Emily Eiffert never knew her little sister Amy, but that doesn't stop her from missing her.
"When I talk about Amy it makes me want to cry," she says. "I feel sad that I'm here and she's not. Amy should be here with me."
Amy died in 1999, two years before Emily was born. She was just 18 months old when she succumbed to what doctors at the time believed to be encephalitis, an inflammation of the brain that can be caused by viral infection. It was only years later, when two-year-old Emily was rushed to hospital after having a seizure, that doctors began to look at the possibility of a genetic cause.
"When Amy was sick there were no tests for mitochondrial disease and very little was known about it," says Emily's mum Alison. "We were told that the cause of her death wasn't anything hereditary."
By the time Emily was in hospital there was a lot more information available about the condition. When neurologists compared Emily's brain scans to Amy's, they discovered tell-tale similarities.
"That's when we became aware for the first time that it was a genetic illness," says Alison.
A muscle biopsy revealed that Emily had Leigh Syndrome, a mitochondrial disorder that affects the brain. Life expectancy for children diagnosed with Leigh Syndrome usually exceeds no more than two or three years.
Emily, however, proved to be an exception. The seizure left her with a neurological condition and partial paralysis down her left side, but she stabilised and pulled through. After spending three weeks in hospital, she was well enough to return home.
"From that point, we didn't know what to expect," says Alison. "We were told Emily would keep having seizures, but that hasn't happened. She's gone through school and has now started at college. She has done incredibly well considering her start in life, but it hasn't been easy for her."
Like all mitochondrial-related diseases, Leigh’s disease is a complex condition that affects individuals in different ways. Emily has an older brother, Adam, who so far has shown no sign of the condition. The Eifferts don't know where in the family the causative gene is carried, and have turned to the Lily Exome Sequencing Project to help ascertain an exact genetic diagnosis.
"We're hopeful that a DNA analysis will reveal how the condition has been passed down," says Alison. "Whether it’s a gene passed between my husband and I or a mitochondria within my egg, we don’t know. If we can identify the gene, we’ll have a better understanding of Emily’s condition and how to treat it going forward."
For now, the Eifferts have no choice but to continue living one day at a time, aware that Emily is defying the odds with every day that passes. Having endured the loss of her first child, Alison is no stranger to heartbreak, but coping with the daily uncertainty of Emily's illness involves a different kind of emotional stress.
"When Amy died that was absolutely devastating. It’s terrible to lose a child. But Emily has to live with this disease every day. She's done so incredibly well, and of course that's a positive thing. But you have that cloud over you the whole time, constantly worrying if she's going to be ok."
There have been some frightening moments. Last summer, the family were flying on holiday when, without any warning, Emily blacked out on the plane.
"One minute she was fine and the next she was passed out, totally gone," recalls Alison. "There was no obvious reason for it and we still don't know what caused it."
Since her initial seizure Emily has regained some strength and movement down her weak left side. However, she still tires easily, suffers from terrible migraines and often finds it difficult to follow conversations. Socialising with her friends can be exhausting, and things are not getting any easier now that she has reached an age when freedom and independence are increasingly important to her.
"I try to keep going, to keep up with everyone else and not show that I am weaker than them," says Emily. "But I do feel like I have missed out with my friends, as I haven’t been able to go to sleepovers and on trips into town. I have tried, but I felt so exhausted and ill afterwards that I didn't want to move."
Alison acknowledges that it's a challenge balancing her desire to protect her daughter with the growing need to let her have the space and independence all teenagers crave.
"I am finding it harder as she's growing up," she admits. "We want her to live a full life, but it's difficult to let go. I’m nervous that she’ll push herself too far and become ill, so it's about acknowledging she has to live her own life and accepting that she needs to do that."
Emily is so determined to manage on her own that she prefers not to let others know about her rare disease unless absolutely necessary. Even at college, where she is training in countryside management, she is reluctant to ask for help.
"I feel awkward when I'm getting extra help at college and no one else is, because I don't want to be seen as different." Emily explains. "Some of my friends know about my condition, and it's nice that if I'm walking slower than everyone else a couple of people will walk with me. But I feel uncomfortable when questioned about it. I worry that I won’t understand what is being asked of me."
While Emily's case remains unusual, the Eifferts have been encouraged in recent years by the increasing number of people with mitochondrial diagnoses who live into adulthood. With support from The Lily Foundation, they have been able to connect with other families in their situation.
"These days, more older children are starting to be recognised with mitochondrial conditions. We have met some at the Lily Family Support Weekend, and knowing there are others out there has been a really positive thing for her," says Alison.
"It gives us hope, knowing there are others who go on and try to live a normal life. It’s a horrendous condition, and having lost a child we know how bad it can be. But Emily has had as much of a good life as we can hope for, and we are grateful for that. Sadly it’s not the same story for everyone, but knowing that with support you can go on and have a good life is a positive thing."
The Eifferts are also encouraged by the recent increase in scientific research into mitochondrial diseases. With diagnostic services improving all the time, along with several promising avenues of research into new treatments, Alison is hopeful that life will get easier for Emily and others like her.
"Things are changing so fast on the research side," she says. "We sometimes think, maybe things will change as Emily gets older. You cling on to the positives as much as you can, and hope that things will improve.
"We’ve been supporting The Lily Foundation for years now, it's so important to keep putting the word out there. There is so much that can be done with science and medicine, and for families who are affected it’s important to see that things are changing and moving forward. That helps you keep going. It's what gets you through."
If you’ve been affected by mitochondrial disease and would like support, call Liz at The Lily Foundation on 0300 400 1234 or 07947 257247, or email [email protected]. All conversations are private and confidential.