To calculate the SNP heritability and estimate the genetic correlation between ASB and a range of cognitive, psychiatric and reproductive traits, we used the (cross-trait) LD score regression method. The LD score method disentangles the contribution of true polygenic signal and bias due to population stratification to the inflated test statistics in GWAS, and optionally calculates a genetic correlation (rg) between different traits (B. K. Bulik-Sullivan et al., 2015). This method is particularly useful since it only requires GWAS summary statistics and is not biased by sample overlap(B. Bulik-Sullivan et al., 2015). Genetic correlations of ASB were calculated with cognitive and psychiatric traits, previously reported to be co morbid with ASB, using summary results from ADHD, schizophrenia and bipolar disorder (Neale et al., 2010; Psychiatric GWAS Consortium Bipolar Disorder Working Group, 2011; Schizophrenia Working Group of the Psychiatric Genomics Consortium, 2014) that are publicly available on the Psychiatric Genomics Consortium (PGC) webpage (https://www.med.unc.edu/pgc/results-and-downloads, accessed 5 September 2015). The summary statistics of neuroticism and educational attainment (defined as ‘number of years in the educational system’) were provided by the Social Science
