There is a marked activation of Rac1 in psoriatic lesional epidermis compared with normal control skin47, and overexpressing a Rac1V12 mutant under a keratin 14 promoter in a transgenic mouse model recapitulated many hallmarks of human psoriasis, including psoriasiform hyperplasia, the Auspitz sign, Koebnerization, joint inflammation and a mutilating arthropathy29. The gene discussed is RAC1; the disease is inflammation.