Polygenic overlap between schizophrenia (SCZ) and Parkinson’s disease (PD). Conditional Q-Q plots of nominal versus empirical −log10 p-values (corrected for inflation) in A) SCZ below the standard GWAS threshold of p<5×10−8 as a function of significance of association with PD, and B) vice versa, at the level of p ⩽ 0.1, p ⩽ 0.01, p ⩽ 0.001, respectively. The blue lines indicate all SNPs. The dashed lines indicate the null hypothesis.