Research: Sex Ratio with MS increasing in Women

Orton SM, Herrera BM, Yee IM, Valdar W, Ramagopalan SV, Sadovnick AD, Ebers GC; Canadian Collaborative Study Group. Lancet Neurol. 2006 Nov;5(11):932-6.

BACKGROUND: Incidence of multiple sclerosis is thought to be increasing, but this notion has been difficult to substantiate. In a longitudinal population-based dataset of patients with multiple sclerosis obtained over more than three decades, we did not show a difference in time to diagnosis by sex. We reasoned that if a sex-specific change in incidence was occurring, the female to male sex ratio would serve as a surrogate of incidence change.
METHODS: Since environmental risk factors seem to act early in life, we calculated sex ratios by birth year in 27 074 Canadian patients with multiple sclerosis identified as part of a longitudinal population-based dataset.
FINDINGS: The female to male sex ratio by year of birth has been increasing for at least 50 years and now exceeds 3.2:1 in Canada. Year of birth was a significant predictor for sex ratio (p<0.0001, chi(2)=124.4; rank correlation r=0.84).
INTERPRETATION: The substantial increase in the female to male sex ratio in Canada seems to result from a disproportional increase in incidence of multiple sclerosis in women. This rapid change must have environmental origins even if it is associated with a gene-environment interaction, and implies that a large proportion of multiple sclerosis cases may be preventable in situ. Although the reasons why incidence of the disease is increasing are unknown, there are major implications for health-care provision because lifetime costs of multiple sclerosis exceed pound1 million per case in the UK

Sex ratio of multiple sclerosis and clinical phenotype.
Ramagopalan SV, Byrnes JK, Orton SM, Dyment DA, Guimond C, Yee IM, Ebers GC, Sadovnick AD. Eur J Neurol. 2010;17(4):634-7. Epub 2009 Nov 24.

BACKGROUND AND PURPOSE: In a longitudinal population-based dataset of patients with multiple sclerosis (MS), we have previously observed a substantial increase in the female to male sex ratio in Canada over the last 50 years. Here, we aimed to determine whether this change in sex ratio is related to the clinical course of MS.

METHODS: e calculated sex ratios by birth year in 11 868 patients with relapsing-remitting (RR) MS and 2825 patients with primary progressive (PP) MS identified as part of the Canadian Collaborative Project on the Genetic Susceptibility to MS.

RESULTS: Year of birth was a significant predictor for sex ratio in RR MS (P < 0.0001, chi(2) = 21.2; Spearman’s rank correlation r = 0.67), but not for PP MS (P = 0.44, chi(2) = 0.6; Spearman’s rank correlation r = 0.11).
CONCLUSIONS: An increase in the number of female RR MS patients over time accounts for the increasing sex ratio of MS.

Here are the reports showing an dramatic increase of Ms in women, these women are mainly developing RRMS.

CoI: Ram is a member of Team G

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  • I thought this Malcolm Gladwell article was fascinating but I don't know if the science is sound.

    It's says that "the modern way of living represents an extraordinary change in female biology" and that "women's bodies are being subjected to changes and stresses that they were not necessarily designed by evolution to handle."

    In traditional societies women "had menarche at seventeen and had five babies and had three hundred fewer menstrual cycles than most women have today"

    The main argument is that "incessant ovulation has become a serious problem for women's health" and is responsible for the increase in various women's cancers.

    Could the changing MS sex ratio be linked to this?

  • Yes I think it plays a role!
    Before the 1950s in Canada the total fertility rate (equivalent to number of children each woman has) was more than 4; it is now close to 1.
    There is definitely an link between having a higher number of children and a reduced risk of breast cancer- I think the same is true for MS.

  • with reference to the comment above, the largest value of difference between the traditional society womefolk's menstrual cycles and modern ones I can derive is 150 rather than the 300 cited by the person above.

    I don't get how the number of menstrual cycles would impact my development of MS – but the decline in MS disease activity during pregnancy and the subsequent rebound does suggest there is some link with female hormones.

    I wonder if the rise in MS in women is linked to their increasingly indoor lifestyle and a commensurate deficiency of vitamin D ?

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