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 (hypotrichosis). 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 small and pointed.

Some people with hypohidrotic ectodermal dysplasia have distinctive facial features, including a prominent forehead, thick lips, and a flattened bridge of the nose. 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.

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

Hypohidrotic ectodermal dysplasia is a genetic condition that can result from mutations in one of several genes. These include EDA, EDAR, EDARADD, and WNT10A. EDA gene mutations are the most common cause of the disorder, accounting for more than half of all cases. EDAR, EDARADD, and WNT10A gene mutations each account for a smaller percentage of cases. In about 10 percent of people with hypohidrotic ectodermal dysplasia, the genetic cause is unknown.

The EDA, EDAR, and EDARADD genes provide instructions for making proteins that work together during embryonic development. These proteins form part of a signaling pathway that is critical for the interaction between two cell layers, the ectoderm and the mesoderm. In the early embryo, these cell layers form the basis for many of the body's organs and tissues. Ectoderm-mesoderm interactions are essential for the formation of several structures that arise from the ectoderm, including the skin, hair, nails, teeth, and sweat glands.

Mutations in the EDA, EDAR, or EDARADD gene prevent normal interactions between the ectoderm and the mesoderm, which impairs the normal development of skin, hair, nails, teeth, and sweat glands. Mutations in any of these three genes lead to the major signs and symptoms of hypohidrotic ectodermal dysplasia described above.

The WNT10A gene provides instructions for making a protein that is part of a different signaling pathway known as Wnt signaling. Wnt signaling controls the activity of certain genes and regulates the interactions between cells during embryonic development. Signaling involving the WNT10A protein is critical for the development of ectodermal structures, particularly the teeth. The WNT10A gene mutations that cause hypohidrotic ectodermal dysplasia impair the protein's function, which disrupts the development of teeth and other structures that arise from the ectodermal cell layer.

When hypohidrotic ectodermal dysplasia results from WNT10A gene mutations, its features are more variable than when the condition is caused by mutations in the EDA, EDAR, or EDARADD gene. Signs and symptoms range from mild to severe, and mutations in the WNT10A gene are more likely to cause all of the permanent (adult) teeth to be missing.

Normal Function

The EDA gene provides instructions for making a protein called ectodysplasin A. This protein is part of a signaling pathway that plays an important role in development before birth. Specifically, it is critical for interactions between two embryonic cell layers called the ectoderm and the mesoderm. In the early embryo, these cell layers form the basis for many of the body's organs and tissues. Ectoderm-mesoderm interactions are essential for the formation of several structures that arise from the ectoderm, including the skin, hair, nails, teeth, and sweat glands.

One version of the ectodysplasin A protein, known as ectodysplasin A1, interacts with a protein called the ectodysplasin A receptor (produced from the EDAR gene). On the cell surface, ectodysplasin A1 attaches to this receptor like a key in a lock. When these two proteins are connected, they trigger a series of chemical signals that affect cell activities such as division, growth, and maturation. Starting before birth, this signaling pathway controls the formation of ectodermal structures such as hair follicles, sweat glands, and teeth.

Health Conditions Related to Genetic Changes

Hypohidrotic ectodermal dysplasia

More than 300 mutations in the EDA gene have been found to cause hypohidrotic ectodermal dysplasia, the most common form of ectodermal dysplasia. Starting before birth, ectodermal dysplasias result in the abnormal development of the skin, hair, nails, teeth, and sweat glands. Hypohidrotic ectodermal dysplasia is characterized by a reduced ability to sweat (hypohidrosis), sparse scalp and body hair (hypotrichosis), and several missing teeth (hypodontia) or teeth that are malformed. EDA gene mutations are the most frequent cause of hypohidrotic ectodermal dysplasia, accounting for more than half of all cases.

