HL-A antigens in psoriasis with special reference to the clinical type, age of onset, exacerbations after respiratory infections and occurrence of arthritis.

HL-A typing was performed in a series of 125 patients with common psoriasis, 12 patients with flexural psoriasis, 16 patients with erythrodermic psoriasis and 16 patients with generalized pustular psoriasis, and compared with typing in a control population. The HL-A antigens 13 and 17 were significantly increased in patients with common psoriasis and erythrodermic psoriasis. HL-A 17 was also found in two of the 16 patients with generalized pustular psoriasis. Neither HL-A 13 nor 17 was increased in patients with flexural psoriasis. It is suggested that flexular psoriasis might be genetically distinct from common psoriasis. TY was increased in patients with common psoriasis. The increase of HL-A 13, 17 and TY was most marked in patients with onset of psoriasis before the age of 40 years. HL-A 13 was found in 38 per cent of the 40 patients with infection-related exacerbations of psoriasis, but only in 17 per cent (p = 0.012) of the remaining 129 patients. HL-A 27 was found in 58 per cent of the 26 patients with sacro-iliitis and in 27 per cent of the 41 patients with peripheral arthritis without sacro-iliitis, but only in eight per cent of the 102 non-arthritic patients (p less than 0.001) and p less than 0.01, respectively).