Ectodermal Dysplasia

Ectodermal dysplasia is a rare group of inherited disorders. It was first 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. At least 150 different forms of ectodermal dysplasia have been identified; some of the most common are presented here.

Individuals affected with ectodermal dysplasia have at least two of the following 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.

At a Glance

Autosomal dominant ectodermal dysplasia characterized by the triad of palmoplantar hyperkeratosis, nail dystrophy, and alopecia. Facial appearance, teeth, and sweating are normal.

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Synonyms

Fischer-Jacobsen-Clouston Syndrome; Hidrotic Ectodermal Dysplasia.

Incidence

Unknown. A higher incidence has been reported in the French Canadian population, but it occurs in all ethnicities.

Genetic Inheritance

Autosomal dominant. The defect has been linked to 13q11-q12.1.

Pathophysiology

Abnormality in the molecular structure of keratin seems to be responsible for the disease.

Diagnosis

Based on the typical clinical features and family history.

Clinical Aspects

In contrast to the X-linked form of ectodermal dysplasia (anhidrotic ectodermal dysplasia), most of the affected patients have normal sweat and sebaceous glands, and the teeth are usually only mildly affected (in contrast to the first description by Clouston). However, as in other forms of ectodermal dysplasia, the patients suffer from severe dystrophy of nails (thickened, striated, very slow growing, often discolored) and hair (resulting in total alopecia, sometimes in infancy but usually after puberty). Ultrastructural analysis of the hair shows an altered organization of hair fibrils with loss of the cuticular cortex suggesting a biochemical defect in the keratin of the integumentary system. Skin changes include palmoplantar hyperkeratosis, which can involve the periungual area and result in thickening of the fingertips with the aspect of clubbing. Skin hyperpigmentation is common over the joints.

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