CARDINALS

INTERVENTION: Subjects will receive oral BID of either placebo or active drug during the 24‐week treatment period. For the optional long‐term treatment period of 28 weeks, all subjects will receive 250 mg of PTC857 oral BID. For subjects who do not proceed to the long‐term study, treatment will be discontinued and a follow‐up telephone consultation will be conducted 4 weeks (Allowance 3 days) after the last dose of study drug. CONDITION: amyotrophic lateral sclerosis ; amyotrophic lateral sclerosis ALS PRIMARY OUTCOME: The primary endpoint is the change from baseline in ALS Functional Rating Scale‐Revised (ALSFRS‐R) in the Intent‐To‐Treat 1 (ITT1) Analysis Set after 24 weeks of treatment. SECONDARY OUTCOME: 1. Safety and tolerability of PTC857; 2. Subject's respiratory function; 3. Subject's motor/limb function and medullary function; 4. Neuropsychological functioning of subjects; 5. Subject survival period; 6. Subject's quality of life; 7. Pharmacokinetics of PTC857 INCLUSION CRITERIA: 1. Males or females aged between 18 and 80 years with a body mass inde Xbetween 18 and 35 kg/m2 at the time of the initial Screening Visit 2. Onset of the first symptom leading to the diagnosis of ALS is within 24 months at the time of the initial Screening Visit 3. Revised El Escorial criteria of either: (i) Clinically definite ALS (ii) Clinically probable ALS 4. A total ALSFRS‐R score of at least 34 at the start of the Screening Period