Additional support for shared genetic liability comes from polygenic score (PGS) studies. A PGS is calculated as a weighted sum of phenotype-associated alleles and represents individual level genetic liability to a phenotype. Previous studies found the PGS for SCZ is positively associated with cannabis use18 and modulates the link between cannabis use and psychosis19 but one study found no link with CUD.20 Recent studies have shown that for a given phenotype, genetically correlated phenotypes may improve the prediction of the target phenotype by using their joint predictive power.21 Yet, to our knowledge, little is known about the potential to improve the prediction efficiency of psychotic disorders using joint genetic liability of psychotic disorders and cannabis phenotypes.
