Families all over the world have them; unexplained health conditions passed down through generations.
This may be why - and now, there might be a way to prevent transmission.
The "family curse" is often referred to by people who've had an unknown condition plaguing the generations - causing unexplained deaths or onsets of various illnesses.
Now, there might be a name for them.
Mitochondrial disease, or 'mito', can come in many forms. From seizures, strokes, muscle weakness, chronic fatigue, blindness, dementia and organ failure - to name a few. It's an umbrella term for at least 350 different conditions and counting.
Mito is even being described by some as the culprit behind their 'family curse'.
Some babies born with mito don't even make it to age 5. Others live with debilitating illnesses and some exhibit little to no symptoms.
Currently, in Aotearoa, mothers with some types of mito have no choice but to pass on their illness if they want a child of their own. Alternatively, they can adopt or seek donor eggs.
Both options would mean the child is not genetically theirs.
There is, however, a solution on the horizon.
Both England and Australia recently legalised mitochondrial donation - a revolutionary technique that involves genetic material from three people[BN3] , reducing the risk of transmission of mito.
Babies have already been born using the technique in the UK.
Reproductive biologist and pioneer of mitochondrial donation, Mary Herbert, said the condition occurs when a mother has a mitochondrial DNA mutation that is passed down.
"All the instructions for our mitochondrial DNA come from our mum, so if she carries a harmful mutation this will be transmitted to her children and passed down the maternal line across multiple generations with a risk of developing serious mitochondrial disease" Prof Herbert explained.
Mitochondria are the "batteries" of the cell - they produce energy. On a basic level - when these "batteries" fail to produce energy or don't produce enough, it can cause major problems.
So, more than 20 years ago, Prof Herbert started working on mitochondrial donation.
The technique works by replacing unhealthy mitochondria with healthy donated mitochondria - all the while maintaining the genetics of the original parents.
"We thought maybe we could essentially just 'change the batteries,'" Prof Herbert said.
Genetically, it's a very small donation. It doesn't contribute to any identifying characteristics - apart from determining whether the baby is healthy or has the disease.
The Mito Foundation played a massive role in legalising mitochondrial donation in Australia. Newshub spoke with their advocacy manager, Clare Stuart, about what the legislation means.
"Talking to women who had assumed that having children of their own was off the cards for them... knowing that science has their back and in Australia parliament voted to give them that choice has been incredibly powerful," she said.
Stuart said the term dementia is increasingly being used to describe symptoms of mito, with cases even being diagnosed in childhood.
"As parents we often think of remembering the first word our child says - for my friend, she talks about the huge grief of remembering the last word that her daughter said."
This is just one example of how mito can impact people's lives.
According to Prof Herbert, the severity of the disease and symptoms can vary depending on the level of mutation and the ratio of normal to mutated mitochondria.
Currently, there is no way of predicting what the mutation load will be.
According to Prof Herbert, a woman who carries one may not have any symptoms herself - but she can produce eggs with a wide range, so her child could be severely affected.
Essentially, it's like reproductive "Russian roulette" and it can be very cruel.
Stuart suggested many countries, including New Zealand, may be choosing to wait for the findings of research projects before they seek to make the technique available.
That being said, the new technology is making waves in the medical world - with a Kiwi researcher in the thick of the debate.
Medical student Olivia Donaldson, from Melbourne's Monash University, has been looking into the ethics of Mitochondrial donation at Oxford.
Donaldson will be exploring both sides of the discussion. A team will also be working with the children born using the technology, whose identities will remain anonymous.
Their aim? To determine if the benefits outweigh the risks.
Opponents claim the technology crosses "nature's boundary". Although this may be true, according to Donaldson, it's a weak argument.
"If you're going to say that it's so unnatural, any sort of assisted reproduction technology is going to have that flaw - it all will. It's not something unique to mitochondrial donation," she said.
Prof Herbert respects opponents' views, although claims her work is justified.
"If we can do something to prevent human suffering and we can do it in a controlled and rational way... there's a moral imperative to do that," she said.
Donaldson said mitochondrial donation is tricky because it's a "heritable form of genetic modification". This means whatever changes it causes will be passed down through the generations.
She claims medical decisions like these used to be a "black line that you could not cross in medicine". Now two countries, Australia and the UK, have already crossed it - albeit under strict regulatory conditions.
There's a reason that line has been crossed. As Donaldson points out, there's no way to know for sure, unless you try.
"We have no way to prove there are flaws unless we get the data."
Stuart believes the research is at a point where the next logical step is to continue working with real families.
"We think it's important - we've shown as much as we can in the lab - now it's the point to say, 'Let's do this as safely as possible and continue learning through that process.'"
Until now, mothers with Mitos have had no alternative aside from living with the inevitability that they will pass on the mutation to their kids. For women in New Zealand, this is still the case.
Stuart said the best place to start is by generating awareness.
"Overwhelmingly the research that we're seeing now is when mitochondrial donation is explained to the general public, the majority support - not only its continued research but its eventual availability to families that can benefit from it."
Both Mary and Stuart believe giving families a choice will change lives. It is not, however, a simple process.
"What happened in Australia leading into the legislation passing through both houses of parliament under a conscience vote in 2022 was a number of years - a multi-stage process that included lots of robust debate."
So, with the technology and research just across the ditch, could Australia be paving the way for New Zealand in the future?
Associate Health Minister Casey Costello said while she hasn’t received any advice on mitochondrial donation, she noted the Advisory Committee on Assisted Reproductive Technology (ACART) is "actively monitoring the trials underway in Australia and the UK".
