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

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

Associations

Associations often occur with mutations in the TP63 gene.

• midfacial defects, mainly cleft lip and palate
• EEC syndrome (ectodermal dysplasia, ectrodactyly, and clefting) ³
• AEC syndrome (ankyloblepharon, ectodermal dysplasia, and cleft lip and/or palate)
• Rapp-Hodgkin syndrome

Pathology

Genetics

Almost 200 distinct disorders of the ectodermal dysplasia spectrum 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

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 categorized into a number of subgroups.

Clinical presentation

• sparse hair (atrichosis or hypotrichosis) that is light in color, 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 overheating, and may rarely be fatal
• 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

Treatment and prognosis

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

Differential diagnosis

Clinical differential considerations for ectodermal dysplasia include:

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