Genetics of Hearing Loss

Approximately 1 in 1000 children in the United States are born with profound hearing loss, and approximately half of these cases are thought to be genetic in origin ("American College of Medical Genetics Statement: Genetics Evaluation Guidelines for the Etiologic Diagnosis of Congenital Hearing Loss," 2002). Of the cases that are considered to be genetic in origin, some children have hearing loss due to a genetic syndrome or a family history that includes several generations of deaf individuals (autosomal dominant hearing loss). However, most cases of genetic hearing loss will be autosomal recessive and non-syndromic. Genetic alterations in a family of genes called the connexins are largely responsible for non-syndromic, sensorineural hearing loss. The most common genetic alterations occur in the GJB2 gene on chromosome 13, which codes for a protein called connexin 26. Genetic changes that alter the connexin 26 protein are called connexin 26 mutations. One in 33 Caucasians is a carrier of a cx26 mutation. The clinical presentation of cx26 hearing loss is variable, ranging from mild to profound even among members of the same family who inherited the same genetic alteration (Garrett, et al., 2006).

Newborn Screening and Early Intervention

Early diagnosis and intervention services have many benefits for children who are deaf, and facilitate acquisition of language skills. Multiple professional societies, advocacy groups, and government agencies participating in the Joint Committee on Infant Hearing (JCIH) endorsed universal newborn hearing screening as an essential component of early detection and intervention for infants with hearing loss ("American College of Medical Genetics Statement: Genetics Evaluation Guidelines for the Etiologic Diagnosis of Congenital Hearing Loss," 2002). As of March 2010, newborn hearing screen is required by law in 36 states, and is available in all 50 states. Newborn hearing screening is performed with ABR (auditory brainstem response) or OAE (otoacoustic emissions) audiological tests. As with metabolic newborn screening, NBHS can miss some infants with mild hearing loss and will miss infants who will develop hearing loss later in childhood. It is also important to realize that false positives occur with NBHS, and follow up testing is important for any infant identified with a hearing loss by NBHS. For more information on newborn screening for deafness, visit the National Newborn Screening and Genetics Resource Center at
http://genes-r-us.uthscsa.edu/.  

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