CYP2D6 100C>T (P34S) is part of some but not all CYP2D6*4 suballeles. Therefore, it is not present in the CYP2D6*4 core allele. However, 100 C>T is part of core allele definitions of a number of CYP2D6 star alleles such as CYP2D6*10.
To reflect the possible presence of 100C>T in the *4 allele, the variant is represented as a “R” using IUPAC nucleotide code. "R" reflects that either a “G” or “A” (positive strand) can be present at the 100C>T position in *4. This is shown on the PharmGKB CYP2D6*4 overview page, which lists 100C>T positions and others next to the *4 key splicing variant 1847G>A (rs3892097).
For CYP2C19*1, the genomic reference sequence at position GRCh38 NC_000010.11:g.94842866 (rs3758581) is "A", which is present in CYP2C19*1.001(*1A), however all other *1 suballeles have a "G" (I331V) at this position. All suballeles of a star (*) are assumed to have similar functional status. The I331V is prominent in CYP2C19 and part of many alleles. To reflect the possibility of either base at this position, the NC_000010.11:g.94842866 position is included as "R" for the CYP2C19*1 allele at PharmGKB.
For more information about cytochrome P450 star alleles and suballeles, see PharmVar .
PharmGKB has been updated to contain annotations on main star alleles such as *2, *3, etc. and not individual suballeles. If a publication specifically mentions a suballele, this association will be annotated on the main star allele and the suballele will be mentioned in the annotation notes.