title: Psoriasis patients who are homozygous for the HLA-Cw*0602 allele have a 2.5-fold increased risk of developing psoriasis compared with Cw6 heterozygotes.
abstract: BACKGROUND
  Psoriasis is strongly associated with certain human leucocyte-associated antigens, especially HLA-Cw*0602. Patients who are HLA-Cw*0602 positive have been reported to have more active disease and a younger age at disease onset than HLA-Cw6-negative patients.
  
  
  OBJECTIVE
  To ascertain whether there are differences in the clinical features and relative risk between HLA-Cw*0602 homozygous and heterozygous psoriasis patients.
  
  
  METHODS
  One thousand and six patients with chronic plaque psoriasis were evaluated clinically and HLA-C typed. In addition, 512 unrelated controls were typed for HLA-C.
  
  
  RESULTS
  Of the patients 646 (64.2%) were HLA-Cw*0602 positive, and 68 (6.8%) were homozygous for this allele. Heterozygosity was associated with a relative risk of developing psoriasis of 8.9 compared with 23.1 for the Cw6 homozygous patients. The homozygous patients also had an earlier disease onset (mean 15.0 vs. 17.8 years, P = 0.04). However, the Cw6 homozygotes did not differ from the heterozygotes with respect to disease severity, guttate onset, distribution of plaques, nail changes or any other clinical parameter recorded.
  
  
  CONCLUSIONS
  Homozygosity for the gene in the major histocompatibility complex region has a major additive impact on the risk of developing psoriasis and predisposes to an earlier disease onset, but does not have any marked influence on the phenotype or the severity of the disease.
authors.affiliation: Department of Immunology, National University Hospital of Iceland, Eiriksgata, 101 Reykjavik, Iceland.
authors.forename: J E
authors.initials: JE
authors.lastname: Gudjonsson
authors.forename: A
authors.initials: A
authors.lastname: Karason
authors.forename: A
authors.initials: A
authors.lastname: Antonsdottir
authors.forename: E H
authors.initials: EH
authors.lastname: Runarsdottir
authors.forename: V B
authors.initials: VB
authors.lastname: Hauksson
authors.forename: R
authors.initials: R
authors.lastname: Upmanyu
authors.forename: J
authors.initials: J
authors.lastname: Gulcher
authors.forename: K
authors.initials: K
authors.lastname: Stefansson
authors.forename: H
authors.initials: H
authors.lastname: Valdimarsson
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D000483:Alleles; D002648:Child; D002675:Child, Preschool; D005838:Genotype; D015236:HLA-C Antigens / Q000235:genetics*; D006720:Homozygote; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008875:Middle Aged; D010641:Phenotype; D011565:Psoriasis / Q000235:genetics* / Q000473:pathology; D012307:Risk Factors
chemical_list: D015236:HLA-C Antigens; C528994:HLA-C*06 antigen