SMA is classified into four primary types based on the age of onset and severity: - Type 1 (Werdnig-Hoffmann Disease): The most severe form, appearing within the first six months of life. - Type 2: Intermediate form, presenting between 6 and 18 months of age. - Type 3 (Kugelberg-Welander Disease): Milder form, with symptoms appearing after 18 months and into early adulthood. - Type 4: Adult-onset, usually beginning after age 30.
