Group of rare genetic diseases affecting the organs originating from the ectoderm: skin, sweat glands, eyes, lungs, teeth, hair, digestive system. About 150 different types of ectodermal dysplasias are currently described.

Different categories have been created to try to classify the ectodermal dysplasias according to the involved ectodermal derived tissues:derivatives:

• ED1: trichodysplasia: hair damage
• ED2: dental involvement: hypo- or anodontia
• ED3: onychodysplasia: nail damage
• ED4: dyshidrosis: involvement of the sweat glands

Different subgroups can thus be defined according to the association of the above-mentioned categories:

• Subgroup 1-2-3-4: anhydrotic ectodermal dysplasia, EEC syndrome, AEC syndrome (Hay-Wells)
• Subgroup 1-2-3: hydrotic ectodermal dysplasia
• Subgroup 1-2-4
• Subgroup 1-2
• Subgroup 1-3
• Subgroup 1-4
• Subgroup 2-3-4
• Subgroup 2-3
• Subgroup 2-4
• Subgroup 3
• Subgroup 4