Deaf baby can hear after 'mind-blowing' gene therapy treatment

A toddler who was born completely deaf due to a rare genetic condition can now hear unaided thanks to a pioneering gene therapy. 

Opal Sandy, who is now an 18-month-old girl from the U.K., is the youngest child in the world to receive this type of gene therapy, which uses a harmless, modified virus to correct genetic mutations in the body's cells. In this case, the therapy replaced a mutant gene associated with deafness with a working copy of that gene, according to a statement released May 9 by Cambridge University Hospitals. 

Very similar gene therapies are being tested in other trials and have shown early success in treating slightly older children with the same type of hearing loss as Opal. 

Known as auditory neuropathy, this type of hearing loss arises when the ears can detect sound but can't relay that information to the brain. The condition is caused by mutations in a gene called OTOF that normally makes otoferlin, a protein needed for the inner ear to talk to neurons that are linked to the brain. The condition accounts for between 1% and 8% of cases of congenital hearing loss that occurs in the absence of other symptoms.

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Opal was diagnosed at 3 weeks old. When she was 11 months old she became the first patient treated in a global trial of the new gene therapy. She was given the new treatment via an injection into her right ear. The virus injected during the procedure — known as an adeno-associated virus — delivers a working copy of OTOF to cells in the ear to replace the mutated version. Afterwards, the virus is naturally eliminated from the body.

Doctors also installed a cochlear implant in Opal's left ear; these devices help users hear some sound by relaying signals to the brain that their ear cells can't.