Exome-wide pharmacogenomic analysis of response to thiopurines in inflammatory bowel disease patients

Background: The response to thiopurine treatment in inflammatory bowel disease patients differs greatly among individuals and nearly 50% of patients experience no benefit. Several factors have been implicated in determining this response, including individual genetic variation. Methods: Aiming to identify genes involved in the response to thiopurine drugs, a two-stage investigation of 20,000 coding single-nucleotide polymorphisms (cSNPs) in 10,000 genes was performed in a Spanish cohort of 257 individuals, 193 showing steroid free remission versus 64 non responder individuals 12 months after initial dose of the drug. The 20 top cSNPs with lower p-values for the association test identified at the first stage (133 responders / 34 non responders), were replicated in a second cohort (60 responders / 30 non responders). Results: Whereas not statistically significant in all of the two analyzed cohorts, the consistent across samples direction of the observed associations and the allelic joined analysis suggest a significant risk for lack of response related to two genes, PION and ZNF673. With a CMH p-value= 4.26x-06, the associated PION cSNP (rs17151692) minor A allele increases risk for treatment failure 4.5 times when all data is combined. Conclusion: These findings might help to understand the biological mechanisms behind thiopurine treatment failure and to tailor treatment for individual inflammatory bowel disease patients.