 Amyotrophic lateral sclerosis ALS, or motor neuron disease MND, is a rapidly progressive, fatal neurodegenerative condition characterized by loss of upper and lower motor neurons in the brain and spinal cord. The terms ALS and MND are often used inter-changeably to cover the different clinical syndromes, which include upper and lower motor neuron disorder, progressive bulbar palsy, and pseudo-polyneuritic form. 