HLA and psoriasis: A genetic study of Northern Italian patients

Background. We evaluated the HLA association in 40 Italian psoriatic patients. Moreover, combining clinical with immunogenetic heterogeneities by means of the correspondence analysis, we designed a 'disease-map' to facilitate the interpretation of the different HLA profiles. Methods. HLA class I, II and III polymorphisms were studied in 40 Caucasian psoriatic patients. Control group was composed by 118 age-matched blood donors. Results. HLA class I alleles revealed a significant increase of Cw6 in patients (p = 0.00073). HLA class II polymorphism showed that the alleles DR7 and DQ9 were overrepresented in patients (p = 0.00019 and p = 0.00002 respectively). At the genomic level, a significant increase of DRB1*0701, DQA1*0201 and DQB1*0303 in patients was found (p = 0.00052; p = 0.00079 and p = 0.00002, respectively). Analysis of C4A and C4B alleles of the HLA class III showed a significant increase of C4A6 in patients (p = 0.00013). The extended ancestral haplotype (AH 57.1) HLA-A1, Cw6, B57, C4A6, C4B1, DRB1*0701, DQA1*0201, DQB1*0303 was significantly represented in patients (p = 0.000127). In particular, it was increased in females, in familial cases and in patients with palmo-plantar psoriasis. Conclusions. The importance of the contribution of HLA genes is reflected in the evaluation of risk ratio that ranges from 3.08 to 29.79 according to the different alleles or haplotypes considered. Correspondence analysis circumvents the statistical difficulties due to the different, multiple associations between HLA and clinical subtypes. From an immunogenetic perspective, psoriasis adheres closely to a multifactorial model of pathogenesis in which several discrete inherited and environmental factors interact.