MS Genetics

MS has no pattern of inheritance

 

A Mendelian disease has a known pattern of inheritance. MS is not a Mendelian disease because no pattern of inheritance has yet been identified. The probability of a child eventually getting MS if a single parent has it is estimated at 2%. This is 10 to 30X higher than the probability of someone getting MS if neither parent has MS. This indicates that some aspect of the potential for the development of MS is inherited.

 

 

There are around 200 known MS genetic markers

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A higher percentage of people with MS have these markers than the general population. However, most people with a specific MS marker never develop MS. It is probable that MS cannot be triggered unless multiple markers are present. It is currently not known what potential combinations of markers are required to trigger MS so it is not currently possible to use these markers to predict the onset of MS. If one identical twin has MS the probability that both will develop MS is 25 to 30%. In other words identical genetic make-up at birth only results in MS 30% of the time. This implies that even if genetic make up is present that is required for MS to occur some kind of environmental exposure is required before MS can actually occur (there is no direct dependence on genetic make up).

 

A number of genetic markers are common to multiple autoimmune diseases. It is believed that the immune system has a feature called self recognition that prevents the body from attacking itself. For any autoimmune disease to occur this self recognition feature would have to be disabled. It is possible that triggering of one or more genetic markers by one or more environmental factors may disable the self recognition feature. Once the self recognition feature is disabled it would be possible for the immune system to incorrectly identify part of the body (such as the myelin nerve sheath) as an antigen. In other words, exposure to two or more environmental factors may be required for the onset of MS (one to disrupt self recognition and one an MS antigen) .

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The worldwide prevalence of most of the 200 genetic makers is currently unknown

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The potential combinations of MS gene markers that could favor development of the disease are also unknown. Based upon currently available information it is not possible to determine if there is a worldwide correlation of gene marker prevalence to MS prevalence. There are many scientifically unsupported claims regarding MS online. For example it is often implied that the higher prevalence of MS in people of European ancestry is genetically driven. Scientific support of this claim would require 1) identification of a combination of MS gene markers unique to the European genome directly correlated to MS 2) Higher prevalence of these genetic markers in European populations 3) Absence of other combinations of genetic markers that could cause MS in other populations. None of these have been demonstrated.