When Jessica Newell was born in December 2013, she seemed to be “a normal, healthy baby”, said Margarette Driscoll in The Sunday Times. But at six months, “her development slowed, and then began to regress”. She was diagnosed with Leigh syndrome, one of several severe conditions caused by faulty mitochondria – the parts of our cells that provide them with energy. As a result, Jessica now “barely moves, and when she does it seems to be in slow motion”. Her swallowing reflex has degenerated, and she is fed through a nasal tube. “She will never walk or talk and is unlikely to live for more than a few years.” Until recently, her parents would never have considered having another child. But thanks to a vote in the House of Commons…