This is an open-label extension (rollover) study designed to evaluate the long-term safety and efficacy of BBP-418 (ribitol) in participants with limb-girdle muscular dystrophy type 2I/R9 (LGMD2I/R9) who have previously participated in Study MLB-01-005 (Fortify).

Participants will receive BBP-418 administered orally at protocol-defined doses and schedules. The study will assess long-term safety through monitoring of adverse events, clinical laboratory evaluations, and other safety assessments. Efficacy will be evaluated using functional measures and other clinical endpoints relevant to LGMD2I/R9.

Participants will be followed for up to 36 months, with a final safety follow-up assessment conducted approximately 30 days after the last dose of study drug.

Inclusion Criteria:

• Completed Study MLB-01-005 on study drug through the final clinic visit (Month 36 or another qualifying end-of-study visit as determined by the Sponsor).
• The participant (or parent/guardian) who signs the ICF understands the study procedures and agrees to participate in the study by giving informed consent (or assent, if <18 years of age).
• Is willing and able to complete all study procedures according to the Schedule of Assessments.
• A WOCBP or a nonsterile male participant must be willing to use an acceptable method of contraception from the time of consent through 30 days after the last dose of study drug in this study.

Exclusion Criteria:

• Has developed clinically significant concomitant disease that would, in the Investigator's opinion, be likely to unfavorably impact study participation, including:

  • Any significant concomitant medical condition, including psychiatric, cardiac, renal, pulmonary, hepatic, or endocrine disease other than that associated with LGMD2I/R9
  • Any other significant laboratory, vital sign, ECG abnormality, clinical history, or finding

• Is pregnant (based on the Baseline / Day 1 pregnancy test result) and/or breastfeeding or planning to conceive children within the projected duration of the study through 30 days after the last dose of study drug in this study.

• Has active suicidal ideation, defined as having a suicide ideation score of 4 (Active Suicidal Ideation with Some Intent to Act, without Specific Plan) or 5 (Active Suicidal Ideation with Specific Plan and Intent) on the C-SSRS at Baseline / Day 1.