• lupus erythematosus, systemic
• autoimmune diseases
• epidemiology

Thanks to their large sample size, thus reducing the risk of selection and participation bias, population-based studies can provide high-quality data on the prevalence and incidence, natural history and treatment, correlates and associations of a disease, and healthcare utilisation.1 Several nationwide research databases exist in the world, one of the oldest in Sweden dating back to 1955. The Taiwan National Health Insurance Research Database (NHIRD) is one of the largest nationwide population databases, covering approximately 23 million residents in Taiwan and data of more than 99% of the population. Using this unique database, investigators have asked important questions regarding the heredity and coaggregation of autoimmune diseases, such as systemic lupus erythematosus (SLE), Sjögren’s syndrome and myasthenia gravis.2–4

Immune thrombocytopenic purpura (ITP), formerly known as idiopathic thrombocytopenic purpura, is an immune-mediated acquired disease of adults and children characterised by a transient or persistent decrease of platelet counts and, depending on the degree of thrombocytopenia, increased risk of bleeding.5 In ΙΤP, an abnormal T cell response, supported by splenic T follicular helper cells, stimulates the proliferation and differentiation of autoreactive B cells producing antiplatelet autoantibodies that facilitate platelet phagocytosis by macrophages, predominantly in the spleen. Macrophages also contribute to the perpetuation of the autoimmune response in ITP, functioning as the principal antigen-presenting cells. Inappropriate bone marrow production due to an immune response against megakaryocytes may also exacerbate thrombocytopenia, while the level of …