The gene responsible for XLHED (XL-HED; MIM*305100) is named ectodysplasin-A (EDA; MIM*300451; Xq12-q13), which encodes a protein that is involved in the normal development of ectodermal appendages including hair, teeth, and sweat glands. The gene discussed is EDA; the disease is hypohidrotic ectodermal dysplasia.