LONDON — (CNN) The parents of baby Charlie Gard stormed out of Britain’s High Court Thursday amid an emotional hearing as they fight to take him to the United States for experimental treatment for a rare genetic disorder.

At a preliminary hearing Monday before the judge who first heard the case, Charlie’s parents, Chris Gard and Connie Yates, were given two days to submit new written evidence regarding the viability of having Charlie treated abroad with experimental nucleoside therapy.

They are battling to keep their terminally ill 11-month-old son on life support so they can take him overseas for the treatment, a step opposed by his doctors on the grounds he may suffer without experiencing any benefit.

The judge, Mr Justice Nicholas Francis, instructed Charlie’s parents Monday to cite the source of all evidence, when it was produced and what difference it would make for their son. Depending on that evidence, he may then reconsider his previous ruling that further treatment would be futile.

But about two hours into Thursday’s hearing, Charlie’s parents abruptly left the court after disagreeing with a comment by the judge.

Yates interrupted Francis as he said that the parents had said they would not want to prolong Charlie’s life in its present state, only if there was hope of improvement. “I never said that!” she exclaimed from her seat behind her barrister.

The judge attempted to clarify that one or other of the parents had said it, but both rose and left the court. Francis offered to stop the hearing until they returned but it continued for a short time before breaking for lunch.

Charlie is at Great Ormond Street Hospital in London, which requested the new hearing last week, saying there was “new evidence relating to potential treatment” for the boy.

The 11-month-old has been there since October, when he began suffering the effects of mitochondrial DNA depletion syndrome, having been born apparently healthy in August.

Judge: Welfare ‘prime concern’

In his opening remarks Thursday, the judge thanked the very large number of medics and other people who “have worked very hard in Charlie’s interest” since Monday’s hearing. “His welfare is the prime concern for all of us though we may approach it in different ways,” he said.

Francis told the court it was clear that the hearing would not finish Thursday, adding that “if there is important new evidence that suggests my decision should be changed then I will change it.”

A US doctor is due to give evidence before the court Thursday afternoon.

At one point, the judge appeared angry that there had been no independent measurement of Charlie’s head circumference since Monday, saying he wanted that resolved within 24 hours. This matters because whether the baby’s brain is growing is a factor in the case.

The family’s barrister, Grant Armstrong, responded vigorously to a remark by the judge that the proposed treatment has never been tried on mice with Charlie’s condition, let alone humans.

“As I understand it, there are only four people in the world with this condition — you can’t do a controlled trial,” he said.

Armstrong added that there were currently no genetically engineered mice with the condition available for testing and that it would take six months to breed them.

‘We are still fighting’

After Yates and Gard first entered the court Thursday, family friend Alasdair Seton-Marsden read a statement to the media on their behalf.

“We are continuing to spend every moment working around the clock to save our dear baby Charlie. We’ve been requesting this specialized treatment since November, and never asked the hospital, the courts, or anyone for anything except for the permission to go,” it said.

“We’ve raised over £1.3 million, and have had invitations from specialized doctors in the US and Italy. They’ve offered their groundbreaking treatment to us, and are confident that they can help Charlie. We will continue to make the case for us to seek treatment for Charlie with doctors that are actually specialized in mitochondrial DNA depletion syndrome, and we hope that the judge and the courts will finally rule in favor of us seeking treatment elsewhere.

“We love him more than life itself. If he is still fighting, then we are still fighting.”

On Sunday, Charlie’s parents gave the hospital a petition with more than 350,000 signatures from around the world. It called for the family to be allowed to travel for the experimental treatment, although a High Court ruling blocked such a move on June 30.

That ruling was preceded by a series of legal attempts by the couple, who have tried to make their cases to judges in the High Court, the Court of Appeal and the Supreme Court in London.

The hospital has countered that it’s in Charlie’s best interest to be removed from life support, as none of the treatments are certain to help him and could cause him to suffer. All three British courts have ruled in favor of the hospital’s request.

Progressive disease

Gard and Yates’ legal battle to prolong Charlie’s life has received international attention, with Pope Francis and US President Donald Trump among those weighing in.

US Vice President Mike Pence told “The Rush Limbaugh Show” on Monday that he was praying Charlie’s family would “be able to choose the greatest extent of life saving treatment that’s available for their child.”

However, it’s unclear whether the experimental treatment could help Charlie. His doctors at Great Ormond Street Hospital do not believe it can and the treatment has never been tried on someone with his condition.

Mitochondrial DNA depletion syndrome is a progressive disease that causes muscle weakness and loss of motor skills, leaving those who have it unable to stand, walk, eat, talk and eventually breathe. Charlie will die from his illness, his doctors have said.

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