Ectodermal dysplasia (ED) refers to a heterogeneous group of genetic disorders that cause abnormal ectoderm development. The effect is a non-progressive defect in the development of two or more tissues derived from embryonic ectoderm.
ED is rare with an estimated prevalence of 1:17,000. It can occur in any race but is most commonly seen in Caucasians.
More than 192 distinct disorders have been described:
- the most common form, which occurs in 80% of ectodermal dysplasias is X-linked recessive hypohidrotic ectodermal dysplasia (Christ-Siemens-Touraine syndrome), where incidence in male is estimated at 1:100,000 births and is inherited through female carriers (carriers-incidence is 17.3:100,000 women) 1; position of the gene at Xq12-q13.1 (XLHED-gene) 2
- the remaining 20% have no sexual predilection
Associations often occur with mutations in theTP63 gene.
- midfacial defects, mainly cleft lip and palate
- EEC syndrome (ectodermal dysplasia, ectrodactyly, and clefting) 3
- AEC syndrome (ankyloblepharon, ectodermal dysplasia, and cleft lip/palate)
- Rapp-Hodgkin syndrome
There are four primary ectodermal dysplasia (ED) defects:
- ED1: trichodysplasia (hair dysplasia)
- ED2: dental dysplasia
- ED3: onychodysplasia (nail dysplasia)
- ED4: dyshidrosis (sweat gland dysplasia)
These are further categorised into a number of subgroups.
- sparse hair (atrichosis or hypotrichosis) that is light in colour, coarse and excessively brittle
- abnormal peg-shaped or pointed teeth, particularly the upper incisors and cuspids which are typically conical
- missing teeth (anodontia or hypodontia) and taurodontism of deciduous molars
- inability to sweat due to lack of sweat glands (anhidrosis or hypohidrosis) this causes intolerance to heat and over heating can rarely be a cause of death
- fingernails and toenails may be absent, thick, abnormally shaped, discoloured, ridged, slow growing, or brittle
- lack of breast development
- absent fingers or toes
- recurrent infections
- missing ears and hearing difficulties
People with ectodermal dysplasia have normal intelligence, life expectancy and can lead a full and productive lives.
Clinical differential considerations include:
- 1. Spfaer JA. A dental approach to carrier screening in X linked hypohidrotic ectodermal dysplasia. J. Med. Genet. 1981;18 (6): 459-60. J. Med. Genet. (link) - Free text at pubmed - Pubmed citation
- 2. Kere J, Srivastava AK, Montonen O et-al. X-linked anhidrotic (hypohidrotic) ectodermal dysplasia is caused by mutation in a novel transmembrane protein. Nat. Genet. 1996;13 (4): 409-16. doi:10.1038/ng0895-409 - Pubmed citation
- 3. Okamura E, Suda N, Baba Y et-al. Dental and maxillofacial characteristics in six Japanese individuals with ectrodactyly-ectodermal dysplasia-clefting (EEC)syndrome. 2012;doi:10.1597/11-123 - Pubmed citation