Evaluation of Topical ATR12-351 in Adults With Netherton Syndrome

Inclusion Criteria: * Adults ≥18 years of age * Confirmed mutation of the serine protease inhibitor of Kazal type 5 (SPINK5) gene * Involvement of ≥20% of body surface area with skin changes consistent with Netherton syndrome Exclusion Criteria: * Use of biologic therapies, antibiotics, antihistamines, corticosteroids, retinoids, disease-modifying antirheumatic drugs (DMARDs), immunosuppressive agents, phosphodiesterase-4 (PDE4) inhibitors, topical calcineurin inhibitors, or topical Janus kinase (JAK) inhibitors * Open wounds or extensive areas of excoriation precluding identification of appropriate application sites in the Investigator's judgment * Concurrent involvement in any other clinical study/expanded access program with an investigational drug or device or has participated in a clinical study within 30 days prior to the screening visit * Residing with an immunocompromised person in the same dwelling from the baseline visit through 2 weeks after the treatment period * History of ultraviolet phototherapy within the planned treatment area 4 weeks prior to baseline