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.
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.
Authors: Gil Benedek; Jun Zhang; Ha Nguyen; Gail Kent; Hilary A Seifert; Sean Davin; Patrick Stauffer; Arthur A Vandenbark; Lisa Karstens; Mark Asquith; Halina Offner Journal: J Neuroimmunol Date: 2017-06-21 Impact factor: 3.478
Authors: M J Chao; S V Ramagopalan; B M Herrera; S M Orton; L Handunnetthi; M R Lincoln; D A Dyment; A D Sadovnick; G C Ebers Journal: Neurology Date: 2011-01-05 Impact factor: 9.910
Authors: Lillian Cruz-Orengo; Brian P Daniels; Denise Dorsey; Sarah Alison Basak; José G Grajales-Reyes; Erin E McCandless; Laura Piccio; Robert E Schmidt; Anne H Cross; Seth D Crosby; Robyn S Klein Journal: J Clin Invest Date: 2014-05-08 Impact factor: 14.808
Authors: James A Rogers; Manoj K Mishra; Jennifer Hahn; Catherine J Greene; Robin M Yates; Luanne M Metz; V Wee Yong Journal: Proc Natl Acad Sci U S A Date: 2017-04-24 Impact factor: 11.205