Mutations in the ectodysplasin-A receptor (EDAR; MIM*604095; 2q12.3), which forms a ligand-receptor pair with ectodysplasin, and EDAR-associated death domain (EDARADD; MIM*606603; 1q42-q43), which interacts with the death domain of EDAR and links the receptor to signalling pathways downstream, are associated with both autosomal dominant and autosomal recessive forms of HED. The gene discussed is EDAR; the disease is hypohidrotic ectodermal dysplasia.