LAUSR

ICAS in the Asian population [7] . Variations in risk factors among populations from different countries may explain differences in the ICAS incidence. The high rate in Japanese population is attributed to the high frequency of hypertension. However, in the Chinese population, the prevalence of hypertension, diabetes mellitus, and hyperlipidemia is not higher than those in white population; therefore, the excess burden of ICAS is unaccounted for in these populations [4] . It is important to determine whether this pattern of outcomes of symptomatic ICAS is present in other Asian countries. The absence of this pattern would provide further evidence of the heterogeneity of stroke outcomes among countries. Because of such heterogeneity, stroke prevention, and therapeutic strategies focusing on gender differences may be most effective if aimed at a national level rather than at a world level. Future nationwide investigations focused on gender differences are needed in many countries for comparisons with the study by Pu et al. [2] . The study by Pu et al. [2] may help to address the pathophysiology of symptomatic ICAS severity. The most common biological explanation for gender differences in stroke is the presence of sex hormones [1] , and Pu et al. [2] discussed gender differences in stroke outcomes, with consideration of sex hormones. In addition, more attention should be paid to anatomical differences. In view of stroke severity in symptomatic ICAS, the major determinants of infarct volume in large-vessel acute stroke are the territory at risk, duration of obstruction relative to oxygen demand, and extent of collateral arteries. Gender differences in cerebral collateral circulation were recently examined in animal models [8] . The differences in human cerebral collateral arteries between men and women or among different races are unclear; however, anatomical differences, including those related to cerebral collaterals, might be additional factors for explaining sex or study differences, and this should be investigated in the future. We need to develop a better understanding of gender differences in stroke incidence, presentation, prevention, and treatment effectiveness. Future research is needed to determine whether the pathophysiology of IS actually differs between men and women and to assess the approach for translating knowledge into specific strategies for the prevention and treatment of IS.