Multiple sclerosis

It is a degenerative disease of the central nervous system due to autoimmune destruction of the myelin sheath protecting nerve fibers. Mild cases may have long periods of remission, while severe cases can be very limiting due to permanent nerve damage. An overall incidence of 2.1 cases per 100,000 persons per year has been estimated.

It is not clear what causes the immune system to attack the myelin sheath, however, studies suggest that in addition to the genetic component, several external factors may contribute to trigger the disease.

  • Age: onset is most common between the ages of 20 and 40, although it can occur at any age.
  • Gender: women are 2-3 times more likely to present relapsing-remitting multiple sclerosis.
  • Viral infections: among them, Epstein-Barr is associated with an increased risk of multiple sclerosis.
  • Race: people especially of Northern European descent are at higher risk compared to those of Asian, African or Native American descent.
  • Climate: more common in countries with temperate climates such as Europe, Canada, northern United States or southeastern Australia.
  • Vitamin D: lower levels of vitamin D and sun exposure are associated with increased risk.
  • Other autoimmune disorders: thyroid disease, pernicious anemia, psoriasis, type 1 diabetes or inflammatory bowel disease increase the risk.
  • Smoking: smokers have an increased risk of relapsing-remitting multiple sclerosis.
  • Childhood obesity: individuals with obesity during adolescence would present an increased risk.

The nature of MS susceptibility is complex and involves environmental and genetic factors, with heritability recently described to be around 8-10%. The GWAS analysis and replication study conducted by the International Multiple Sclerosis Genetics Consortium on a total of over 47,000 cases and 68,000 controls has provided the largest and most comprehensive assessment of MS genetic susceptibility to date.s most comprehensive assessment of genetic susceptibility to MS to date, with the identification of 193 risk loci involved in the innate and adaptive immune response. Although the study points to the involvement of brain-resident immune populations that would direct the autoimmune process to the CNS, it has been suggested that it would have its initiation in peripheral immune responses.

Symptoms

Multiple sclerosis (MS) can cause a wide range of symptoms and affect any part of the body. Each person is affected differently depending on the location of the affected nerve fibers. Symptoms are unpredictable, sometimes developing and worsening steadily, while at other times they come and go. Periods when symptoms worsen are known as relapses while those when they improve or disappear are known as remissions.

Most people with MS have only a few of these symptoms, which are the most common:

  • Fatigue, numbness, tingling, pain.
  • Muscle spasms, stiffness and weakness.
  • Tremors, lack of coordination or unsteady gait, mobility problems.
  • Speech and swallowing difficulties.
  • Problems with thinking, learning and planning.
  • Depression and anxiety.
  • Vision, sexual, urinary, bowel problems.
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Prevention

There are no effective preventive measures since the causes that trigger the autoimmune attack against the central nervous system are unknown. However, as in almost all pathologies, there are certain recommendations that could be useful, mainly related to a healthy lifestyle. Quitting smoking, eating a healthy diet low in saturated fats, keeping stress levels low and exercising regularly. In addition, sun exposure and supplementing vitamin D intake if necessary are recommended.

Number of observed variants

13.5 million variants

Number of risk loci analyzed in the study

190 loci

Bibliography

Walton C et al. Rising prevalence of multiple sclerosis worldwide: Insights from the Atlas of MS, third edition. Mult Scler. 2020;26(14):1816-1821.

National Health Services [April 2022]

Mayo Clinic [April 2022]

International Multiple Sclerosis Genetics Consortium. Multiple sclerosis genomic map implicates peripheral immune cells and microglia in susceptibility. Science 2019; 27;365(6460):eaav7188.

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