For the score based analysis, only pairwise independent autosomal SNPs (r2<0.25) with MAF>0.02 and p<0.5 were used. The total GWAS sample was divided at random into two halves. The first half was used as the discovery sample (667 patients; 1,084 controls) and the second half was used as the target sample (666 patients; 1,084 controls). On the basis of the association results of single marker tests in the discovery sample, a polygenic score was calculated for the subjects in the target sample. For a detailed description of the method see Purcell et al. (2009). To build the polygenic score for an individual, the number of minor alleles of this subject on any of the included loci was multiplied by the log(OR) of the respective marker. The sum of all of these products was then calculated and finally divided by the number of included loci. Testing for association between disease status and polygenic score was performed in the target sample using a logistic regression approach and the following two models: a) using disease status as a response variable, and the polygenic
