Purpose: Thiopurines are effective in attaining and maintaining remission in patients with inflammatory bowel
diseases (IBD). The major drawback of these drugs are their serious adverse effects (SAE), highlighting the importance of
preemptive identification of patients at risk. We aimed to examine whether gene polymorphisms in GSTM1, GSTT1 and
TPMT, combined with various clinical parameters, can predict thiopurine induced SAE.
Methods: A retrospective cohort of 176 Crohn's Disease (CD) patients treated with thiopurines (131 with 6MP and 45
with azathioprine) was genotyped for common polymorphisms in GSTM1, GSTT1 and TPMT. Clinical data including
SAE, age, ethnicity, gender and smoking status were extracted from patient charts. SAEs evaluated were
myelosuppression, hepatotoxicity and pancreatitis. Associations between demographic, clinical, and genetic variables and
thiopurine induced SAE were assessed.
Results: Twenty-four patients (14%) developed SAE, revealing a significant association between thiopurine induced SAE
and GSTM1-null genotype (P=0.05), older age (P=0.016) and active smoking status (P=0.043) and SAE. On multi-variant
analysis, past or current smokers were at increased risk for developing thiopurine related SAE (OR 2.915, CI 95%: 1.199-
7.084), specifically pancreatitis (p<0.001). No association was found between TPMT or GSTT1 polymorphisms and the
development of SAE.
Conclusions: Active smoking and GSTM1-null genotype appear to be risk factors for thiopurine induced SAEs (i.e.
myelosuppression, hepatotoxicity and pancreatitis) in patients with CD. Corroboration of these associations in larger
cohorts is warranted.