Inclusion Criteria:

• Subjects must voluntarily provide informed consent, approved by an Ethics Committee prior to initiation of any Screening or study-specific procedures.
• At the time of subject enrollment, the subject must have an identified, reliable caregiver, who is willing and able to administer study drug or other study responsibilities if the subject is unable to self-administer study drug or comply with needed study procedures alone. The caregiver must be willing to provide informed consent.
• Subject must provide consent for genetic testing, prior to initiation of any Screening or study specific procedures.
• Adult male or female, between 18 and 80 years of age, at Screening.
• Confirmed diagnosis of Familial ALS or Sporadic ALS.
• Meets probable, laboratory-supported probable, or definite diagnosis of ALS (revised World Federation of Neurology El Escorial criteria) at Screening.
• Onset of muscle weakness or symptomatology consistent with ALS ≤ 36 months before Screening.
• SVC of ≥ 50% (predicted for sex, age, ethnic origin, and height) at Screening.
• Able to swallow solids, including study drug granules, at the time of Screening.
• Subject has no known active Coronavirus Disease 2019 (COVID-19) infection at Screening, does not exhibit signs/symptoms of COVID-19 infection at Screening, and has had no known exposure to a confirmed case of COVID-19 during the 14 days prior to Screening. Subjects who have fully recovered from COVID-19 may be eligible for Screening after they meet the following COVID-19 criteria:
  • Symptomatic subjects: 2 negative viral tests in a row, ≥ 24 hours apart after at least 10 days have passed since recovery, defined as resolution of fever without use of antipyretics and improvement in respiratory symptoms;
  • Asymptomatic subjects: 2 negative viral tests in a row, ≥ 24 hours apart after at least 10 days have passed since prior positive result;
  • Frequency or timing of COVID-19 testing and interval between testing for the above viral clearance criteria may be adjusted to account for epidemiological trends, updated information regarding infectivity, and local/institutional guidelines.
• Subject must be willing to use appropriate contraceptive method from Screening until 30 days after the last dose of study drug. 

Exclusion Criteria:

• History of dementia/severe cognitive problems (ALS-CBS ≥ 11 for the cognitive portion, ≥ 33 for the behavioral portion) at Screening.
• Use of riluzole (Rilutek®) at a dose which has NOT been stable for > 3 months prior to Baseline.
• Use of edaravone (Radicava®) within 1 month prior to Screening or intention of initiating edaravone within 3 months after receiving the first dose of ABBV-CLS-7262.
• Use of any moderate or strong cytochrome (CYP) P450 3A4 (CYP3A4) inhibitor or inducer within 30 days or 5 half-lives (whichever is longer) prior to Baseline and throughout the study.
• Use of any CYP2C8, CYP2C9 and CYP2C19 sensitive substrates within 30 days or 5 half-lives (whichever is longer) prior to Baseline and throughout the study.
• History of clinically significant medical conditions (other than ALS) or any other reason, including any physical, psychological, or psychiatric condition that, in the opinion of the Investigator, would compromise the safety or interfere with the subject’s participation in the study, or would make the subject an unsuitable candidate to receive study drug, or would put the subject at risk by participating in the study.
• History of abnormal screening laboratory or imaging results that, in the opinion of the Investigator, are indicative of any significant cardiac, endocrinologic, hematologic, hepatic, immunologic, infectious, metabolic, urologic, pulmonary, gastrointestinal, dermatologic, psychiatric, renal, neurologic, and/or other major disease that would preclude administration of ABBV-CLS-7262.
• If female, is known to be pregnant, breastfeeding, considering becoming pregnant, or donating/banking eggs during the study or within 30 days or > 5 half-lives (whichever is longer) after the last dose of study drug.
• If male, plans to donate sperm or father a child during the study or within 30 days after the last dose of study drug.
• Known to have received any investigational product within 30 days or 5 half-lives of the drug (whichever is longer) prior to the first dose of study drug or is currently enrolled in another clinical study.
• History of ABBV-CLS-7262 use prior to participation in this study.