The HL-A system and psoriasis.

A study of 157 psoriatic patients showed that 48.4% were HL-A 17 positive (control 6.0%). The relative risk of psoriasis in HL-A 17 positive individuals (14.7) was significantly higher than that reported from other centes, whilst that for HL-A 13 was lower. HL-A 17 was commoner in femal patients and associated with an earlier age of onset of psoriasis than when HL-A 17 was absent. The earlier age of onset in females is largely due to the higher frequency of HL-A 17. Family studies show that often the ingeritance of HL-A 17 is a necessary condition for psoriasis to appear and this probably applies in some instances to HL-A 13. It is likely that there is interaction between HL-A 17 and HL-A 13 and other genes predisposing to psoriasis. In some families there appears to be no association between psoriasis and the HL-A system. The general significance of these findings is discussed.