Variations in single nucleotides — the building blocks of DNA — in two genes may help predict the safety and efficacy of methotrexate (MTX) treatment in individual children with juvenile idiopathic arthritis (JIA), a preliminary study found.

The study, “The impact of single nucleotide polymorphisms in ADORA2A and ADORA3 genes on the early response to methotrexate and presence of therapy side effects in children with juvenile idiopathic arthritis: Results of a preliminary study,” was published in the International Journal of Rheumatic Diseases.

MTX is an immunosuppressant used in the first-line treatment of JIA. The exact mechanism of the therapy’s anti-inflammatory properties is unknown, but it is thought to involve the stimulation of immune cells to release the anti-inflammatory agent adenosine. Upon its release, adenosine binds to and activates two receptors, called ADORA2A and ADORA3, reducing inflammatory factor levels.

Still, 30% of JIA patients treated with MTX fail to achieve clinical remission. In rheumatoid arthritis, small mutations known as single nucleotide polymorphisms, or SNPs, in the ADORA genes have been shown to affect MTX treatment efficacy and safety. SNPs occur when one of four possible nucleotides — adenine (A), thymine (T), guanine (G), and cytosine (C) — in a DNA sequence is switched with another.

Now, researchers in Poland sought to identify SNPs in the ADORA2A and ADORA3 genes that impact JIA disease activity as well as MTX treatment outcomes. 

Conducted over three years, the study involved 100 patients — 77 girls and 23 boys — from a pediatric rheumatology center in Poland. All participants were or had been on MTX treatment. Their median age at diagnosis was 8 years, and most of the children (64%) had oligoarticular JIA. Typically the disease’s mildest form, oligoarticular JIA is usually marked by joint pain and swelling.

For the study, MTX was administered orally or by subcutaneous (under-the-skin) injection once per week at 10-15 mg per square meter of body surface area, with a folic acid supplement to prevent the folate deficiency often associated with MTX treatment.

The researchers evaluated levels of two inflammation markers, C-reactive protein and erythrocyte sedimentation rate, the number of joints with active arthritis, physician- and patient or parent-assessment of disease activity, and functional ability using the Childhood Health Assessment Questionnaire (CHAQ).

MTX-related adverse events (AEs) also were analyzed. These included gastrointestinal events, liver damage, skin irritation, damage to the nervous system, and infections. 

Through genetic analysis, the scientists identified two SNPs in the ADORA2A gene — named rs2236624 and rs2298383 — and one in ADORA3, called rs3393). Three variants (CC, CT, TT) of each gene were analyzed. 

Treatment with MTX caused AEs in 29 children, with gastrointestinal events and liver damage being the most common. The treatment was ineffective in 26% of study participants, requiring the patients to switch to biologic therapies after the study ended. 

Compared with children with other gene variants, patients with the TT variant of ADORA3 rs3393 (43%) had elevated levels of inflammation markers before and after MTX treatment. These children also had a higher number of arthritic joints and diminished functional ability six months into treatment. Those with the TT or CT variants of ADORA2A rs2236624 (39%) were 3.5 times more likely to develop MTX-related gastrointestinal effects, consistent with the results of the previous study in rheumatoid arthritis.

These findings suggest that the ADORA3 rs3393 and ADORA2A rs2236624  gene variants could be early predictors of MTX outcome and potential targets for clinical treatment. 

“As the anti-inflammatory effect of adenosine is perceived as the leading mechanism of low-dose MTX action, genotyping ADORA2A (rs2236624, rs2298383) and ADORA3 (rs3393) may prompt the clinician to identify patients with higher disease activity and at risk of developing MTX treatment AEs, therefore individualizing the treatment strategy at the baseline of the disease,” the researchers wrote.

Among the study limitations, said the investigators, were its small sample size and overrepresentation of patients with oligoarticular JIA. Further research in larger, more representative JIA populations is required to validate these findings, they concluded.