To count as an inherited condition, MS would have to be passed on in a predictable way, which it isn’t.
Inherited conditions are caused by faulty genes which are passed on from one generation to another. Typically, a child has either a one in two or a one in four chance of inheriting the condition from their parents. Examples of conditions inherited in a predictable way are Haemophilia and Muscular Dyastrophy.
In inherited conditions, identical twins will either both have the condition or both be free of it because they carry identical genes. This doesn’t happen in MS. If one identical twin has MS, the other twin only has about a one in four chance of having MS, again showing that MS is not a truly inherited condition.
Also, most people with MS have no history of MS in the family so it seems to have appeared from nowhere.
The role of genes in MS
Genes do play a part in MS. Some genes make it more likely that someone gets MS but having those genes is definitely not enough on its own. Other factors are needed to trigger MS in someone who carries genes that make them more susceptible to getting MS.
Recent research has found over 100 genes that contribute to susceptibility to MS. Each gene represents a tiny part of the risk so the more of these different genes that someone carries, the more their risk is increased. Consequently, there isn’t a simple genetic test to say whether someone is susceptible or not.
Other factors that play a part
So, what factors can trigger MS in someone who has got the genes that make them more susceptible? A whole range of factors have been investigated and the evidence for which factors might be triggers is patchy. The strongest contenders are:
- lack of sunshine which is linked to lack of vitamin D
- exposure to the very common Epstein Barr virus which causes glandular fever in some people
Adding it all together
The bottom line is that MS is not inherited but there is an increased risk in families who already have a member with MS because they carry some of the same genes. However, other factors are needed to trigger the condition and, overall, MS is still considered as a relatively rare condition compared with, for example, diabetes or breast cancer.
The risk of MS in a family member depends on how closely related they are. The more closely related, the more likely that both will have MS. In a recent study of over 42,000 people in Sweden who had a parent with MS, only 515 (1.2%) had also been diagnosed with the condition. This translates into roughly a one in eighty chance of a parent and their child both having MS. This compares with a roughly one in 400 chance in completely unrelated people.
Is MS hereditary or not?
Returning to the original question at the top of this blog: MS is not inherited in the true sense of the word and this is what many neurologists tell people with MS. However, there is an increased risk in families so it is not surprising to sometimes hear of two members of the same family both having MS.