About 1 in 1000 infants are born with severe to profound sensorineural hearing loss, according to an article in Audiology HealthCare News (Autumn 2001). About half of these children inherit the condition from their parents, who may or may not be deaf themselves. In most of these cases (about 70%), hearing loss is not accompanied by a recognizable set of symptoms (nonsyndromic). In addition, hearing loss is autosomal (not on a sex chromosome) recessive in about 75% of the infants with inherited deafness.
Although several genes affect hearing, researchers have identified GJB2 (gap-junction beta 2) as accounting for "up to 50% of hereditary pre-lingual severe-to-profound nonsyndromic hearing loss," according to a study by W. McGuirt and R. Smith [Connexin as a Cause of Hereditary Hearing Loss. Amer J of Audiology (Dec. 1999), 8: 93-100]. This gene determines the function of the protein Connexin 26 (Cx26), which maintains high potassium concentrations in the cochlea's scala media. About 2.5% of the population in Midwestern United States carry a mutated form of this gene.
Genetic testing for Cx26 is available in the United States. The test may help clarify the etiology of pre-lingual severe to profound sensorineural hearing loss for some people. Most of the testing is done, however, on people with no family history of hearing loss, according to this article. W. McGuirt and R. Smith recommend that appropriate explanations and counseling accompany the genetic test so that participants understand what the results mean. If one parent has severe congenital sensorineural hearing loss caused by a Cx26 mutation and the other does not carry a form of the mutated gene, it is very unlikely that any of their children will be born with impaired hearing. All of their children, however, will carry the mutated gene. On the other hand, if two hearing parents each carry a mutated Cx26 gene, each of their children has a 25% chance of being born with severe to profound hearing loss. In addition, the couple's normal-hearing children have a 66% chance of carrying the mutated Cx26 gene.
Cennoxin 26 as a Cause of Hereditary Hearing Loss. Audiology HealthCare New., 2001 Autumn.
COPYRIGHT 2002 The Townsend Letter Group
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