Genotyping of human cytochrome P450 2A6 (CYP2A6), a nicotine C‐oxidase

Abstract

Cytochrome P450 2A6 (CYP2A6) is a polymorphic enzyme responsible for the oxidation of certain precarcinogens and drugs and is the major nicotine C-oxidase. The role of CYP2A6 for nicotine elimination was emphasised recently by the finding that smokers carrying defective CYP2A6 alleles consumed fewer cigarettes [Pianezza et al. (1998) Nature 393, 750]. The method used for CYP2A6 genotyping has, however, been found to give erroneous results with respect to the coumarin hydroxylase phenotype, a probe reaction for the CYP2A6 enzyme. The present study describes an allele-specific PCR genotyping method that identifies the major defective CYP2A6 allele and accurately predicts the phenotype. An allele frequency of 1^3% was observed in Finnish, Spanish, and Swedish populations, much lower than described previously.z 1998 Federation of European Biochemical Societies.

CYP2A6 genotype and smoking

“…Our results do not support the results by London et al, however, for the overrepresentation of subjects with two null alleles among non-smokers, 2 since there were no such individuals among our 965 subjects. Our results strongly suggest that the actual allele frequency of CYP2A6-null alleles is less than 3% among Caucasians, as recently observed among Finnish, Spanish and Swedish populations, 3 and that the frequencies of subjects having null alleles, as reported by Pianezza et al 1 and London et al 2 (12-24%), are erroneously high because of their genotyping method. 4 Furthermore, the present results are considered to better represent the CYP2A6 genotype frequencies among smokers and non-smokers, because the data were obtained from a large unselected, and representative, racially homogenous population sample.…”

“…1,2 Our data, derived from a novel and specific genotyping method 3 that was applied to a large and racially homogenous representative population sample, strongly suggest that CYP2A6 alleles expressing decreased enzymatic activity are not associated with a reduced risk of tobacco dependence or lower levels of cigarette smoking.…”

“…4 Furthermore, the present results are considered to better represent the CYP2A6 genotype frequencies among smokers and non-smokers, because the data were obtained from a large unselected, and representative, racially homogenous population sample. 2,3 Different studies for the VNTR polymorphism failed to reveal any significant association with bipolar and unipolar affective disorders and it is unlikely that it has a major influence on disease risk. 4 However, the analysis of the association between the 5-HTTLPR polymorphism and susceptibility for several psychiatric diseases (including mood disorders, autism, panic disorder, schizophrenia, Alzheimer's disease, obsessive compulsive disorder, personality traits and depressive symptomatology in mood disorders) in different populations has shown some positive but contradictory findings.…”

“…In both of the aforementioned studies, the CYP2A6 genotype was identified by the method of Fernandez-Salguero et al, 4 which was recently reported to give erroneous results relative to coumarin hydroxylase phenotype, a probe reaction for the CYP2A6 enzyme. 3 Therefore, we decided to study the association between the CYP2A6 genotype and tobacco smoking by using a new allele-specific PCR genotyping method that identifies the major defective CYP2A6 allele and accurately predicts the phenotype. 3 We have used PCR-primers which specifically amplified exons 1-4 of the CYP2A6 gene without amplifying highly homologous CYP2A13 genes or CYP2A7 genes or CYP2A7 pseudogenes.…”

“…3 Therefore, we decided to study the association between the CYP2A6 genotype and tobacco smoking by using a new allele-specific PCR genotyping method that identifies the major defective CYP2A6 allele and accurately predicts the phenotype. 3 We have used PCR-primers which specifically amplified exons 1-4 of the CYP2A6 gene without amplifying highly homologous CYP2A13 genes or CYP2A7 genes or CYP2A7 pseudogenes. This 1.8-kb PCR fragment was subsequently used as a template for an allele-specific PCR reaction as described in detail by Oscarson et al 3 The study population consisted of participants from the Kuopio Ischemic Heart Disease Risk Factory Study (KIHD), a population-based epidemiologic study (participation rate 82.6%) that was begun about 10 years ago to investigate previously unestablished risk factors for myocardial infarction, the progression of atherosclerosis, and other major health outcomes in middle-aged men.…”