A motor neuron disease (MND) is any of several neurological disorders that selectively affect motor neurons, the cells that control voluntary muscles of the body. They include amyotrophic lateral sclerosis (ALS), primary lateral sclerosis (PLS), progressive muscular atrophy (PMA), progressive bulbar palsy (PBP) and pseudobulbar palsy; spinal muscular atrophies are also sometimes included in the group. They are neurodegenerative in nature and cause increasing disability and eventually, death.