• Genetic confirmation of SMA with homozygous deletion of SMN1 or compound heterozygous deletion/mutation of SMN1

• Two, three, or four copies of SMN2

• Age 5 to 20 years

• Non-ambulatory participants: maximum function sitting or standing with support, never walked independently, still able to sit independently for 5 seconds at screening, with active ankle plantar flexion strength of at least 3 N with hand-held myometry and capable of performing repetitive maximal plantar flexion effort for 120 seconds. HFMSE score at screening between 10 and 45 points.

• Ambulatory participants: minimum function of independent walking, able to walk unassisted a minimum of 100 meters at screening, ankle plantar flexion strength of at least 10 N with hand-held myometry and capable of performing repetitive maximal plantar flexion for 120 seconds. HFMSE score at screening between 40 and 60.

• SMN-directed therapy inclusion:

‣ Current Evrysdi prescription

• Must have Evrysdi prescription through their treating physician but have not yet initiated treatment OR

⁃ Current Spinraza or Zolgensma prescription

• For patients on Spinraza, must have been taking Spinraza for at least 12 months at screening (4 loading and 2 maintenance doses) and following the FDA-recommended dosing schedule

∙ For patients on Zolgensma, must have been dosed at least one year prior to screening

∙ Must have Spinraza or Zolgensma prescription through their treating physician OR

⁃ Changing from Spinraza or Zolgensma to Evrysdi

• For patients on Spinraza, must have been taking Spinraza for at least 12 months at screening (4 loading and 2 maintenance doses) and following the FDA-recommended dosing schedule

∙ For patients on Zolgensma, must have been dosed at least one year prior to screening

∙ Must have voluntarily decided to switch therapies based on discussion with their treating physician

∙ Must have Evrysdi prescription through their treating physician but have not yet initiated treatment OR

⁃ Have never received any SMN-directed therapies