From her earliest moments, Leni Forrester radiated health and joy. There was no indication that a grave diagnosis would soon cast its shadow over her young life. 

The toddler, from Sevenoaks in Kent, appeared to be developing just like any other child - happy, energetic and completely ordinary.

However, after a relative undergoing IVF discovered they were a carrier of Sanfilippo syndrome - an ultra-rare genetic condition often described as childhood dementia - Leni was swept into uncertainty. 

At the time, her parents, Emily and Gus Forrester, were trying for another baby and the revelation sent them searching for answers.

Initially, they were reassured: Leni had no obvious signs of the condition, and both parents would have to be carriers for Sanfilippo to be passed on.

Yet that reassurance was short-lived. As they looked closer, subtle signs in Leni -bushy eyebrows, frequent ear infections, mild digestive issues, and even early physical quirks - began to take on a far more sinister meaning.

When pieced together, these seemingly minor traits formed what Mrs Forrester, 33, later described as a chilling 'tick box' of symptoms.

However, the family did have a moment of hope. A private genetic test for Leni's father, Mr Forrester, 35, returned negative, seemingly ruling out the couple's worst nightmare.

But in a cruel twist of fate, that hope was ripped away. A later NHS genetics consultation raised fresh concerns, and fast-tracked Leni's case for urgent testing.

Just two weeks later, shortly after returning from a family holiday, the couple's worst nightmare was confirmed. Both parents were carriers - and their beloved daughter, Leni, had Sanfilippo syndrome.

Adding to the heartbreak, there is currently no approved treatment for Sanfilippo in the UK. Experimental therapies exist only in America, still in the clinical trial stage, and funding for patients has not yet been approved.

Mr and Mrs Forrester have since begun fundraising on GoFundMe to secure necessary treatments for their daughter - but it is a race against time before she begins to regress. 

Speaking to the Daily Mail, Mrs Forrester, a marketing professional, recounted how  Leni's young life was flipped upside down within months - but how she has remained steadfast in her determination to ensure her daughter will enjoy a normal childhood. 

She said: 'One of the most shocking things about Leni's condition, but also her diagnosis, is that she doesn't have any pronounced symptoms - or didn't at the time -so we didn't suspect anything was wrong.

'I had a very, very normal pregnancy, normal birth, no complications, and had all the genetic screenings that are available to you on the NHS. Nothing was flagged, and we have no history of any issues in on either side of the family.'

However, the first warning sign that something was not quite right came from a close relative undergoing fertility treatment.

Mrs Forrester said: 'A close family member was going through IVF and had a routine genetic screening as part of that.

'She was flagged as a carrier for Sanfilippo syndrome. It was just more as a precaution to make sure, and none of us dreamed that anything was wrong with Leni.'

But as Mrs and Mr Forrester, who works for Lloyds of London, began researching the condition, small, seemingly unrelated traits suddenly took on a far more worrying meaning.

Mrs Forrester said: 'We did look at the symptoms and the tricky thing with Sanfilippo is how it presents itself - children develop typically until they're two, three years old without any obvious symptoms.

'And then, because Sanfilippo is essentially an accumulation of a toxic waste on the brain, it just hasn't accumulated enough to cause any symptoms at Leni's age.

'Then, affected children basically start regressing and they lose all skills that they've learnt.

'And the first thing to go is usually their cognition and they lose their speech and all cognitive ability.'

She began to recognise early signs in Leni - though each one, on its own, seemed harmless.

She said: 'A bloated tummy and loose stools are an early sign, but we were having Leni investigative for lactose intolerance or some kind of intolerance.

'She also had frequent ear infections, but again, nothing abnormal for a toddler.

'She was also born with her feet turned in, but it was corrected with physio, but again, that is an early sign.'

It was only when everything was considered together that the couple began to fear the worst.

Mrs Forrester said: 'When the close family member told us they were a carrier and we looked at those early symptoms, our hearts just completely sank because we were like, well, she does have all of those things.

'I was pulling up pictures of Leni against other children on Google with Sanfilippo - it was obviously just completely tearing us apart.

'We then did a full investigation to try and get paint a full picture of what was going on. Those initial assessments with each of the specialists took place over a two-month window, with the genetics being the last assessment.

'She was diagnosed by the audiologists as having severe hearing loss, and at the speech and language, she was diagnosed as having a moderate speech delay, but everyone kind of thought, well, she's got severe hearing loss.

'So, once the hearing aids are in, hopefully her speech will catch up. Again, we just couldn't believe that this genetic condition was lurking.'

Yet despite their fears, there was a brief moment of hope for Leni and her parents.

Mrs Forrester said: 'My husband went and got a private genetic test and that actually came back negative.

'We were celebrating - it couldn't possibly be this awful condition that we were dreading.'

Still, the uncertainty became unbearable for the couple, prompting them to relocate from London to quieter Kent during Leni's early diagnosis. They continued with NHS genetic testing - a decision that would ultimately confirm their worst fears. 

Mrs Forrester said: 'We explained the situation to the geneticist.

'Because of the questions he was asking and the analysis that he was doing, like looking at like the creases in the palms of her hands and measuring the width of her feet, I could just tell he thought something was wrong genetically.'

Leni's case was then fast-tracked.

Mrs Forrester said: 'The geneticist then put us forward for something called a rapid response test – there's only 100 of those licensed for use in the UK every year.

'His exact words were that rapid response tests are reserved for the worst and most urgent cases.

'At that point, it had gone beyond his suspicion that something is wrong. For Leni to qualify for that there must be kind of good reason when there's obviously so few tests available.

