The first success for gene therapy in the United Kingdom has restored health to an infant who last year was confined to a sterile room and needed to be kept alive by a ventilator.

Rhys Evans, now 18 months old, suffered from X chromosome linked severe combined immunodeficiency disorder, popularly known as “baby in the bubble” syndrome, after the sterile plastic spheres used to protect some babies from infection. He now lives a normal life at home.

At a …