There are few things more heartwarming than videos of children with deafness gaining the ability to hear, showing them happily turning their heads at the sound of their parents' voices and joyfully bobbing to newly discovered music. Thanks to recent advances in gene therapy, more kids are getting those sweet and triumphant moments—with no hearing aids or cochlear implants needed.

At the annual conference of the American Society for Gene & Cell Therapy held in Baltimore this week, researchers showed many of those videos to their audiences of experts. On Wednesday, Larry Lustig, an otolaryngologist at Columbia University, presented clinical trial data of two children with profound deafness—the most severe type of deafness—who are now able to hear at normal levels after receiving an experimental gene therapy. One of the children was 11 months old at the time of the treatment, marking her as the youngest child in the world to date to receive gene therapy for genetic deafness.