spinal muscular atrophy Proximal spinal muscular atrophy type 3 Kugelberg-Welander disease SMA-III MESH:D014897 DOID:12376 ICD10:G12.1 OMIM:253400 SMA type 3 SNOMEDCT:54280009 NCIt:C118847 orphanet Proximal spinal muscular atrophy type 3 (SMA3) is a relatively mild form of proximal spinal muscular atrophy (see this term) 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. Juvenile spinal muscular atrophy SMA3 Genetic motor neuron disease