We used the Genome-wide Complex Trait Analysis (GCTA) program version 1.26.0 to estimate the genetic relationship matrix (GRM) between all pairs of individuals from SNPs (26). Then, we used PLINK 2.0 to extract the top principal components (PCAs) from the variance-standardized relationship matrix (for more details, see Supplementary Materials). We performed restricted maximum likelihood (REML) analysis, implemented in GCTA, to estimate heritability of OCD attributable to SNP genotypes. Because the OCD diagnosis is dichotomous, we scaled the phenotypic variance to an underlying liability scale using the population prevalence of 1%, similar to our most recent estimate of population prevalence in Sweden using data from the Swedish national registers (1) (for more details, see Supplementary Materials, where we also provide results for 2% prevalence).
