This project is primarily designed to perform a genome-wide association study for obsessive-compulsive disorder and related conditions. We will use GWAS data from up to 5000 OCD cases (currently 1200 genotyped) and up to 10.000 controls (currently 3000 available). Quality control and imputation is achieved using standardized pipelines developed on the basis of state-of-the-art analytical software packages (PLINK, METAL, IMPUTE, SHAPEIT and others) and a series of perl scripts. The pipeline (available here: https://sites.google.com/a/broadinstitute.org/ricopili/ and here: https://github.com/Nealelab/ricopili) has been extensively used in the field of statistical genetics and amongst others also relies on R. Next to the categorical phenotype GWAS of OCD we also plan to do perform GWAS on various continuous/quantitative traits including but not limited to dimensional obsessive-compulsive symptoms, treatment response and others. We will perform gene X environment interaction studies by both means of genomic risk profiles and at the single marker level. Our study is a collaboration between the groups of Christian Rück at KI and David Mataix-Cols (also KI) with support from other members at KI (Robert Karlsson).