The first drug that can delay the onset of type 1 diabetes is being made available on the NHS in England and Wales.
Teplizumab is a form of immunotherapy that can give people three extra years before they develop symptoms and need lifelong insulin treatment.
The NHS medicines body described its decision as "genuinely exciting", with hundreds of children and young people likely to benefit each year.
Type 1 diabetes can develop at any time, but the most common age of diagnosis is in early teenage years.
Groups representing patients describe the potential impact of the drug as "momentous", after decades of work to bring it to this stage.
"If it were your child or someone you love, you would want to do everything possible to give them more years without the daily burden of managing this relentless condition," says Karen Addington, the chief executive of the charity Breakthrough T1D.
"We now have a treatment that can help make that possible".
Type 1 diabetes is caused when the body's own immune system starts attacking the insulin-producing cells in the pancreas.
It is different from the type 2 form of the disease, which is often - but not always - associated with being overweight.
People with type 1 diabetes must monitor their blood glucose levels and administer insulin, either through injections or a pump, to replace the hormone their bodies can no longer produce enough of.
Theo Sebastian-Jenkins, now eight, was diagnosed when he was four, after his parents took him to A&E – he had been feeling unusually tired at home, was constantly thirsty and had been losing weight.
At the time, he was too young to qualify for the new drug, which can be given from eight years old.
He is now doing well but his condition needs to be carefully managed – his diet must be closely watched and his blood sugar checked.
If it goes too low it can be a medical emergency.
And if levels are high for a long time, it can damage the blood vessels and nerves.
"It's something which you can never switch off from," says his mum Vicky.
"When you make breakfast, you've got to weigh everything, counting how many carbohydrates are in it, so that you know the right amount of insulin to give."
His parents say any medicine that could delay the onset could make a real difference to hundreds of other children each year.
"It would be huge for any family to have those three years of childhood back without the worry and the things he's had to deal with," says his dad Ben.
Teplizumab must be given as an infusion (by drip into a vein) before symptoms develop, meaning patients first need a blood test showing the immune system has started attacking the pancreas.
Italy is the only county in the world that has a national screening programme for children and young people.
In the UK, routine testing for the disease is not yet available on the NHS, although it is something diabetes charities are campaigning for.
Instead, people are likely to learn they are at risk through blood tests carried out for other medical reasons or because the condition runs in their family.
Most of those diagnosed have no close family history though, suggesting environmental factors may also play an important role in triggering it.
Dima Boichak, from Newbury in Berkshire, was nine when he discovered he was highly likely to develop the disease, after he took part in a UK-wide research study funded by diabetes charities.
The family signed up partly because Dima's cousin had been diagnosed and was already on insulin.
“If we hadn't done it, Dima might have been diagnosed much later, possibly at a stage where he'd need urgent intervention, like my niece," says his mum Elena.
He became one of the first to be given teplizumab on compassionate grounds before the treatment was recommended by the body which advises the NHS on which medicines should be offered to patients.
The new drug needed to be given in hospital through a drip into his vein once a day for 14 days in a row.
Elena describes the one-time process as "hard work" but believes it was ultimately worth it to give her son what she hopes will be extra years before he moves on to insulin treatment.
"The biggest gift teplizumab gives us is time - just time being a normal kid, living a normal life," she says.
"That's wonderful for him, and for me, as his mother."
The published price of teplizumab works out at around £150,000 per course of treatment, although the NHS has negotiated a confidential discount with the drugmaker Sanofi.
The National Institute for Health and Care Excellence, which has recommended the drug in both England and Wales, estimates that around 1,100 adults and children could be eligible in its first year, with around 820 per year offered it in the longer term once a backlog in demand has cleared.
"This is a genuinely exciting recommendation," says Helen Knight, director of medicines evaluation at NICE.
"For the first time, we have a treatment that can give people diagnosed at an early stage precious extra time before they need to manage the full demands of the condition."
Breakthrough T1D, which funded earlier research that helped make the drug possible, said that a number of other type 1 diabetes immunotherapy treatments are now in development.
In the future, the hope is that new patients will eventually be given a personalised combination of those drugs and will never have to become dependent on insulin therapy.
NICE guidance does not automatically apply in Northern Ireland, while in Scotland a separate body, the Scottish Medicines Consortium, decides which drugs the NHS should offer.
The SMC said it expects to issue advice for teplizumab in early 2027.
