MS ExplainedWho gets MS?
How many people have MS?
MS is the most common disease of the central nervous system affecting young adults. An estimated 2,500,000 people in the world have MS.
Research by the London School of Hygiene and Tropical Medicine in 2009 suggested that the number of people with MS in the UK may be about 100,000.
Similarly, if the results of local area studies are applied nationwide it suggests that about 2,500 people are diagnosed with MS in the UK each year, or about 50 a week.
Who gets MS?
Most people with MS are diagnosed in their 20s or 30s, although it can appear in people who are older than this, and, less frequently, in children.
Research suggests that one person in 50 with MS is diagnosed in their teens or younger, although precise figures are unknown.
Due to the age at which it is diagnosed, MS is sometimes referred to as a condition affecting younger people. However, as it only has a small effect on life expectancy, most people live with the condition for a long time.
More women than men are diagnosed with MS. Roughly two women have MS for every man with the condition, although research suggests that the proportion of women with MS may be growing. Recent studies in north America suggest that the figure may be closer to three women to each man diagnosed.
When MS is diagnosed in people in their teens, the proportion of women to men is about 3:1. When MS is diagnosed in older people or in those whose MS is progressive from onset, the numbers of women and men are more equal.
The reason for the larger proportion of women with MS is unknown but this pattern occurs in most other autoimmune conditions.
Where is MS more common?
The distribution of MS around the world is uneven. As a rough guide, the prevalence increases as you travel further north or south from the equator. Those parts of Asia, Africa and America that lie on the equator have extremely low levels of MS, whilst Canada and Scotland have particularly high rates.
For instance, studies in countries near the equator have shown a prevalence rate in Peru of about 4 cases per 100,000, 8 in Saudi Arabia and just 1 amongst Indians in Mumbai.
In contrast, studies in Australia show a range from 11 in the north to 68 in Tasmania in the south. This increasing prevalence is more marked in the northern hemisphere. Studies in the UK suggest that the rate in England and Wales is between 100 and 120 per 100,000, about 160 in Northern Ireland and as high as 190 in Scotland. Individual studies in Orkney have recorded rates of over 200.
A simple geographical spread is not the whole picture. Studies show that some ethnic groups have a markedly lower prevalence of MS, despite living in countries where MS is relatively common. For instance, the Sami (Lapps) of northern Scandinavia and the Inuit in Canada have very low rates of MS. A similar pattern is observed amongst the Maoris of New Zealand.
In contrast, a study in Kuwait showed that the rate for Kuwaitis was half that of the ethnic Palestinian population - many of whom had been born and raised in Kuwait. Similarly, the same studies in India that showed very low rates for Indians found that the rate for Parsis, an ethnic group that originated in Persia, was much higher and equivalent to areas in southern Europe.
Vikings and Scots
The fact that MS is most prevalent in Northern Europe, North America, Australia and New Zealand has led to speculation that it has been carried around the world by European colonists and settlers. It has been suggested that the origins can be traced back to the Vikings who colonised those parts of Northern Europe where MS is now most pronounced and that 'Viking' genes can make people particularly susceptible to MS.
It has also been noted that Scotland has a much higher rate of MS than England or Wales and that areas of high MS prevalence around the world have been settled by Scottish immigrants. In Ireland for instance, the prevalence rate of MS in the Irish Republic - based on an old study from 1971 - is about 66. In Northern Ireland, which was extensively settled by immigrants from Scotland from the 17th century, the rate was recorded in 1996 as 168.
Research looking at the effect of migration on the risk of developing MS suggests that the age someone moves is important. If someone moves from an area of low risk to an area of high risk as an adult, they retain the risk level of the location from which they originally came. People who move as children and the subsequent children of immigrants have a risk of MS similar to that found locally.
This explains the old fashioned, incorrect idea that MS was a condition that only affected white people and was rare or unknown amongst black or Asian people. Whilst this might have been true for the initial immigrant generations, it is not the case for the people born and brought up in the UK.
The geographic spread of MS suggests the genetic make up of people from different parts of the world has an impact on risk of MS; the migration studies point to there being an environmental element at play as well.
Next page - The possible causes of MS?