Sex ratio of multiple sclerosis and clinical phenotype.
OBJECTIVE
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
We 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. This has implications for pathogenesis, for assessment of clinical trial results and for disease prevention. The factors underlying the selective increase in MS in females need to be uncovered.
Ramagopalan
S V
SV
Wellcome Trust Centre for Human Genetics,University of Oxford, Oxford, UK.
Byrnes
J K
JK
Orton
S-M
SM
Dyment
D A
DA
Guimond
C
C
Yee
I M
IM
Ebers
G C
GC
Sadovnick
A D
AD
D002170:Canada / Q000453:epidemiology; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D020528:Multiple Sclerosis, Chronic Progressive / Q000453:epidemiology*; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000453:epidemiology*; D010641:Phenotype; D012737:Sex Factors; D013997:Time Factors