A Study of Lanadelumab to Prevent Hereditary Angioedema (HAE) Attacks in Children

Inclusion Criteria:

• Be a child (male or female) 2 to lesser than (<) 12 years of age at the time ofscreening.
• Documented diagnosis of HAE (Type I or II) based upon both of the following:

1. Documented clinical history consistent with HAE (SC or mucosal, nonpruriticswelling episodes without accompanying urticarial).
2. Diagnostic testing results obtained during screening from a sponsor- approvedcentral laboratory that confirm C1-INH functional level < 40 percent (%) of thenormal level. Participants with functional C1 esterase inhibitor (C1-INH) level 40-50% of the normal level may be enrolled if they also have a complement4 (C4)level below the normal range. With prior sponsor approval, participants may beretested during the baseline observation period if results are incongruent withclinical history or believed by the investigator to be confounded by recentcomplement1 (C1) inhibitor use.

• A historical baseline HAE attack rate of at least 1 attack per 3 months. Note: Inaddition, participants who experience greater than or equal to (>=)1.0 angioedemaattacks per three months during the 12-week baseline observation period and who remaineligible per the inclusion criteria will enter the lanadelumab treatment period.
• Agree to adhere to the protocol-defined schedule of treatments, assessments, andprocedures.
• Have a parent(s)/legal guardian who is informed of the nature of the study and canprovide written informed consent for the child to participate in the study before anystudy-specific procedures are performed (with assent from the child when appropriate).
• Females of childbearing potential must agree to be abstinent or agree to comply withthe applicable contraceptive requirements of this protocol through the duration of thestudy from screening through 70 days after the final study visit.

Exclusion Criteria:

• Concomitant diagnosis of another form of chronic, recurrent angioedema, such asacquired angioedema (AAE), HAE with normal C1-INH, idiopathic angioedema, or recurrentangioedema associated with urticaria.
• Dosing with an investigational drug or exposure to an investigational device within 4weeks prior to screening.
• Be pregnant or breastfeeding.
• Have initiated androgen treatment (eg, stanozolol, danazol, oxandrolone,methyltestosterone, and testosterone) within 2 weeks prior to entering the observationperiod.
• Exposure to angiotensin-converting enzyme (ACE) inhibitors or any estrogen-containingmedications with systemic absorption (such as oral contraceptives or hormonalreplacement therapy) within 4 weeks prior to screening.
• Have any active infectious illness or fever defined as an oral temperature greaterthan (>) 38 degree celsius (°C) (100.4 fahrenheit [°F]), tympanic > 38.5°C (101.3°F) ,axillary > 38°C (100.4°F), or rectal/core > 38.5°C (101.3°F) within 24 hours prior tothe first dose of study drug in treatment period A.
• Have any HAE attack that is not resolved prior to the first dose of study drug intreatment period A.
• Have any of the following liver function test abnormalities: alanine aminotransferase (ALT) > 3upper limit of normal (ULN), or aspartate aminotransferase (AST) > 3ULN, ortotal bilirubin > 2*ULN (unless the bilirubin elevation is a result of Gilbert'ssyndrome).
• Have any condition (any surgical or medical condition) that, in the opinion of theinvestigator or sponsor, may compromise their safety or compliance, preclude thesuccessful conduct of the study, or interfere with interpretation of the results (eg,significant pre-existing illness or other major comorbidity that the investigatorconsiders may confound the interpretation of study results).
• Participant has a known hypersensitivity to the investigational product or itscomponents.