Monday 3 July 2017

Flawed Fish Jaws Shed Light on Hearing Loss in Humans


Genetic Mutation – Malformation of Jaw

As per USC research in Scientific reports, the same genetic tweak which tends to cause malformed jaws in the case of fish could be responsible for some issues in hearing in humans which seems to have some evolutionary origins. Scientists are of the belief that the arrangements which seem to support the jaws of primeval ancestral fish gave rise to three tiny bones towards the middle ear of humans as well as other mammals which transmit sound vibrations where the bones are known as malleus, incus and stapes.

 In zebra fish, a genetic mutation could result in malformation of the jaw and hence USC researchers speculated if an equivalent genetic change could activate hearing defects in mice and humans. To comprehend the query, Camilla Teng, USC PhD student coordinated along with the other colleagues in the USC Stem Cell laboratories of Gage Crump, Rob Maxson, and Neil Segil and with clinical experts in radiology, audiology and genetics at the Keck School of Medicine of USC and Children’s Hospital Los Angeles.

They researched on two genes JAG1 and NOTCH2 which were mutated in most patients with Alagille syndrome - AGS which a genetic condition causing several symptoms in various parts of the body inclusive of the liver.

Hearing Loss – Deficits in Sensory Cells of Inner Ear

A person with Alagille syndrome tends to have less than normal number or small bile ducts in the liver which is the organ in the abdomen between the chest and hips that makes blood proteins, bile storing energy and nutrients, combats infection as well as eliminates harmful chemicals from the blood.At least in half of the patients, the syndrome tends to affect hearing loss besides liver, eye, heart and skeletal defects.

Though some of this could be hearing loss due to deficits in the sensory cells of the inner ear, the researchers have been speculating on the conductive hearing loss that involves essential components of the middle ear like the vibrating bones.

With the introduction of mutations in mice, the researchers observed flaws in the incus as well as the stapes bones together with corresponding hearing loss. Thereafter they attended Alagille Alliance meetings in 2011 and 2014 performing hearing tests later on 44 human patients affected with Alagille syndrome to determine if their hearing loss had been conductive, sensor in neural or mixed.

Conductive Hearing Loss

As predicted by their discoveries in zebra-fish and mice, they observed conductive hearing loss had been the most common type which had affected almost one third of all ears. The CT scans of 5 AGS patients showed a more considerable complex picture, an unexpected variety of basi cflaws in the middle ear having variable effects on hearing.

One out of the five patients had a stapes flaw precisely related with conductive hearing loss.Teng commented that their study emphasized a generally unnoticed phenotype of Alagille Syndromes.

According to Teng, the study provided some insight on generally overlooked issue arising among individuals with Alagille syndrome. She stated that if patients tend to be conscious of possible conductive hearing loss earlier in life, they can seek medical aidin time for abetter quality of life.

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