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At a glance

A heterogeneous genetic disorder caused by abnormal development of the ectodermal tissue and characterized by the association of hypohidrosis, hypotrichosis, defective dentition, peculiar facies, abnormal thermoregulation, and exocrine gland insufficiency.

Synonyms

Anhidrotic Ectodermal Dysplasia 1; X-Linked Anhidrotic Ectodermal Dysplasia; Hypohidrotic Ectodermal Dysplasia.

History

This is the condition affecting the “Toothless Men of Sind,” members of a Hindu kindred living in the vicinity of Hyderabad (the capital of Andhra Pradesh in India) and was described by Charles Darwin in 1875, and later by K.I. Thadani in 1934.

Incidence

Approximately 1:100,000 of the general population is affected. Christ-Siemens-Touraine Syndrome the most common ectodermal dysplasia.

Genetic inheritance

X-linked recessive. The disease is caused by a mutation in the EDA (Ectodysplasin A) gene, which has been mapped to Xq13.1. As a member of the tumor necrosis factor ligand superfamily, Ectodysplasin is a membrane protein involved in signal transduction, promoting not only cell adhesion to the extracellular matrix, but also regulating the development of ectodermal appendages and epithelia-mesenchymal interactions. Usually only men are affected and women act as carriers of the disease; however, the clinical picture in heterozygous females is highly variable, ranging from no symptoms to severe disease. Rarely, the disease is transmitted in an autosomal recessive or an autosomal dominant pattern.

Diagnosis

Mainly based on the clinical findings. Skin biopsy of the palm demonstrates the absence or hypoplasia of sweat glands. The clinical triad of hypo- or anhidrosis, hypotrichosis, and hypodontia is helpful for diagnostic purposes.

Clinical aspects

Often the disorder presents in the first year of life with episodes of unexplained hyperthermia. Thermography can reveal abnormal skin temperature patterns consistent with altered peripheral vascular perfusion. Hypoplasia or aplasia of sebaceous and eccrine sweat glands leads to a lack of sebum and sweat causes with dry, scaly, and wrinkled skin (atopic-like dermatitis) with decreased sweating capabilities, heat intolerance, and risk for hyperthermia. Hypoplasia or aplasia of the mammary glands with hypoplastic or absent nipples may be present. Lacrimation and Meibomian glands may be absent or hypoplastic. Hair follicles may be absent, hypoplastic, and/or decreased in numbers affecting scalp and body hair resulting in fine, brittle, and scant hair (hypotrichosis), and scant or absent eyelashes and eyebrows. Onychodysplasia manifests as spoon-shaped nails. Dental anomalies include hypo- or anodontia, taurodontism (teeth with abnormally short roots and enlarged pulp chambers), conical crowns, and underdevelopment of the alveolar ridges. Respiratory tract mucous glands may also be affected be hypoplastic/aplastic, resulting in increased risk for bronchitis and pneumonia. Laryngeal incompetence with dry mucosal atrophy (often manifesting as hoarse voice) is not uncommon and may contribute to recurrent chest infections. Associated features include characteristic facies described as frontal bossing, prominent supraorbital ridges, hypertelorism, saddle nose with depressed ...

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