BioQuakes

AP Biology class blog for discussing current research in Biology

Tag: hearing loss

Embryo Gene Editing can Ensure Offspring Do Not Inherit a Deafness Gene!

Denis Rebrikov, A scientist in Russia has done research regarding ways in which he can edit the genome sequence of an embryo in order to prevent the fetus from developing certain gene mutations, specifically in this case a hearing problem or possible complete deafness. His plans are very controversial to some, who believe the possible risks of very harmful mutations to DNA that would be passed onto direct and future offspring, outweigh the possible benefits. However, some people find this scientific possibility to be worth the risk, if it means not passing a potentially very harmful gene down to offspring. If these methods are done correctly, it should alter the genome sequence in the embryo so that future offspring off that embryo will not inherit the negative mutation.

One couple shared their story in detail, in which both parties have a hearing deficiency, the man with partial deafness, and the woman completely deaf. Their biggest hope is to have children who will not inherit hearing issues, because of the apparent challenges they have had to face themselves because of them. They would be the first couple to perform this gene editing on an IVF embryo, so they obviously have some reservations. One of those being publicity, but more importantly the potential risks of using the CRISPR genome editor. They already have a daughter with hearing loss, but they never chose to test her genes for mutations, nor did they get her a cochlear implant to aid her hearing, because of the potential risks of that. When they finally tested her genes, they learned that she had the same common hearing loss mutation called 35delG in both her copies of a gene called GJB2. The parents then tested themselves, realizing they were both 35delG homozygous, meaning their daughter’s mutations were not unique to her, they had been inherited.

If either the mother or father had a normal copy of the GJB2 gene, a fertility clinic could have more easily created embryos by IVF and tested a few cells in each one to select a heterozygote–with normal hearing–to implant. At this stage, Denis Rebrikov informed them that CRISPR genome editing would be their only option. However, the process presents possibly deal breaking risks, such as mosaicism, in which a gene edit might fail to fix the deafness mutation, which could create other possible dangerous mutations like genetic disorders or cancer. The couple has not decided to go through with the editing just yet, but it is something they are open to in the future as more possible new research or test subjects become available.

Explaining the CRISPR Method: “The CRISPR-Cas9 system works similarly in the lab. Researchers create a small piece of RNA with a short “guide” sequence that attaches (binds) to a specific target sequence of DNA in a genome. The RNA also binds to the Cas9 enzyme. The modified RNA is used to recognize the DNA sequence, and the Cas9 enzyme cuts the DNA at the targeted location… Once the DNA is cut, researchers use the cell’s own DNA repair machinery to add or delete pieces of genetic material, or to make changes to the DNA by replacing an existing segment with a customized DNA sequence.” -US National Library of Medicine Genetics Home Reference

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Woman with a hearing aid 

If you had the opportunity to alter something in the gene’s of your baby’s embryo, would you? Under what circumstances would you consider this, and what risks might stop you from deciding to do it? Comment down below.

 

 

Hearing Loss Clue Uncovered

In the United States, approximately forty-eight million (twenty percent) of men and women suffer some degree of hearing loss, as it is the third most common physical condition after arthritis and heart disease. While it is most often associated with the population sixty-five and
older, hearing loss effects all ages, as thirty school children per out one-thousand are afflicted in some varying degree. An individual is able to hear sound involving the ear’s main structures. In age-related hearing loss, one or more of these structures is damaged: the external ear canal, the middle ear, and the inner ear. External ear canal impairment is related exclusively to conducive hearing loss. The middle ear, which is separated from the ear canal by the eardrum may be caused by sensorineural hearing loss. Lastly, the inner ear, which contains the cochlea, the main sensory organ of hearing. When the vibrations from the middle ear enter the cochlea it causes the fluid to move and the sensory hair cells pick up this movement. In response to the movement of the fluid the hair cells send an electrical signal up the auditory nerve to the brain where it’s recognized as sound.

 

Now, how do these different internal departments of the human ear gradually induce hearing loss? While we get older, some may develop presbycusis, which causes the tiny hair-like cells in the cochlea to deteriorate over time. Clarity of sound decreases, as the hairs are unable to vibrate as effectively in response to sound. Recently, otolaryngologists have discovered new evidence that human hearing loss relates to a certain genetic mutations. A study at the University of Melbourne revealed “a novel genetic mutation was first identified in 2010 as causing hearing loss in humans… now discovered that this mutation induces malfunction of an inhibitor of an enzyme commonly found in our body that destroys proteins – known scientifically as SERPINB6. Individuals who lacked both copies of this “good gene” were shown to have lost their hearing by twenty years of age.

 

Although this discovery is changing the way scientists previously viewed hearing loss, the answer to why this mutation, SERPINB6, is a catalysts for such loss, is inconclusive. However, this mutative gene has created a revelation for many: it is now not unusual to show gradual signs of hearing loss under the age of sixty years.

 

To better understand the effects of the mutant gene, mice were used in order to imitate the condition from youth to adulthood. At only three weeks of age, mice with SERPINB6 had begun to lose hearing – three weeks is equivalent to pubescent or teenage years in humans. And as we could have predicted, the mice continued to show a decrease in hearing ability, much the same as humans. Researchers examined the mice’s inner ear, which revealed the cells responsible for interpreting sound (sensory hair cells) had died.

 

Fortunately, this new discovery of a mutant gene in human sensory cells has created new attention to better understand the case of those who are effected by the condition. 

 

 

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