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