Hypohidrotic ectodermal dysplasia

Hypohidrotic ectodermal dysplasia is a genetic disorder characterized by the abnormal development of ectodermal tissues, specifically affecting the skin, hair, nails, teeth, and sweat glands.

Description

Hypohidrotic ectodermal dysplasia is one of more than 100 types of ectodermal dysplasia. Starting before birth, these disorders result in the abnormal development of ectodermal tissues, particularly the skin, hair, nails, teeth, and sweat glands.

Most people with hypohidrotic ectodermal dysplasia have a reduced ability to sweat (hypohidrosis) because they have fewer sweat glands than normal or their sweat glands do not function properly. Sweating is a major way that the body controls its temperature; as sweat evaporates from the skin, it cools the body. Reduced sweating can lead to a dangerously high body temperature (hyperthermia), particularly in hot weather. In some cases, hyperthermia can cause life-threatening health problems.

Affected individuals tend to have sparse scalp and body hair. The hair is often light-colored, brittle, and slow-growing. Hypohidrotic ectodermal dysplasia is also characterized by several missing teeth (hypodontia) or teeth that are malformed. The teeth that are present erupt from the gums later than usual and are frequently pointed.

Some people with hypohidrotic ectodermal dysplasia have distinctive facial features, including a prominent forehead, thick lips, and a depressed nasal bridge. Additional features of this condition can include thin, wrinkled, and dark-colored skin around the eyes; chronic skin problems such as eczema; and a bad-smelling discharge from the nostrils (ozena).

Intellectual ability and growth are typically normal in people with hypohidrotic ectodermal dysplasia.

Frequency

Hypohidrotic ectodermal dysplasia is the most common form of ectodermal dysplasia. It is estimated to occur in 1 in 20,000 newborns worldwide.

Causes

Hypohidrotic ectodermal dysplasia is a genetic condition that can result from mutations in one of several genes, including EDA, EDAR, EDARADD, and WNT10A. EDA gene mutations are the most common cause of the disorder, accounting for more than half of all cases.

• EDA, EDAR, and EDARADD: These genes provide instructions for proteins that form a signaling pathway critical for the interaction between the ectoderm and mesoderm cell layers during embryonic development. Mutations prevent normal interactions, impairing the development of skin, hair, nails, teeth, and sweat glands.
• WNT10A: This gene is part of the Wnt signaling pathway, which regulates cell interactions during development. Mutations impair protein function, disrupting the development of ectodermal structures, particularly teeth.

Inheritance

Hypohidrotic ectodermal dysplasia has several different inheritance patterns:

• X-linked: Most cases are caused by mutations in the EDA gene. In males, one altered copy is sufficient to cause the condition. In females, one altered copy often leads to less severe features, though some may have more severe symptoms.
• Autosomal Dominant: One copy of the altered gene in each cell is sufficient to cause the disorder.
• Autosomal Recessive: Both copies of the gene in each cell have mutations. Parents of an affected individual each carry one copy of the mutated gene.

Other Names for This Condition

• Anhidrotic ectodermal dysplasia
• Christ-Siemens-Touraine syndrome
• CST syndrome
• HED