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This page answers frequent questions about why people get MND and how researchers are trying to learn more about causes of the disease.

What causes MND?

 In the vast majority of cases of MND, there is no history of the disease in any of the immediate family members (grandparents, parents, brothers or sisters). This is called sporadic MND, because the disease appears for no apparent reason. However, in about 10% of cases, family history of the disease indicates that inherited genetic damage causes the condition; this is termed familial MND.

How do you know whether someone has the inherited form of MND?

 

The rare, inherited form of MND affects more members of the same family than can be accounted for by chance. In these families there is evidence that the disease is present in a close relative of the affected person and has been passed on to some (not all) members of the following generations. More detailed information on the inherited form of MND is available in Research Information Sheet B - Inherited MND (87 kb).

Do insect bites and tick bites cause MND?

 As far as we know, insect bites and tick bites do not contribute to the development of MND. Tick bites can cause a bacterial infection know as Lyme Disease, which initially causes flu-like symptoms but if left untreated can involve neurological symptoms similar to those seen in MND. However, Lyme Disease also produces a range of other symptoms - it does not just affect motor neurones. Lyme Disease can be treated with antibiotics.

Are there any specific occupations that may increase the risk of developing MND?

  Researchers have investigated a number of occupations where the employees may be at a slightly greater risk of developing MND. These include military service, particularly Gulf War Service; the electrical industry, agriculture and professional sports, particularly football. The factors that may increase the risk of developing MND in these occupations includes exposure to chemicals known as organophosphates, to electrical trauma and to high levels of physical exercise. The evidence ranges from anecdotal reports to published research papers;  unfortunately the results of these research studies often contradict each other and there are no clear conclusions. While all of these factors may contribute to the risk of developing MND, none of them cause the disease on their own.

Are there specific lifestyle factors that contribute to the development of MND?

  There is some evidence that smoking is a risk factor for developing MND. Another risk factor of high levels of physical exercise has anecdotally been suggested. As mentioned above, evidence ranges from anecdotal reports to publication of contradicting research papers. While all of these factors may contribute to the risk of developing MND, none of them cause the disease on their own.

The evidence obtained in these studies has often been circumstantial or conflicting. With such limited information it is not possible to provide advice or guidance to reduce the risk of developing MND.

How can I tell if there really is a cluster of MND cases?

 Some people report that there are clusters of MND in towns or villages near where they live. In order to establish if this is true, there are a number of factors that need to be considered. These include: is there a comparison place or town of a similar size and average age of population etc. How many of the cases are familial compared to sporadic? How do the numbers affected compare in the two places? How many more cases are there in the first town compared to the comparison town? Is an increased number of cases of MND noted because people have an interest in the disease?

As the symptoms of MND develop after the disease process has started on a cellular level, the cause of MND of people living in a given area may not be due to their current lifestyle and environment.

Are more people living with MND today than in the past?

  The term used for the number of people living with a disease at any one time is “prevalence”. The prevalence of MND does appear to be increasing. This can probably be explained by the following factors:
• The population is ageing. We know that older age is associated with an increased risk of MND. It therefore follows that as the number of people in the higher risk age group increases, so will the number of people who get the disease.
• It is possible that diagnosis is improving and that people are getting diagnosed a little sooner (although still not soon enough in many cases). There is still no definitive diagnostic test for MND.
• Once people have been diagnosed with MND, some might be living with the disease for longer than they would have done in the past. One reason for this is the introduction of the drug riluzole, which was approved for the treatment of MND in 2001 and extends survival by a few months on average. Other possible reasons are improvements in multi-disciplinary care and the more widespread use of supportive measures such as non-invasive ventilation and PEG feeding.

Is there any relationship between incidence and race?

 It is currently believed that MND affects all populations equally, with an incidence of roughly two in every 100,000 people. However, most studies into incidence and prevalence of MND – that is, the number of people developing and living with the disease – have mostly involved populations with Western European ancestors.

Where studies have looked at ethnicity, they have suggested that MND is less common amongst black and Asian populations compared to white. More research is needed to establish whether ethnicity itself makes the difference, rather than external factors such as access to health care and shorter life expectancy.

How is information on possible risk factors collected for research?

 The field of research investigating the causes of disease is known as epidemiology. Generally, epidemiology research is approached from two points of view.

Firstly where a possible risk factor has been identified; a larger, more rigorous study would be conducted to explore this risk. The second point of view is looking at a distinct group of people or population where a higher than expected number of people developed MND than could be accounted for by chance. In the second type of study, it is necessary to establish that the numbers of people affected really are higher than can be accounted for by chance, before explanations can be explored.

What epidemiological research is currently being undertaken e.g. investigation into lifestyle, previous history? Are any databases being built?

 To date, research suggests that most forms of MND are likely to involve a combination of a wide variety of genetic and environmental risk factors. Possible environmental “triggers” have been extensively researched over the years - studies have identified possible links with a number of factors but the evidence obtained through this research has often been circumstantial or conflicting. Because of the practical difficulties involved in carrying out epidemiological studies, the majority of current MND research is conducted in the laboratory.

Registries have been established in various countries including Scotland and the Republic of Ireland that aim to record the clinical features and medical care of people with MND. Such registries can be used as a basis for epidemiological investigation into causes of the disease but are primarily used to assess variations in methods of care and their effect on disease outcome. For example, the Irish MND Registry was used to assess the effect of early administration of Riluzole on survival.

What other research into the underlying causes of MND is taking place?

  Thanks to new technology, it has become easier for researchers to look for subtle genetic variations that may make a person more vulnerable to MND. Finding such variations could point to possible treatment strategies and may even provide clues to some of the environmental factors associated with the disease.
Various studies are underway around the world to hunt for these genetic variations, using DNA samples from people with MND. One of these projects, which is partly funded by the MND Association, is using DNA samples from the Association's DNA Bank.

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