Some mutations in the EDA gene change single DNA building blocks (base pairs), whereas other mutations insert or delete a larger section of DNA. These changes lead to the production of a nonfunctional version of the ectodysplasin A1 protein. A shortage of functional ectodysplasin A1 prevents the protein from interacting effectively with its receptor, which impairs chemical signaling needed for interactions between the ectoderm and the mesoderm in early development. Without these signals, hair follicles, teeth, sweat glands, and other ectodermal structures do not form properly, which leads to the characteristic features of hypohidrotic ectodermal dysplasia.

Other disorders

EDA gene mutations have also been reported in some people with a condition called nonsyndromic tooth agenesis. This condition causes one or more teeth not to form. Although missing teeth is a common feature of ectodermal dysplasias, "nonsyndromic" suggests that in these cases tooth agenesis occurs without the other signs and symptoms of those conditions. It is unclear why the effects of some mutations in this gene appear to be limited to tooth development, while other mutations affect the formation of multiple ectodermal tissues.

Other Names for This Gene

• Ectodermal dysplasia protein
• ectodysplasin
• ectodysplasin-A
• ED1
• ED1-A1
• EDA-A1
• EDA-A2
• EDA1
• EDA_HUMAN
• HED
• XHED
• XLHED

Genomic Location

Normal Function

The EDAR gene provides instructions for making a protein called the ectodysplasin A receptor. This protein is part of a signaling pathway that plays an important role in development before birth. Specifically, it is critical for interactions between two embryonic cell layers called the ectoderm and the mesoderm. In the early embryo, these cell layers form the basis for many of the body's organs and tissues. Ectoderm-mesoderm interactions are essential for the formation of several structures that arise from the ectoderm, including the skin, hair, nails, teeth, and sweat glands.

The ectodysplasin A receptor interacts with a protein called ectodysplasin A1 (produced from the EDA gene). On the cell surface, ectodysplasin A1 attaches to this receptor like a key in a lock. When these two proteins are connected, they trigger a series of chemical signals that affect cell activities such as division, growth, and maturation. Starting before birth, this signaling pathway controls the formation of ectodermal structures such as hair follicles, sweat glands, and teeth.

Studies suggest that common variations (polymorphisms) in the EDAR gene are associated with the thickness and straightness of scalp hair, particularly in East Asian populations. EDAR appears to be one of many genes that influence these hair traits.

Health Conditions Related to Genetic Changes

Hypohidrotic ectodermal dysplasia

More than 50 mutations in the EDAR gene have been found to cause hypohidrotic ectodermal dysplasia, the most common form of ectodermal dysplasia. Starting before birth, ectodermal dysplasias result in the abnormal development of the skin, hair, nails, teeth, and sweat glands. Hypohidrotic ectodermal dysplasia is characterized by a reduced ability to sweat (hypohidrosis), sparse scalp and body hair (hypotrichosis), and several missing teeth (hypodontia) or teeth that are malformed. EDAR gene mutations account for about 10 percent of all cases of hypohidrotic ectodermal dysplasia.

Most of the EDAR gene mutations associated with hypohidrotic ectodermal dysplasia change a single protein building block (amino acid) in the receptor protein. Some of the mutations that cause this condition lead to the production of an abnormal version of the ectodysplasin A receptor. Other mutations prevent cells from producing any functional receptor. All of these genetic changes prevent the receptor from interacting with ectodysplasin A1, which impairs chemical signaling needed for interactions between the ectoderm and the mesoderm in early development. Without these signals, hair follicles, teeth, sweat glands, and other ectodermal structures do not form properly, which leads to the characteristic features of hypohidrotic ectodermal dysplasia.

Other disorders

EDAR gene mutations have also been reported in some people with a condition called nonsyndromic tooth agenesis. This condition causes one or more teeth not to form. Although missing teeth is a common feature of ectodermal dysplasias, "nonsyndromic" suggests that in these cases tooth agenesis occurs without the other signs and symptoms of those conditions. It is unclear why the effects of some mutations in this gene appear to be limited to tooth development, while other mutations affect the formation of multiple ectodermal tissues.

