Gene Editing Technologies On Hearing Loss and Deafness
Mon, April 19, 2021

Gene Editing Technologies On Hearing Loss and Deafness

Chinese biophysicist He Jiankui used CRISPR technology to gene edit human embryos to make them immune to HIV infection in November 2018, narrated Catlin Nalley of The Hearing Journal, the most respected publication in hearing health care. They were implanted and led to the birth of twin girls. He was condemned in the scientific community, sparking bioethical discussions on the safety and ethical implications of his work and calling for a global moratorium on human germline gene editing.

He was convicted of “illegal medical practice” in December 2019 and despite the outrage at the biophysicist, another scientist recently announced his intention to use CRISPR technology in a similar way to target hereditary deafness. Denis Rebrikov, a molecular biologist from Russia, shared his plans in July 2019 to stop children from inheriting a form of deafness caused by mutations in the GJB2 gene.

He informed journal portal Nature that he already started gene editing eggs that were donated by hearing women to learn how to allow deaf couples to bear children without the genes associated with deafness. Germline gene editing alters the genes in eggs or sperm cells of even those of an embryo, which could be inherited by future generations.

By the Numbers: Perceptions On Gene Editing

Cary Funk and Meg Hefferon of Pew Research Center, a non-partisan think tank, found in their 2018 survey of 2,537 adults that about seven in 10 or 72% of Americans believed that changing an unborn baby’s genetic characteristics to treat a serious disease and condition that the baby would have was seen as an appropriate use of medical technology.

Meanwhile, 27% said this was taking technology too far. When asked if they would change a baby’s genes to reduce their risk of developing a serious disease or condition over their lifetime, 60% said it was appropriate while 38% believed it would be taking medical technology too far. Interestingly, 19% of Americans said it would be appropriate to use gene editing to make a baby smarter, while eight in ten or 80% said it was taking medical technology too far.

Men are more accepting than women with regard to the usage of gene editing to alter a baby’s genetic makeup. For example, more men (43%) than women (24%) are supportive of gene-editing technology if it required embryonic testing to develop. 76% of men were also found to be more supportive than women (68%) of utilizing gene editing to treat a congenital disorder.

Key Facts on Deafness and Hearing Loss

According to the World Health Organization, the United Nations specialized agency, around 466 million individuals worldwide have disabling hearing loss. 34 million of these people are children. By 2050, it is estimated that more than 900 people or one in every 10 individuals will have disabling hearing loss. The Centers for Disease Control and Prevention (CDC), the US’s leading national public health institute, found that genes are responsible for hearing loss among 50% to 60% of children with hearing loss.

About 20% of babies with genetic hearing loss have a “syndrome” such as Down syndrome or Usher syndrome. Infections during pregnancy in the mother, other environmental factors, as well as complications at birth are responsible for hearing loss among almost 30% of babies with hearing loss. 14% of those exposed to congenital cytomegalovirus (CMV) infection— a preventable risk factor for hearing loss in children — during pregnancy develop sensorineural hearing loss (SNHL) of some type.

The Risks of Gene Editing

The above-mentioned surveys show that people are supportive of gene editing but when it comes to hearing loss and deafness, is it moral to use gene-editing technology like CRISPR— which hasn’t been proven to be safe?

Brad Walters, PhD, an assistant professor in the department of neurobiology and anatomical sciences and the department of otolaryngology and communicative sciences at the University of Mississippi Medical Center (UMMC) said, “We know from numerous sources that CRISPR-based gene editing, when introduced into a single-cell embryo, does not usually edit the genome right away.” This means it only edits the DNA as the cell divides.

There is a high probability of a gene edit being mosaic and not actually taking place in the cells. Hence, hearing loss might not actually be prevented by the gene edit. Walters warned that the gene-editing tool is known for causing off-target effects, thereby introducing other mutations into the embryo that could have dire effects in the ear and in the body.

People need to weigh other options to prevent or treat hearing loss or even reduce the risk of having a child that will have a “deafness-causing mutation.” Such alternatives include cochlear implants, IVF, genetic screening of embryos, the use of a sperm or egg donor, or waiting for the technology to be developed and tested for safety, Walters said.

Technology As A Clinical Option

There are different avenues to explore when it comes to gene editing for deafness and hearing loss. Walter stated that in their lab, they have this belief that they’re going to develop “a therapeutic intervention to restore or rehabilitate hearing for someone who has sensorineural hearing loss” at some point in time.

He acknowledged that there are a fair number of people who have lost their hearing and would like their sense of hearing to be restored if they can. Hence, his colleagues are focused on attempting to determine the genes that are essential in regenerating the sensory cells in the inner ear. Walters and his team are aware of deaf cultures and communities.

Walters explained, “We're not actively trying to push these technologies and correct any and every hearing loss mutation that we come across.” They want to present that option clinically, but it’s up to the person if they want to live with hearing loss or allow it to progress in cases of progressive hearing loss.

“There needs to be a greater awareness that a cure is not always the solution for deafness,” asserted Jaipreet Virdi, PhD, an assistant professor at the University of Delaware. In fact, health care providers need to incorporate information from Deaf social workers or ASL teachers when educating hearing parents about alternatives for raising their deaf child. This is to ensure that the parents are educated, enabling them to make more informed and intelligent decisions about their child.

Diversity In Discussing Gene Editing Technologies

A discussion between audiologists and other clinicians about gene editing technologies is critical in ensuring that the patients’ voices are heard, as justified by Christopher Spankovich, AuD, PhD, MPH, an associate professor and the vice chair of research in the department of otolaryngology and communicative sciences at UMMC.

“Advocating for Deaf culture is extremely important; we also need to advocate for patients who do want to see this technology move forward in an ethical and safe way.” Likewise, audiologists should also play a role in enhancing the usage of these technologies.  

Most individuals are supportive of gene editing their baby to reduce their chances of developing a serious disease later on, perceiving such an option as acceptable. But they also need to consider the risks of gene editing technologies.

When it comes to hearing loss and deafness, these tools should be presented as an option and no one should be forced to use it. For now, audiologists and other experts need to collaborate on the ethical and enhanced use of these technologies.