Spinal muscular atrophy type III is an autosomal recessive neuromuscular disorder characterized by progressive proximal muscle weakness and atrophy affecting the upper and lower limbs. It is classified as the juvenile form, with onset typically in childhood or adolescence. This rare genetic condition involves degeneration of alpha motor neurons in the spinal cord and lower brain stem, leading to muscle weakness that is more pronounced in the legs than in the arms. Symptoms usually appear between 18 months and adulthood, with patients developing the ability to stand and walk, often surviving into adulthood. The disease is caused by mutations in the SMN1 gene on chromosome 5q13.