Other Names for This Gene

• DL
• ectodysplasin 1, anhidrotic receptor
• ectodysplasin A1 isoform receptor
• ectodysplasin receptor
• ED1R
• ED3
• ED5
• EDA-A1R
• EDA1R
• EDA3
• EDAR_HUMAN

Genomic Location

Normal Function

The EDARADD gene provides instructions for making a protein called the EDAR-associated via death domain (EDARADD) protein. This protein is part of a signaling pathway that plays an important role in development before birth. Specifically, it is critical for interactions between two embryonic cell layers called the ectoderm and the mesoderm. In the early embryo, these cell layers form the basis for many of the body's organs and tissues. Ectoderm-mesoderm interactions are essential for the formation of several structures that arise from the ectoderm, including the skin, hair, nails, teeth, and sweat glands.

The EDARADD protein interacts with another protein, called the ectodysplasin A receptor, which is produced from the EDAR gene. This interaction occurs at a region called the death domain that is present in both proteins. The EDARADD protein acts as an adapter, which means it assists the ectodysplasin A receptor in triggering chemical signals within cells. These signals affect cell activities such as division, growth, and maturation. Starting before birth, this signaling pathway controls the formation of ectodermal structures such as hair follicles, sweat glands, and teeth.

Health Conditions Related to Genetic Changes

Hypohidrotic ectodermal dysplasia

Fewer than 10 mutations in the EDARADD gene have been found to cause hypohidrotic ectodermal dysplasia, the most common form of ectodermal dysplasia. Starting before birth, ectodermal dysplasias result in the abnormal development of the skin, hair, nails, teeth, and sweat glands. Hypohidrotic ectodermal dysplasia is characterized by a reduced ability to sweat (hypohidrosis), sparse scalp and body hair (hypotrichosis), and several missing teeth (hypodontia) or teeth that are malformed. EDARADD gene mutations are an infrequent cause of hypohidrotic ectodermal dysplasia, accounting for only about 1 percent of all cases.

Most of the EDARADD gene mutations associated with hypohidrotic ectodermal dysplasia change single protein building blocks (amino acids) in the receptor protein. These changes occur in or near the death domain, preventing the EDARADD protein from interacting effectively with the ectodysplasin A receptor. As a result, the receptor cannot trigger the signals needed for ectoderm-mesoderm interactions in early development. Without these signals, hair follicles, teeth, sweat glands, and other ectodermal structures do not form properly, which leads to the characteristic features of hypohidrotic ectodermal dysplasia.

Other Names for This Gene

• ectodysplasia A receptor associated death domain
• ectodysplasin A receptor associated adapter protein
• EDAD_HUMAN
• EDAR-associated death domain

Genomic Location

Normal Function

The WNT10A gene is part of a large family of WNT genes, which play critical roles in development starting before birth. These genes provide instructions for making proteins that participate in chemical signaling pathways in the body. Wnt signaling controls the activity of certain genes and regulates the interactions between cells during embryonic development.

The protein produced from the WNT10A gene plays a role in the development of many parts of the body. It appears to be essential for the formation of tissues that arise from an embryonic cell layer called the ectoderm. These tissues include the skin, hair, nails, teeth, and sweat glands. Researchers believe that the WNT10A protein is particularly important for the formation and shaping of both baby (primary) teeth and adult (permanent) teeth.

Health Conditions Related to Genetic Changes

Hypohidrotic ectodermal dysplasia

Several mutations in the WNT10A gene have been found to cause hypohidrotic ectodermal dysplasia, the most common form of ectodermal dysplasia. Starting before birth, ectodermal dysplasias result in the abnormal development of the skin, hair, nails, teeth, and sweat glands. Hypohidrotic ectodermal dysplasia is characterized by a reduced ability to sweat (hypohidrosis), sparse scalp and body hair (hypotrichosis), and several missing teeth (hypodontia) or teeth that are malformed. WNT10A gene mutations account for about 5 percent of all cases of hypohidrotic ectodermal dysplasia.

