A gene therapy that has allowed several children born deaf to hear for the first time is being hailed as a "game changer" that raises hopes of the first new treatment for hereditary deafness in decades.

Several medical teams around the world are trialing the procedure, which focuses on a rare genetic mutation that affects only a small number of the 26 million people with congenital deafness globally.

But several success stories announced this week are already being seen as a turning point.