• Participants with a clinical diagnosis of Type 3 SMA.

• Participants who are ambulatory, defined as being able to walk at least 50 metres without walking aids at screening during the 6-minute walk test.

• Participant with genetic confirmation of diagnosis (e.g., homozygous deletion or compound heterozygous deletion and mutation of survival of motor neuron 1 gene \[SMN1\])

• Participant with 3 to 5 copies of survival of motor neuron 2 gene \[SMN2\].

• Participant has a body mass index (BMI) within the range 19-35 kg/m2 (inclusive).

• Participant is male or female.

• Contraceptive use by men and women must be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.

• Participant is capable of giving signed informed consent which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in the protocol.