The family of a boy with a rare form of childhood dementia said he had been given “a death sentence” after his treatment was withdrawn amid a collapsed takeover deal. Harley Bond, 11, was diagnosed seven years ago with a condition called Sanfilippo syndrome, which gradually limits a child’s ability to walk, talk and eat. Harley is not expected to live past the age of 14 but his parents and doctors said that his decline has been stemmed since he enrolled on a pioneering clinical trial in 2019. The boy from Sheffield had lost the ability to recognise his parents and stopped saying “mummy” and “daddy” before the treatment. But he has since relearned to talk and has spent the past four years as a “healthy, happy boy” who loves trampolining and Toy Story and playing with his three-year-old brother Arlo, according to his father, Wayne. However, the world-leading clinical trial that was treating Harley and 14 other children was abruptly halted last month. A deal to buy the US-based drug maker, Allievex, fell through and the company ran out of money. In a letter seen by the Guardian, Allievex told clinicians at Great Ormond Street children’s hospital (GOSH) in London, where two children were receiving the treatment, that “all clinical activity should be stopped without delay”. The company said it had been unable to raise enough money to support a new trial, and added: “Know that this is a heartbreaking time for all Allievex employees and shareholders, clinicians, parents and most importantly, Sanfilippo patients.” Wayne said: “We’re extremely angry about it. It works. Harley’s living proof. There’s 22 other kids around the world that are living proof that it’s working but now it’s going to be denied so the next generations are going to suffer.” Wayne and his partner, Emma Siddall, 42, are pleading for a pharmaceutical company to support Allievex and restart the trial without delay. “Please don’t give my son a death sentence,” he said. “Let him enjoy his life like he has done for the last 11 years. Don’t take this chance away from Harley and all the other children that are benefiting. “It really works. The doctors know it works. The nurses know it works. It’s heart-wrenching to know that we’re stranded, basically.” Many other trials involving treatments for Sanfilippo syndrome have failed but this cutting-edge drug, tralesinidase alfa, has shown promising results in clinical trials. It works by releasing a small amount of enzyme into the brain that is missing in children with the condition. Industry experts said the collapse of the trial is in large part due to the challenging economic environment for producing drugs for rare diseases, which cost roughly five times more than treatments for more common conditions. Tom Mathers, the chief executive of Allievex, said: “The hardest decision that I have ever had to make was to pause our ongoing treatment of children with this devastating disease. It is most frustrating because we have a treatment that we know works, and provides tremendous benefits to the children and their families.” Mathers said the “regulatory uncertainty” in the US and Europe meant that it was “impossible” to raise enough money to develop treatments for rare diseases. Allievex needs to raise $70m to complete the next stage of the clinical trial and manufacturing work, he said. Bob Stevens, chief executive of the MPS Society, which represents youngsters with Sanfilippo syndrome and other conditions, said children were “having their futures robbed” due to systemic failures in the way rare disease treatment programmes are funded. “I find it very difficult to live with the fact that we’ve had a young child on a treatment that is undoubtedly working and now he’s losing access to it,” he said. “It’s a tragic situation that should not have come about but has as a result of several parts of the system not working.” A spokesperson for Great Ormond Street said: “We have been caring for Harley and his family for many years at GOSH and have seen the benefit of this research treatment for him and other patients. “We know how impossibly hard this situation is for all involved and our efforts are now focused on supporting Harley and his family. “Our teams will continue to work closely with them, and others at GOSH, who have been impacted by this news, as we explore options and support them through their next steps.”