Motor neuron diseases are a group of progressive and ultimately fatal neurodegenerative disorders of the motor system, includeing amyotrophic lateral sclerosis, primary lateral sclerosis, progressive muscular atrophy, and progressive bulbar palsy. Because of the ageing of the population worldwide, the prevalence of motor neuron diseases is expected to increase during the ensuing decades, resulting in an increased proportion of people with functional disability, loss of independence, and reduced life expectancy.