Identification of novel polymorphisms in the 5 ' flanking region of CYP1A2, characterization of interethnic variability, and investigation of their functional significance

CYP1A2 activity has been demonstrated to be bimodally or trimodally distrib uted in several populations, consistent with a codominant or recessive func tional genetic polymorphism. However, studies aimed at identifying polymorp hisms in CYP1A2 have not yet adequately accounted for this distribution pat tern. To search for functional polymorphisms, we performed genome-walking, polymerase chain reaction (PCR) sequencing, and cloning, and identified thr ee novel polymorphisms in the 5' flanking region of CYP1A2: a T(-3591)G sub stitution, a G(-3595)T substitution, and a T-3605 insertion. The frequency of the T-3591G substitution was determined by a PCR-restriction fragment le ngth polymorphism assay, and found to be significantly higher (P < 0.0001) in Taiwanese (allele frequency 0.128, n = 125) compared to Caucasians (0.01 7, n = 87) or African Americans (0.024, n = 104). The functional consequenc e of the T(-3591)G and the G(-3595)T substitutions was determined by site-d irected mutagenesis followed by transient transfection experiments. The T(- 3591)G mutation was shown to be nonfunctional, while although the G(-3595)T mutation appeared to result in an increase in promoter activity, this was only to a small degree and therefore unlikely to be important in vivo. In a ddition, we report 532 bases of 5' flanking sequence further upstream than that reported to date, and four sequence discrepancies compared to the orig inal published sequence (G(-3649)C, <Delta>T-3650, DeltaA(-4072), and C-409 3 ins). Pharmacogenetics 10:695-704 (C) 2000 Lippincott Williams & Wilkins.