As with negative symptoms, we also found evidence for PRS predicting positive symptoms in the two models tested. Though the amount of variance in positive symptoms (0.7%) explained by both models were the same (potentially suggesting a negligible effect of neurocognition on positive symptoms), model 2 controlling for neurocognition did not survive permutation correction and again could likely be explained by our smaller sample size. PRS association of positive symptoms is contradictory to previous studies that did not show a polygenic loading on positive symptoms (Fanous et al., 2012). This could likely be explained by the differences in sample characteristics. We had a less heterogeneous group (only chronic patients) in comparison to previous studies. It's been suggested that positive symptoms that emerge in adolescence may be strongly influenced by environmental factors such as childhood trauma and/or cannabis use, hence a lack of association in adolescence or first episode patients; PRS associations with positive symptoms may therefore emerge in patients with a later onset of such symptoms (Jones et al., 2016). Our findings could be suggestive of this difference in the pathogenicity and require further study.
