To calculate the sex-specific narrow-sense SNP-based heritability (h2), (i.e., the proportion of phenotypic variation attributable to the additive effect of all SNP variants in each sex), we used two methods: 1) LD score regression (LDSC) as implemented in LDSC v1.0.0 (B. K. Bulik-Sullivan et al. 2015) and 2) restricted maximum likelihood analysis (REML) implemented in GCTA v1.24.4 (Yang et al. 2011). LDSC analysis was performed on the sex-stratified meta-analysis summary statistics from all study datasets. Meta-analyzed imputed SNPs which overlapped with a panel of high confidence HapMap SNPs were used for the LD score regression. Because our dataset is composed of European individuals, we downloaded precomputed LD scores (B. K. Bulik-Sullivan et al. 2015; B. Bulik-Sullivan et al. 2015). Using all individuals, we calculated the total and sex-stratified heritability, checked for residual population stratification (based on the LDSC intercept (B. K. Bulik-Sullivan et al. 2015)), and calculated the genetic correlation between males and females. A range of 1–3% OCD population prevalence was used to transform from the observed heritability scale to the liability scale.
