MS ExplainedWho gets MS?
How many people have MS?
Multiple sclerosis is the most common disease of the central nervous system diagnosed in young adults. An estimated 2,500,000 people in the world have MS.
There is currently no comprehensive register of people with MS in the UK and so the number of people with MS is an estimate based on a number of studies of local areas. The studies look at the number of people with the condition in a particular geographic area, which is referred to as the prevalence, and are usually expressed as the number of cases per 100,000 people. The prevalence rates from the studies are then applied to the national population, and from this it is estimated that around 100,000 people live with MS in the UK.
Similarly, if the results of local area studies are applied nationwide it suggests that nearly 3,000 people are diagnosed with MS in the UK each year, or around 50 to 60 a week. The number of new cases in the population within a specified period of time is known as the incidence rate.
The University of Swansea is working with the MS Society to develop a UK MS Register that will combine personal information with clinical and NHS data to provide a more accurate picture of the number of people with MS in the UK. More information about the register, including how to join, can be found at: www.ukmsregister.orgAn incidence register of MS in Scotland has also been launched, which will collate data on all new cases of MS in Scotland from the 1st January 2010. As well as collecting data about the number of new cases of MS in Scotland each year, the register will examine patient management from referral to diagnosis. More information about the register can be found at: www.msr.scot.nhs.uk
Most people with MS are diagnosed in their 20s or 30s, although it can be diagnosed in people who are older than this, and, less frequently, in teenagers and children. However, the number of cases of MS in this age group is rising and research suggests that somewhere between 1 in 37 and 1 in 50 people with MS are diagnosed in their teens or younger, although precise figures are unknown.
Due to the age at which it is diagnosed, MS is often thought of as a condition that affects 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 it has been suggested that the proportion of women with MS may be growing. Recent studies in North America indicate that the figure may be closer to three women to each man diagnosed.
When MS is diagnosed in people in their teens, the proportion is about three women to one man. When MS is diagnosed in older people, or in whose MS is progressive from onset, the numbers of women and men are equal (see page 30 for more on types of MS).
The reason for the larger proportion of women with MS is unknown but this pattern also occurs in most other autoimmune conditions (see page 10 for more on 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 countries such as Canada and Scotland have particularly high rates.
Studies in countries near the equator have shown a prevalence rate of about 4 cases per 100,000 in Peru, 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 120 and 140 per 100,000, about 180 in Northern Ireland and as high as 210 in Scotland. Individual studies in Orkney have recorded rates of over 400 per 100,000.
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 more prevalent in northern Europe, North America, Australia and New Zealand has led to speculation that it was 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 national rate of MS in the Irish Republic was looked at in 2007 and was shown to vary from 145 per 100,000 in Wexford in the south, to 290 in Donegal in the northwest. In Northern Ireland, which was extensively settled by immigrants from Scotland from the 17th century, the rate was recorded in 2004 as 230 per 100,000.
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 their subsequent offspring, have a risk of MS similar to that found locally.
This explains the outdated belief that MS is a condition that only affects white people and is rare or unknown amongst black or Asian people. Whilst this might have been true for the first generation immigrants, it is not the case for successive generations born and brought up in the UK, with MS increasingly being seen in black and Asian communities.
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?