The mysteries of mitochondrial disease
Tamara Robins had a vague recollection from her high school biology classes that human cells contained structures called mitochondria and that they had something to do with energy.
The memory flooded back but was of no help when doctors told her and husband Jason that their two-year-old twin son Noah had Leigh syndrome, an incurable neurodegenerative disease caused by mitochondrial gene mutations.
“Neither of us had any idea what mitochondrial disease meant so we went home and did the research and it was pretty grim,” says Robins, who lives with her family in the Swan Valley, north-east of Perth.
Now 15, Noah is unable to walk or talk, and his muscles constantly jerk. On bad days he is often too weak to sit up.
“The most frustrating thing is that in the 13 years since diagnosis, nothing has changed in terms of treatment or cure for Noah’s condition,” says Robins.
Mitochondria are microscopic compartments found in all human cells, except red blood cells, and their main job is to convert the sugars, fats and proteins we eat to produce most of the chemical energy (adenosine triphosphate or ATP) needed to power the body’s vital organs.
The mitochondrion has its own DNA (mtDNA) that encodes the building blocks for energy production and is semi-independent of the DNA in the cell nucleus. Mitochondrial disease – which is linked to about 300 conditions, from cardiac disease to diabetes – occurs due to mutations in the mtDNA.
One Australian baby is born every week with a severely disabling form of mitochondrial disease, according to figures from the Mito Foundation. Although it primarily affects children, onset in adulthood is becoming more common. It’s estimated that one in 200 Australians carry a genetic mutation that could potentially lead to mitochondrial disease.
The proportion of mutant mtDNA in most cases determines the severity of the disease, and most damage occurs in parts of the body that consume the most energy, such as muscles, nerves and brain.
In about half of all known cases, mitochondrial disease is caused by mutations in the mtDNA that we inherit from our mothers. In other cases, mitochondrial disease is caused by genetic mutations in the nuclear DNA we inherit equally from our mother and our father.
In what is considered a major step towards reducing the risk of transmitting mitochondrial disease, the federal government is now considering law changes to allow for mitochondrial donations to be used in IVF programs.
Despite the fact mitochondrial disease is quite common, Robins says it is not widely understood. “It’s complicated, and trying to explain it to people is not easy because it manifests itself in different ways among different people,” she says. “In Noah’s case, I tell people it’s like running a household including the lights, airconditioning, fridge, television and washing machine on a single AA battery.”
Another blow for the Robins family came just two weeks after Noah’s initial diagnosis when his brother, Harrison, was diagnosed with autism. Doctors have not ruled out the possibility that the mitochondrial gene mutation he shares with Noah is responsible.
Mutations in mtDNA were only found to cause disease in 1988, which makes it a very new area of medicine. As such many knowledge gaps exist.
Professor Aleksandra Filipovska, lead mitochondrial researcher at Perth’s Harry Perkins Institute of Medical Research, agrees that while there has been a renaissance in this field of research in the past decade, much of mitochondrial pathology remains a mystery.
“What makes mitochondria interesting to study is the fact they have their own DNA which co-exists in the cell with the nuclear DNA,” she says. “It’s fascinating that the DNA inside the mitochondria originally came from bacteria [over a billion years ago when it was incorporated into primitive host cells] but is now used by our cells to make most of the energy we need.”
While faulty mitochondria can lead to many diseases, Filipovska says more fundamental research is required to understand this process. “Conditions like cardiac disease, epilepsy or diabetes might run in the family, and mitochondria defects may contribute but are not always the underlying cause,” she says. “It depends on what the disorder is, and to properly determine the cause would require complex gene sequencing in research laboratories.
“We still don’t know enough to treat these diseases, which can impact on generations in the one family. So my team’s focus is discovery science to unravel just how mitochondrial DNA works and how the mutations cause the disease.”
Her team has made several documented discoveries on how genes are regulated in mitochondria, and the ultimate aim is to design drugs to specifically target the mutations.
Filipovska says the Perkins Institute is one of many Australian research centres that are supporting the call for law changes to allow for IVF mitochondrial donations.
The new technology, pioneered in Britain, means couples can have their nuclear genes put into healthy mitochondrial DNA background using a donor egg that has the potential to eliminate the transmission risk. But it involves genetic material from more than two people and for this reason it is prohibited in Australia on legal and ethical grounds.
Some critics have prophesied that such a move would lead to designer babies, but Tamara and Jason Robins fully support it. “Why wouldn’t you do that when it could help stop the disease from passing down and harming future generations?” says Robins. “We’ve known four children with Leigh syndrome, and two are no longer with us.”
Despite the huge workload and worry of caring for two teens with health issues, Robins says every birthday is a milestone to be celebrated.
“Both our boys bring us so much joy in their own special way. Harrison is very serious but he has a dry sense of humour, and he’s very protective of his brother. He’s now in year 10, and excels at maths to the point where he speaks like a professor,” she says with a warm laugh. “Noah on the other hand is cheeky and a little ratbag who likes to stir his brother to get a bite out of him.”
Noah attends a special school and can sign but he mostly communicates through a device containing pictures to indicate his needs and feelings.
“On his good days he scoots around the house on his bottom or in his wheelchair,” says his mother.
“We sometimes call him the Mito Man because he’s a daredevil and does things with no thought for safety, which might have something to do with the lesions the disease has left on his brain.”
Robins admits there have been many times when Noah has missed out on birthday parties, sleepovers and camping trips, but there are also many treasured moments.
“A group of volunteers from Disabled Surfers Association WA recently took both boys to Leighton Beach near Fremantle where they formed a line in the water to allow Noah his first surfboard ride. To watch him thumping his chest for more was an indescribable moment for us,” she says.
But it’s the little things that most parents take for granted that clearly upset Robins. “We’ve never heard Noah say ‘Mum’ or ‘Dad’, and we’ve never had him run down the hall and jump on our bed,” she says. “Sometimes I’ll ask for a hug but there’s no way he can wrap his arms around me so he turns his body toward me and struggles to get one arm over my shoulder, and that’s it.
“The boys are our lives so we do a lot of fundraising to help the Mito Foundation. It’s taken time but awareness, through events like The Bloody Long Walk, is improving.
“We will never lose hope that one day there will be a breakthrough that can help Noah, so until then we’ll keep screaming from the rooftop.”
This article was first published in the print edition of The Saturday Paper on Apr 25, 2020 as "Hard cells".
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