The time-adjusted HAE attack rate was calculated as number of IC HAE attacks occurring from Week 1 to Week 25, divided by the number of days the participant contributed to the period multiplied by 28 days. An HAE attack was defined as an event with signs or symptoms consistent with an attack in at least 1 of the locations: peripheral angioedema (cutaneous swelling involving an extremity, the face, neck, torso, and/or genitourinary region), abdominal angioedema (abdominal pain, with or without abdominal distention, nausea, vomiting, or diarrhea), laryngeal angioedema (stridor, dyspnea, difficulty speaking, difficulty swallowing, throat tightening, or swelling of the tongue, palate, uvula, or larynx).

An adverse event (AE) was defined as any unfavorable and unintended sign (including an abnormal laboratory finding, for example), symptom, or disease temporally associated with the use of a medicinal (investigational) product, whether or not the AE is considered related to the medicinal (investigational) product. TEAEs were defined as those AEs that either started or worsened in severity on or after the date/time of first administration of study drug in this OLE Study. TEAEs included both serious and non-serious TEAEs.

Clinical laboratory tests including clinical chemistry, hematology, coagulation, complement, inflammatory, urinalysis were performed. The percentage of participants with clinically meaningful changes were reported. Clinical meaningfulness was determined by the investigator.

Vital sign measurements including heart rate, respiratory rate, body temperature, systolic and diastolic blood pressure and pulse pressure were assessed. Percentage of participants with clinically meaningful changes in the vital signs were reported. Clinically meaningfulness was determined by the investigator.

The ECG parameters included ventricular rate, PR interval, QRS duration, QTc, QT corrected using the Fridericia's formula (QTcF), QT corrected using the Bazett's formula (QTcB), and overall interpretation. Percentage of participants with clinically meaningful changes in the ECG parameters were reported. Clinical meaningfulness was determined by the investigator.

Concomitant medications include medications that participants were exposed to on or after the first dose of ISIS 721744 in the OLE study. Percentage of participants who received at least one concomitant medication were reported.

The Week 1 to end of on-treatment period HAE attack rate was calculated for each participant as number of HAE attacks occurring from Week 1 to 28 days after the last dose date divided by the number of days the participant contributed to the period multiplied by 28 days. An HAE attack was defined as an event with signs or symptoms consistent with an attack in at least 1 of the locations: peripheral angioedema (cutaneous swelling involving an extremity, the face, neck, torso, and/or genitourinary region), abdominal angioedema (abdominal pain, with or without abdominal distention, nausea, vomiting, or diarrhea), laryngeal angioedema (stridor, dyspnea, difficulty speaking, difficulty swallowing, throat tightening, or swelling of the tongue, palate, uvula, or larynx).