A Study to Explore Safety, Pharmacokinetics, and Early Clinical Signal of Efficacy of DS-2325a in Patients With Netherton Syndrome

Inclusion Criteria: * Male or female participants aged 18 to 65 years with clinical diagnosis of NS including at least 3 out of the 4 following clinical criteria: * Neonatal erythroderma * Bamboo hair and/or alopecia * Chronic atopy specified as food allergy and/or asthma and/or rhino-conjunctivitis and/or eczema for at least 2 years * Ichthyosis linearis circumflexa or scaling erythroderma or equivalent * Immunohistochemistry documentation of absence of LEKTI in the skin or confirmed SPINK5 gene mutations * NS involvement of ≥20% of Body Surface Area (BSA) * Patients must give written informed consent to participation in the study prior to Screening * Participants must be willing and able to understand and comply with study requirements * Participants must be willing to have skin tape harvests collected from lesional and nonlesional skin areas Exclusion Criteria: * Any skin disease that may interfere with the diagnosis or evaluation of NS * Any infection requiring treatment with systemic antibiotics, antivirals, antiparasitics, or antifungals within 2 weeks before Screening visit * Concomitant systemic disease not controlled by treatment. Stability for 3 months prior to Screening is required * Kidney or liver disease with significant impairment of organ function (creatinine clearance \<30 mL/min, calculated using the Cockcroft-Gault Equation, and Child-Pugh Class C; ALT and AST \>2 × ULN range; total bilirubin \>1 × ULN). * Concomitant disease or condition that m…