Extension Study of AG-348 in Adult Participants With Pyruvate Kinase Deficiency Previously Enrolled in AG-348-006 or AG348-C-007

Inclusion Criteria:

- Be willing and able to comply with study visits and procedures;

- Have signed written informed consent prior to participating in this extension study;

- Have completed either antecedent study AG348-C-006 or AG348-C-007 through the Part 2
Week 24 Visit;

- Cohorts 2 and 3: Have demonstrated clinical benefit from AG-348 treatment in the
antecedent study, in the opinion of the Investigator;

- For women of reproductive potential, have a negative pregnancy test at the
Screening/Day 1 Visit;

- 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 (both men and
women) following the last dose of study drug.

Exclusion Criteria:

- Have a significant medical condition (including clinically significant laboratory
abnormality) that developed during his/her antecedent AG- 348 study that confers an
unacceptable risk to participating in this extension study, that could confound the
interpretation of the study data, and/or that compromises the ability of the
participant to complete study visits and procedures.

- Are currently pregnant or breastfeeding.

- Have a splenectomy scheduled during the study treatment period.

- Meet the withdrawal criteria of his/her antecedent AG-348 study at the Screening/Day 1
Visit of this study.

- Are currently receiving medications that are strong inhibitors of cytochrome P450
(CYP)3A4, strong inducers of CYP3A4, strong inhibitors of P-glycoprotein (P-gp), or
digoxin (a P-gp sensitive substrate medication) that have not been stopped for a
duration of at least 5 days or a timeframe equivalent to 5 half-lives (whichever is
longer) prior to Screening/Day 1 of this extension study.

- Have received anabolic steroids, including testosterone preparations, within 28 days
prior to Screening/Day 1 of this extension study.

- Have received hematopoietic stimulating agents (eg, erythropoietins, granulocyte
colony stimulating factors, thrombopoietins) within 28 days prior to Screening/Day 1
of this extension study.

- Have exposure to any investigational drug other than AG-348, device, or procedure
within 3 months prior to Screening/Day 1 of this extension study.