It is not age that is to blame for senile hearing loss, but a gene
Many elderly people suffer from hearing loss. Age–related hearing loss is a disease with a complex name presbyacusis. It is expressed in the fact that a person begins to hear high-frequency sounds worse. The simplest thing is to associate such a disease with a lifestyle or simply with aging. But, it turns out, he also has a genetic background. It was possible to prove its presence by the standard method – the study of twins. However, no one could have imagined the need for such an analysis. Therefore, until now, no one has conducted a full-scale genetic study of age-related hearing loss.
The specialists of the Hearing Institute at the Gonda Research Center for Cell and Molecular Biology (House Ear Institute, Gonda Research Center for Cell and Molecular Biology) were the first to come up with a new approach to hearing loss. Specialists from Los Angeles worked together with the Translational Genomics Research Institute and the University of Antwerp (Belgium).
They studied 3,434 twin patients from eight medical centers in six European countries aged 53 to 67 years. Having assessed the level of hearing by standard methods, the doctors selected 846 couples in which one of the brothers (sisters) is hearing impaired, and the second is not.
Related genomes were marked with a variety of genetic markers and began a comparative analysis. Scientists were looking for places with different nucleotides in the same genes. And we managed to find several such genes. As a result, only one candidate remained by the method of elimination. This is the GRM7 gene, which is involved in the metabolism of glutamate – it encodes one of the receptors of this amino acid.
Glutamate (or glutamic acid) is the most important excitatory neurotransmitter in the mammalian nervous system. It works in different parts of the brain, providing the transmission of a nerve impulse. A study in mice and humans has shown that the GRM7 gene is active in hair cells and spiral ganglion cells of the inner ear. At the same time, in high concentrations, glutamate is very toxic. If there is too much of it, neurons are overexcited until they die.
It seems that it was the excess of glutamate that caused the twins' hearing loss, the authors of the work believe. Genetic analysis has shown that when removing "protein casts" from some variations of the GRM7 gene, an incorrectly functioning glutamate receptor is obtained. Because of this, apparently, the amino acid accumulates in the synaptic cleft and damages the hair cells in the cochlea of the inner ear. They perform a very important role – the conversion of mechanical vibrations into an electrical pulse. At a serious stage of the disease, the number of hair cells in the cochlea is reduced by more than half.
According to WHO, around 600 million people over 65 suffer from hearing loss worldwide, and by 2020, according to forecasts, there will be more than 1 billion of them. And the authors hope that their discovery will help to find effective means of their treatment. At the next stage, they are going to develop a laboratory model on animals to evaluate promising pharmacological drugs.
Source: League of HearingPortal "Eternal youth" www.vechnayamolodost.ru