Genotypic analysis of thiopurine S-methyltransferase in patients with Crohn's disease and severe myelosuppression during azathioprine therapy.
OBJECTIVE
Myelosuppression in patients with Crohn's disease (CD) treated with azathioprine has been attributed to low activity of thiopurine S-methyltransferase (TPMT). Allelic variants of the TPMT gene responsible for changes in the enzyme activity have been characterized. We investigated the distribution of mutant alleles associated with TPMT deficiency in patients with CD and myelosuppression during azathioprine/6-mercaptopurine therapy.


METHODS
Forty-one patients with CD were included. They developed leukopenia or thrombocytopenia during azathioprine or 6-mercaptopurine treatment. Polymerase chain reaction-based methods were used to search for mutations associated with TPMT deficiency.


RESULTS
Four patients (10%) had 2 mutant alleles associated with TPMT deficiency, 7 (17%) had 1 mutant allele, and 30 (73%) had no known TPMT mutation. The delay between administration of the drug and occurrence of bone marrow toxicity was less than 1.5 months in the 4 patients with 2 mutant alleles, and ranged from 1 to 18 months in patients with 1 mutant allele and from 0.5 to 87 months in patients with normal genotype.


CONCLUSIONS
Twenty-seven percent of patients with CD and myelosuppression during azathioprine therapy had mutant alleles of the TPMT gene associated with enzyme deficiency. Myelosuppression is more often caused by other factors. Continued monitoring of blood cell counts remains mandatory in patients treated with azathioprine.
Colombel
J F
JF
Service d'Hépato-Gastroentérologie, Hôpital Huriez, CHRU Lille, France. jfcolombel@chru-lille.fr
Ferrari
N
N
Debuysere
H
H
Marteau
P
P
Gendre
J P
JP
Bonaz
B
B
Soulé
J C
JC
Modigliani
R
R
Touze
Y
Y
Catala
P
P
Libersa
C
C
Broly
F
F
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D001379:Azathioprine / Q000008:administration & dosage*; D001853:Bone Marrow / Q000187:drug effects* / Q000276:immunology; D003424:Crohn Disease / Q000188:drug therapy* / Q000235:genetics* / Q000276:immunology; D004252:DNA Mutational Analysis; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000276:immunology; D005838:Genotype; D006720:Homozygote; D006801:Humans; D007166:Immunosuppressive Agents / Q000008:administration & dosage*; D007958:Leukocyte Count; D007970:Leukopenia / Q000139:chemically induced; D008297:Male; D008780:Methyltransferases / Q000235:genetics*; D008875:Middle Aged; D009154:Mutation; D010641:Phenotype; D016133:Polymerase Chain Reaction; D018807:Polymorphism, Single-Stranded Conformational; D013921:Thrombocytopenia / Q000139:chemically induced
D007166:Immunosuppressive Agents; D008780:Methyltransferases; C022745:thiopurine methyltransferase; D001379:Azathioprine