Why don't people listen better

Better hearing with genes : Reactivate the self-healing powers of hearing

Hearing impairment is the most common sensory disorder in humans. The World Health Organization (WHO) even regards hearing loss as a pandemic, a global problem that also has an economic dimension: in the USA alone, 50 billion US dollars are spent annually to eliminate hearing problems. Around 71 million people in Europe are currently affected by hearing damage. Almost half of them are older than 75 years. However, around a billion people around the world are at risk of premature hearing damage. “That partly has to do with headphones,” said neuroscientist and hearing expert Ulrich Müller from Johns Hopkins University last week at a lecture in the “flagship store” of the headphone manufacturer Sennheiser at Berlin's Tauentzien as part of a new lecture series entitled “Medium-sized companies meets science ”, organized by the Einstein Foundation and the Federal Association of Medium-Sized Enterprises (BMWV).

A gene that is involved in half of all hereditary hearing disorders

Noise is not the only cause of hearing loss. Middle ear infections, viruses and, above all, hereditary diseases can also lead to hearing loss. "The investigation of such hereditary diseases helps us to understand how hearing damage occurs," said Müller. For example, that the "Connexin 26" gene in the inner ear plays an important role in converting sound into a nerve impulse. It is therefore “the gene most commonly associated with a disease” in mankind: “50 percent of all hereditary cases of hearing damage are due to a change in this one gene.”

When hearing, the air vibrations of the sound are transmitted via the eardrum to the fluid in the cochlea of ​​the inner ear, in which the sensory cells for perceiving the sounds are located. "When you wind up the cochlea, it looks like a piano - the sensory cells for perceiving high notes are on one end, for low notes on the other." Depending on the pitch, the fluid in the inner ear presses the "keys" of the hearing organ, the so-called hair cells. They convert the mechanical signals of the sound into electrical signals that are passed on to the brain.

15,000 hair cells per ear - that must be enough for a lifetime

For this, however, hair cells have to be intact. And a person is born with only around 15,000 of these sensitive cells per ear. "If they die, they are lost forever, humans cannot regenerate them," says Müller. And noise affects the cells in such a way that 10 percent of all hearing damage in adults can be traced back to it. "Even the sound you have in your ear the day after a rock concert is a sign that the connections between hair cells and nerve cells are disrupted," said Müller.

In the meantime, knowledge about the hearing process and the cells and genes involved has led to new therapeutic approaches - for example in regenerative medicine. Here it is already possible to grow hair cells in the laboratory and also in animal experiments. But imitating these processes in the human ear is “still utopian at the moment,” said Müller. Companies such as "Frequency Therapeutics" are already trying to stimulate hair cell regeneration with drugs.

Müller considers gene therapies to be more promising: The idea is to smuggle genes into defective but still living hair cells that have a repair effect. This works very well in pre-clinical studies. Clinical studies are in preparation.

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