Anhidrotic Ectodermal Dysplasia, also known as Hypohidrotic Ectodermal Dysplasia (HED), is a rare, inherited condition involving the abnormal development of specific tissues. It is one of over 180 disorders known as ectodermal dysplasias, which stem from irregularities in the embryonic ectoderm. This layer of cells develops into hair, teeth, nails, skin, and sweat glands. The term “anhidrotic” or “hypohidrotic” refers to the condition’s primary characteristic: a severely reduced or absent ability to sweat. HED is congenital and its features may become more apparent over time.
Key Symptoms and Physical Characteristics
The defining symptom is a reduced ability to sweat (hypohidrosis) or a complete inability to sweat (anhidrosis), which occurs because sweat glands are missing, sparse, or non-functional. Since sweating is the body’s cooling mechanism, its absence can lead to high body temperatures (hyperthermia), particularly in warm weather or during physical activity. In infants, this may present as unexplained fevers or irritability in warm environments.
The condition also affects hair and teeth. Hair is often sparse, fine, and light-colored on the scalp (hypotrichosis), and eyebrows and eyelashes may also be sparse or absent. Dental abnormalities are common, ranging from having few teeth (hypodontia) to no teeth (anodontia), and any teeth that are present are often small, pegged, or conical.
Many individuals share distinct facial features, including a prominent forehead, a flattened “saddle” nose, and thicker lips. The skin around the eyes may appear thin, wrinkled, or darker. The skin itself is often dry and thin and prone to issues like eczema due to a lack of protective glands.
Genetic Origins and Inheritance
HED is caused by mutations in genes responsible for developing ectodermal structures. While several genes can be involved, mutations in the EDA, EDAR, and EDARADD genes are the most common causes. These genetic changes disrupt the pathways that guide the formation of sweat glands, teeth, hair, and skin before birth.
The most common inheritance pattern is X-linked recessive, caused by mutations in the EDA gene. Because males have only one X chromosome, a single mutated copy results in the full condition. Females, with two X chromosomes, are carriers and may show mild or no symptoms, as the normal gene on their second X chromosome can compensate.
Less frequently, the condition is inherited in an autosomal recessive pattern, requiring an individual to inherit two mutated gene copies, one from each parent. In an autosomal dominant pattern, only one copy of a mutated gene is needed to cause the condition. A new mutation can also occur in a child without either parent carrying the altered gene.
The Diagnostic Process
Diagnosis begins with a clinical evaluation of physical characteristics. A physician may suspect HED in an infant with unexplained fevers or when a child’s teeth do not emerge as expected or appear conical. The combination of sparse hair, distinct facial features, and skin condition supports the initial assessment.
Molecular genetic testing provides a definitive diagnosis. An analysis of a blood sample can identify the specific mutation in genes like EDA, EDAR, or EDARADD. This testing confirms the diagnosis and helps determine the inheritance pattern, which is useful for family planning.
Other tests can support the diagnosis. A small skin biopsy can reveal a reduced number or absence of sweat glands. A sweat test can also be used to measure sweat production and confirm hypohidrosis.
Management and Care Strategies
Since there is no cure, management focuses on addressing symptoms to improve quality of life. A primary concern is managing heat intolerance by avoiding overheating. This includes limiting time in hot weather, using air conditioning, and having cooling aids like spray bottles or vests available.
Dental care is another component of management, and early intervention from an experienced dental team is beneficial. Treatment plans are individualized and may involve dentures, bridges, or crowns to restore function and appearance. As an individual grows, dental implants can become a long-term solution for replacing missing teeth.
Skin and hair care involves routines to address dryness and cosmetic concerns. Regular application of moisturizers helps combat dry skin and prevent eczema. Since hair is often sparse, care is cosmetic and may include specialized haircuts or the use of wigs.
Some individuals experience respiratory issues due to a lack of mucus-producing glands, leading to dry nasal passages and more frequent infections. Management includes using saline nasal sprays to keep passages moist and treating infections promptly. With consistent care, most individuals have a normal life expectancy.