Motor neuron disease is a progressive neuro-degenerative disease that causes muscle weakness and gets worse over time.

The condition is typically life-shortening and there is currently no cure.

Professor Luke O’Neill explained on the Show Me the Science podcast that it has the third highest incidence rate among neuro-degenerative diseases, after Parkinson's and Alzheimer's.

“They’re all neuro-degenerative, which means your brain gets attacked and begins to get broken down and different parts of the brain get attacked,” he said.

“In the case of Alzheimer’s, it’s the hippocampus part of your brain that sadly gets attacked.

“In the case of Parkinson’s, it’s the substantia nigra, in the case of motor neuron disease it's the motor neurons.

“Now, the motor neurons are a particular type of nerve cell in our bodies and their job is to control muscles and in particular voluntary muscles.”

Prof O’Neill said that as the motor neurons get attacked by the immune system, a person’s muscles begin to deteriorate.

The neurologist doctor testing knee of male patient by finger pulpation. Image: Oksana Krasiuk / Alamy. 13 March 2018

He also said that while it is believed both environmental and genetic factors play a part in motor neuron disease, it is still not fully understood what causes it.

“Viruses have been found that increase the risk of it and there’s also genetic aspects,” he said.

“I think maybe a one-in-10 cases have a strong genetic component, that means 9-in-10 don’t.

“That means you can carry certain genes, variants of genes, that increase your risk but they aren’t definitive.

“Sometimes with identical twins, one will have it and one won’t, and that means it can’t be fully genetic and there must be these environmental factors that are coming into it.

“They reckon that overall 15% of ALS is genetic and the rest, the genetic component is much less important.”

ALS, amyotrophic lateral sclerosis, is a form of motor neuron disease.

“That means something in the environment will be triggering it and there’s been lots of effort into trying to spot that,” he said.

“Smoking is a risk factor, especially in men.”

However, Prof O’Neill said that most people who smoke don’t develop the disease.

He also said that people who work with heavy metals have a slightly higher risk of developing motor neuron disease.

Main image: Split image showing Luke O'Neill (L) and red DNA strands (R).