Ectodysplasin-A (EDA) is a trimeric type II membrane protein related to the tumor necrosis factor (TNF)-related ligand family. Activation of the NF-kappaB pathway by the tumor necrosis factor receptor superfamily member EDAR (EDAR) and its downstream adaptator EDAR-associated death domain (EDARADD) is essential for the development and regulation of hair follicles, teeth, exocrine glands and other ectodermal structures (Yan et al. 2002). EDA isoform 1 specifically binds EDAR. A small number of hypohidrotic ectodermal dysplasias (HEDs) are caused by mutations in EDARADD (Chassaing et al. 2010).