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Characteristics of SMA Type 1, 2, and 3
| SMA type 1 | ⇒onset between birth and 6 months of age ⇒never able to sit without support |
| SMA type 2 | ⇒onset before the age of 18 months ⇒never able to stand or walk without aid |
| SMA type 3 | ⇒onset after the age of 18 months ⇒develops the ability to stand and walk; may later be lost |
