Analyses using real data have also been performed. Rheumatoid arthritis (RA) genotype data on 1999 cases and 1504 controls have been obtained from WTCCC [44 (link)]. Genotypes from the Affymetrix GeneChip 500 K Mapping Array Set have been filtered using the usual quality controls tests on DNA quality (percentage of genotyped marker for any given individual above 90%), markers quality (percentage of genotyped individuals for any given marker above 90%), genotypes frequencies (markers with a p-value below a Bonferroni adjusted 5% threshold under the hypothesis of Hardy-Weinberg equilibrium in the controls cohort have been discarded). Missing genotypes for the GeneChip markers have been imputed using impute2 software [45 (link)]. This procedure led to 312583 SNP to be analyzed for the 2 cohorts. Zhang et al. [46 ] and [47 (link)] also used this dataset to infer potential interactions. These studies will therefore serve as a comparison for the results obtained with our approach.
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