The most reported sub-phenotype of ED is hypohidrotic ectodermal dysplasia (HED; MIM 305100) characterized by hypotrichosis, hypo- or anodontia (abnormal or absent teeth) and hypo-or anhidrosis (reduced or absent sweating) with disease-causing mutations in four genes, namely EDA (MIM 300451), EDAR (MIM 604095), EDARADD (MIM 606603) and TRAF6 (MIM 602355). This evidence concerns the gene EDA and hypohidrotic ectodermal dysplasia.