What is CHARGE syndrome?
CHARGE syndrome is a disorder that affects many areas of the body. CHARGE stands for coloboma, heart defect, atresia choanae (also known as choanal atresia), retarded growth and development, genital abnormality, and ear abnormality. The pattern of malformations varies among individuals with this disorder, and infants often have multiple life-threatening medical conditions. The diagnosis of CHARGE syndrome is based on a combination of major and minor characteristics.
The major characteristics of CHARGE syndrome are more specific to this disorder than are the minor characteristics. Many individuals with CHARGE syndrome have a 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 can affect a person's vision, depending on its size and location. Some people also have small eyes (microphthalmia). One or both nasal passages may be narrowed (choanal stenosis) or completely blocked (choanal atresia). Individuals with CHARGE syndrome 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 (hyponosmia) or completely absent (anosmia), and mild to profound hearing loss. People with CHARGE syndrome also typically have middle and inner ear abnormalities and unusually shaped ears.
The minor characteristics of CHARGE syndrome are not specific to this disorder; they are frequently present in people without CHARGE syndrome. The minor characteristics include heart defects, slow growth starting in late infancy, developmental delay, and an opening in the lip (cleft lip) with or without an opening in the roof of the mouth (cleft palate). Individuals frequently have hypogonadotropic hypogonadism, which affects the production of hormones that direct sexual development. Males are often born with an unusually small penis (micropenis) and undescended testes (cryptorchidism). External genitalia abnormalities are seen less often in females with CHARGE syndrome. Puberty can be incomplete or delayed. Individuals may have a tracheoesophageal fistula, which is an abnormal connection (fistula) between the esophagus and the trachea. People with CHARGE syndrome also have distinctive facial features, including a square-shaped face and difference in the appearance between the right and left sides of the face (facial asymmetry). Individuals have a wide range of cognitive function, from normal intelligence to major learning disabilities with absent speech and poor communication.
How common is CHARGE syndrome?
CHARGE syndrome occurs in approximately 1 in 8,500 to 10,000 individuals.
What genes are related to CHARGE syndrome?
Mutations in the CHD7 gene cause more than half of all cases of CHARGE syndrome. The CHD7 gene provides instructions for making a protein that most likely 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. Chromatin remodeling is one way gene expression is regulated during development. When DNA is tightly packed, gene expression is lower than when DNA is loosely packed.
Most mutations in the CHD7 gene lead to the production of an abnormally short, nonfunctional CHD7 protein, which presumably disrupts chromatin remodeling and the regulation of gene expression. Changes in gene expression during embryonic development likely cause the signs and symptoms of CHARGE syndrome.
About one-third of individuals with CHARGE syndrome do not have an identified mutation in the CHD7 gene. Researchers suspect that other genetic and environmental factors may be involved in these individuals.
How do people inherit CHARGE syndrome?
CHARGE syndrome is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Most cases result from new mutations in the CHD7 gene and occur in people with no history of the disorder in their family. In rare cases, an affected person inherits the mutation from an affected parent.
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