The phenotypes of autosomal dominant and recessive forms of HED, linked to EDAR mutation, are similar to the XLHED phenotype, including hypohidrosis, hypotrichosis and oligodontia, which reflects the common developmental patterns of many ectodermal derivatives.37,20 However, some differences are evident. The gene discussed is EDAR; the disease is hypohidrotic ectodermal dysplasia.