As previously mentioned, SMA has a wide range of symptom severity, and not all symptoms might be present at the same time or with the same severity. Common SMA symptoms include (2):

Muscle weakness: According to the SMA subtype, this weakness can range from as little as mild weakness diagnosed during adulthood (type 4) up to severe debilitating generalized muscle weakness impairing neonatal development (type 1). Infants with severe SMA typically present with:

• Difficulty swallowing and suckling while breastfeeding
• Difficulty holding up their heads
• Difficulty sitting up
• Difficulty reaching normal developmental milestones

In some milder/intermediate forms of SMA, infants might be able to sit normally, but might not be able to walk

• Muscle Atrophy: Muscle atrophy is defined as wasting of muscles or reduced muscle mass due to the long-term lack of innervation and movement. This process of atrophy increases with age the longer the period of absent innervation and movement.
• Reduced muscle tone (Hypotonia)
• Respiratory problems: This is seen in severe SMA subtypes due to respiratory muscle weakness. Infants with severe SMA could develop aspiration, collapsed lungs, and could have recurrent respiratory infections as a result. Some children might have respiratory failure as a result of this respiratory weakness.
• Reduced lifespan: For people affected with the more severe types, especially type 1, the lifespan of these patients is unfortunately compromised.