ITPA and hepatitis C virus infection: Studies have shown that single nucleotide polymorphisms (SNPs) in several genes involved in IFN‐related signal pathways, such as IFN‐lambda (IFN‐λ,‐including IFNL1, IFNL2, IFNL3, and IFNL4) and IFN‐gamma (IFN‐γ), could be predictive for treatment response in patients with hepatitis C.3, 4Interestingly, the polymorphic hereditary traits foretell not only the efficacy of IFN therapy but also the toxicity of the treatment, as SNPs in the inosine triphosphate pyrophosphatase (ITPA) gene induce more cytopenia in IFN‐treated hepatitis C patients.5, 6