The parents of a seven year old boy who died in a clinical trial have spoken of their “indescribable” pain.

Ender Nihat, from Essex, suffered organ failure after receiving chemotherapy during experimental stem cell treatment.

An inquest heard Hassan and Nahide Nihat’s concerns they had not been made fully aware of the risks before agreeing to take part.

But the man who ran the trial at London’s St Mary’s Hospital said a 1-5% chance of death had been properly explained to them.

Ender, from Sible Hedingham, suffered with Transfusion-Dependent Beta-Thalassemia, in which not enough haemoglobin is produced to carry oxygen around the body.

He needed monthly blood transfusions.

The new treatment was a gene editing therapy called CTX001, developed by US based Vertex Pharmaceuticals, which also sponsored the trial.

The treatment had been approved for adults and the purpose of the trial was to learn more about its safety and efficacy in children.

Westminster Coroner’s Court heard how Ender was given a chemotherapy drug called Busulfan in February 2024, to create space in his bone marrow.

He then received his own modified cells.

Weeks later Ender became poorly.

He was diagnosed with Veno Occlusive Disease (VOD) a known potential side effect of Busulfan.

Ender entered paediatric intensive care where he also developed macrophage activation syndrome, a rare inflammatory condition, and his breathing had to be supported.

Cardiopulmonary resuscitation (CPR) was initiated on several occasions when his heart stopped beating.

During this time he also suffered acute respiratory distress syndrome, lung bleeding, kidney failure and antibiotic resistant pneumonia.

Four months later, on 13 July 2024, Ender died.

Speaking to the BBC, Mrs Nihat said: “It is just like we have died as well.

“I’m trying to continue for our daughter, his twin sister, but there’s a massive hole left in our hearts, in our lives.”

Her husband Hassan said Ender was essentially healthy before he entered the trial.

He added: “He was an amazing boy. He was very compassionate, very loving, very friendly. He was just full of life.”

Professor Josu de la Fuente said Ender’s Beta-Thalassemia had a very high chance of causing organ damage in later life.

He told the inquest VOD could occur in any bone barrow transplant and not just those involving stem cell replacement.

Ender’s parents were carefully appraised of the Busulfan risk, Professor de la Fuente added.

“The consenting process was extensive. There was appropriate documentation. I think it was well written. It had been approved by lay people so it could be well understood,” he said.

Recording a narrative verdict, Assistant Coroner Jean Harkin said the death was due to a recognised complication of Busulfan and there had been a “robust” consent process.

Professor Julian Redhead, medical director at Imperial College Healthcare NHS Trust said they were “devastated’ by what had happened.

“Our clinical teams put great emphasis on sharing the risks, including potential complications, and what to expect during a research trial. We have undertaken a detailed investigation into Ender’s care and treatment and we are making improvements,” he said.

Vertex said Ender’s death was not related to their therapy and that “patient safety is always our top priority and we continue to monitor our clinical trials”.

For Hassan and Nahide Nihat, a gap has opened in their lives which can never be closed.

“We go out to eat and where we used to be four, we are now three,” Mr Nihat said.

His wife added: “His twin sister has been robbed of her brother. We sit at the dinner table and there’s an empty space.

“Going to school, they used to hold both my the hands and now one of my hands is just empty.”