Here, former Hollyoaks and Casualty actor Colin Wells tells Sky News why he is hopeful a cure will be found after his two children were diagnosed with a rare form of the condition.
One of the reasons I left Hollyoaks was to be able to help care for my daughter Rachael and son Joseph, or Jo-Jo as we call him.
It’s extremely rare to have both children diagnosed with mitochondrial disease – the odds are astronomical.
Rachael was fine until she was about seven years old when she went deaf in one ear and later lost hearing in both ears.
But it was in her early teens that we noticed things about her that were slightly different.
We could tell something was wrong because she became a bit clumsy and she’d started to lose weight.
After a check-up we were sent to see a geneticist. Rachael was diagnosed with a form of mitochondrial depletion syndrome known as RRM2B. It was a huge shock for the family.
We know a lot of doctors, some of whom are close friends, and none of them could explain what the condition was. So we did some research ourselves.
My wife Joanna was in a terrible state about the diagnosis and rang a support group for advice but it turned out to be hugely unhelpful.
The woman on the end of the phone said this was going to be the end of the story and we should start preparing for the funeral.
I wish we had found The Lily Foundation then as they do amazing work fighting mitochondrial disease.
The truth is that many people with the condition can improve their strength by looking after themselves.
Rachael is 20 now and uses a wheelchair. She can walk a little and she’s fed intravenously.
She has a ventilator at night because she could stop breathing without it when she falls asleep.
We have to help her get dressed and she’s unable to work because the condition leaves her with no energy.
But Rachael is always positive. She loves drama and reading and she’s able to ride horses with support.
Her brother Jo-Jo, who is 15, was diagnosed the same condition two years ago.
He was seen by a doctor who came round to the house, closed the kitchen door and broke the news to us.
I just didn’t want it to be true. In some ways it’s worse for Jo-Jo because he looks at his sister and can see what is coming. Jo-Jo has a great sense of humour but he’s scared of what is going to happen.
He has a few good friends but withdraws himself at school. Very often he can’t finish the day because he’s tired and upset and texts me so I can pick him up.
We’re hoping that in a couple of years there is a cure, or at least some form of treatment, to help our children improve their quality of life.
There have been massive improvements in some children around the world with TK2-related mitochondrial DNA depletion syndrome so there is reason to be hopeful.
More people seem to be aware of mitochondrial disease after the tragic case of Charlie Gard. I’ve met Charlie’s mum Connie and she firmly believes it can be treated.
Without an improvement in treatment for my children’s condition, life expectancy is usually mid-20s to early 30s because it attacks the major organs in the body. Finding a cure really is a matter of life or death.
:: Rachael and Joseph Wells have donated gene samples for pioneering research on the use of nucleoside therapy for mitochondrial depletion syndrome, which is being jointly funded by The Lily Foundation.