The change in the sex ratio in multiple sclerosis is driven by birth cohort effects

Ongoing increase in incidence and prevalence of multiple sclerosis in south-eastern Iran: A three decade study

BACKGROUND

Prevalence of multiple sclerosis has been increased during the last decades throughout the world. Epidemiological studies could improve our understanding relating to its intrinsic and extrinsic causes.

OBJECTIVES

The current study has been conducted to determine the epidemiological features of MS in south-eastern Iran which is a semi-tropical area with different ethnicities.

METHODS

This longitudinal descriptive study was carried out in south-eastern Iran, based on information of MS patients registered at Zahedan University of Medical Sciences database from 1990 to 2020.

RESULTS

A total of 1045 cases were enrolled into the study. The age-standardized prevalence ratio of MS increased to 42.2/100,000 population by 2020. These figures showed increasing trends both in females and males and reached to 61.5 and 22.6 per 100,000 population, respectively by the year 2020. Likewise, the total incidence rate grew to its maximum amount of 4.5 in 2015. Female incidence also revealed an upward trend and peaked in 2016 to 6.4 while male incidence rate reached at its highest level of 1.8 in 2009.

CONCLUSION

MS prevalence ratios and incidence rates in south-eastern Iran have been increasing steadily, especially in women during the last three decades. The south-eastern part of Iran should be considered a high-risk region.

Global, regional, and national burden of multiple sclerosis from 1990 to 2019: Findings of global burden of disease study 2019

BACKGROUND

The global rising prevalence and incidence of multiple sclerosis (MS) has been reported during the past decades. However, details regarding the evolution of MS burden have not been fully studied. This study aimed to investigate the global, regional, and national burden and temporal trends in MS incidence, deaths, and disability-adjusted life years (DALYs) from 1990 to 2019 using the age-period-cohort analysis.

METHODS

We performed a secondary comprehensive analysis of incidence, deaths, and DALYs of MS by calculating the estimated annual percentage change from 1990 to 2019 obtained from the Global Burden of Disease (GBD) 2019 study. The independent age, period, and birth cohort effects were evaluated by an age-period-cohort model.

RESULTS

In 2019, there were 59,345 incident MS cases and 22,439 MS deaths worldwide. The global number of incidences, deaths, and DALYs of MS followed an upward trend, whereas the age-standardized rates (ASR) slightly declined from 1990 to 2019. High socio-demographic index (SDI) regions had the highest ASR of incidences, deaths, and DALYs in 2019, while the rate of deaths and DALYs in medium SDI regions are the lowest. Six regions which include high-income North America, Western Europe, Australasia, Central Europe, and Eastern Europe had higher ASR of incidences, deaths, and DALYs than other regions in 2019. The age effect showed that the relative risks (RRs) of incidence and DALYs reached the peak at ages 30-39 and 50-59, respectively. The period effect showed that the RRs of deaths and DALYs increased with the period. The cohort effect showed that the later cohort has lower RRs of deaths and DALYs than the early cohort.

CONCLUSION

The global cases of incidence, deaths, and DALYs of MS have all increased, whereas ASR has declined, with different trends in different regions. High SDI regions such as European countries have a substantial burden of MS. There are significant age effects for incidence, deaths, and DALYs of MS globally, and period effects and cohort effects for deaths and DALYs.

The changing course of multiple sclerosis: rising incidence, change in geographic distribution, disease course, and prognosis

PURPOSE OF REVIEW

This review provides a brief update of new research findings on the changing epidemiology, disease course, and prognosis of multiple sclerosis (MS).

RECENT FINDINGS

Evidence not only continues to support the female predominance in incidence and prevalence of the disease but also supports an increase in incidence of MS in geographic areas that were previously considered to be low incidence for the disease.

SUMMARY

An increased interest in population-based registries and databases will provide more valid epidemiological measures and observational studies conducted in well-defined study populations. Such studies are crucial for an accurate description of both changing prognosis of MS and differential characteristics of the various MS phenotypes.

Hypothesis: Multiple sclerosis is caused by three-hits, strictly in order, in genetically susceptible persons

Multiple Sclerosis is a chronic, progressive and debilitating neurological disease which, despite extensive study for over 100 years, remains of enigmatic aetiology. Drawn from the epidemiological evidence, there exists a consensus that there are environmental (possibly infectious) factors that contribute to disease pathogenesis that have not yet been fully elucidated. Here we propose a three-tiered hypothesis: 1) a clinic-epidemiological model of multiple sclerosis as a rare late complication of two sequential infections (with the temporal sequence of infections being important); 2) a proposal that the first event is helminthic infection with Enterobius Vermicularis, and the second is Epstein Barr Virus infection; and 3) a proposal for a testable biological mechanism, involving T-Cell exhaustion for Epstein-Barr Virus protein LMP2A. We believe that this model satisfies some of the as-yet unexplained features of multiple sclerosis epidemiology, is consistent with the clinical and neuropathological features of the disease and is potentially testable by experiment. This model may be generalizable to other autoimmune diseases.

Incidence of MS has increased markedly over six decades in Denmark particularly with late onset and in women

OBJECTIVE

To describe the pattern of development of incidence of multiple sclerosis (MS) over 60 years in Denmark with age-period-cohort analyses and seasonality of birth.

METHODS

Data on virtually all patients with onset of MS have since 1950 been prospectively recorded and kept in the Danish Multiple Sclerosis Registry with multiple sources of notification. Annualized incidence rates per 100,000 were directly standardized to the European Standard Population.

RESULTS

We have registered 19,536 cases with clinical onset of confirmed MS in Denmark from 1950 to 2009. From the 1950-1959 to the 2000-2009 onset period, incidence more than doubled in women, with an increase from 5.91 (95% confidence interval [CI]: 5.60-6.24) to 12.33 (95% CI: 11.91-12.75) per 100,000 per year compared with a modest 24% increase in men from 4.52 (95% CI: 4.24-4.81) to 6.08 (95% CI: 5.79-6.38). With age at onset of 50 years and older, incidence increased with a factor 4.30 in women and 2.72 in men. The female/male sex ratio increased over time and with year of birth. Age-period-cohort analysis revealed a significant birth cohort effect in addition to the age and period effect. We found no statistically significant seasonality of births.

CONCLUSION

The incidence of MS has doubled in women, most pronounced with late onset, and has only modestly increased in men. Lifestyle changes in the female population that could include fewer childbirths, increased occurrence of obesity, and increased cigarette consumption may have a role.

Sex ratio in multiple sclerosis mortality over 65 years; an age-period-cohort analysis in Norway

Increasing female: male ratio in multiple sclerosis (MS) has been assigned to cohort effects, with females in more recent birth cohorts possibly being more exposed or vulnerable to environmental risk factors than males. We collected MS mortality data in Norway from 1951 to 2015 from The Norwegian Cause of Death registry. Age-Period-Cohort analysis was conducted using log-linear Poisson models, including sex interaction terms. MS was registered as the underlying, contributing or direct cause in 6060 deaths. MS associated mortality remained stable with a slight preponderance among males until after 1980, and have since increased preferentially among females. Throughout the study period the mean annual increase was 1.25% for females and 0.3% for males (p < 0.0001). Age-period-cohort analysis revealed limited evidence of cohort effects for the gender differences; the best fitting model only included gender-age and gender-period interaction terms. The period effect evened out for males in the last three decades but increased for females, especially among the oldest age-groups. In conclusion, the increased female: male mortality ratio in MS associated mortality is driven mainly by increased mortality among females in the three last decades, particularly in the older age groups. It is best explained by disproportional period effects, providing evidence of time-varying external factors including improved access to diagnosis among females.