• \<2 years of age at the time of informed consent

• Confirmed diagnosis of 5q-autosomal recessive SMA, including genetic confirmation of homozygous deletion or compound heterozygosity predictive of loss of function of the Survival of Motor Neuron 1 (SMN1) gene

• Confirmed presence of two SMN2 gene copies as documented through laboratory testing

• Administration of onasemnogene abeparvovec pre-symptomatically or post-symptomatically

• Has received onasemnogene abeparvovec for SMA no less than 13 weeks prior to enrollment

• If treated with risdiplam prior to onasemnogene abeparvovec, risdiplam treatment must not have exceeded 3 weeks and must be discontinued 1 day prior to onasemnogene abeparvovec administration.

• In the opinion of the investigator, has demonstrated a plateau or decline in function post-gene therapy (with a duration of 26 weeks or less) documented by 2 individual time points in the functions as follows: swallowing AND one additional function/ability (respiratory, motor function, other) per appropriate expectation.