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Common Genes Increase Risk Of Type-1 Diabetes, Multiple Sclerosis Among Sardinians

Common genes shared by lifelong residents of Sardinia appear to contribute to a high susceptibility of both multiple sclerosis and type-1 diabetes mellitus.

The findings among the island population lead Dr Maria Marrosu and colleagues from the Department of Neuroscience, Multiple Sclerosis Center, Cagliari, Italy, to speculate that "Sardinians seem to be a suitable population in which to study what genes might trigger and sustain autoimmunity."

The researchers point out that Sardinians are an insular Italian population genetically characterized by a low degree of large scale genetic heterogeneity, and by a distribution of alleles at multiple loci different from other Europeans.

Dr Marrosu postulated that these diseases may be due to the particular genetic structure of the population. Their aim was to ascertain whether or not the high prevalence of these diseases in Sardinians is a coincidence, and if development of one of the diseases results in increased risk of the other.

In the cohort study, the clinicians assessed the prevalence of type 1 diabetes in 1,090 people with multiple sclerosis, and in 2,180 of their parents their parents and 3,300 of their siblings. All of them were born and living in Sardinia.

They found that the prevalence of diabetes in people with multiple sclerosis was about three-fold greater than their healthy sibling and about five-fold greater than in the general population. Presence of other relatives with multiple sclerosis conferred increased risk of type 1 diabetes to healthy siblings of individuals with multiple sclerosis.

The risk of diabetes 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.

"Our findings suggest that loci or genes that predispose to familial multiple sclerosis also contain an enrichment of genes that predispose to diabetes," Dr Marrosu and colleagues said.

Their data seems to indicate that common genes, either in the HLA region or outside it, affect susceptibility to both multiple sclerosis and type 1 diabetes, and that the genetic makeup of individuals from Sardinia might contain a particular combination of genes that predispose to these diseases and an absence of genes that protect against them.
Lancet 2002; 359: 1461-65. "Patients with multiple sclerosis and risk of type 1 diabetes mellitus in Sardinia, Italy: a cohort study"

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