Hearing Loss and Balance in Elderly can be Restored by Gene Therapy

A research team from the National Institute on Deafness and Other Communication Disorders (NIDCD), along with scientists from the Johns Hopkins University School of Medicine, used gene therapy to restore balance and hearing on genetically modified mice, that had a condition which was similar to Usher Syndrome. Usher syndrome is a genetic condition in which there is partial or total hearing loss among humans, and causes dizziness and progressive vision loss. Abnormalities in the inner ear are associated with dizziness and vision loss.

Dizziness and Hearing Loss among the Elderly

Many elderly people suffer from dizziness and imbalance. A population-based study conducted in the United States shows that among people who are older than 72 years, 24% suffer from dizziness. Dizziness among the elderly is a cause for concern among caregivers, as well as to society, as they are prone to falls or accidents. The consequent risk of injuries is the prime reason for hospital admission as well as accidental death. There is an increased fear of falling associated with dizziness, which affects the emotional health of the individual.

There are changes in the balance system of the body, whether it is sensory, visual, neurologic, or even muscular in origin. The functions of these systems tend to deteriorate with advancement in age. Statistics from the Centers for Disease Control reveal that in the United States, one in three people aged between 65 and 74 years have hearing loss, with almost half of those older than 75 years finding it hard to hear. Women are found to be less likely to develop loss of hearing when compared to men.

Usher Syndrome

This is one of the most common reasons for loss of hearing and vision when they occur together. The symptoms associated with Usher syndrome include retinitis pigmentosa and hearing loss. Retinitis pigmentosa leads to night blindness with a loss of peripheral vision. As the vision loss progresses, it leads to a tunnel vision, where only central vision remains. People diagnosed with Usher syndrome have balance problems. The three types of Usher syndrome are type 1, type 2, and type 3. Types 1 and 2 are most common.

Gene Therapy for Usher Syndrome

Neuro-otologist and associate professor of the Head and Neck Surgery team at Johns Hopkins University, Dr. Wade Chien, who is the principal study investigator and his team, studied the effect of gene therapy on genetically modified mice with Usher syndrome. The scientists analyzed the effect of gene therapy provided to the inner ear of these mice which carried the mutation for Usher syndrome. The mice showed classical symptoms of Usher syndrome with difficulty in balance and absence of hearing, from birth.

The study on gene therapy showed that

• There was restoration of balance among the genetically modified mice.
• There was improvement in hearing.
• This was the first study to utilize gene therapy to improve hearing and balance function among mice.

Dr. Chien stated that the study aided in determining that gene therapy of the inner ear was a potential form of treatment for patients with dizziness and hearing loss. The results of the study are preliminary, and further studies on humans will help determine the effectiveness of treatment; however, he said it holds promise.

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Gene Therapy for Retinal Degeneration in Usher Syndrome

D S Williams and colleagues from the University of California in Los Angeles (UCLA) used gene therapy for retinal degeneration in Usher syndrome. The main aspect of gene therapy for these patients lay in early identification of patients, prior to significant retinal damage. While most forms of retinal degeneration are detected only after there has been significant vision loss, in types 1 and 2 of Usher syndrome, the presence of congenital deafness allows identification of the condition. While deafness is treated with cochlear implants, gene therapy could be used for retinal degeneration. Gene therapy studies were carried out on Usher genes using lentiviral (LV) method of transport of MYO7A, the gene which is associated with the development of Usher syndrome 1B (USH1B).

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The study on gene therapy for retinal degeneration was carried out on mice and, though, it was found to be helpful in improving vision, the results among humans is yet to be determined. Similar to gene therapy for deafness and dizziness for Usher syndrome, this study also holds potential as a new form of therapy for this rare genetic disorder.

The research shows that this method of treatment holds a lot of promise and will provide patients with a new line of therapy. Current treatment methods for Usher syndrome include strategies that prevent further deterioration of vision and hearing; but there is no method available to restore the failing faculties. Such studies will help in identifying a method of treatment which could restore vision and hearing loss.

References:

1. Usher Syndrome - (https://www.nidcd.nih.gov/health/usher-syndrome)

Source-Medindia