Inclusion criteria

The main purpose of the Human Cytochrome P450 (CYP) Allele Nomenclature website is the management of an official and unified allele designation system, as well as the provision of a database of CYP alleles and their associated effects.

The nomenclature system adheres to the guidelines provided in Shows et al (1987), Daly et al (1996), Antonarakis and the Nomenclature Working Group (1998) and den Dunnen and Antonarakis (2001).



  1. On this website only human CYP and POR alleles are considered.
  1. The gene and the allele name is separated by an asterisk followed by Arabic numerals designating the specific allele (e.g. CYP1A1*3). 

  1. For allele designation, sequence information of at least all exons and exon-intron borders must be submitted.

  1. To be assigned a unique allele name, the sequence should contain at least one nucleotide change that has been shown to affect transcription, splicing, translation, posttranscriptional or posttranslational modifications or result in at least one amino acid change. So-called sub-alleles containing additional non-functional variations in addition to the functional ones described (e.g. CYP2D6*10B) will no longer be designated.

5.      If a new sequence variation causing functional consequences is shown to exist in different combinations with other sequence variations not causing functional effects, the sequence with the lowest number of additional variations will be chosen for allele designation.

  1. If a sequence variation causing detrimental effects (e.g. the 1846G>A variation in CYP2D6*4 causing a splicing defect) is shown to exist together with other variations causing functional effects, the variation causing the detrimental effect will determine the name of the allele (e.g. CYP2D6*4B).

  2. If sequence variations causing functional effects of similar magnitude (e.g. amino acid substitutions) are found to exist together as well as on their own, the combination allele will be given a new allele name (see e.g. CYP2D6*102 and *103).

  3. For extra gene copies (n) placed in tandem on the same chromosome the entire allelic arrangement should be referred to as e.g. CYP2D6*2Xn. 

  4. Nucleotides are numbered according to the base A in the initiation codon ATG as +1 and the base before A as -1. 

  5. The names for the corresponding proteins have a period between the name of the gene product and the allele number (e.g. CYP2D6.2). If the allele is unable to produce full length protein, no protein name will be assigned.

  1. SNPs that are not easily assigned to a specific allele are listed at the bottom of the corresponding gene webpage in a separate SNP table.

  2. Novel sequence variations causing functional consequences that have an unclear linkage with other variations causing functional effects will not be assigned.

  1. All submissions are kept confidential and new allele names are on request kept confidential until publication. Authors are encouraged to submit their novel allele to the CYP-allele website prior to submission to a journal, especially since many Editors request naming of new alleles by the CYP-allele website prior to publication. Journal publication is however not a requirement for publication on the CYP-allele website. 

14.  Usage of star (*) allele designations resembling those officially designated by the CYP-allele Nomenclature committee is highly discouraged due to the apparent risk of confusion.

15.  Further information on in vitro or in vivo activity analyses for known CYP alleles can at any time be submitted to the CYP-allele website for inclusion with the respective allele.

  1. All variants identified through Next Generation Sequencing (NGS) techniques must be confirmed through Sanger sequencing or another independent method. Furthermore, NGS sequence data must at a minimum have 100% coverage over exons and exon-flanking regions to be considered for allele name assignments.



Home Page Inclusion criteria

 This page was updated 10-Aug-2014 by Sarah C Sim
Questions and comments are always welcome