Propylthiouracil (PTU), an anti-thyroid thiourylene, is helpful in chronic plaque psoriasis. A precursor protein, Involucrin, is upregulated in psoriasis. In psoriasis, there is an increased expression of involucrin, which leads to abnormal keratinocyte differentiation and the formation of psoriatic plaques. The therapeutic effect of PTU in psoriasis may be attributable to the downregulation of involucrin. The gene discussed is IVL; the disease is psoriasis.