Juvenile-Idiopathic-Arthritis

Growth is the question paediatric rheumatologists ask of any JAK inhibitor, because growth hormone signals through JAK2. In 225 children with JIA followed for a median of 3.6 years on tofacitinib, height stayed close to age-appropriate norms, younger children grew faster than the WHO reference, and IGF-1, IGFBP3 and osteocalcin did not fall. It is a post hoc analysis with no untreated comparator, so it reassures rather than proves.

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.