Abstract Background/Aims Mixed connective tissue disease (MCTD) is a rare systemic autoimmune condition defined by overlapping features of systemic lupus erythematosus, systemic sclerosis, and myositis, alongside anti-U1 RNP antibody positivity. Although MCTD can present at any age, the influence of age at onset on disease characteristics remains unclear. This study compared clinical manifestations and antibody profiles among three MCTD cohorts: paediatric, adult-onset, and adults with paediatric-onset disease, to determine whether age of onset influences disease phenotype. Methods A retrospective study was conducted between Liverpool University NHS Foundation Trust and Alder Hey Children’s NHS Foundation Trust. Patients were identified using electronic case records using key search terms of MCTD over the preceding 5 years. This was cross referenced with all RNA positive antibody patients. Included patients met international MCTD classification criteria. Demographic, clinical, and serological data were collected from case records and collated for comparative descriptive analysis. Results In total 76 patients were identified: paediatric MCTD (n = 22), adults with paediatric-onset MCTD (n = 12), and adult-onset MCTD (n = 42). Differences in clinical manifestations were identified (Table 1). Myositis and digital ulcers in adults, were more common in those with paediatric-onset disease. Sicca symptoms were more prevalent in both adult cohorts compared to the paediatric cohort. All patients were ANA positive. In the paediatric cohort, a greater number were also anti-topoisomerase positive (9/22 (41%) vs 0 in adult cohorts, p-value 0.001). No other significant differences were detected across ENA or myositis-specific antibodies. Conclusion Some MCTD features appear to be influenced by age of onset although this could also be explained by disease duration and requires further evaluation. Sicca symptoms were more common in adults (also reported in Sjogren’s syndrome). However, our findings may be related to reporting bias, an issue in retrospective studies. Paediatric patients were more likely to display anti-topoisomerase and anti-RNP antibody dual positivity. Whether the disease evolves into a more systemic sclerosis phenotype is unclear. Longterm prospective studies including children and adults are needed to validate these findings. We demonstrate the universality of clinical manifestations whatever age of onset and highlight the importance for all rheumatologists to routinely assess for all disease manifestations. Disclosure S. Gall: None. B. Almoosawi: None. L. Gatti: None. C. Pain: None. A. Reeves: None. F. Dell’Accio: None. D. Kane: None. R. Benson: None.
Gall et al. (Wed,) studied this question.