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Ectodermal Dysplasia (ED) is a rare group of inherited disorders. It was originally described by Charles Darwin in 1875. The disorders arise from disturbances in one or more ectodermal structures and their accessory appendages. The absence, or deficient function, of at least two derivatives of the ectoderm constitutes a form of ectodermal dysplasia. Each combination of defects represents another type of ectodermal dysplasia and has a specific name.

Individuals affected with ectodermal dysplasia have at least two of the following clinical manifestations:

  • Absent or malfunctioning sweat glands. Temperature regulation can be dysfunctional and lead to hyperthermia.

  • Dental anomalies, including missing or underdeveloped teeth.

  • Varying degrees of alopecia resulting from defective hair follicles.

  • Malformed or missing fingers or toes.

  • Malformed fingernails and toenails.

  • Cleft lip/palate, deficient saliva, hearing and visual defects, and inadequate eye fluids and tears.

  • Neurologic and respiratory abnormalities may be present.

Classification

The first classification system for EDs was proposed by Pinheiro and Freire-Maia in 1982. The patients are classified into subgroups based on the presence or absence of the following: (1) trichodysplasia, (2) dental abnormalities, (3) onychodysplasia, and (4) dyshidrosis.

At least 180 different forms of ectodermal dysplasia have been identified in the literature until now. The 10 most common forms listed by the National Foundation of Ectodermal Dysplasias (NFED; https://www.nfed.org/blog/top-10-most-common-ectodermal-dysplasias/) are:

  • Ectodermal Anomalies, Unspecified Type: Ectodermal dysplasias (EDs) are a heterogeneous group of disorders characterized by developmental dystrophies of a wide array of ectodermal structures, most frequently involving hypohidrosis, trichodysplasia, onychodysplasia, and hypodontia or anodontia. Without a specific diagnosis, it is more difficult to offer specific medical help particularly for inheritance purpose. This said, patients can still be treated.

  • X-linked Hypohidrotic Ectodermal Dysplasia (XLHED; Anhidrotic Ectodermal Dysplasia; Christ-Siemens-Touraine Syndrome): Characterized by hypohidrosis (inability to sweat when exposed to warm environment or during exercise), hypotrichosis, hypodontia or teeth that are malformed. The classical features most common to all subjects affected with this condition include a facial appearance with thin, dark skin beneath the eye with extra folds or wrinkles, a depressed “saddle” nose, small narrow jaw, and small pointed teeth. It is inherited as an X-linked recessive disease.

  • Hypohidrotic Ectodermal Dysplasia (HED): Rare inherited multisystem ectodermal dysplasia medical disorder. As with most of these conditions, individuals affected present with clinical features involving the hair, teeth, nails, sweat glands, and/or skin. Anhidrosis or hypohidrosis, heat intolerance, and fever are essential to the diagnosis. Hypotrichosis, hypodontia, and the periorbital skin are often hyperpigmented and prematurely aged. Respiratory problems, such as asthma, recurrent lung infections amongst others are often present in children. HED is usually inherited as an X-linked recessive genetic trait and is caused by a mutation in the ectodysplasin-A (EDA) gene. The disorder is fully expressed in males only. The incidence is established around 1 in 5,000 to 10,000 newborns.

  • EEC Syndrome (Ectrodactyly-Ectodermal Defects-Clefting Syndrome; Split Hand-Split Foot-Ectodermal Dysplasia-Cleft Syndrome): Characterized by abnormalities affecting the ...

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