Research Article The HLA-Cw12 Allele Is an Important Susceptibility Allele for Psoriasis and Is Associated with Resistant Psoriasis in the Turkish Population Nahide Onsun , 1 Serpil Pirmit, 2 Dilek Ozkaya , 1 Firin Çelik, 1 Aylin Rezvani, 3 F. Pelin Cengiz, 1 and Cigdem Kekik 4 1 Department of Dermatology, Bezmialem Vakif University Medical School, Turkey 2 Istanbul Lepra Hospital, Ministry of Health, Turkey 3 Deparment of Rheumatology, Bezmialem Vakif University Medical School, Turkey 4 Istanbul University Medical School Medical Biology Department, Turkey Correspondence should be addressed to Nahide Onsun; nonarir2011@hotmail.com Received 3 January 2019; Revised 7 May 2019; Accepted 2 June 2019; Published 25 June 2019 Academic Editor: Masao Ota Copyright © 2019 Nahide Onsun et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Psoriasis is a multifactorial immune-mediated infammatory disease triggered by both genetic and environmental factors. Te strong association between psoriasis and HLA-C∗06 allele has been demonstrated in various races. Te HLA- C∗12 allele is closely related to the HLA-C∗06 family of alleles and shares identical sequences. To the best of our knowledge, there is no information about the relationship between HLA-C∗12 and psoriasis in the Turkish population. Te present study aims to determine this relationship. Methods. Tis case control study involved 150 patients with plaque-type psoriasis and 145 age- and gender-matched healthy individuals. Severity of psoriasis was measured using the PASI scores of all patients and joint involvement was investigated with CASPAR criteria. HLA-C alleles were determined with a Tepnel-Lifecodes system. Results. HLA-C∗06, HLA-C∗12, and HLA-C∗04 alleles were most commonly observed in psoriasis patients. HLA-C∗06 and HLA-C∗12 were signifcantly more frequent in the psoriasis group. HLA-C∗06 was 4.11 times more common in psoriasis patients. An increase in PASI (Psoriasis Area Severity Index) scores was compatible with HLA-C∗12 positivity. A need for systemic treatment was highly noticeable in patients with the HLA-C∗12 allele. Conclusions. HLA-C∗12 was found as the second most frequent allele with psoriasis in Turkish population and was associated with severe psoriasis. Our study is limited as we could not investigate other potentially related alleles other than HLA-C alleles and risk factors increasing severity of psoriasis. 1. Introduction Psoriasis is a chronic infammatory disease characterized by T-cell-mediated hyperproliferation of keratinocytes. Both environmental and genetic factors are involved in the aeti- ology of psoriasis [1]. Te HLA-C locus on chromosome 6p21.33 is accepted as a susceptibility locus for psoriasis. Te association between psoriasis and the HLA-C∗06 allele has been demonstrated in various genetic studies [2–5]. Early- onset psoriasis is more likely to be familial and associated with HLA-C∗06, according to the results of population studies [6]. Te HLA-C∗12 family of alleles is closely related to HLA- C∗06 alleles, sharing identical sequences in their alpha-2 domains, peptide binding pockets A, D, E, and all 3 introns [7]. HLA-C∗12 has also been found to be a risk factor for psoriatic arthritis [8]. Large epidemiological studies are lacking in Turkey. In a study done with limited number of patients the prevalence was found as 1.3% [8]. Since there are limited numbers of studies that have been made in Turkey for genetic susceptibility factors in patients with psoriasis, we aimed to investigate frequency of HLA-C alleles in the Turkish population. Hindawi e Scientific World Journal Volume 2019, Article ID 7848314, 5 pages https://doi.org/10.1155/2019/7848314