Psoriasis is a common, chronic, inflammatory dis- ease characterised by T-cell mediated hyper- proliferation of keratinocytes. The disease affects approximately 2% of people in the northern Euro- pean population. Although the pathogenesis of psoriasis still remains elusive, its genetic back- ground is undoubted. The major susceptibility lo- cus for psoriasis (PSORS1) is located within the MHC region on chromosome 6p21.3 (Trembath et al. 1997). At the PSORS1 locus, HLA–Cw*06 is the most susceptible allele for psoriasis in most populations. On the basis of bimodal distribution of age at onset, psoriasis vulgaris (PV) was classi- fied into early-onset psoriasis (type I, with onset before 40 y) and late-onset psoriasis (type II, rare, with onset after 40 y). The concept of 2 types of psoriasis vulgaris: with early and late onset, first reported by Henseler and Christophers (1985), has been widely accepted in many reports from vari- ous populations, also in the psoriatic population of northern Poland (Szczerkowska et al. 1996). How- ever, the usefulness of this classification in analy- ses of genetic and epidemiological data has been recently questioned (Gudjonsson et al. 2006). Early-onset psoriasis is associated with the HLA–Cw6 antigen, which occurs in approxi- mately 60% of patients, compared to 15% of con- trol subjects in Caucasian populations, and very often is characterized by familial inheritance (Henseler and Christophers 1985; Szczerkowska- Dobosz et al. 1996; £uszczek et al. 2003). Late-onset psoriasis (LOP) is rarely familial and clinically is less extensive than early-onset psoria- sis. Because of the rare occurrence of LOP, there J Appl Genet 48(3), 2007, pp. 273–275 Short communication Lack of association of HLA–C alleles with late-onset psoriasis in the northern Polish population Aneta Szczerkowska-Dobosz 1 , Katarzyna Niespodziana 2 , Krzysztof Rêba³a 2 , Joanna Garstecka 3 , Magdalena Lange 1 , Wioletta Barañska-Rybak 1 1 Department of Dermatology, Medical University, Gdañsk, Poland 2 Department of Forensic Medicine, Medical University, Gdañsk, Poland 3 Department of Dermatology, Nicolaus Copernicus Hospital, Gdañsk, Poland Abstract. The HLA (human leukocyte antigen) Cw*06 allele demonstrates the strongest association with suscep- tibility to early-onset psoriasis in most populations. Recent data have indicated that late-onset psoriasis (LOP) demonstrates only a weak association with Cw*0602, and suggest that this type of psoriasis may represent a dis- tinct subtype of the disease. The aim of this study was to compare the frequency of human leukocyte antigen C (HLA–C) alleles in patients with LOP and in healthy subjects within the same ethnic group in northern Poland. HLA–C alleles of 89 patients with psoriasis with onset at the age of 40 y or later and 80 control subjects were de- termined by a polymerase chain reaction (PCR), low-resolution method. The results showed that the Cw*05 allele was detected less frequently in patients with LOP than in control subjects, but this failed to retain significance af- ter correction for multiple comparisons. There were no differences in the frequency of other HLA–C alleles be- tween the patients and the control group. Our results confirm no association between HLA–C alleles and LOP in the northern Polish population. The lack of this association supports the hypothesis about different genetic back- grounds of early- and late-onset psoriasis. Keywords: HLA–Cw*06, late-onset psoriasis, PSORS1. Received: January 15, 2007. Accepted: March 12, 2007 Correspondence: A. Szczerkowska-Dobosz, Department of Dermatology, Medical University of Gdañsk, Dêbinki 7, 80–211 Gdañsk, Poland; e-mail: adobosz@amg.gda.pl