Clouston syndrome is a form of ectodermal dysplasia, a group of about 150 conditions characterized by abnormal development of some or all of the ectodermal structures, which include the skin, hair, nails, teeth, and sweat glands. Specifically, Clouston syndrome is characterized by abnormalities of the hair, nails, and skin, with the teeth and sweat glands being unaffected.

In infants with Clouston syndrome, scalp hair is sparse, patchy, and lighter in color than the hair of other family members; it is also fragile and easily broken. By puberty, the hair problems may worsen until all the hair on the scalp is lost (total alopecia). The eyelashes, eyebrows, underarm (axillary) hair, and pubic hair are also sparse or absent.

Abnormal growth of fingernails and toenails (nail dystrophy) is also characteristic of Clouston syndrome. The nails may appear white in the first years of life. They grow slowly and gradually become thick and misshapen. In some people with Clouston syndrome, nail dystrophy is the most noticeable feature of the disorder.

Many people with Clouston syndrome have thick skin on the palms of the hands and soles of the feet (palmoplantar hyperkeratosis); areas of the skin, especially over the joints, that are darker in color than the surrounding skin (hyperpigmentation); and widened and rounded tips of the fingers (clubbing).

Clouston syndrome is caused by mutations in the GJB6 gene. This gene provides instructions for making a protein called gap junction beta 6, more commonly known as connexin 30. Connexin 30 is a member of the connexin protein family. Connexin proteins form channels called gap junctions, which permit the transport of nutrients, charged atoms (ions), and signaling molecules between neighboring cells. The size of the gap junction and the types of particles that move through it are determined by the particular connexin proteins that make up the channel. Gap junctions made with connexin 30 transport potassium ions and certain small molecules.

Connexin 30 is found in several different tissues throughout the body, including the skin (especially on the palms of the hands and soles of the feet), hair follicles, and nail beds, and plays a role in the growth and development of these tissues.

GJB6 gene mutations that cause Clouston syndrome change single protein building blocks (amino acids) in the connexin 30 protein. Although the effects of these mutations are not fully understood, they lead to abnormalities in the growth, division, and maturation of cells in the hair follicles, nails, and skin.

Normal Function

The GJB6 gene provides instructions for making a protein called gap junction beta 6, more commonly known as connexin 30. Connexin 30 is a member of the connexin protein family. Connexin proteins form channels called gap junctions that permit the transport of nutrients, charged atoms (ions), and signaling molecules between adjoining cells. The size of the gap junction and the types of particles that move through it are determined by the particular connexin proteins that make up the channel. Gap junctions made with connexin 30 transport potassium ions and certain small molecules.

Connexin 30 is found in several different tissues throughout the body, including the brain, inner ear, skin (especially the palms of the hands and soles of the feet), hair follicles, and nail beds. Because of its presence in the inner ear, researchers are interested in this protein's role in hearing. Hearing requires the conversion of sound waves to electrical nerve impulses. This conversion involves many processes, including maintenance of the proper level of potassium ions in the inner ear. Some studies indicate that gap junctions made with connexin 30 help to maintain the correct level of potassium ions.

Health Conditions Related to Genetic Changes

Clouston syndrome

At least four GJB6 gene mutations have been identified in people with a skin disorder called Clouston syndrome, which is also known as hidrotic ectodermal dysplasia 2. Characteristics of Clouston syndrome include fingernail abnormalities, hair loss, and thickened skin on the palms of the hands and soles of the feet. The GJB6 gene mutations that cause Clouston syndrome change single protein building blocks (amino acids) in the connexin 30 protein. Although the effects of these mutations are not fully understood, they lead to abnormalities in the growth, division, and maturation of cells in the hair follicles, nails, and skin.

Nonsyndromic hearing loss

Researchers have identified a few GJB6 gene mutations in individuals with nonsyndromic hearing loss, which is loss of hearing that is not associated with other signs and symptoms. Mutations in this gene cause a form of nonsyndromic hearing loss called DFNA3. This form of hearing loss can either be present before a child learns to speak (prelingual) or begin after a child learns to speak (postlingual). The hearing loss ranges from mild to profound, becomes more severe over time, and particularly affects the ability to hear high-frequency sounds.

At least two GJB6 gene mutations have been reported to cause DFNA3. Each of these mutations changes a single amino acid in connexin 30. The mutations are described as "dominant negative" because they lead to an abnormal version of connexin 30 that appears to block the formation of functional gap junctions. A shortage of these channels may alter the level of potassium ions in the inner ear, which would disrupt the conversion of sound waves to nerve impulses.

Other Names for This Gene

• CX30
• CXB6_HUMAN
• DFNA3
• ED2
• EDH
• gap junction protein, beta 6
• gap junction protein, beta 6, 30kDa
• HED

Genomic Location

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

In most cases, an affected person inherits 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.

The prevalence of Clouston syndrome is unknown. Cases have been reported in many populations; the disorder is especially common among people of French-Canadian descent.