December 22 (HealthDay News) -- In women, hormones increase the frequency of an inherited form of severe migraine accompanied by visual disturbances called auras, according to a Massachusetts General Hospital study.

Like other types of migraine, familial hemiplegic migraine affects women more than men. Most cases of familial hemiplegic migraine are caused by mutations in the CACNA1A gene. However, it hasn't been clear whether these mutations lead to spreading depression -- the event in the brain that suppresses nerve cell activity and has been linked to non-genetic forms of migraine with aura, according to background information in the study.

The study authors found that mice expressing either one or two different CACNA1A mutations that lead to familial hemiplegic migraine in humans had increased susceptibility to spreading depression. The mutation associated with more severe familial hemiplegic migraine caused a greater increase in susceptibility to spreading depression than the mutation linked to a milder form of familial hemiplegic migraine.

Female mice were more likely to have spreading depression than male mice, but this difference was reversed if the female mice had their ovaries removed and then partially restored by replacement of the hormone estrogen.

The researchers concluded that both genetic and hormonal factors affect a person's susceptibility to migraines with aura.

The study was published in the current issue of the Journal of Clinical Investigation.

SOURCE: Journal of Clinical Investigation, news release, Dec. 22, 2008