Spinal muscular atrophy type I is a severe neuromuscular disorder caused by mutations in the SMN1 gene, leading to degeneration of motor neurons in the spinal cord and brain stem. Symptoms typically appear before 6 months of age and include progressive muscle weakness, poor muscle tone, feeding difficulties, and respiratory problems. Patients with SMA type I never achieve the ability to sit without support. The disease is inherited in an autosomal recessive manner and can be diagnosed through genetic testing. SMA type I is characterized by symmetrical muscle weakness and atrophy, affecting voluntary muscles, with the most severe form being Werdnig Hoffmann disease. If left untreated, SMA type I is the most common genetic cause of infant death.