421C>A is assigned a decreased function based strong evidence with numerous in vitro and clinical studies supporting decreased function. It has been found to decrease the expression of BCRP (25236865, 21091277, 22098950, 18464048, 18958403). Expression of the BCRP protein was reported to be 30–40% that of protein with the reference sequence, and expression in the placenta, specifically, was also reportedly lower (15475413, 15553238). The c.421C>A variant has been found to affect the pharmacokinetics of, response to, and toxicity of compounds that are BCRP substrates, including chemotherapeutics and endogenous compounds (10646850, 11688982, 11309344, 25639366, 26914831). Therefore, consensus among experts was decreased function with strong evidence.