ITPA Activity and Methotrexate Response in JIA
Up to 40% of children with JIA don’t respond to methotrexate, and we currently have no way to know in advance. This three-centre study of 195 patients found that erythrocyte ITPA enzyme activity measured before the first dose separates responders from non-responders, and outperforms genotyping the ITPA variant. But the cutoffs run at 60% sensitivity and 63% specificity — enough to shift a prior, not enough to decide on its own.