The OCD GWAS reported here, comprising over 53,000 cases, identified 30 independent genome-wide significant loci. Common SNPs explained 6.7% of the variation in OCD risk in our meta-analysis (LDSC with an assumed population prevalence of 1%), a significant reduction from the 28% reported previously10. However, differences in the assumed population prevalence (where a lower assumed prevalence for LDSC heritability calculation results in a lower heritability estimate) and an increase in sample heterogeneity likely contributed to this discrepancy. The reduction in SNP-heritability is in line with previous observations for closely related psychiatric disorders such as ADHD33,34 or depression17,35–37, where expanding the phenotype definition increased genetic heterogeneity, potentially accounting for the observed decrease in SNP heritability. This aligns with the fact that heritability estimates for more homogeneous OCD subgroups were higher: 16.4% for the clinically-ascertained subgroup and 13.3% for the comorbid subgroup (Supplementary Note 10). The current estimates are comparable to those of other psychiatric and substance use disorders, with SNP-heritability estimates ranging between 9% and 28%38.
