FinnTwin12 were assessed at age 14. Accordingly, endorsements of alcohol problems at this age may represent a more severe phenotype than those at age 18 in ALSPAC. The age and measurement differences across the ALSPAC and FinnTwin12 samples may explain, in part, the low percentage of variance accounted for by the polygenic score. Finally, the polygenic approach adopted here is limited in that it does not attempt to implicate the specific genes involved in alcohol problems. Additional methods, such as gene set approaches that examine whether SNPs included in a polygenic score are located in functionally related genes [52], are well suited to identify the potential biological mechanisms underlying polygenic effects.
