Ultrarapid metabolizers of debrisoquine: Characterization and PCR‐based detection of alleles with duplication of the CYP2D6 gene

Abstract

Up to 7% of Caucasians may demonstrate ultrarapidassays for the CYP2D6*3, CYP2D6*4, CYP2D6*5, CYmetabolism of debrisoquine due to inheritance of alleles with P2D6*6 and CYP2D6*7 null alleles [4--11]. duplicated functional CYP2D6 genes. Here we describe the Up to 7% of Caucasians are ultrarapid metabolizers (UMs) genomic organization of the duplicated CYP2D6 genes in the 42 of debrisoquine due to inheritance of alleles with duplication kbXbalallele. We postulate that this duplication originates from of functional CYP2D6 genes [12][13][14]. The mechanism by a homologous, unequal cross-over event which involved two 29 kb which this duplication has occurred is not known. When subXbaI wild-type alleles, and had break points within a 2.8 kb jected to standard doses of CYP2D6 substrates, UMs may direct repeat (CYP-REP) flanking the CYP2D6 gene. Moresuffer from therapeutic failure because of the very rapid metaover, we have designed two different PCR assays for detection of bolic conversion of the drugs [15,16]. Phenotyping with probe alleles with duplicated CYP2D6 genes. Both assays correctly drugs may be used to identify both PM and UM subjects. identified 29 out of 29 subjects positive for the 42 kb XbaI allele.However, the procedure is time-consuming and expensive, No false negative or false positive reactions were observed, and phenotype determination can b~ confounded by concomi- by a deletion of the entire CYP2D6 gene, and contains only CYP2D6 enzyme activity can be measured in vivo after oral the pseudogenes CYP2D8 and CYP2D7 [6,20]. In addition, a intake of a single dose of the probe drugs debrisoquine or 42 kb XbaI allele with two copies of the CYP2D6 gene as well sparteine with subsequent determination of the ratio between as one copy of each of the pseudogenes CYP2D8 and the urinary recovery of the drug and the metabolite. In Cau-CYP2D7 has been described [12][13][14]. The duplicated casian populations, there is a large variation in the metabolic CYP2D6 genes are usually functional, and the 42 kb allele ratio (MR) of the probe drugs, leading to the classification of has therefore been associated with the UM phenotype. three different phenotypes: poor, extensive and ultrarapid meWe have recently demonstrated the presence of two large tabolizers, direct repeats (CYP-REP) flanking the CYP2D6 locus [11,20]. 5-10% of Caucasians are classified as poor metabolizersThe break points of the CYP2D6*5 gene deletion allele are (PMs) of debrisoquine due to inheritance of two mutant present within the 2.8 kb CYP-REP regions, indicating that CYP2D6 null alleles [2,3]. With some CYP2D6 drug subthe deletion has occurred by homologous, unequal recombistrates, PM subjects may develop toxic plasma concentrations nation [20]. We also proposed that alleles with duplication of and adverse reactions at the standard recommended dose due CYP2D6 could be explained as a reciprocal of the deletion to impaired metabolism. Most of the non-functional CYP2D6 event, involving the same CYP-REP units. alleles have been described and ch...

Molecular diversity at the CYP2D6 locus in the Mediterranean region

“…Three parallel long PCRs were run for each sample. We looked for CYP2D6 gene duplication using the primer pair pCYP-207-F and pCYP-32-R. 22 A control band was obtained adding the pCYP-13-F forward primer 6 to the reaction mix. To detect the presence of the entire gene deletion, having at the same time an internal control band, we used again a set of three different primers: pCYP-13-F/pCYP-207-F/ pCYP-24-R 6,22 ( Figure 2).…”

Sigara Bagimliliginin Genetigi

“…Bu enzimin homozigot çekinik alleline sahip kişiler (CYP2D6*3*4 ve*5) yavaş metabolizör, hetorozigot alleline sahip kişiler (CYP2D6*1,*2) hızlı metabolizör, homozigot dominant alleline sahip kişiler ultra hızlı metabolizör olarak tanımlanır. [10] Nikotini yavaş metabolize eden kişilerde sigara bağımlılığına yatkınlığının artmış olduğunu belirten çalış-malar da bulunmaktadır. [11] Son dönemde yapılan çalışmalar CYP2D6 genotiplerinin sigara bağımlılığından daha çok sigara içme davranışları ile ilişkisi olduğu ve ağır sigara içicisi kişiler arasında ultrahızlı metabolizör kişilerin oranının hiç içmeyen grubun dört katı, hafif içici olan grubun iki katı olduğu bildirilmiştir.…”

Er farmakogenetisk CYP2D6-testing nyttig?

“…In a northern European population, screening for these four alleles is expected to reveal at least 95 % PMs for CYP2D6-mediated metabolism (9,19). UM-associated duplications of the CYP2D6 gene were investigated by means of longrange PCR (20). When two non-functional alleles were detected, the genotype was denoted a PM.…”