Table 6.

CPIC (2018). Assignment of likely CYP2D6 Phenotype based on Genotype

PhenotypeaGenotypeExamples of CYP2D6 diplotypesb
Metabolizer statusActivity score
CYP2D6 ultrarapid metabolizer>2.0An individual with duplications of functional alleles*1/*1xN, *1/*2xN, *2/*2xNc
CYP2D6 normal metabolizer1.5–2.0An individual with 2 normal function alleles or one normal function and one decreased function allele*1/*1, *1/*2, *1/*9, *1/*41, *2/*2
CYP2D6 normal metabolizer or intermediate metabolizer (controversy remains)b1.0An individual with 2 decreased function alleles or one normal function and one no function allele.
An activity score (AS) of 1.0 is associated with decreased tamoxifen metabolism to endoxifen compared with an AS of 1.5 or 2.		*1/*4, *1/*5, *41/*41
CYP2D6 intermediate metabolizer0.5An individual with one decreased function and one no function allele*4/*10, *4/*41, *5/*9
CYP2D6 poor metabolizer0An individual with only no functional alleles*3/*4, *4/*4, *5/*5, *5/*6
a

See the CYP2D6 frequency table 1 in (4) for race-specific allele and phenotype frequencies.
bFor a complete list of CYP2D6 diplotypes and resulting phenotypes, see the CYP2D6 genotype to phenotype table in (4). Note that genotypes with an activity score of 1 are classified as normal metabolizers in the online CPIC CYP2D6 genotype to phenotype table (4).
cWhere xN represents the number of CYP2D6 gene copies. For individuals with CYP2D6 duplications or multiplications, see supplemental data for additional information on how to translate diplotypes into phenotypes.
dIndividuals with an activity score of 1.0 may be classified as intermediate metabolizers by some reference laboratories. A group of CYP2D6 experts are currently working to standardize the CYP2D6 genotype to phenotype translation system. CPIC will update the CPIC website accordingly (CYP2D6 genotype to phenotype table).

This Clinical Pharmacogenetics Implementation Consortium (CPIC) table is adapted from (4).

From: Tamoxifen Therapy and CYP2D6 Genotype

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