Mutations in mouse Eda or its human homologue EDA result in hypohydrotic ectodermal dysplasia (HED), a syndrome variably characterized by absent or hypoplastic teeth, hair, sweat glands, sebaceous glands, lacrimal glands, salivary glands, mammary glands and/or nipples, and mucous glands of the bronchial, esophageal and colonic mucosa [14-22]. Here, EDA is linked to hypohidrotic ectodermal dysplasia.