Concordance and heritability of multiple sclerosis in Finland: study on a nationwide series of twins

Abstract

OBJECTIVES: To evaluate the changes in the multiple sclerosis (MS) concordance in twins, and the contribution of genetic and environmental factors to the aetiology of MS in Finland. BACKGROUND: Both genes and the environment contribute to the development of MS. A well-conducted twin study is an excellent means to assess the relative contribution of heritability and environmental factors. METHODS: Multiple sclerosis concordance was assessed for 10 Monozygotic and 14 dizygotic twin pairs using pairwise and probandwise concordance rates. The tetrachoric correlations in liability to disease for twin pairs were computed and a polygenic multifactorial model was used to estimate heritability. RESULTS: The pairwise concordance for MZ twins was 30% and for the DZ twins 14.3%, compared with 30% for MZ and 0% for DZ 20 years ago. The corresponding probandwise concordance rates were 46.2% and 25%. The genetic variance (heritability) was 15.3% (95% Cl 0.0-77.6), the common environmental variance 73.7% (95% Cl 14.1-93.9) and the unique environmental variance 11.1% (95% Cl 2.3-30.0). CONCLUSIONS: As the concordance of MS in DZ twins has increased during the past two decades and the heritability estimate is low, it seems that the reported increase in MS incidence in Finland is mainly caused by environmental factors.