How does age at onset influence autoimmune rheumatic diseases?

Background/Purpose: Age at onset of disease (AOD) refers to the time period at which a patient experiences the first sign (s) and symptom(s). AOD varies among autoimmune diseases (ADs) and has been related to prognosis in some of them. Genetic, epigenetic, and environmental factors may influence the AOD. The objective was to evaluate the influence of AOD on the clinical course and outcome in adult patients (> 17 years) with autoimmune rheumatic diseases, namely rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and Sjögren’s syndrome (SS).

Methods: This was a cross sectional analytical study in which 1,082 consecutive adult patients fulfilling international criteria for RA (n=517), SLE (n=271), and SS (n=294) were included. Information on patients socio-demographic and cumulative clinical and laboratory data were obtained by interview, standardized report form, physical examination and chart review. Early AOD was categorized according to the lower quartileof AOD in every AD (i.e., 17-34 years in RA, 17-23 years in SLE, and 17-35 years in SS). Data were analysed by Fisher´s exact test, Chi square and Kruskal–Wallis test.

Results: There were significant differences between important demographic and clinical variables according to AOD (Table). Early AOD was associated with a more severe clinical course in RA and SLE. No relevant differences between early-SS and late-SS were observed. Late-AOD was associated with environmental exposure in RA and SLE.

Conclusion: Our findings support the hypothesis of an influence of AOD on illness course in patients with ADs. Early-onset traits are more sensitive to genetic influence while late-onset to environmental variation. These results may serve to design better strategies aimed to discover the etiological factors of ADs.