However, the results of the polygenic analyses do provide strong evidence that OCD and TS have at least some distinct genetic risk factors. First, the individual disorder analyses confirm that OCD has a significant polygenic component. The proportion of OCD variance explained by directly interrogated SNPs (3.2%) is similar to the findings in schizophrenia (3–6%) and bipolar disorder (2.8%)(25), indicating that OCD likely arises from the joint influence of a large number of susceptibility genes spread across the genome, either as common variants or as rare variants in tight linkage disequilibrium with GWAS SNPs. This result is consistent with a parallel heritability study of the same datasets using mixed linear modeling which found that OCD heritability is concentrated in common variants with minor allele frequencies (MAF)>30% (10).
