Ectodermal dysplasia

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. 

Epidemiology

ED is rare with an estimated prevalence of 1:17,000. It can occur in any race but is most commonly seen in Caucasians.

Pathology

Genetics

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

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 

Classification

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.

Clinical featurespresentation

• 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

Prognosis

People with ectodermal dysplasia have normal intelligence, life expectancy and can lead a full and productive lives. 

Differential diagnosis

Clinical differential considerations include:

• alopecia areata
• aplasia cutis congenita
• focal dermal hypoplasia syndrome
• incontinentia pigmenti
• Naegeli-Franceschetti-Jadassohn syndrome
• pachyonychia congenita