Ectodysplasin-A is involved in epithelial-mesenchymal signaling during morphogenesis of ectodermal organs. Isoform 1 of ectodysplasin-A binds only to the receptor EDAR, while isoform 3 binds e, Xenopus/Amphibian,clusively to the receptor , Xenopus/Amphibian,EDAR. Defects in ectodysplasin-A are the cause of ectodermal dysplasia type 1 (ED1), also known as Christ-Siemens-Touraine syndrome or , Xenopus/Amphibian,-linked hypohidrotic ectodermal dysplasia (, Xenopus/Amphibian,LHED). Ectodermal dysplasia defines a heterogeneous group of disorders due to abnormal development of two or more ectodermal structures. ED1 is a disease characterized by sparse hair (atrichosis or hypotrichosis), abnormal or missing teeth and the inability to sweat due to the absence of sweat glands. ED1 is the most common form of over 150 clinically distinct ectodermal dysplasias.