Correspondence on 'Systemic evaluation of the relationship between psoriasis, psoriatic arthritis and osteoporosis: observational and Mendelian randomisation study'.

We read with great interest the published paper by Xia et al 1 which provided an in-depth analysis regarding the relationship between psoriasis, psoriatic arthritis (PsA) and osteoporosis. By comprehensively analysing the datasets from three Genome-Wide Association Studies and UK Biobank, the authors concluded that the association between PsA and estimated bone mineral density (eBMD)/osteoporosis/fracture was not genetically determined but secondary (eg, treatment with methotrexate or ciclosporin). Although the conclusion was drawn based on very stringent confounders controlling, there are a few points in this study that are worth mentioning. First, typically, many background characteristics should be controlled in an observational study, especially with large datasets. In association analysis part, only seven confounders (ie, age, height, weight, smoking, drinking, regular physical …