CYP2B6*27 (c.593T>C, p.M198T) – Uncertain function: CYP2B6*27 is assigned uncertain function. Three in vitro studies using cDNA expression systems found that CYP2B6*27 demonstrated decreased enzyme activity compared to the *1 reference for most substrates, although increased activity was seen for one non-drug probe substrate (21746968, 17235330, 30201214). This discrepancy is probably due to differences in the in vitro expression systems and substrates used. One subject with the CYP2B6*6/*27 genotype had an elevated efavirenz AUC compared to the *1 reference (17235330). Consensus was not achieved among experts due to insufficient evidence of this variant in human subjects. Therefore, uncertain function was assigned based on inadequate evidence.