A Study to Evaluate Efficacy and Safety of AG-348 in Not Regularly Transfused Adult Participants With Pyruvate Kinase Deficiency (PKD)

Inclusion Criteria: * Informed consent; * Male or female, aged 18 years or older; * Documented clinical laboratory confirmation of pyruvate kinase (PK) deficiency, defined as documented presence of at least 2 mutant alleles in the PKLR gene, of which at least 1 is a missense mutation; * Hemoglobin (Hb) concentration less than or equal to 10.0 grams per deciliter (g/dL) regardless of gender (average of at least 2 Hb measurements \[separated by a minimum of 7 days\] during the Screening Period) * Considered not regularly transfused, defined as having had no more than 4 transfusion episodes in the 12-month period up to the first day of study treatment and no transfusions in the 3 months prior to the first day of study treatment; * Received at least 0.8 mg oral folic acid daily for at least 21 days prior to the first dose of study treatment, to be continued daily during study participation. * Adequate organ function; * Women of reproductive potential, have a negative serum pregnancy test; * For women of reproductive potential as well as men with partners who are women of reproductive potential, be abstinent as part of their usual lifestyle, or agree to use 2 forms of contraception, 1 of which must be considered highly effective, from the time of giving informed consent, during the study, and for 28 days following the last dose of study treatment for women and 90 days for men following the last dose of study treatment; * Willing to comply with all study procedures for the duratio…