The functional experiments indicates that acitretin can be pumped into cells by the SLCO1B1 and SLC22A1 transporters, and that the rs4149056C and rs2282143T alleles reduce the uptake of acitretin, and are significantly associated with clinical effective responsiveness in psoriasis patients when treated by acitretin. The gene discussed is SLC22A1; the disease is psoriasis.