What is Multiple Sclerosis?
Multiple sclerosis (MS) is a chronic autoimmune disease that affects the central nervous system. MS targets myelin, which is the insulating layer of the nerves that allows electric signals to transmit more efficiently. While symptoms differ from person to person, multiple sclerosis usually manifests as weakness in the limbs, vision problems, slurred speech, fatigue, and dizziness. Here in Canada, where Circa Pain is based, we have one of the highest reported rates of MS worldwide. One estimate reveals that 1 in every 400 Canadians is living with the disease (Statistics Canada, 2018). No definite cause of MS has been determined to date. However, some risk factors that increase MS incidence have been found, such as genetics, smoking, and sex.
MS Incidence and Latitude
Newer research suggests that latitude might be another risk factor that correlates with MS incidence. One study conducted at the University of Tasmania, Australia found a notable association between MS severity and latitude (Tao et al, 2021). The researchers used age of disease onset as a marker for MS severity (with earlier onset being more severe) and found that the onset of symptoms was on average two years earlier for those living at higher latitudes. This finding echoes an older Australian study conducted in Queensland that also found a significant relationship between latitude and MS prevalence (Hammond et al, 1987).
However, a study within Asia found that geographical latitude was not a factor affecting the prevalence of MS (Zhang et al, 2020). The researchers conducted a meta-analysis of epidemiological data of MS from China, Japan, and neighbouring countries. They found that there was no correlation between geographical latitude and MS prevalence in those populations. As such, more studies need to be conducted to determine whether latitude or another underlying factor, such as exposure to sunlight, is behind the observed correlation in the Australian studies.
How this Correlation Relates to Our Work
People living with multiple sclerosis experience a variety of symptoms that can fluctuate within a day. We are particularly interested in the work done in the aforementioned studies since the latitude at which you live determines how many daylight hours you are exposed to. This, in turn, can disrupt the body’s natural circadian rhythm, which is a term that describes the collection of biological functions that follow the 24-hour cycle (read more about circadian rhythms here). This is where our lab group comes in. In our work, we are looking to determine if circadian disruption plays a role in the development and progression of MS.
Written by Tima Al-Shammaa
This article was originally posted on the blog for our ‘sibling-study,’ CircaPain.
References:
1. Hammond, S. R., et al. (1987). The epidemiology of multiple sclerosis in Queensland, Australia. Journal of the neurological sciences, 80(2-3), 185–204. https://doi.org/10.1016/0022-510x(87)90154-7
2. Multiple sclerosis: Prevalence and impact. (2018, January 17). Statistics Canada. https://www150.statcan.gc.ca/n1/pub/82-003-x/2018001/article/54902-eng.htm
3. Tao C, et al. Higher latitude is significantly associated with an earlier age of disease onset in multiple sclerosis, Journal of Neurology, Neurosurgery & Psychiatry 2016; 87:1343-1349.
4. Zhang, et al. (2020). Incidence and prevalence of multiple sclerosis in China and other Asian countries (Barcelona, Spain), S0213-4853(20)30269-3. Advance online publication. https://doi.org/10.1016/j.nrl.2020.07.022
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