Key Inclusion Criteria:

• Male or non-pregnant, non-lactating female aged 18 to 55 years, inclusive (Parts 1 and 2), 18 to 65 years, inclusive (Part 3), or 12 to 65 years, inclusive (Part 4)
• Confirmed diagnosis of Netherton syndrome (Parts 3 and 4)
• IGA score of ≥ 3 (Parts 3 and 4) and IASI score of ≥ 16 (Part 4)
• BMI between 18 and 30 kg/m^2, inclusive (Parts 1 and 2)
• Estimated glomerular filtration rate (eGFR) of ≥ 90 mL/min/1.73 m^2 (Parts 1 and 2) or ≥ 60 mL/min/1.73 m^2 (Part 3)
• Agree to follow the protocol contraception requirements from screening until 90 days after the last dose of study drug
• In the opinion of the investigator, expected to adequately comply with all required study procedures and restrictions for the duration of the study