the survey. A PRS then reflects an omnibus, single measure of an individual’s genetic risk for a given outcome across the genome. These sorts of analyses have been used in interesting ways to examine genetic overlap across different presentations of disorders. For example, SCZ PRSs evinced a stronger positive association with BIP characterized by mood-incongruent psychosis than BIP with mood-congruent psychosis or without psychosis (Allardyce et al., 2018). In addition, SCZ PRSs have been positively associated with earlier age of onset of BIP (Ruderfer et al., 2018).
