In psychiatric disorders, only weak evidence exists to suggest that the PRS for disorder susceptibility might be predictive of treatment response in depression [70, 71] or psychosis [72]. Further studies to identify specific treatment response polygenic risk scores are in progress in these disorders, but it is challenging to achieve sufficiently large sample sizes, with accurately captured response measures. Meta-analysis studies are underway, pooling clinical trials and observational studies of response to anti-depressants and to anti-psychotics. These would identify polygenic predictors for treatment response that might be useful in, for example, deciding between pharmacological and psychological treatment for depression [73]. Only one third of patients respond to the first anti-depressant prescribed [74], so a polygenic predictor might be useful to guide treatment; even a modest increase in the proportion of patients responding could have a substantial impact on the effectiveness and time to recovery. An important perspective in genetic testing for treatment response is in identifying patients who are unlikely to respond to a specific drug, as Gibson highlights [75, 76]. This could reduce the time taken by clinicians to
