The following information was recorded in web-based case report forms: demographic, clinical and radiographic data; physical examination findings, including tender and swollen joint counts (TJC and SJC); nail and skin involvement; Disease Activity Score-28 for Rheumatoid Arthritis with Erythrocyte Sedimentation Rate (DAS 28-ESR); Bath Ankylosing Spondylitis Disease Activity Index (BASDAI); Maastricht Ankylosing Spondylitis Enthesitis Score (MASES); Psoriasis Area Severity Index (PASI); Bath Ankylosing Spondylitis Radiology Index for the spine (BASRI-s); Health Assessment Questionnaire (HAQ); Bath Ankylosing Spondylitis Functional Index (BASFI); Health Assessment Questionnaire for the spondyloarthropathies (HAQ-s); Psoriatic arthritis quality of Life scale (PsAQoL); Short Form 36 (SF-36); Hospital Anxiety Depression Scale (HADS); Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F); and Fibromyalgia Rapid Screening Tool (FiRST) scores.
Obesity is linked with late-onset psoriasis and PsA, while normal weight is associated with the presence of the HLA-B*27 allele and an earlier onset of the disease.
Although there are many similarities among AS patients possessing HLA-B*27 versus those lacking this gene, the former group has a younger age of onset, a shorter delay in diagnosis, a better clinical response to tumor necrosis factor inhibitors, a greater familial occurrence, a greater risk for occurrence of acute anterior uveitis, and a lower risk for occurrence of psoriasis and IBD.
After controlling for the age of psoriasis onset no association of PsA to HLA-C*06:02 (p=0.07) was observed; instead, the most significant association was to amino acid at position 97 of HLA-B (p=1.54×10<sup>-9</sup>) where the presence of asparagine or serine residue increased PsA risk.
Moreover, we need to determine allele-specific effects of ERAP1 variants in the context of HLA-B*51 and HLA-Cw*6, which are associated with Behçet's disease and psoriasis, respectively.
Of note, these 'MHC-I-opathies' show a differential immunopathology, probably reflecting antigenic differences within target tissues: HLA-B(*)51 is linked to ocular and mucocutaneous disease but not gut involvement, and HLA-C(*)0602 is linked to type I psoriasis but not scalp or nail disease.
The human leukocyte antigen-C0602 allele confers the highest risk for psoriasis whereas several human leukocyte antigen-B alleles were identified as 'PsA-specific' genes.
Articles were selected, following predefined criteria, from case-control studies on the association between psoriasis and HLA-B published between 1 January 1972 and 11 November 2012, and included in the PubMed and ISI Web of Knowledge databases.
Our findings indicate that IL12B plays a fundamental role on the pathophysiology of TAK in combination with HLA-B(∗)52:01 and that common autoimmune mechanisms underlie the pathology of TAK and other autoimmune disorders such as psoriasis and inflammatory bowel diseases in which IL12B is involved as a genetic predisposing factor.
The MICA-129 methionine (Met) allele, particularly Met/Met homozygosity, was strongly associated with both cutaneous psoriasis (PsC) and psoriatic arthritis (PsA) independently of HLA-B and HLA-C in Toronto patients, and was also associated with PsA in St. John's patients, but with no additional effect of Met/Met homozygosity.
This includes several HLA class I alleles associated with HIV-1 control; amino acid residues at HLA-B positions 67, 70, and 97 that mediate HIV-1 peptide binding; and the deletion polymorphism rs67384697 associated with high surface expression of HLA-C. We also found that the compound genotype KIR3DS1 plus HLA-B Bw4-80I, which respectively encode a natural killer cell activating receptor and its putative ligand, significantly increased psoriasis susceptibility.
The following HLA alleles were over-transmitted to PsA compared with psoriasis: HLA-C*12 (p=0.005), HLA-B*38 (p=0.04), HLA-B*39 (p=0.03), HLA-B*27 (p=0.002).
High-need patients with psoriasis had a lower frequency of HLA-Cw*06 but a higher prevalence of HLA-B*46 compared with general patients with psoriasis in our population.
After adjusting for significant HLA-B and HLA-C alleles in multivariate analyses, MICA*016 remained significantly associated with psoriasis [odds ratio (OR) = 5.5, P = 0.008].
More importantly we find that rs9468925 in HLA-C/HLA-B is associated with both psoriasis and vitiligo, providing first important evidence that two major skin diseases share a common genetic locus in the MHC, and a basis for elucidating the molecular mechanism of skin disorders.