Autoimmune disease in families with multiple sclerosis: a population-based study.

BACKGROUND: Evidence of an association between multiple sclerosis (MS) and other autoimmune diseases would substantiate the hypothesis that MS is an autoimmune disease, and implicate a common mechanism. We aimed to investigate and compare the rate of autoimmune disease in MS patients, in their first-degree relatives, and in their unrelated spouses. METHODS: We used data from a national, multicentre, population-based sample to investigate the rate of autoimmune disease in 5031 MS patients, 30 259 of their first-degree relatives, and 2707 spousal controls. We asked patients and controls whether they had any of ten autoimmune diseases: Crohn's disease, ulcerative colitis, rheumatoid arthritis, type 1 diabetes, psoriasis, pernicious anaemia, systemic lupus erythematosus, autoimmune thyroid disease, vitiligo, and myasthenia gravis. MS probands were also asked whether their first-degree relatives had Crohn's disease, ulcerative colitis, rheumatoid arthritis, or type 1 diabetes. FINDINGS: After correction for age and sex, we did not identify any increased risk of autoimmune diseases in MS patients compared with their spousal controls (odds ratio [OR]=1.07, 95% CI 0.86-1.23, chi(2)=0.47, p=0.49), or in the first-degree relatives of MS probands compared with controls (OR=0.89, 0.63-1.17, chi(2)=1.11, p=0.29). However, the reported frequency of autoimmune diseases did differ according to the sex of the interviewee (female vs male patients chi(2)=92.2, p<0.0001; female vs male spousal controls chi(2)=87.1, p