Key Inclusion Criteria: 1. Capable of, and willing to, provide written informed consent and comply with study procedures, including visits to the study site and visit requirements 2. Male or female ≥ 18 years of age 3. Has a diagnosis of ALS according to the El Escorial criteria (Brooks, et al., 2000) (probable, laboratory results supported; clinically probable, clinically definite) 4. Confirmed absence of ALS caused by FUS and SOD1 gene mutations confirmed by laboratory tests. 5. A maximum of 18 months since first appearance of weakness (e.g., limb weakness, dysarthria, dysphagia, shortness of breath) 6. Erect (seated) SVC % predicted ≥ 80% at Screening 7. Treatment Research Initiative to Cure ALS (TRICALS) risk score between -2 and -6 at Screening 8. Has a reliable caregiver/partner/legal representative willing and able to support the participant in participation in the study and to give informed consent on behalf of the participant in the case that disease progression prevents the participant of giving consent (local legal rules will apply). 9. Treatment with riluzole and/or edaravone is allowed if treatment was started and has remained at a stable dose for at least 2 weeks (riluzole) or one treatment cycle (edaravone) before the Screening visit 10. Women of childbearing potential (WOCBP) and male participants with female partners who are WOCBP must agree to use highly effective contraception during and after the study. WOCBP cannot be pregnant or breastfeeding 11. Women of nonchildbearing potential must be post-menopausal or surgically sterile (e.g. hysterectomy, bilateral tubal ligation, ovaries removed) Key Exclusion Criteria: 1. Diagnosis of a significant CNS or peripheral nervous system disease other than ALS that may be a cause for the participant's ALS symptoms or may confound study objectives 2. Spinal, cervical, or brain MRI/MRA indicating clinically significant abnormality 3. Presence of tracheostomy and feeding tube at Screening 4. Contraindications to corticosteroid use (e.g. due to osteoporosis, uncontrolled blood pressure, diabetes or cholesterol). 5\. Significant concomitant disease or condition within 6 months of Screening that could pose an unacceptable safety risk to the participant or interfere with the participant's ability to comply with study procedures, e.g. heart disease, uncontrolled diabetes, liver disease, autoimmune diseases needing strong immune-suppressing drugs, cancer, etc or a current psychiatric diagnosis. 6\. Clinically significant abnormalities in laboratory test results at Screening for example poor liver or kidney function, abnormal clotting or infections such as Hepatitis or HIV 7\. Use of blood thinners (e.g., warfarin, heparin, and novel oral anticoagulants) and being unable to safely stop them before certain study procedures. 8\. Contraindications to imaging methods MRI, MRA, CT due to claustrophobia and/or intolerance to contrast agents. 9\. Contraindications to general anaesthesia (GA) or deep sedation 10 Positive test for illegal drugs (except prescribed medications or permitted medicinal/recreational marijuana if used responsibly) 11\. Generally frail or if the Investigator deems participation in the study would not be in the best interest of the participant or is likely to prohibit further participation during the study Other protocol-defined inclusion/exclusion criteria may apply \-