Familial autoimmunity in systemic sclerosis -- results of a French-based case-control family study

To assess the prevalence of autoimmune diseases in first-degree relatives of patients with systemic sclerosis (SSc), and to compare those results with control families in order to identify patterns of autoimmune diseases in relatives.

A retrospective case-control postal questionnaire survey was performed in France to recruit patients with SSc belonging to an association of patients with SSc and unrelated age-matched and sex-matched controls. Each participant was asked to self-report on the existence of autoimmune diseases in their first-degree relatives. The prevalence of autoimmune diseases in the families of patients with SSc was compared with the corresponding prevalence in the families of controls.

A total of 121 families out of 373 (32.4%) with a member having SSc reported at least 1 autoimmune disease in 1 or more first-degree relatives. The most frequent autoimmune diseases in SSc families when adjusted for family size were autoimmune thyroid disease (AITD; 4.9%), rheumatoid arthritis (4.1%), psoriasis (3.9%), and type 1 diabetes mellitus (2.9%). Compared with control families, AITD and connective tissue diseases (SSc, systemic lupus erythematosus, or Sjögren's syndrome) were more likely to occur in families with SSc (p = 0.01 and p = 0.01, respectively), with OR of 3.20 (95% CI 1.25-8.18) and 5.20 (95% CI 1.22-21.8). In contrast, inflammatory bowel disease was less likely to occur within families with SSc (p = 0.02, OR 0.29, 95% CI 0.11-0.80). In addition, the coexistence of more than 1 autoimmune disease in the index SSc case was associated with familial aggregation of autoimmune diseases.

Our results show that autoimmune diseases cluster within families of patients with SSc. This supports the notion that these diseases might arise on a shared genetic basis underlying several autoimmune phenotypes.