A Study to Find Out How BIIB141 (Omaveloxolone) is Processed in the Body and to Learn More About Its Safety in Participants With Friedreich's Ataxia Aged 2 to 15 Years Old

Recruitment will be limited to the U.S. only as participants will be able to remain on Part 2 of the study until they turn 16 and can access commercially-available drug which is FDA approved for age 16 and above. The part 1 primary objective of the study is to evaluate the pharmacokinetics (PK) of omaveloxolone following administration of a single dose in 3 age cohorts (2 to <7 years, 7 to <12 years, and 12 to <16 years) and secondary objective is to evaluate safety and tolerability of drug. The part 2 primary objective is to evaluate long term safety and tolerability of omaveloxolone.

Part 1:

Inclusion criteria

• Have genetically confirmed FA.
• Have a left ventricular ejection fraction ≥ 40% (based on ECHO performed at Screening Visit).
• During screening, during the treatment period, and until 28 days following administration of the last dose of omaveloxolone, females of childbearing potential must practice at least 1 of the acceptable methods of birth control.
• During screening, during the treatment period, and until 28 days after the last dose of omaveloxolone, fertile males who have female partners of childbearing potential must practice one of the acceptable methods of birth control.

Exclusion criteria

• Have uncontrolled diabetes (haemoglobin A1c [HbA1c] >11.0%).
• Have B-type natriuretic peptide (BNP) level >200 picograms per milliliter (pg/mL) at screening.
• Have a history of clinically significant (CS) left-sided heart disease and/or CS cardiac disease, with the exception of mild to moderate cardiomyopathy associated with FA.
• Presence of outflow tract obstruction defined as a peak instantaneous gradient >50 mmHg (based on ECHO performed at screening).
• Have taken any moderate or strong inhibitors and/or inducers of cytochrome P450 3A4 within the 7 days prior to Day 1 or plan to take during study participation (eg, itraconazole, carbamazepine, phenytoin, ciprofloxacin, grapefruit juice, cannabidiol, fluconazole, fluvoxamine, verapamil, diltiazem).
• Have a history of CS liver disease (eg, fibrosis, cirrhosis, hepatitis), or have clinically relevant deviations in laboratory tests at screening
• Plan to or have participated in any other interventional clinical study within the 30 days prior to Day 1.
• Have a cognitive impairment that may preclude ability to comply with study procedures, in the opinion of the investigator.
• Be unable to comply with the requirements of the study protocol or be unsuitable for the study for any reason, in the opinion of the investigator.
• Have previously documented mitochondrial respiratory chain disease.
• Have a history of thromboembolic events within the past 5 years.
• Plan to or have taken anticoagulant therapy within 30 days prior to Day 1 with the exception of a daily low dose aspirin (up to 81 mg).
• Plan to or have scheduled surgical treatment for scoliosis or foot deformity during the study.
• Have had significant suicidal ideation within 30 days prior to Screening Visit, as per investigator judgment, or any history of suicide attempt.
• For females, be pregnant or breastfeeding.

Part 2:

• No discontinuation criteria have been met.
• Safety and tolerability data from Part 1 are supportive of continuation in the judgement of the Investigator.

In the event of intercurrent illness or other change in health status of the participant, additional Part 1 Screening assessments may be repeated prior to initiation of Part 2, based on the judgement of the Investigator in consultation with the Medical Monitor.

NOTE: Other protocol- defined Inclusion/Exclusion criteria may apply.