Paediatric nurse's chances of having healthy kids will be determined by outcome of three-parent vote

Rachel Steel is used to getting up early to start her shift at the Royal Victoria Infirmary in Newcastle. The 24 year old is a paediatric nurse who works hard to look after the children in her care. But when the alarm went off at six this morning she packed a small bag and caught the train to London. Because a vote taking place in the Commons today could determine Rachel's chances of having healthy kids of her own.

It is four years since the former British gymnast was told she carried faulty mitochondrial genes. Rachel was diagnosed in the hospital she works in now, by the same doctors who have pioneered research that could change her life.

The Wellcome Trust Centre for Mitochondrial Research helps the Trust look after 500 families who, like Rachel, are affected by a disease that is passed on from generation to generation.

The body's mitochondria are similar to tiny battery packs that deliver power to its cells. When they don't work properly the organs that need the most energy, like the brain, the heart and the kidney, begin to shut down.

Effects of the disease can be quick and catastrophic - many babies don't live longer than 48 hours. Or parents are left to watch helplessly as the developmental gains made in the first few years of their child's life are relentlessly reversed.

There is no cure for mitochondrial disease and children rarely survive beyond five years old.

So Rachel, like an estimated two and a half thousand women in the UK, must face a terrible choice. Although everyone has mitochondria in their cells, only mothers pass them on. Rachel is desperate to be a mum, but knows her genetic heritage means her babies may not live for more than a few hours.

That's why she's on the busy commuter service from Newcastle to London, sitting with two research scientists who have spent a decade working out how to use a tiny amount of mitochondrial DNA from a donor egg to stop the disease being passed from mother to child. Next to them is a specialist nurse who has watched child after child die from diseases we now have the technology not to cure, but to prevent, before an embryo is even formed.

And there's the rub. Critics - amongst them the Catholic Church and some from the Church of England - believe that without more scrutiny the process could open the door to the possibility of "designer babies".

So as the train cuts through snow-dusted fields, ever closer to London, the table from Newcastle grows quieter. Flicking through the headlines on her mobile phone, Catherine Feeney, a mitochondrial specialist nurse says: "I was feeling so optimistic, but now I am getting nervous. The religious lobby has a lot of resources that we don't. They say there hasn't been enough scrutiny but there have been three independent reviews and a public consultation".

For Rachel Steel, who has always wanted a family, it is even simpler. She'll be watching from the public gallery in the Commons, knowing if MPs vote no, her future will be forever bleaker. "I'll just be devastated", she says. "But I have to be there."