Normal function allele: *1, *1S
Unknown function allele: *3D, *24
Probable reduced function allele: *8
No function alleles: *2, *3A, *3B, *3C, *4
Normal Metabolizer: Presence of two copies of a normal activity allele in the TPMT gene.
Diplotypes: *1/*1, *1/*1S, *1S/*1S
Intermediate Metabolizer: Presence of one copy of a normal function allele and one copy of a no function allele in the TPMT gene. This is consistent with intermediate activity of TPMT. Such patients are at risk for myelosuppression with normal doses of drugs in the thiopurine class.
Diplotypes: *1/*2, *1/*3A or *3B/*3C, *1/*3B, *1/*3C, *1/*4, *1S/*2, *1S/*3A, *1S/*3B, *1S/*3C, *1S/*4
Poor Metabolizer: Presence of two copies of a no function allele in the TPMT gene. This can be observed as either compound heterozygous or homozygous variant alleles. This is consistent with low or deficient activity of TPMT. These patients are at high risk for life-threatening myelosuppression with normal doses of drugs in the thiopurine class.
Diplotypes: *2/*2, *2/*3A, *2/*3B, *2/*3C, *2/*4,
*3A/*3A, *3A/*3B, *3A/*3C, *3A/*4, *3B/*3B, *3B/*4, *3C/*3C, *3C/*4, *4/*4
Indeterminate activity – CPIC: Presence of either one or two copies of an unknown allele in the TPMT gene, including the probable function alleles. At the time of this publication, it is not possible to predict the actual activity of TPMT, and hence the expected phenotype for this patient cannot be determined by genotyping alone.
Diplotypes: *1/*3D, *1/*24, *1S/*3D, *1S/*24, *2/*3D, *2/*24,
*3A/*3D, *3A/*24, *3B/*3D, *3B/*24, *3C/*3D, *3C/*24, *3D/*3D, *3D/*4, 3D/*24,
*4/*24, *1/*8, *1S/*8, *2/*8, *3A/*8, *3B/*8, *3C/*8, *3D/*8, *4/*8, *8/*8, *8/*24,
TPMT Phenotype Frequencies in Multiple Race/Ethnic Groups1