Blood tests showed baby KJ had sky-high levels of ammonia, a toxic substance the body usually expels. The root cause was his genes - or more particularly a specific gene mutation.

The race was on to try and treat him before his condition took a firm hold. His doctors came up with a radical solution - for the first time ever, they designed and applied a gene-editing drug in record time, specifically for him. Have we seen breakthrough in preventing genetic diseases? With Fyodor Urnov, a professor in the Molecular and Cell Biology Department at the University of California, Virginijus Šikšnys professor at the Life Science Center of Vilnius University, Waseem Qasim from the UCL Institute of Child Health in Great Ormond Street Hospital in London and Jennifer Doudna, Professor, University of California, Berkeley and founder of the Innovative Genomics Institute.

Presented by Tanya Beckett. Produced by Bob Howard. Researched by Mauve Schaffer Edited by Tara McDermott.