Proximal spinal muscular atrophy type 3 (SMA3) is a relatively mild form of proximal spinal muscular atrophy characterized by muscle weakness and hypotonia resulting from the degeneration and loss of the lower motor neurons in the spinal cord and the brain stem nuclei. The disease is Monarch Disease Ontology entry MONDO_0009672 (spinal muscular atrophy, type III). Also known as: Kugelberg Welander Syndrome, Kugelberg-Welander disease, SMA type 3, SMA type III, SMA-III, SMA3, spinal muscular atrophy III, spinal muscular atrophy type 3.