Sequential evaluation of thiopurine methyltransferase, inosine triphosphate pyrophosphatase, and HPRT1 genes polymorphisms to explain thiopurines' toxicity and efficacy.
OBJECTIVE
To evaluate the polymorphisms of several genes involved in the azathioprine and mercaptopurine metabolism, in an attempt to explain their toxicity and efficacy in Crohn's disease and ulcerative colitis.


METHODS
In 422 consecutive patients (250 with Crohn's disease and 172 with ulcerative colitis) and 245 healthy controls, single nucleotide polymorphisms of thiopurine methyltransferase, inosine triphosphate pyrophosphatase and hypoxanthine phosphoribosyl transferase (HPRT1) genes were related to the occurrence of adverse drug reactions (ADRs) and efficacy of therapy.


RESULTS
Seventy-three patients reported 81 episodes of ADRs; 45 patients did not respond to therapy. Frequency of thiopurine methyltransferase risk haplotypes was significantly increased in patients with leucopenia (26% vs. 5.7% in patients without ADRs, and 4% of controls) (P < 0.001); no correlation with other ADRs and efficacy of therapy was found. Conversely, the frequency of inosine triphosphate pyrophosphatase and HPRT1 risk genotypes was not significantly different in patients with ADRs (included leucopenia). Non-responders had an increased frequency of inosine triphosphate pyrophosphatase risk genotypes (P = 0.03).


CONCLUSIONS
The majority of azathioprine/mercaptopurine-induced ADRs and efficacy of therapy are not explained by the investigated gene polymorphisms. The combined evaluation of all three genes enhanced the correlation with leucopenia (43.5% vs. 23% in controls) (P = 0.008), at the expense of a reduced accuracy (60%).
Palmieri
O
O
U.O. Gastroenterologia ed Endoscopia Digestiva, Ospedale IRCCS Casa Sollievo della Sofferenza San Giovanni Rotondo (Fg), Italy.
Latiano
A
A
Bossa
F
F
Vecchi
M
M
D'Incà
R
R
Guagnozzi
D
D
Tonelli
F
F
Cucchiara
S
S
Valvano
M R
MR
Latiano
T
T
Andriulli
A
A
Annese
V
V
D000328:Adult; D005260:Female; D005765:Gastrointestinal Agents / Q000008:administration & dosage* / Q000009:adverse effects / Q000493:pharmacokinetics; D005838:Genotype; D006801:Humans; D015212:Inflammatory Bowel Diseases / Q000188:drug therapy*; D007970:Leukopenia / Q000139:chemically induced; D008297:Male; D008780:Methyltransferases / Q000009:adverse effects* / Q000378:metabolism; D008875:Middle Aged; D011110:Polymorphism, Genetic; D011755:Pyrophosphatases / Q000009:adverse effects*; D016896:Treatment Outcome; D000097630:Inosine Triphosphatase
D005765:Gastrointestinal Agents; D008780:Methyltransferases; D011755:Pyrophosphatases; D000097630:Inosine Triphosphatase