ASSOCIATION OF HLA-C*06 WITH SUSCEPTIBILITY TO PSORIATIC ARTHRITIS AND ITS CLINICAL PHENOTYPE IN ROMANIA O. M. Popa1, L. Popa2, M. I. Dutescu3, M. Bojinca4, V. Bojinca5, C. Ciofu4, C. Bara1, F. Mrazek6, M. Petrek6 ASSOCIATION OF HLA-C*06 WITH SUSCEPTIBILITY TO PSORIATIC ARTHRITIS AND ITS CLINICAL PHENOTYPE IN ROMANIA O. M. Popa1, L. Popa2, M. I. Dutescu3, M. Bojinca4, V. Bojinca5, C. Ciofu4, C. Bara1, F. Mrazek6, M. Petrek6 1Department of Immunology and Pathophysiology, Faculty of Medicine, University "Carol Davila", Bucharest, Romania 2Molecular Biology Department, Grigore Antipa National Museum of Natural History, Bucharest, Romania3National Hematology Institute Prof. Dr. C.T. NICOLAU, Bucharest, Romania4Department of Rheumatology, Faculty of Medicine, University "Carol Davila", "I.C. Cantacuzino" Hospital, Bucharest, Romania 5Department of Rheumatology, Faculty of Medicine, University "Carol Davila", ”St. Maria” Hospital, Bucharest, Romania6Laboratory of Immunogenomics and Proteomics, Department of Immunology, Palacky University, Olomouc, Czech Republic INTRODUCTION   Psoriatic arthritis (PsA) is a complex disease characterized by inflammation of the skin (psoriasis) and joints (arthritis).   Genome-wide association study on PsA Caucasian patients showed strong association with HLA class I region (1).   Studies concerning HLA-C locus showed positive association of C*06 with psoriatic arthritis in some populations, but no association in others. 1. Liu Y, PLoS Genet. 28; 4(3):e , 2008AIMS The aim of this study was to determine the influence of HLA-C alleles on susceptibility to psoriatic arthritis in Romanian population and to compare the distribution of HLA-C alleles among different disease subtypes. SUBJECTS AND METHODS   57 Romanian psoriatic arthritis patients diagnosed according to the Moll & Wright diagnostic criteria;   124 Romanian unrelated healthy control subjects;   We have established three subgroups of patients according to the following main disease phenotypes: arthritis with axial involvement (spondylitis) – 30%, oligoarthritis (no more than 4 joints affected) – 21%, polyarthritis (5 or more joints affected) – 49%;   The HLA-C genotyping was performed by polymerase chain reaction with sequence specific primers (PCR-SSP) using HLA-C-SSP low resolution kit (Olerup, Sweden);   The data were analyzed using the OpenEpi Collection of Epidemiologic Calculators Version 2.3. The significance of the association (p<0.05) was determined using the Mid-P exact test and Bonferroni correction was applied for the number of compared HLA-C allelic groups. RESULTS   We have found an association between HLA-C*06 and psoriatic arthritis (Pcorr=0.03, OR 2.9).   A weak negative association (“protective effect”) with PsA was found for HLA-C*04, but this was not significant after correction (pun=0.04, pcorr=NS).   In the subanalysis according to the PsA phenotypes, the patients with axial form of arthritis (spondylitis) showed an increased frequency of HLA-C*06 (pcorr=0.03, OR 5.1).   There was a lower phenotype frequency of HLA-C*07 in polyarthritis group compared with controls (26% versus 46), but not significant after correction (P=0.03) CONCLUSION  This is the first study reporting the HLA-C alleles distribution in psoriatic arthritis patients in Romania;  We confirmed here in the Romanian population the association of HLA-C*06 with psoriatic arthritis association found previously in other populations;  In Romanian population HLA-C*06 allelic group is associated with axial form of psoriatic arthritis;  Genetic studies regarding the HLA-C locus in psoriatic arthritis point to the fact that the HLA-C gene confers a genetic risk for this disease at least in some ethnic groups. GRANT SUPPORT: CNCSIS-UEFISCSU, project number PNII-IDEI 311/2007, ROMANIA and IGA UP project no. LF_2010_008, CZECH REPUBLIC Figure 1. Comparison of HLA-C*06 phenotype frequency in psoriatic arthritis (PsA) patients/controls (P=0.0025, Odds Ratio=2.9, 95% CL ) and PsA spondylitis subgroup/controls (p=0.0021, Odds Ratio=5.1, 95% CL ). EUROPEAN IMMUNOGENETICS AND HISTOCOMPATIBILITY CONFERENCE (EFI) May 15-18, 2010, Florence, ITALY