Study of PTC844 in Participants With Active Rheumatoid Arthritis

Key Inclusion Criteria:

* Historical diagnosis of RA as per the American College of Rheumatology (ACR)/European Alliance of Associations for Rheumatology (EULAR) diagnostic criteria.
* Active RA disease with a threshold of moderate activity or higher as confirmed via DAS28-CRP (score of ≥3.2) at screening.
* Naïve to disease-modifying treatments for RA or have had an inadequate response to background treatment for RA and/or inability to tolerate disease-modifying antirheumatic drugs, as per investigator's discretion.
* Disease-modifying antirheumatic drugs should be stable and unchanged from 30 days prior to the start of the Screening Period and intend to remain stable and unchanged throughout the course of the study.
* CRP of ≥5 milligrams (mg)/liter (L) at screening.

Key Exclusion Criteria:

* Presence of any clinically significant abnormality at screening, or prior or ongoing medical condition (for example, concomitant illness, psychiatric condition), surgical procedure, medical history, or physical findings that, in the investigator's opinion, could adversely affect the safety of the participant or could impair the assessment of study results.
* Participants with Class IV RA.
* Past medical history of blood dyscrasia, bone marrow abnormality and/or suppression, drug induced thrombocytopenia or idiopathic thrombocytopenia, or bleeding diathesis.
* Past medical history of inflammatory joint disease other than RA or fibromyalgia.
* Rheumatoid arthritis onset at \<17 years of age.
* Past medical history of malignancy within 5 years prior to screening, except for nonmelanoma skin cancers cursed via local resection.
* Participant has a known hypersensitivity to any of the ingredients of PTC844 or to any excipients of the study drug.
* Use or intended use of any prescribed disease-modifying treatments for RA within 30 days or 5 half-lives (whichever is longer) before the Screening Period until completion of the Follow-Up Visit, except for methotrexate, low dose prednisone (\<10 mg/day), hydroxychloroquine, or sulfasalazine, which are permitted as established background single-therapy medications.
* Use or intended use of a combination of methotrexate, low dose prednisone (\<10 mg/day), hydroxychloroquine, or sulfasalazine within 30 days or 5 half-lives (whichever is longer) before the Screening Period until completion of the Follow-Up Visit.

Note: Other protocol-defined inclusion/exclusion criteria may apply.