Natural History of Duchenne Muscular Dystrophy

Inclusion Criteria:

1. Male

2. 4 to 9 years old inclusive

3. Body-weight ≤ 95th percentile or the BMI scale ≤ 95th percentile (according tovalidated scale in force in country site). Related to the DMD disease:

4. Diagnosis of DMD based upon documented gene testing with detailed genotyping

5. Able to achieve at inclusion and screening visits:

6. NSAA (North Star Ambulatory Assessment) scale > 18 or ≥ 16 if participant isbetween 4 and < 5 years old at screening and:

7. Gowers test < or = 7 sec and/or

8. 6-Minute Walk Test (6MWT): a distance ≥ 350 meters at inclusion visit (M0)

9. Ongoing corticosteroid therapy or initiation of corticosteroid therapy according tostandard of care prior to Screening visit Related to the study protocol and ICH/GCP (Good Clinical Practice) requirements:

10. Signed informed consent by at least one parent or both parents or legal guardianrepresentative(s), when applicable and according to the country regulation

11. Affiliated to or a beneficiary of a Health Care scheme (according to countryregulation)

Exclusion Criteria: Subject will be excluded from enrolment into the study for any of the followingreasons: Related to the DMD disease severity:

9. Cardiomyopathy based on physical/cardiological examination and echocardiography withLeft Ventricular Simpson biplane Ejection Fraction (LVEF) below 55%

10. Respiratory Assistance: need for either a diurnal and/or a nocturnal ventilation

11. Any co-morbidity (ies) and or previous or planned surgical event(s) which mayinterfere with DMD natural evolution and or evaluation of outcomes designed toassess DMD Natural History Related to specific assessments:

12. Muscle testing: inability to cooperate with

13. MRI: metal implants in regions of interest for the study Related to the study protocol and ICH/GCP requirements:

14. Unwilling and/or unable to comply with all the study protocol requirements and/orprocedures

15. Previous inclusion to another clinical trial with an Investigational MedicinalProduct (IMP), within the 3 months or IMP washout period (whichever is longer) priorto the screening visit of the study

16. Previously treated with a gene therapy drug for DMD, such as:

• any AAV mediated gene transfer products or any gene editing products in aclinical trial or in a clinical setting,

• if exons skipping drug was used, the last dose of exon skipping drug within 5half-lives prior to the screening visit

17. Concomitant participation to any other interventional clinical trial