Patients with multiple sclerosis and risk of type 1 diabetes mellitus in Sardinia, Italy: a cohort study.

BACKGROUND: Individuals from Sardinia, Italy, are at high risk of developing multiple sclerosis and type 1 diabetes mellitus. We attempted to assess the prevalence in this region of type 1 diabetes mellitus in individuals with multiple sclerosis, and to ascertain disease risk factors.
METHODS: We did a cohort study to assess prevalence of type 1 diabetes in 1090 people with multiple sclerosis, and in their parents (n=2180) and siblings (n=3300), all born and living in Sardinia. All participants were patients at the multiple sclerosis clinic in Cagliari, and were judged representative of the total Sardinian outpatients and inpatients. We asked patients whether their parents or siblings had multiple sclerosis or diabetes, confirming replies by examining clinical records. We identified risk factors for diabetes with univariate and multivariate logistic regression analyses.
FINDINGS: Diabetes prevalence in people with multiple sclerosis was, respectively, about three-fold and five-fold that in their healthy siblings (p=0.001) and in the general population (p<0.0001). Presence of other relatives with multiple sclerosis conferred increased risk of type 1 diabetes to healthy siblings of individuals with multiple sclerosis (odds ratio=3.41, p=0.0019). Diabetes risk was six-fold higher in patients with relatives having multiple sclerosis than in healthy siblings of multiple sclerosis patients without other relatives with the disease (p=0.0001).
INTERPRETATION: In Sardinian families with genetic inheritance of multiple sclerosis type 1 diabetes is prevalent, both in multiple sclerosis patients and in healthy siblings. This finding indicates that common genes contribute to susceptibility to both diseases in this population.