Induction of CYP26B1 and CYP26A1 . A. Fold induction of CYP26B1 mRNA expression. CYP26B1 was induced significantly more (*P < 0.05) in the control cells as compared to the Subject 1 (S1) cells with a chromosomal deletion of CYP26B1 after treatment with ATRA. B. Induction of CYP26A1 mRNA expression in ATRA-treated cells. There was no significant difference (n.s.; P > 0.05) in CYP26A1 induction between the control cells and Subject 1 cells.