How hearing works
In the process of hearing, the outside portion of the ear (the pinna) collects sound waves and funnels them into the ear canal. Sound waves then travel down the ear canal and meet the tympanic membrane (the eardrum), causing it to vibrate. The eardrum is connected to three tiny bones called the ossicles, which vibrate due to movements from the eardrum and pass those vibrations on to the cochlea. There is a small window in the cochlea that the ossicles attach to and transmit the sound vibrations into. The cochlea is filled with a fluid that moves back and forth with sound waves and causes the movement of tiny hair cells, which transform the movement into signals in the nervous system. The nerve signals then travel to the brain, which interprets them as sound.
The pinna and ear canal make up the outer ear. The eardrum, ossicles, and the space around them comprise the middle ear. The cochlea makes up the inner ear.
How might XLH affect hearing?
There are many ways in which XLH may cause hearing impairment or loss. One way is through a protein called fibroblast growth factor 23 (FGF23). Low levels of PHEX, due to mutations in the PHEX gene, result in high levels of FGF23, which leads to a decrease in phosphate in the body (hypophosphatemia). This can lead to malformation of the bones in the middle ear.
Hypophosphatemia could lead to an ion imbalance in the inner ear and interfere with nerve signals traveling to the brain.
The increase in FGF23 also could cause a decrease in the tissue non-specific alkaline phosphatase (TNAP) enzyme. When there isn’t enough of this enzyme glycoproteins accumulate inside nerve cells that play a role in hearing and may cause damage.
Hearing impairment related to XLH
There have been many reports of hearing impairment or loss associated with XLH in research literature. These included loss of low- and high-frequency sounds, tinnitus (ringing of the ears), and vertigo.
However, it is difficult to relate all of them directly to the disease because several factors, including age and damage caused by listening to loud music, for instance, can cause hearing impairment or loss.
How doctors treat hearing loss?
The treatment that your physician recommends will depend on the cause of the hearing loss. Conductive hearing loss occurs when sound doesn’t fully make it through the outer or middle ear. Issues such as bone malformation in the middle ear, or middle ear infections, can cause conductive hearing loss. Surgery can treat the bone malformation, and antibiotic/anti-fungal medications can treat the infections.
Most reports of hearing loss in XLH patients are sensorineural in nature, however. These are issues related to the inner ear and the nerve cells that detect sound. XLH patients with these types of hearing loss may require hearing aids or a cochlear implant, depending on the level of neural damage.
Last updated: Oct. 9, 2020
XLH News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health providers with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.