What causes MND is the biggest and possibly the most frequently asked question by researchers.
Most cases of MND occur for no apparent reason, in people without a family history of the disease. This is known as sporadic MND. In about 5–10% of cases however, family history of the disease indicates that inherited gene mutations cause the condition. This is called familial MND.
There are many theories about the causes of MND. These include exposure to environmental toxins and chemicals, infection by viral agents, immune-mediated damage, premature aging of motor neurons, loss of growth factors required to maintain motor neuron survival and genetic susceptibility.
Scientists believe that the randomly occurring sporadic form of MND is likely to be caused by many small contributory risk factors, including subtle genetic and environmental influences, that in combination may 'tip the balance' towards someone developing the disease.
Exposure to environmental factors that might contribute to the development of sporadic MND has been widely studied. Studies have identified possible links with prior exposure to agricultural chemicals, pesticides and a variety of heavy metals, high levels of exercise and exposure to mechanical and/or electrical trauma. However, the evidence obtained in these studies has often not been convincing and there are no clear conclusions at this time.
Researchers worldwide continue to try and find out what causes MND with the ultimate goal of discovering how to stop, slow down or prevent the disease.
It is not yet possible to provide advice on how to reduce the risk of developing MND.
At the 2018 Australasian Symposium on MND, Professor Ammar Al-Chalabi, director of King's MND Care and Research Centre in the UK, described some of the remarkable progress we have made in understanding the causes of MND - and why some aspects remain a mystery.