CYP2B6*29 (CYP2B7-CYP2B6 hybrid gene) – Decreased function: CYP2B6*29 is assigned decreased function. This allele is a hybrid consisting of CYP2B7 (exons 1-4) and CYP2B6 (exons 5-9) harboring 23 amino acid changes compared to the protein encoded by the CYP2B6*1 reference. Among those is c.516G>T which is one of the function-altering variants defining CYP2B6*6. CYP2B6*29 was identified in a subject with an elevated efavirenz AUC compared to the *1 reference and similar to those seen in patients carrying one decreased function allele (17885627). One in vitro study found that primary human hepatocytes of subjects with a CYP2B6*29 allele had slightly lower protein expression and enzyme activity compared to the *1 reference (28181240). The same study also showed that the AUC for 4-OH-cyclophosphamide was significantly lower for patients with a CYP2B6*1/*29 genotype compared to *1/*1 (28181240). Therefore, consensus among experts was decreased function based on limited evidence.