CYP2B6*20 (c.503C>T, p.T168I; c.516G>T, p.Q172H/splice defect; c.785A>G, p.K262R) – Decreased function: CYP2B6*20 is assigned decreased function. CYP2B6*20 contains c.516G>T which causes aberrant splicing (see CYP2B6*6 for more information). Three in vitro studies using cDNA expression systems found decreased enzyme activity of CYP2B6*20 compared to the *1 reference with various substrates (16272958, 21746968, 30201214). As is the same for *6, the mechanism for decreased activity is aberrant splicing caused by c.516G>T, which leads to reduced amounts of protein and thus, activity (14551287, 18171905, 24260284). As a result, alleles having c.516G>T are considered decreased function, regardless of the functional status of additional other variants unless these cause no function (e.g., CYP2B6*13 and CYP2B6*38). Therefore, the consensus among experts was decreased function based on the presence of c.516G>T and limited evidence.