Alport syndrome is a genetic disease associated with a lack of a protein called type IV collagen, essential to both proper kidney function and the stability of the eyes and inner ears.
Alport syndrome and hearing
Low levels of type IV collagen cause defects in the development of the inner ear that can lead to progressive hearing loss, often called sensorineural deafness, although the extent usually depends on disease severity. Specifically, the collagen makeup of the basement membranes of the cochlea is abnormal in Alport patients. How these defects lead to hearing loss is not fully understood, and ways to prevent or reverse such loss are currently not known.
Alport syndrome affects hearing progressively, and symptoms indicating inner-ear damage may not appear until late childhood or early adolescence. Loss of middle- and high- frequency hearing tends to be a more common sign. Early identification of Alport syndrome-related hearing loss is important, as difficulties with hearing usually correlate to declining kidney function and often is apparent before kidney problems are evident. Because of this, doctors typically recommend that children, especially boys, undergo regular audiological or hearing tests.
Alport syndrome is largely an X-linked genetic disease (about 80% of cases), and its symptoms — hearing loss and kidney disease — are typically more severe in males than females (who inherit two X chromosomes, with the likelihood that one is normal).
In many patients, hearing aids can compensate for difficulties in following conversations.
How hearing tests work
Hearing tests for Alport syndrome patients should establish their audible range for tones and speech. Tests are generally carried out in a sound-treated room to prevent background noise that might interfere with testing, or by using soundproof headphones.
Generally, hearing tests use headphones that allow the person being tested to listen to words and sounds given at different pitches and levels. The audiologist will guide patients and provide instructions, with patients indicating when a tone is heard. These tests give the audiologist a good idea of the frequencies and tones that a person is able to hear. After an initial ear exam, tests given may consist of a tone test, bone conduction test that checks for problems in the middle ear cavity, and a tympanometry.
A tympanometry is used to judge the workings of the middle and inner ear by evaluating changes in air pressure in the ear canal, and the movement of the eardrum (tympanic membrane) and tiny bones in the air-filled middle ear. It is a key test in determining if a person can be cleared for a hearing aid.
This test typically begins with a lighted scope, called an otoscope, that an audiologist or doctor will use to visually examine the ear. Then, a probe with a rubber tip is usually placed in the ear, causing pressure in the ear canal to change and producing low tones. Those changes in pressure vibrate the middle ear, allowing measurements of the eardrum’s response to be recorded.
This test is capable of distinguishing the sensorineural hearing loss associated with Alport syndrome, and caused by damage to the inner ear or the auditory nerve, from conductive hearing loss, which affects how sound moves from the ear drum to the inner ear.
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