LAUSR

Background The genetic studies of tumour necrosis factor inhibitors (TNFi) response in patients with rheumatoid arthritis (RA) have largely relied on the changes in complex disease scores as a measure of treatment response. It is expected that genetic architecture of such complex score is heterogeneous and not very suitable for pharmacogenetic studies. Objectives We aimed to select the most optimal phenotype for TNFi response using heritability estimates using genome-wide association studies (GWAS) in the Korean population. Methods Disease Activity Scores based on 28 joint counts (DAS28) and Clinical Disease Activity Index (CDAI) were assessed at baseline, and after 6 months in 370 Korean RA patients who started TNFi due to moderate or high disease activity. Genotypes were generated on the Illumina HumanOmni2.5Exome array (2.5 million variants) in TNFi-treated Korean patients with RA. We estimated heritability using a linear mixed-modelling approach (GCTA) for the TNFi drug-response phenotype ΔDAS28, ΔCDAI and its separate components, such as Δ swollen joint count (SJC), Δ tender joint count (TJC), Δ erythrocyte sedimentation rate (ESR), Δ visual-analogue scale of general health (VAS-GH) and Δ provider global assessment of disease activity (PrGA). Furthermore, a multivariate GWAS approach was implemented, analysing separate DAS28 and CDAI components simultaneously Results The highest heritability estimates were found for ΔPrGA (h2=0.76) and ΔTJC (h2=0.73); lower heritability was found for ΔDAS28 (h2=0.32) with estimates for ΔESR (h2=0.66), ΔSJC (h2=0.62), ΔCDAI (h2=0.60) and ΔVAS-GH (h2=0.53) (all p-value<0.005). Conclusions Our results indicate that multiple SNPs together explain a substantial portion of the variation in change in provider global assessment of disease activity in TNFi-treated patients with RA. In conclusion, optimal phenotype based on heritability suggests the use of changes in clinical disease activity index (CDAI) including provider global assessment than DAS28 in pharmacogenetic study. Disclosure of Interest None declared