In the general population in the UK, about 1 in 600 people has MS.
MS is not considered hereditary. A hereditary condition is directly transmitted from parent to child or further generations, which is not the case in MS.
One of the elements that combine to cause an individual to develop MS is a genetic susceptibility to the condition. More than 230 genes have been found that each increase the risk of developing MS to a small degree. None of them directly causes the condition itself and someone with MS will have a combination of many of these genes.
As family members will share some of the same genes, this does mean that there is a higher risk of developing MS if there is already MS in the family. However, there is no certainty that the particular combination of genes that make a person in one generation susceptible will occur in subsequent generations. Many people diagnosed with MS do not have a family history of the condition.
Whilst the rate of MS within families suggests that there is a genetic factor involved in developing the condition, studies of identical twins show that genes are not the whole story. Identical twins have exactly the same genetic make up as each other. If MS were solely dependent on genes, it would be expected that if one identical twin developed the condition, so would the other, which isn't the case.
Studies have shown that, whilst still small, the risk of developing multiple sclerosis is higher for people who already have someone with MS in their family.
An Australian study published in 2013 combined the results of 18 previous studies to get a better estimate of the risk of MS in family members. In families where one member was already diagnosed with MS, the risk was highest for more closely related members.
Lifetime risk of MS by relationship to someone with MS:
- Identical twin - 1 in 5
- Non-identical twin - 1 in 22
- Other brothers or sisters - 1 in 37
- Parent - 1 in 67
- Child - 1 in 48
- Relatives that were less closely related had a lower risk.
- The lifetime risk in the general population is about 1 in 330
The researchers calculated that genes contributed just over half (54%) of the risk factors. The remainder would probably be due to environmental factors.
In 2014, a study using health records dating back to the 1960s captured information on most people diagnosed with MS in Sweden. This found that the risks were lower than in previous studies. The risk of the brother or sister of someone with MS also developing the condition was about seven times higher than in the general population. Previous studies suggested this risk was about nine times higher. The risk for children of someone with MS was five times higher, rather than the previously reported seven times.
MS risk in context
It is worth putting MS in context with other conditions.
- 1 in 3 people will develop some form of cancer
- 1 in 9 women will develop breast cancer at some point in their lives
- 1 in 9 men will develop prostate cancer
- 1 in 20 people over the age of 65 have dementia
- 1 in 22 people have chronic heart disease
- 1 in 33 people have diabetes
- 1 in 500 people have Parkinson's Disease
- 1 in 520 people in England and Wales have a stroke each year
- Cell 2018 Oct 13. [Epub ahead of print] Full article Low-frequency and rare-coding variation contributes to multiple sclerosis risk
- Neuroepidemiology 2013;40(1):1-12. Full article (PDF 692kb) Modelling genetic susceptibility to multiple sclerosis with family data.
- Brain 2014;137(3):770-778. Full article Modest familial risks for multiple sclerosis: a registry-based study of the population of Sweden.