How deaf became cure

The diagram illustrates the synaptic ribbon structure inside an Inner Hair Cell (IHC) in the cochlea, which is responsible for transmitting sound signals to Auditory Nerve Fibers (ANFs).

Children born with certain forms of genetic deafness—such as DFNB9, caused by mutations in the **OTOF** gene—lack the functional protein (*otoferlin*) required for these synaptic vesicles to release neurotransmitters to the auditory nerve.

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**How Gene Therapy Restores Hearing**

* **Targeting the Defect:** In genetic inner-ear deafness, sound vibrations reach the inner hair cell normally, but because of a missing or mutated protein (like otoferlin), the neurotransmitters cannot be released across the synapse to activate the nerve fibers.

* **Dual-Vector Delivery:** Because large genes like *OTOF* are too big to fit inside a single standard delivery virus, researchers split the gene into two halves and pack each half into an Adeno-Associated Virus (AAV) vector.

* **Surgical Injection:** The viral mixture is injected directly into the fluid of the cochlea (often via the round window membrane).

* **Protein Assembly & Signal Restoration:** Once inside the inner hair cells, the two gene halves recombine, allowing the cell to produce fully functional otoferlin proteins.

* **Synaptic Transmission:** With otoferlin present, calcium ions ($Ca^{2+}$) trigger the synaptic ribbon to dock and fuse neurotransmitter vesicles, allowing electric signals to pass to the auditory nerve and reach the brain as sound.