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Lancet Neurol. 2006 Nov;5(11):932-6.

Sex ratio of multiple sclerosis in Canada: a longitudinal study.

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1
Wellcome Trust Centre for Human Genetics and Department of Clinical Neurology, University of Oxford, Oxford, UK.

Abstract

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.

PMID:
17052660
DOI:
10.1016/S1474-4422(06)70581-6
[Indexed for MEDLINE]
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