Natural History of Netherton Syndrome

Inclusion criteria \[for Part 1 and Part 2\] 1. Confirmed diagnosis of NS by at least one of the following: * Genetic testing of mutations in Serine Protease Inhibitor of Kazal Type 5 (SPINK5); * Absence or major deficiency of the protein Lympho-Epithelial Kazal-Type-Related Inhibitor (LEKTI) in skin biopsy; * Clinical assessment (signs and symptoms). 2. Provision of consent or assent (i.e., by parent or legal guardian) as required by local regulations: * \[Part 1\] to authorise access to existing medical records for study data collection; * \[Part 2\] to participate in the longitudinal 52-week evaluation of disease severity and clinical outcome assessments. \[for Part 2 only\] 3. Not participating in a clinical trial at the time of study enrolment for Part 2. Exclusion criteria \[for Part 1 and Part 2\] 1. Patient who has died prior to 2002. 2. Patient whose last known survival status is dated prior to 2002 (i.e., patient has been lost to clinical follow-up since 2002).