Around 2.5 million people around the world live with multiple sclerosis, an unpredictable condition affecting the central nervous system. Among many other symptoms, blurred vision, loss of balance, slurred speech, tremors, blindness and memory problems are characteristic of MS, but the problems can come and go and may worsen over time.
More than 100,000 people in the UK have been diagnosed with the neurological condition, with almost three times as many women as men affected. On World MS Day, marked on 27 May, IBTimes UK looks at facts and figures about MS.
Each nerve fibre in the brain and spinal cord is surrounded by a layer of protein called myelin, which protects the nerve and helps electrical signals from the brain travel to the rest of the body. In people with MS, the myelin becomes damaged, which disrupts the transfer of these nerve signals.
MS is known as an autoimmune condition, which is where something goes wrong with the immune system – the body's defence against infection – and it mistakenly attacks healthy body tissue. In the case of MS, it attacks the myelin.
Symptoms usually appear between the 20s and 30s, but individuals as young as two and as old as 75 have developed MS.
Studies suggest that genetic risk factors increase the risk of developing MS, but there is no evidence to suggest MS is directly inherited. Family members have a slightly higher risk of developing MS, according to the Multiple Sclerosis Trust.
Low levels of vitamin D and smoking cigarettes have been cited as environmental factors that may contribute to the risk of MS, according to the MS Society.
MS is most common in Caucasians of northern European ancestry, although it occurs in most ethnic groups.
Symptoms of MS depend entirely on the individual and differ with each person.
There is currently no cure for MS but the treatments can relieve symptoms and help prevent relapses.
MS is not fatal, but complications can arise from severe MS, such as pneumonia, which can be life-threatening.
As a result, the average life expectancy for people with MS is around five to 10 years lower than the population at large. However, with increased research and improved medical care, the gap appears to be getting smaller.