What is Nonsyndromic Hearing Loss and Deafness, MT-RNR1-related?
Non-syndromic hearing loss is a partial or total loss of hearing that is not associated with other signs and symptoms. In contrast, syndromic hearing loss occurs with signs and symptoms affecting other parts of the body.
The characteristics of nonsyndromic hearing loss varies among the different types. Hearing loss can affect one ear (unilateral) or both ears (bilateral). Degrees of hearing loss range from mild (difficulty understanding soft speech) to profound (inability to hear even very loud The term “deafness” is often used to describe severe-to-profound hearing loss. Hearing loss can be stable, or it may be progressive, becoming more severe as a person gets older. Particular types of nonsyndromic hearing loss show distinctive Patterns of hearing loss. For example, the loss may be more pronounced at high, middle, or low tones.
The forms of nonsyndromic hearing loss are described as sensorineural, which means they are associated with a permanent loss of caused by damage to structures in the inner ear. The inner ear processes sound and send the information to the brain in the form of electrical nerve Impulsive. Less commonly, nonsyndromic hearing loss is described as conductive, meaning it results from changes in the middle ear. The middle ear contains three tiny bones that help transfer sound from the eardrum to the inner ear. Some forms of nonsyndromic hearing loss, a type called DFNX2, engaged changes in both the inner ear and the middle ear. This combination is called mixed hearing loss.
Depending on the type, nonsyndromic hearing loss can become apparent at any time from infancy to old age. Hearing loss that is present before a child learns to speak is classified as prelingual or congenital. Hearing loss that occurs after the development of speech is classified as Postlingual.
Mitochondrial forms of the condition, which result from changes to mtDNA, account for less than 1 percent of all nonsyndromic hearing loss in the United States. These cases are inherited in a mitochondrial pattern, which is also known as maternal inheritance. This pattern of inheritance applies to genes contained in mtDNA. Because egg cells, but not sperm cells, contribute mitochondria to the developing embryo, children can only inherit disorders resulting from mtDNA mutations from their mother. These disorders can appear in every generation of a family and can affect both males and females, but fathers do not pass traits associated with changes in mtDNA to their children.
In some cases, hearing loss occurs in people with no history of the condition in their family. These cases are described as sporadic, and the cause of the hearing loss is often unknown. When hearing loss results from environmental factors, it is not inherited.
How common is Nonsyndromic Hearing Loss and Deafness, MT-RNR1-related?
Between 2 and 3 per 1,000 children in the United States are born with detectable hearing loss in one or both ears. The prevalence of hearing loss increases with age; the condition affects 1 in 8 people in the United States age 12 and older, or about 30 million people. By age 85, more than half of all people experience hearing loss.