'We had a holiday booked the following week, and the geneticist said the rapid response test would take the wait time down to two weeks for Leni's results.

'We decided to go on that holiday anyway, and we are really, really glad that we did because we were in ignorant bliss at that point that there was nothing wrong with Leni and we made obviously very special memories.

The day the family were flying home, however, came the news they were dreading. 

Mrs Forrester said: 'His secretary called on the day that we were due to fly home and said that he needed to urgently speak to us. But unfortunately, the only time he could do was whilst we were in air on a flight.

'So, we were obviously just filled with anxiety and it was booked in for very early the next morning.'

It was then, confirmation of Leni's devastating diagnosis came.

Mrs Forrester said: 'He called us and told us that we were both carriers and that Leni was affected with Sanfilippo.'

She described the moment as unbearable.

She said: 'The devastation is - I can't even explain. It's like primal - all of our dreams for our daughter and our plans for our family unit were completely crushed.

'It was just complete, complete heartbreak.'

And in an even crueller twist, it was then revealed the earlier private test had missed Mr Forrester's rare genetic mutation - leading the family into a false sense of hope.

Mrs Forrester said: 'It has since transpired through investigation that Gus carries an extremely rare form of the very rare genetic mutation, that has never before been logged to have caused a child affected with Sanfilippo.

'The only reason that it was flagged in the NHS test and not the private was because they did it as a mapping with Leni's DNA as well. It's now logged in the database and any future people, it will be flagged up.

'But just unluckily for us, it wasn't. So, we got Leni's diagnosis and it was just complete shock and trauma, and we completely crumbled to be honest.

'But we also have a normal two-year-old that needs looking after. So, you just have to carry on. There's no choice there.'

And as the family tried to process the diagnosis, they were dealt another heartbreaking blow.

Mrs Forrester said: 'We said at the time, the only way this could be worse is if I was pregnant.

'And then two weeks later, we found out that actually I was pregnant. We told the geneticist about it, and he said that the baby could be tested in utero for Sanfilippo, but I would need to carry the baby to three months for the testing.

'We had the test done at three months, and unfortunately the baby was also affected with Sanfilippo.

The family chose to terminate the pregnancy.

Mrs Forrester added: 'I had a termination because there are no treatments and there is no cure. We felt we just didn't have a choice, knowingly bringing a child into the world and knowing the kind of the decline and the devastation and the suffering that they would face.

'It just it wasn't something that we felt we could do.'

Now, Mr and Mrs Forrester are looking to the future with Leni – and are racing against time to save their daughter from the regression inevitable with Sanfilippo.

Mrs Forrester said: 'It is a race against time because her condition is so rapidly neurodegenerative. If she is treated now, she could go on to live a normal life.

'But even six months later, it could be too late.'

And while experimental treatments exist for Sanfilippo, access remains limited. 

Mr and Mrs Forrester have since launched a GoFundMe to raise the money needed to give Leni a chance to access treatment before regression begins, however, it does not come cheap. 

Mrs Forrester said: 'There actually are treatments that have been proven to be incredibly effective and transformative for these children. But they just aren't approved yet.

'Leni's condition is because she has a fault in a gene that produces a specific enzyme, and without that enzyme, toxic waste builds up on various organs in the body, but most importantly, the brain, and causes irreversible brain damage.

'There's an enzyme replacement treatment, which has been approved for clinical trial in America but a final submission to the FDA is needed for the funding to be approved.

'However, the issue with this treatment is that it is a weekly infusion of the enzyme for life. It would be a permanent relocation because she would need it weekly for life.

As such, Mrs Forrester said the main effort of their fundraising is to support a UK trial site for the therapy.

She said: 'Great Ormond Street was previously a trial site for this specific treatment when it was in trial before.

'So, our goal would be for them to reestablish Great Ormond Street as a trial site for the final confirmatory trial and then he could access it in the UK.' 

However, there may also be another treatment option available to Leni - one that is already hopefully closer to home. 

Mrs Forrester said: 'The other option is a UK born and bred treatment in Edinburgh by Dr Brian Biggar, who has pioneered this gene replacement therapy.

'The results of this are transformative, with the youngest children, at the moment developing as typical children, with no symptoms whatsoever. But again, the key is that they need to be treated as young as possible.

'This trial is ready for patients, pending funding and they are hoping to start this in December, January.

However, accessing this treatment is also now without its complications. 

She added:  'But due to various complexities around the fact that because the UK government doesn't provide any support or research or funding, they have had to seek a research grant from the US federal government by partnering with UCLA.'

Due to the challenges in accessing treatments and the lack of funding for affected children, Mrs Forrester has emphasised the shortage of awareness and support for families like hers. 

She said: 'The government doesn't offer any support. Families are expected to just go home and cope – it is just cruel.'

'The disparity in funding and research and support from the government.

The condition, Mrs Forrester explained, is relentless.

She said: 'It's essentially an old person problem in a young person's body. We're looking at 10 to 15 years of this.

'There's no roadmap for these children. The system as a whole is broken.

'To you see your child develop to a certain point that, and they are just, you know, this incredible, happy, lovely little child and then the prospect of all of that being taken away is extremely cruel.'

For now, however, Leni continues to defy her diagnosis.

Mrs Forrester said: 'Leni is in mainstream nursery and she's thriving there.

'There is nothing to differentiate her from other children really at this stage.

'She's so energetic, very, very happy. She actively tries to make people laugh. She's very loving and very empathetic.'