We included in the analysis four brain-related complex traits, i.e., ever-smoked (smoking), fluid intelligence score (IQ), years of education (EduYears), and schizophrenia (SCZ). GWAS summary statistics for EduYears (n = 293,723) and SCZ (36,989 cases and 113,075 controls) were from the latest meta-analyses47,48, and summary data for smoking (n = 453,693) and IQ (n = 146,819) were from GWAS analyses of the latest release of the UK Biobank (UKB) data56. Quality control and imputation of the UKB data have been detailed elsewhere56. We used 456,426 individuals of European descent and 7,288,503 common SNPs (MAF > 0.01) imputed from the Haplotype Reference Consortium (HRC)57 reference panel in the analysis. IQ was measured by 13 fluid intelligence questions and detailed description of the measurement can be found at the UKB website (URLs). We adjusted IQ (n = 146,819) by age and sex, and standardized the adjusted phenotype by rank-based inverse-normal transformation. The GWAS analyses were performed in BOLT-LMM58 using all 7.3 million SNPs with a subset of 0.7 million SNPs in common with HapMap359 used to control for population structure and polygenic
