One in every 347 men and 436 women can be expected to develop motor neurone disease (MND) during their lifetime, a new Irish study into the genetics of the condition has found.

According to the study's senior author, consultant neurologist, Prof Orla Hardiman, this latest study "will help us to find new treatments for this devastating condition".

MND is the name given to a group of diseases in which there is progressive degeneration of the motor neurones in the brain and spinal cord. Motor neurones are the nerve cells that control muscles, and their degeneration leads to weakness and wasting of the body's muscles.

This causes an increasing loss of mobility in the limbs and difficulties with speech, swallowing and breathing. Death usually occurs within an average of two to three years.

There are over 350 people living with MND in Ireland and one person is newly diagnosed here every three days.

Researchers at Trinity College Dublin (TCD) set out to assess the impact of genetics on the condition. In the largest study of its kind, they looked at 1,117 people who had been diagnosed with MND.

They found that genetics account for about 52% of the risk of developing MND. This means that other important factors or exposures must also be present for the condition to develop. As a result, the overall risk to other family members of developing MND remains low.

"The main message is that genetic and non-genetic factors contribute equally to one's risk of developing MND. The fact that 50% of the risk is found within our genes supports our ongoing search to identify the many interacting genes that contribute to the causes of motor neurone disease," commented the study's lead author, Dr Marie Ryan.

The researchers also looked at those who carried known genetic mutations that are linked with MND. In around 10% of people with the condition in Ireland, it is caused by an abnormality in one gene - C9orf72. This gene runs in families.

The study found that those who carried an abnormal copy of this gene and went on to develop MND, were more likely to have inherited it from their mothers.

"While different inheritance patterns based on who transmits the gene have been reported in other neurological disorders, this is the first time this kind of inheritance pattern has been discovered among those with motor neurone disease," Dr Ryan noted.

Prof Hardiman said that the study will help scientists to find new treatments "by pursuing a precision medicine approach".

"We have already found that MND can cluster with other conditions including dementia, schizophrenia, bipolar disorder, autism and addiction disorders in around 30% of families.

"This means that multiple genetic factors working together are likely to play an important role in developing MND. Finding how these genes interact will help us to find new and better treatments," she said.

Details of these findings are published in the medical journal, JAMA Neurology.