Inclusion Criteria:

• The participant must have read, understood, and signed an Institutional Review Board (IRB)- approved Informed Consent Form and must be willing and able to comply with study procedures and instructions
• Aged ≥ 12 years of age at the time of informed consent/assent
• Documented clinical diagnosis of HHD with confirmed ATP2C1 variant by genetic testing
• A negative pregnancy test prior to initial dose for subjects of child-bearing potential
• If taking systemic therapies, subject must be on a stable dosing regimen 1 month prior to Screening and throughout the 12-week treatment period
• An acceptable form of contraception must be taken from the first dose (Week 1) through 3 months after the last dose of IP for subjects of childbearing potential

Exclusion Criteria:

• Participation in another clinical study or treatment with an investigational agent 30 days or 5 half-lives, whichever is longer, prior to initial dosing in Week 1
• Participant who is pregnant or nursing
• Participant who is unwilling to comply with contraception requirements per protocol (for subjects of child-bearing potential)
• Participant who is known to be non-compliant or is unlikely to comply with the requirements of the study protocol, in the opinion of the Investigator
• Presence of any dermatologic or systemic condition that might hinder the efficacy of the study treatment or its evaluation, could possibly interfere with the interpretation of study results, or could be judged by the Investigator to be incompatible with the study visit schedule or conduct