This project is primarily designed to perform a genome-wide association study for obsessive-compulsive symptoms and related dimensional and categorical traits / phenotypes. We will use GWAS data from up to 15000 individuals from the SWE twin registers and phenotype information from up to 35000 individuals. 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 but optimized for twin modeling. 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. In addition a derivate of this pipeline optimized for analysis of family-based data (which can be found here: https://github.com/Nealelab/picopili/blob/master/bin/imp_prep.pl) will be used. Next to the dimensional phenotype GWAS of OCS we also plan to do perform GWAS on various continuous/quantitative traits (through data linkage with the Swedish National Registers). We will perform gene X environment interaction studies by both means of genomic risk profiles (e.g. for OCS but also other dimensional traits such as neuroticism) 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).