Does Down's syndrome protect against multiple sclerosis?

Abstract

BACKGROUND: A higher incidence of certain autoimmune disorders has been reported in Down's syndrome (DS) but only 1 case of DS associated with multiple sclerosis (MS) has been published to date. METHODS: We performed a calculation based on population and prevalence data of each condition to estimate the expected coprevalence of both diseases. As no published data on DS prevalence are available, a rough estimate was calculated from live birth rates and published life tables. RESULTS: In a total of 116,939 assumed cases of patients with DS in Western Europe 102 patients with concordant MS would be expected at any time point according to the incidence of MS, but only 1 case was reported. CONCLUSION and HYPOTHESIS: We propose the hypothesis that despite a propensity in DS for certain autoimmune diseases there is a negative association of DS and MS. Genes located on chromosome 21 may thus confer protection against MS. Candidate genes for protective immunomodulation might include interferon receptor I and II and S100b. Substantiated by further epidemiologic data, the identification of these and other chromosome 21 gene products may provide new hints for the understanding of modulatory genes in the pathogenesis of MS. In more general terms, this negative association also may allow to study basic principles of how certain candidate genes might act on autoimmune disease expression.