X-linked hypohidrotic ectodermal dysplasia (XLHED; #MIM 305100), a rare hereditary disease characterized by missing or dysplastic skin appendages and teeth, is caused by deficiency of the signaling protein ectodysplasin A1 (EDA1) during early development (Mikkola and Thesleff, 2003). This evidence concerns the gene EDA and X-linked hypohidrotic ectodermal dysplasia.