New research has gone some way to explaining why multiple sclerosis (MS) affects up to three times more women than men after it found that females are more likely to carry a gene linked to the illness than males with the condition.
Women are also more susceptible to having the condition passed on to them from a female relative, according to the research which appeared in the journal Neurology.
The study, funded by the MS Society, said that in the 1950s the number of men and women with MS was approximately equal but the ratio of females to males now stands at 2:1 in the US and 3:1 in Scotland.
Some 6,500 of the 10,000 people who have MS in Scotland are women, the MS Society said.
The research paper said: "There is general consensus that the incidence and prevalence of MS has been rising with an increased penetrance among women ... Moreover, there is a maternal parent-of-origin effect, with a higher number of affected mother–daughter pairs and few father–son pairs."
But scientists played down suggestions that the rise in MS among females was caused by genetic factors alone because the increase had occurred in such a small space of time.