Hypohidrotic ectodermal dysplasia (HED) is a rare genetic disorder affecting the development of structures that originate from the ectoderm. This condition is present from birth and impacts various bodily systems. It is characterized by the abnormal development of the skin, hair, teeth, nails, and sweat glands.
Understanding Hypohidrotic Ectodermal Dysplasia
HED is the most common form of ectodermal dysplasia, a broader group of conditions involving abnormalities in at least two ectodermal structures. It is estimated to affect at least 1 in 17,000 people worldwide.
Recognizing the Characteristics
The signs and symptoms of HED often become noticeable during childhood. A defining characteristic is reduced or absent sweating, known as hypohidrosis or anhidrosis, due to a partial or complete absence of sweat glands. This reduced ability to sweat can lead to heat intolerance and elevated body temperature.
Another common feature is abnormally sparse hair, or hypotrichosis, which can affect the scalp and body. The hair may appear thin, lightly pigmented, and grow slowly. Dental abnormalities are also highly prevalent, including missing teeth (hypodontia) or abnormally shaped teeth, which may be conical or pointed. The eruption of teeth can be delayed, or only a few may emerge.
Individuals with HED often share a characteristic facial appearance, which may include a prominent forehead, a sunken nasal bridge, unusually thick lips, and a large chin. The skin across most of the body can be abnormally thin, dry, and soft, sometimes with a lack of pigmentation. The skin around the eyes may exhibit darker pigmentation and fine wrinkles. Other potential features include nail issues, recurrent respiratory infections, and chronic inflammation of the nasal passages.
Diagnosis and Management
Diagnosis of hypohidrotic ectodermal dysplasia relies on observing characteristic clinical symptoms. Genetic testing can confirm the diagnosis by identifying mutations in specific genes. Tests to assess sweat gland function may also be performed.
Managing HED focuses on alleviating symptoms and providing supportive care, as there is currently no cure for the underlying genetic condition. Strategies for managing heat intolerance include avoiding overheating through air conditioning, wearing cool clothing, and having access to water for external cooling. Dental issues often require comprehensive care, with prosthetics frequently beginning in early childhood and continuing with implants in adulthood.
Skin care involves regular moisturizing to address dry, thin skin. Nasal secretion problems may be managed with saline sprays and humidifiers. A multidisciplinary approach involving various medical specialists, such as dermatologists, dentists, ear, nose, and throat (ENT) specialists, and geneticists, is recommended. Early intervention and regular follow-up with this team can improve the quality of life for affected individuals.
Genetic Basis
The genetic underpinnings of hypohidrotic ectodermal dysplasia primarily involve mutations in certain genes. The most common form of HED is inherited in an X-linked recessive manner, caused by a mutation in the ectodysplasin-A (EDA) gene, located on the X chromosome. This inheritance pattern explains why males are typically more severely affected, as they have only one X chromosome. Females who carry one copy of the altered gene may exhibit some milder symptoms, such as sparse hair, reduced sweating, or missing teeth.
Other less common genetic causes or inheritance patterns exist, including mutations in the EDAR or EDARADD genes, which can result in autosomal dominant or autosomal recessive inheritance. These genes, along with WNT10A, provide instructions for making proteins that work together during embryonic development. These proteins form part of a signaling pathway that is important for the interaction between the ectoderm and mesoderm cell layers, which are foundational for the development of structures like skin, hair, nails, teeth, and sweat glands.