HLA Cw*06 is not essential for streptococcal‐induced psoriasis

Summary Background  Streptococcal throat infections and HLA Cw6 (Cw*06) have been implicated in the pathogenesis of psoriasis, particularly in the guttate form. Objectives  To study 105 Irish patients with psoriasis to investigate the relationship between streptococcal infections and Cw*06. Methods  The patients were divided into two groups: those with guttate psoriasis or guttate flare (guttate group, GG, n  = 64) and those with chronic plaque psoriasis (chronic plaque group, CPG, n  = 41). Results  The incidence of Cw*06 was 86% in the GG and 73% in the CPG, which was not significantly different ( P =  0·1725) but the incidence in both groups was significantly higher than in an Irish control group (18%) ( P <  0·0001 vs. GG and P  < 0·0001 vs. CPG). Evidence for streptococcal infection was higher in the GG (56%) than in the CPG (32%) ( P =  0·0231). Of those patients with evidence of streptococcal infection, 30 of 36 GG (83%) and nine of 13 CPG (69%) patients possessed the Cw*06 genotype. Conclusions  Thus, not all patients with streptococcal‐related psoriasis carry Cw*06. The role of Cw*06 in psoriasis, if any, has yet to be determined.