Disease-specific clustering is seen among first-degree relatives in autoimmune rheumatic diseases: A cross-sectional, multi-centre study

• The study confirms a pronounced familial clustering of autoimmune diseases, particularly disease specific in RA, SLE and SSc. • First-degree relatives show the highest frequency of autoimmune conditions, while second-degree clustering in SLE and SSc indicates broader generational and environmental contributions. • Familial aggregation of diabetes and hypertension among relatives of RA and SSc patients suggests overlapping genetic and environmental determinants linking immune and metabolic dysregulation. • The study findings highlight the value of obtaining detailed family histories in autoimmune diseases to identify at-risk relatives early and guide preventive, multidisciplinary management strategies. This study aimed to assess the prevalence and pattern of familial autoimmunity and comorbidities among patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and systemic sclerosis (SSc). This multicentre, cross-sectional study utilized data from the Indian Rheumatology Association database and included patients diagnosed with RA, SLE, or SSc according to ACR/EULAR criteria. Family histories of autoimmune diseases and comorbidities (diabetes, hypertension, and cardiovascular disease) were recorded up to third-degree relatives. Data were analyzed using descriptive statistics, Pearson’s chi-square, and Fisher-Freeman-Halton exact tests. Among 4,384 RA, 819 SLE, and 180 SSc patients, valid family history data were available for 3,638, 489, and 135 cases, respectively. A positive family history of autoimmune disease was observed in 19.6% of RA, 11.4% of SLE, and 10% of SSc patients (P < 0.001). Familial RA was most common among RA patients (13.3%), whereas SLE-like disease was more frequent among relatives of SLE patients (2.6%). First-degree relatives were predominantly affected (RA 91%, SLE 89.3%, SSc 83.3%). Diabetes (16.7–22.2%) and hypertension (9.5–13.9%) were the most prevalent familial comorbidities, with diabetes showing higher aggregation in SSc families (P = 0.002). Familial autoimmunity is common across major AIRDs, showing strong first-degree aggregation and disease-specific clustering. Distinct familial patterns are observed for autoimmune and metabolic comorbidities. RA demonstrates the strongest immediate familial clustering, whereas SLE displays a broader generational spread.