Change from Baseline = Serum LDH levels at Week 25 - Baseline Serum LDH levels. Baseline was the baseline value from the primary Study ACH471-100.

Change from Baseline = Hgb levels at Week 25 - Baseline Hgb levels. Baseline was the baseline value from the primary Study ACH471-100.

Change from Baseline = reticulocyte count at Week 25 - Baseline reticulocyte count. Baseline was the baseline value from the primary Study ACH471-100.

The PNH clone size refers to the percentage of PNH-affected cells versus normal cells within the total cell population. Change from Baseline = PNH clone size at Week 25 - Baseline PNH clone size. Baseline was the baseline value from the primary Study ACH471-100.

Serum AP functional activity was measured by the Wieslab functional immunoassay method. Change from Baseline = Serum AP functional activity at Week 25 - Baseline Serum AP functional activity. Baseline was the baseline value from the primary Study ACH471-100.

Change from Baseline = free Hgb at Week 25 - Baseline free Hgb. Baseline was the baseline value from the primary Study ACH471-100.

An AE was as any untoward medical occurrence associated with the use of a drug in humans, whether or not considered drug related. An SAE was an AE that met at least 1 of the following criteria: resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization for the AE, persistent or significant disability/incapacity or substantial disruption of the ability to conduct normal life functions, congenital anomaly/birth defect (in the child of a participant who was exposed to the study drug), important medical event or reaction. The intensity of an AE was graded according to the Common Terminology Criteria for Adverse Events (CTCAE) Adverse Event Severity Grading Table. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.