Following discussions with the FDA, a Phase 1 safety study is being initiated in X-Linked Hypohidrotic Ectodermal Dysplasia (XLHED)-affected adults to develop safety and exposure data for EDI200 in anticipation of dosing XLHED-affected neonates. Selecting XLHED-affected adults for this study provides a genetic match and biologic relevance to XLHED-affected neonates. Both males and females will be enrolled, providing safety experience with EDI200 that will inform the planned neonate study as well as supportive data for potential future trials of antenatal EDI200 administration.