The purpose of this study is to evaluate the safety and effectiveness of an experimental drug called ER004 in X-linked hypohidrotic ectodermal dysplasia (XLHED) when given before birth (injected into the amniotic fluid that surrounds a fetus). XLHED is a genetic condition that affects the sweat glands, skin, teeth, and nails. Researchers want to assess the long-term effectiveness of ER004 on sweating ability (sweat volume) in male XLHED patients as the children grow older, focusing on ages 4 and 5. Study procedures will include measuring how much the participants sweat, checking the number of sweat pores, dental check-ups, eye exams, testing saliva production, skin check-ups, and monitoring growth and development.