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 When it comes to the sexes, multiple sclerosis (MS) is not an equal-opportunity disease. And it seems to be getting more biased by the decade. Prior to 1940, the estimated ratio of American women to men with a diagnosis of MS was 2:1. By the turn of the millennium, this ratio had increased to 4:1.The same phenomenon has been seen elsewhere. In Canada, the number of women with a diagnosis of MS has approximately tripled in the last 60 years. In Denmark, increased diagnoses in women compared to men became evident beginning in the 1970s.
These data may be somewhat misleading. For example,women in earlier decades of life may have been less likely than men to receive a proper diagnosis of MS; the use of better diagnostic tools may now allow for a more accurate count. On the other hand, because women generally live longer than men, their diagnoses may have been overrepresented in some studies. Still, today’s experts generally agree that women are 2–3 times more likely than men to have MS.What accounts for this difference? And how does MS uniquely impact the lives of modern women? Here we revisit the complicated relationship between gender and MS.
Gender and MS: Focus on Hormones
MS is an autoimmune disease, meaning that it develops when elements of the body’s immune system begin to mistakenly attack normal tissue. In the case of MS, that tissue is the myelin sheath, a fatty covering that insulates nerve fibers in the central nervous system (CNS). Laboratory researchers have already teased out fundamental gender-related differences in the autoimmune activity against myelin. For instance, studies in mice with a type of MS suggest that males are less likely than females to have a gene variant that increases interferon gamma, a chemical messenger linked to myelin autoimmunity. In female mice, the longevity of essential myelinproducing cells called oligodendrocytes was found to be shorter than in male mice, a condition that would leave the females more vulnerable to irreparable myelin damage. However, in pregnant mice,myelin-producing cells reportedly increased, as did myelin formation and the capacity to repair myelin.A milk-stimulating hormone called prolactin was found to be regulating these changes. Could hormones account for the other male-female differences observed?
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