A Study to Learn More About the Effects and Long-Term Safety of BIIB141 (Omaveloxolone) in Participants With Friedreich's Ataxia Aged 2 to 15 Years Old

In this study, researchers will learn more about the effects and safety of BIIB141, also known as omaveloxolone or SKYCLARYS®. This drug has been approved, or made available for doctors to prescribe, for people with Friedreich's Ataxia (FA) who are at least 16 years old. But, it is not yet available for children and teens with FA who are younger than 16 years old. The main objective of this study is to learn how BIIB141 works in the body and about its safety in children and teens who are 2 to 15 years old.

The main questions researchers want to answer in this study are:

* How does BIIB141 affect the participants' FA symptoms balance and stability?
* How many participants have medical problems during the study?
* Are there any changes in the participants' overall health during the study?
* Are there any changes in the participants' heart health?
* Are there any changes in how the participants move through puberty? Puberty is the time in someone's life when their body changes from a child to an adult.

Researchers will also learn more about:

- How the body processes BIIB141 in children and teens

This study will be done as follows:

* Participants will be screened to check if they can join the study. The screening period will be up to 28 days, after which participants will check into their study research center.
* There are 2 parts in this study. During Part 1, participants will take either BIIB141 or a placebo once a day.
* In Part 1, participants will take BIIB141 or the placebo in a study research center on Day 1, and then at in-person visits at Week 4, Week 12, Week 26, and Week 52. On all other days, they will take BIIB141 or the placebo at home. Part 1 lasts up to 52 weeks.
* During Part 2, participants from Part 1 will either continue taking BIIB141 or start it if they were taking the placebo. Part 2 will last up to 104 weeks.
* In Part 1, participants will have up to 10 visits to their study research center and a phone call at Week 2. In Part 2, participants will have visits at Weeks 4, 8,12, 26, and every 26 weeks after that until they leave the study, and a phone call at Week 2. There will be a final phone call to check on the participants' health 31 days after their last dose.
* Each participant will be in the study for up to about 3 years

The primary objective of Part 1 randomized controlled trial (RCT) is to evaluate the efficacy of omaveloxolone at Week 52 and the secondary objectives are to evaluate safety of omaveloxolone through Week 52 and the concentration of omaveloxolone after single and multiple dose administration. The primary objective of Part 2 open-label extension (OLE) trial is to evaluate the safety and tolerability of long-term omaveloxolone use and the secondary objective is to evaluate the efficacy of omaveloxolone following long-term use.

Eligibility Criteria:
Part 1 RCT: Key inclusion criteria:

* Diagnosed with genetically confirmed Friedreich's Ataxia (FA), i.e., homozygous for guanine-adenine-adenine (GAA) repeat expansion in intron-1 of the frataxin gene, or GAA repeat expansion in 1 allele and with point mutations or deletions, or other non-GAA expansion mutations in the other allele.
* Symptomatic for FA as reported by the participant and/or the parent/caregiver a. Children 7 to \< 16 years must also have an upright stability score (USS) score of 10 to ≤ 34 at baseline

Part 1 RCT: Key exclusion criteria:

* Glycosylated hemoglobin A1C (HbA1c) \> 11%
* B-type natriuretic peptide (BNP) \> 200 picograms per milliliter (pg/mL) at screening
* Ejection fraction (EF) \< 40% \[based on echocardiogram (ECHO) performed at screening visit\]
* Clinically significant cardiac disease except mild to moderate cardiomyopathy

Part 2 OLE: Eligibility criteria:

* Participants have completed Part 1 RCT of the study and no discontinuation criteria have been met
* Safety and tolerability data from Part 1 RCT are supportive of continuation in the judgement of the investigator

  1. If alanine aminotransferase (ALT), aspartate aminotransferase (AST), and/or total bilirubin (TBL) are \> 2× upper limit of normal (ULN) at the previous visit assessment, Part 2 Day 1 should be delayed until ALT and AST are \< 1.5× ULN and TBL is \< 2× ULN
  2. If BNP is \> 200 pg/mL at the previous visit assessment, Part 2 Day 1 should be delayed until BNP is \< 200 pg/mL
  3. If any other clinically significant laboratory abnormalities are present based on the previous visit assessments, Part 2 Day 1 should be delayed until the abnormalities are resolved
  4. 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.