A Pilot Study of the Efficacy and Safety of Dupilumab Versus Placebo in Patients With Netherton Syndrome

Inclusion Criteria: * Adult patients affiliated to a social insurance protection regimen. * Clinical diagnosis of NS (7) (trichorrhexis invaginata, extensive scaling, skin inflammation, allergic manifestations) and absent or marked reduction of LEKTI staining. * Moderate to severe forms: NASA (Netherton Area Severity Assessment score) score ≥ 5/12 at inclusion. * Patients able to understand the study procedures including the ability to complete patient-based self-assessment questionnaires. * Patients who agree to sign the written informed consent. Exclusion Criteria: * Hypersensitivity to dupilumab or its excipients. * Modification of the usual treatment (emollients and topical corticosteroids used on a regular basis) within 2 weeks before inclusion. * Treatment with topical calcineurin inhibitors 1 week before inclusion. * Treatment with oral immunosuppressant (including cyclosporine, methotrexate, azathioprine, mycophenolate mofetil), oral retinoids (acitretin, alitretinoin, isotretinoin) or phototherapy within 4 weeks before inclusion. * Treatment with immunomodulating biologics (Tumor Necrosis Factor (TNF) inhibitor) 16 weeks before inclusion. * Treatment with another investigational drug within 8 weeks before inclusion. * Treatment with a systemic antibiotic within 2 weeks before inclusion. * Active skin infection requiring the use of a systemic therapy within 2 weeks before the inclusion. * Any other condition that according to the investigator will impair the ability to evaluate treatment effect. * Known or suspected history of immunosuppression, including history of invasive opportunistic infections (e.g., tuberculosis, histoplasmosis, listeriosis, coccidioidomycosis, pneumocystis, aspergillosis). * Current infections including infection with helminthes. * Pregnant or breastfeeding women, or women planning to become pregnant or breastfeed during the study. Women of childbearing age, potentially sexually active, and unwilling to use adequate birth control methods. * Mental or physical incapacity to fill in the questionnaires.