CHARGE syndrome is a disorder that affects many areas of the body. CHARGE is an abbreviation for several of the features common in the disorder: coloboma, heart defects, atresia choanae (also known as choanal atresia), growth retardation, genital abnormalities, and ear abnormalities. The pattern of malformations varies among individuals with this disorder, and the multiple health problems can be life-threatening in infancy. Affected individuals usually have several major characteristics or a combination of major and minor characteristics.

The major characteristics of CHARGE syndrome are common in this disorder and occur less frequently in other disorders. Most individuals with CHARGE syndrome have a gap or hole in one of the structures of the eye (coloboma), which forms during early development. A coloboma may be present in one or both eyes and may impair a person's vision, depending on its size and location. Some affected individuals also have abnormally small or underdeveloped eyes (microphthalmia). In many people with CHARGE syndrome, one or both nasal passages are narrowed (choanal stenosis) or completely blocked (choanal atresia), which can cause difficulty breathing. Affected individuals frequently have cranial nerve abnormalities. The cranial nerves emerge directly from the brain and extend to various areas of the head and neck, controlling muscle movement and transmitting sensory information. Abnormal function of certain cranial nerves can cause swallowing problems, facial paralysis, a sense of smell that is diminished (hyposmia) or completely absent (anosmia), and mild to profound hearing loss. People with CHARGE syndrome also typically have middle and inner ear abnormalities, which can contribute to hearing problems, and unusually shaped external ears.

While the minor characteristics of CHARGE syndrome are common in this disorder, they are also frequently present in people without the disorder. The minor characteristics include heart defects; slow growth starting in late infancy; delayed development of motor skills, such as sitting unsupported and walking; and an opening in the lip (cleft lip) with or without an opening in the roof of the mouth (cleft palate). Affected individuals frequently have hypogonadotropic hypogonadism, which affects the production of hormones that direct sexual development. As a result, males with CHARGE syndrome are often born with an unusually small penis (micropenis) and undescended testes (cryptorchidism). Abnormalities of external genitalia are seen less often in affected females. Puberty can be incomplete or delayed in affected males and females. Another minor feature of CHARGE syndrome is tracheoesophageal fistula, which is an abnormal connection (fistula) between the esophagus and the trachea. Most people with CHARGE syndrome also have distinctive facial features, including a square-shaped face and differences in appearance between the right and left sides of the face (facial asymmetry). Affected individuals have a wide range of cognitive function, from normal intelligence to major learning disabilities with absent speech and poor communication.

Less common features of CHARGE syndrome include kidney abnormalities; immune system problems; abnormal curvature of the spine (scoliosis or kyphosis); and limb abnormalities, such as extra fingers or toes (polydactyly), missing fingers or toes (oligodactyly), an inward and upward turning foot (club foot), and abnormalities of the long bones of the arms and legs.

CHARGE syndrome occurs in approximately 1 in 8,500 to 10,000 newborns.

Mutations in the CHD7 gene cause most cases of CHARGE syndrome. The CHD7 gene provides instructions for making a protein that regulates gene activity (expression) by a process known as chromatin remodeling. Chromatin is the complex of DNA and protein that packages DNA into chromosomes. The structure of chromatin can be changed (remodeled) to alter how tightly DNA is packaged. When DNA is tightly packed, gene expression is lower than when DNA is loosely packed. Chromatin remodeling is one way gene expression is regulated during development.

Most mutations in the CHD7 gene lead to the production of an abnormal CHD7 protein that is broken down prematurely. Shortage of this protein is thought to disrupt chromatin remodeling and the regulation of gene expression. Changes in gene expression during embryonic development likely cause the signs and symptoms of CHARGE syndrome.

A small percentage of individuals with CHARGE syndrome do not have an identified mutation in the CHD7 gene. Some of them may have a genetic change affecting the CHD7 gene that has not been found, and others may have a change in a different gene, although additional genes associated with CHARGE syndrome have not been identified.

Normal Function

The CHD7 gene provides instructions for making a protein called chromodomain helicase DNA binding protein 7. This protein is found in many parts of the body before birth, including the eye, the inner ear, and the brain. In the brain, the CHD7 protein is active in several areas, including a bundle of nerve cells (neurons) called the olfactory bulb that is critical for the perception of odors.

The CHD7 protein belongs to a family of proteins that are thought to play a role in the organization of chromatin. Chromatin is the complex of DNA and protein that packages DNA into chromosomes. The CHD7 protein regulates the activity (expression) of several other genes through a process known as chromatin remodeling. The structure of chromatin can be changed (remodeled) to alter how tightly DNA is packaged. When DNA is tightly packed, gene expression is lower than when DNA is loosely packed. Researchers are working to determine which genes the CHD7 protein regulates.

Health Conditions Related to Genetic Changes

CHARGE syndrome

Mutations in the CHD7 gene cause CHARGE syndrome, a disorder that affects many areas of the body. CHARGE is an abbreviation for several of the features common in the disorder: coloboma, heart defect, atresia choanae (also known as choanal atresia), growth retardation, genital abnormality, and ear abnormality. More than 600 mutations that can cause CHARGE syndrome have been identified, and they occur throughout the CHD7 gene. Most of these mutations lead to the production of an abnormal CHD7 protein that is broken down prematurely. Shortage of this protein is thought to disrupt chromatin remodeling and the regulation of gene expression. Changes in gene expression during embryonic development likely cause the signs and symptoms of CHARGE syndrome.

Kallmann syndrome

More than 50 mutations in the CHD7 gene have been identified in people with Kallmann syndrome, a disorder characterized by the combination of hypogonadotropic hypogonadism (a condition affecting the production of hormones that direct sexual development) and an impaired sense of smell. Mutations in this gene account for 5 to 10 percent of all cases of Kallmann syndrome.

Many people with Kallmann syndrome caused by a CHD7 gene mutation have some of the features of CHARGE syndrome (described above), such as abnormally shaped ears and hearing loss. However, the signs and symptoms tend to be much less severe. Researchers suspect that Kallmann syndrome resulting from a CHD7 gene mutation may actually represent a mild form of CHARGE syndrome.

Most of the CHD7 gene mutations that cause Kallmann syndrome alter single protein building blocks (amino acids) in the CHD7 protein. Studies suggest that these mutations have a less severe effect on protein function than those that cause CHARGE syndrome. The altered protein affects the development of the olfactory bulb, which impairs the sense of smell. It also disrupts the development of certain neurons needed for the production of sex hormones, which interferes with normal sexual development.

Coloboma

MedlinePlus Genetics provides information about Coloboma

Other Names for This Gene

• CHD7_HUMAN
• FLJ20357
• FLJ20361
• IS3
• KIAA1416

Genomic Location

Genetic testing is available for CHARGE syndrome. The CHD7 gene is the only gene in which mutations are known to cause CHARGE syndrome. The CHD7 mutation detection rate when sequence analysis is performed is estimated to be 65%-70% for all typical and suspected cases combined.