The ectodermal dysplasias are inherited disorders that involve defects in the hair, nails, sweat glands and teeth. When a person has at least two types of abnormal ectodermal features—for example, malformed teeth and extremely sparse hair—the individual is identified as being affected by ectodermal dysplasia.
The conditions are a remarkably diverse group of disorders which may also affect other parts of the body. The ectoderm contributes to the formation of the lens of the eye, parts of the inner ear, the fingers and toes, and nerves, among others. Therefore, ectodermal dysplasia may cause these parts of the body to develop abnormally.
There are more than 150 different types of ectodermal dysplasias. Symptoms range from mild to severe. Only in rare cases does ectodermal dysplasia affect lifespan and very few types involve learning difficulties.
Teeth may be missing, pointed, widely spaced, or prone to cavities because of defective enamel. Dental treatment is almost always necessary and children may need dentures as early as two years of age. Multiple denture replacements are needed as the child grows, and dental implants may be an option in adolescence. Orthodontic treatment may also be necessary.
Scalp and body hair may be absent, sparse, thin, very light in color, excessively brittle, curly, or even twisted. Wigs can mask defects in hair development.
Fingernails and toenails may be thick or thin, abnormally shaped, discolored, ridged, slow-growing, or brittle. The cuticles may be prone to infections.
Many individuals affected by ectodermal dysplasia cannot perspire. Their sweat glands may function abnormally or may not have developed at all. Without normal sweat production, the body cannot regulate temperature properly. Therefore, overheating is a common problem, especially during hot weather. Access to cool environments is important.
Skin may be thin and pale, dry, scaly and easily irritated, prone to rashes, infections and sunburn, or thick over the palms and sole. Skin erosions or open areas of the skin on the scalp, hands and feet are possible. Care must be taken to prevent cracking, bleeding, and infection.
In some cases, problems occur with other parts of the body which also develop from the ectoderm: dryness of the eye, sensitivity to sunlight, cataracts, vision defects, hearing problems, respiratory infections, cleft lip and/or palate, or missing fingers and toes.
ED can be classified by inheritance (autosomal dominant, autosomal recessive, and X-linked) or by which structures are involved (hair, teeth, nails, and/or sweat glands).
There are several different types with distinct genetic causes:
- Hay-Wells syndrome, Rapp-Hodgkin syndrome and EEC syndrome are all associated with TP63.
- Hypohidrotic ectodermal dysplasia can be associated with EDA, EDAR, and EDARADD
- Margarita Island ectodermal dysplasia is associated with PVRL1
- Ectodermal dysplasia with skin fragility is associated with PKP1
- Clouston's hidrotic ectodermal dysplasia is associated with GJB6
- Naegeli syndrome/Dermatopathia pigmentosa reticulariss is associated with KRT14
- Pachyonychia congenita is caused by multiple keratins
- Focal dermal hypoplasia is associated with PORCN
- Ellis–van Creveld syndrome is associated with EVC
- Palmoplantar ectodermal dysplasia refers to several different conditions selectively affecting the hands and feet