[Genetic aspects in multiple sclerosis: I. Twin studies].

The authors make a review and critical analysis of twin studies in multiple sclerosis (MS). The concordance rate among homozygotic twins is significantly greater than in heterozygotic twins. The average hertability in MS is about 28%; no single gene was identified as a sole risk factor for the development of the disease. MS may be considered a polygenic disease triggered by environmental factors in a genetically predisposed individual.