Does persistence to methotrexate treatment in early rheumatoid arthritis have a familial component?

Objectives To assess whether persistence to treatment with methotrexate (MTX) in early rheumatoid arthritis (RA) is shared among first-degree relatives with RA and to estimate any underlying heritability. Methods First-degree relative pairs diagnosed with RA 1999-2018 and starting MTX (in monotherapy) as their first disease-modifying anti-rheumatic drug (DMARD) treatment were identified by linking the Swedish Rheumatology Quality Register to national registers. Short- and long-term persistence to MTX was defined as remaining on treatment at 1 and 3 years, respectively, with no additional DMARDs added. We assessed familial aggregation through relative risks (RR) using log-binomial regression with robust standard errors and estimated heritability using tetrachoric correlations. We also explored the familial aggregation of EULAR treatment response after 3 and 6 months. To mimic the clinical setting, we also tested the association between having a family history of MTX persistence and persistence within the index patient. Results Familial persistence was not associated with persistence at 1 (RR=1.02, 95% CI 0.87-1.20), only at 3 (RR=1.41, 95% CI 1.14-1.74) years. Heritability at 1 and 3 years was estimated to be 0.08 (95% CI 0-0.43) and 0.58 (95% CI 0.27-0.89), respectively. No significant associations were found between family history and EULAR response at 3 and 6 months, neither overall nor in the clinical setting analysis. Conclusions Our findings imply a familial component, including a possible genetic element, within the long-term persistence to MTX following RA diagnosis. Whether this component is reflective of characteristics of the underlying RA disease or determinants for sustained response to MTX in itself will require further investigation.