Familial recurrence risks and inheritance of multiple sclerosis.

The cause of multiple sclerosis is unknown. There is considerable circumstantial evidence that multiple sclerosis is a complex trait, probably autoimmune in nature, and is determined by both genetic and environmental factors. It is recognized that relatives of multiple sclerosis patients are at greater risk for developing the disease than the general population, although this risk is still relatively low in absolute terms. Monozygotic co-twins of multiple sclerosis patients appear to have the highest risk of any group of relatives, although the absolute risk is well under 100%, as would be predicted if multiple sclerosis is purely a genetic disorder.