SLCO1B1*40 contains the rs4149056C>T variant that decreases function (also present in *5) and the rs34671512A>C variant that may increase function (present in *19 and *20). Based on evidence supporting the function of rs4149056C>T (11477075, 32961594, 21245207), SLCO1B1*40 is assigned uncertain function due to no evidence.