Most of the WNT10A gene mutations associated with hypohidrotic ectodermal dysplasia change single protein building blocks (amino acids) in the WNT10A protein, which impairs its function. The resulting shortage of functional WNT10A protein disrupts Wnt signaling during the development of ectodermal tissues, particularly the teeth.

Hypohidrotic ectodermal dysplasia can result from mutations in several genes. When the condition is caused by WNT10A gene mutations, its features are more variable than when the condition is caused by mutations in any other gene. Signs and symptoms range from mild to severe, and mutations in this gene are more likely to cause all of the permanent teeth to be missing.

Keratoconus

MedlinePlus Genetics provides information about Keratoconus

Other disorders

Mutations in the WNT10A gene have been reported to cause several other, rare forms of ectodermal dysplasia, including odonto-onycho-dermal dysplasia (OODD) and Schopf-Schulz-Passarge syndrome (SSPS). OODD is characterized by dry hair, missing teeth, a smooth tongue, fingernail and toenail abnormalities, thickened skin on the palms of the hands and soles of the feet (palmoplantar keratoderma), and increased sweating (hyperhidrosis) of the palms and soles. The major features of SSPS include missing teeth, hypotrichosis, palmoplantar keratoderma, and fluid-filled sacs (cysts) on the edges of the eyelids.

WNT10A gene mutations are also frequently associated with a condition called nonsyndromic tooth agenesis. This condition causes one or more teeth not to form. Although missing teeth is a common feature of ectodermal dysplasias, "nonsyndromic" suggests that in these cases tooth agenesis occurs without the other signs and symptoms of those conditions.

More than 70 WNT10A gene mutations have been identified in people with various forms of ectodermal dysplasia or nonsyndromic tooth agenesis. Most of these mutations change single amino acids in the WNT10A protein, which impairs its function. The resulting shortage of functional WNT10A protein disrupts Wnt signaling during the development of ectodermal tissues, including the skin, hair, nails, teeth, and sweat glands. Researchers are working to determine why mutations in this gene can cause several different disorders.

Other Names for This Gene

• OODD
• protein Wnt-10a precursor
• STHAG4
• wingless-type MMTV integration site family, member 10A

Genomic Location

Hypohidrotic ectodermal dysplasia has several different inheritance patterns. Most cases are inherited in an X-linked pattern and are caused by mutations in the EDA gene. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females, who have two copies of the X chromosome, one altered copy of the gene in each cell often leads to less severe features of the condition. Signs and symptoms can include a few missing or abnormal teeth, sparse hair, and mild problems with sweat gland function. However, some females with one copy of the mutated gene have more severe features of this disorder.

Less commonly, hypohidrotic ectodermal dysplasia has an autosomal dominant or autosomal recessive pattern of inheritance. Mutations in the EDAR, EDARADD, or WNT10A gene can cause either autosomal dominant or autosomal recessive hypohidrotic ectodermal dysplasia.

Autosomal dominant inheritance means one copy of the altered gene in each cell is sufficient to cause the disorder. Some affected individuals inherit the mutation from one affected parent. Other cases result from new mutations in the gene and occur in people with no history of the disorder in their family.

Autosomal recessive inheritance means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene. Some mutation carriers have mild signs and symptoms of hypohidrotic ectodermal dysplasia, including a somewhat reduced ability to sweat and less severe dental abnormalities.

In most cases, hypohidrotic ectodermal dysplasia can be diagnosed after infancy based upon the physical features in the affected child. Genetic testing may be ordered to confirm the diagnosis. Other reasons for testing may include to identify carriers or for prenatal diagnosis.

Clinical testing is available for detection of disease causing mutations in the EDA,EDAR, and EDARADD genes. Those interested in pursuing genetic testing are encouraged to consult with a health care provider or a genetics professional to learn more about available testing options.