Characterization of a complexCYP2D6genotype that caused an AmpliChip CYP450 Test® no-call in the clinical setting

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Background:CYP2D6, a major drug-metabolizing enzyme, is encoded by a highly polymorphic and complex gene locus. We have identified a patient who failed to produce a CYP2D6 genotype with the AmpliChip P450 Test® (AmpliChip), whereas his CYP2C19 genotype was readily determined. The aim of this investigation was to fully characterize the patient's CYP2D6 gene locus to resolve the AmpliChip no-call.Methods:The case, a brother, and son were genotyped with the AmpliChip and subsequently characterized using long-range (XL)-PCR coupled with TaqMan assay technology. Copy number variation was assessed by XL-PCR and quantitative PCR. Selected XL-PCR products were sequenced.Results:The AmpliChip also produced a no-call for the son; the brother produced a result. The two alleles of the case were subsequently found to carry additional gene units that likely caused the AmpliChip no-calls. One was characterized as a CYP2D6*68+*4 tandem (CYP2D6*68 is a hybrid gene composed of 2D6 and 2D7), the other as a rare CYP2D6*13+*2 tandem (CYP2D6*13 is a 2D7/2D6 hybrid formerly known as CYP2D6*77). A novel CYP2D6*2 subvariant was identified in the son; the brother also carried the CYP2D6*68+*4 tandem.Conclusions:The implementation of pharmacogenetics-guided drug therapy relies on accurate clinical-grade genotype analysis. Although the AmpliChip is deemed to be a reliable platform, numerous more recently discovered allelic variants and gene arrangements are not detected or trigger no-calls. Although such cases may be rare, the clinical/genetic testing community must be aware of the challenges of CYP2D6 testing on the AmpliChip platform and implications regarding accuracy of test results.

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