X-linked hypohidrotic ectodermal dysplasia (XLHED), a rare genetic disorder, has been treated successfully with a recombinant ectodysplasin A1 replacement protein, Fc-EDA. The treatment was administered either postnatally or prenatally at 26 weeks of pregnancy. Long-term follow-up showed that prenatal treatment led to the development of sweat glands and the ability to sweat, which are typically absent in untreated individuals with XLHED. The study supports further clinical investigation of EDA1 replacement therapy in utero as a new means of treating genetic disabilities.