title: Characterization and PCR-based detection of two different hybrid CYP2D7P/CYP2D6 alleles associated with the poor metabolizer phenotype.
abstract: The majority of humans deficient in the cytochrome P450 CYP2D6 enzyme, so-called poor metabolizers (PMs), can now be identified by genotyping for several different PM-associated mutations. However, additional null alleles remain to be identified as demonstrated by subjects with the PM phenotype in the absence of a corresponding genotype. The rare 11 kb band on Xba I RFLP analysis, which is distinct from the 13 kb CYP2D6D (CYP2D6*5) allele, has been proposed to constitute such a unique non-functional allele. Here we demonstrate that the 11 kb band represents at least two different nine exon CYP2D7P/CYP2D6 hybrids generated by large deletions in the CYP2D gene cluster due to unequal cross-over or looping-out mechanisms. The total allele frequency was approximately 0.001-0.01 in European and North American Caucasians. The most common variant (CYP2D6*16) had breakpoints lying between the end of exon 7 and the start of exon 9 of the respective genes. The "CYP2D7-like' part of the gene was most homologous to the previously described CYP2D7AP and CYP2D7 (44/11.5) sequences. The other chimeric allele consisted of exon 1 of CYP2D7 and exons 2-9 from CYP2D6, and may be similar to a hybrid gene termed CYP2D6*13 recently described in a French individual. Two different routine PCR assays were developed for rapid and sensitive detection of these alleles, namely amplification of a 8 kb fragment from both CYP2D6*13 and CYP2D6*16, together with a CYP2D6*16-specific method which gave a 1.4 kb PCR product. The 8 kb assay for the CYP2D6*13 and CYP2D6*16 alleles also produced a 9.5 kb fragment in samples positive for the 13 kb CYP2D6*5 allele. Therefore, it is now possible to screen for the large CYP2D gene deletions by a single long PCR method.
authors.affiliation: Department of Pharmacological Sciences, University of Newcastle upon Tyne, Medical School, UK. A.K.Daly@newcastle.ac.uk
authors.forename: A K
authors.initials: AK
authors.lastname: Daly
authors.forename: K S
authors.initials: KS
authors.lastname: Fairbrother
authors.forename: O A
authors.initials: OA
authors.lastname: Andreassen
authors.forename: S J
authors.initials: SJ
authors.lastname: London
authors.forename: J R
authors.initials: JR
authors.lastname: Idle
authors.forename: V M
authors.initials: VM
authors.lastname: Steen
mesh_terms: D000483:Alleles; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D005787:Gene Frequency; D006801:Humans; D008660:Metabolism / Q000235:genetics*; D010641:Phenotype; D016133:Polymerase Chain Reaction; D015183:Restriction Mapping
chemical_list: C102835:cytochrome P-450 CYP2D7P; D003577:Cytochrome P-450 Enzyme System; D019389:Cytochrome P-450 CYP2D6