Study of familial aggregation of autoimmune rheumatic diseases in Asian Indian patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) and other autoimmune rheumatic diseases (AIRD) tend to co-aggregate in families, making positive familial history a risk factor. We aimed to estimate familial aggregation of AIRD in SLE patients and to compare between ones having a positive and negative family history of autoimmunity in our cohort. We included families of 157 consecutive SLE patients in a hospital-based, cross-sectional design for a three-generation pedigree study. Clinical and laboratory parameters of these patients were recorded. AIRD was seen in families of 39 SLE patients amounting to a familial prevalence of 24.8% [95% confidence interval (CI) 18.1, 31.6] with a relative risk (λ) of 4.3 for first-degree relatives (FDRs) and 1.1 for second-degree relatives (SDRs). SLE was the commonest AIRD seen in families of 19 patients with a familial prevalence of 12.1% (95% CI 7.0, 17.2) and λ of 78.2 for FDRs and 18.1 for SDRs. AIRD as a whole and SLE alone were seen more commonly with parental consanguinity (p < 0.05). Familial aggregation in SLE patients also showed a relatively higher percentage of affected males and lesser presentation with constitutional features (p < 0.05) than sporadic SLE patients. Rheumatoid arthritis (RA) was the second most common AIRD seen in 16/39 (41%) families with a RR of 3.1 in FDRs of SLE patients. In conclusion, Asian Indian SLE patients seem to have a high familial aggregation of AIRD, which is more pronounced in the background of parental consanguinity. SLE is the commonest AIRD seen amongst FDRs and SDRs of SLE patients, followed by RA, with FDRs being at highest risk.