Autoimmune diseases (ADs) are chronic and heterogeneous conditions that affect specific target organs or multiple organ systems. They are caused by the interactions over time between hereditary and environmental factors leading to a breakdown in immune tolerance and the ensuing tissue damage. The fact that these disorders share several clinical signs and symptoms (i.e., subphenotypes such as arthritis, alopecia, fatigue, photosensitivity, Raynaud's phenomenon as well as non-specific autoantibodies, e.g., antinuclear antibodies, rheumatoid factor, anti-Ro antibodies), physiopathological mechanisms (e.g., type I interferon activation, reduced B and T cell regulatory function), and genetic factors at both the MHC and non-MHC loci, has been called the autoimmune tautology and indicates that they have several common mechanisms . One of the strongest arguments supporting the autoimmune tautology is polyautoimmunity, defined as the presence of more than one AD in a single patient [2,3]. When three or more ADs coexist, this extreme phenotype is called multiple autoimmune syndrome (MAS) . Polyautoimmunity has been described in most of the ADs including systemic lupus erythematosus (41%), type 1 diabetes mellitus (35%), Sjögren's syndrome (33%), primary biliary cirrhosis (32%), antiphospholipid syndrome (28%), vitiligo (27%), systemic sclerosis (26%), autoimmune thyroid diseases (15%), multiple sclerosis (15%), rheumatoid arthritis (15%), myasthenia gravis (13%), and alopecia areata (10%). The main factors associated with polyautoimmunity are familial autoimmunity (i.e., the presence of diverse ADs in a nuclear family) and Amerindian ancestry. Based on polyautoimmunity and depending on severity, ADs may be categorized as major and minor diseases. In this sense, how polyautoimmunity affects major ADs has not fully evaluated. The main difference between polyautoimmunity and the overlapping syndromes lies in the fact that the former is the presence of two well-defined ADs while the later is the partial presence of autoimmune signs and symptoms. Nevertheless, most of the overlapping syndromes evolve over time towards the full spectrum of an AD. When this does not happen, protective factors are considered to be responsible for preventing the progression of the overlapping conditions towards a complete phenotype. The identification of the common mechanisms of ADs through the study of polyautoimmunity will enhance our understanding of these complex, frequent, and sometimes devastating diseases and will allow us to predict them at the population level in order to establish preventive measures for at-risk individuals for whom healthcare should be personalized and participatory.
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Disclosure of Interest None declared