LONDON — An American doctor testifying in the case of a British couple seeking the right to take their critically ill infant to the United States for treatment said Thursday it was worth trying an experimental therapy that has only recently emerged.
The doctor, whose name and institution cannot be named because of a court order, told Britain’s High Court of Justice that new clinical data has emerged about the effectiveness of the treatment proposed for 11-month-old Charlie Gard, who suffers from a rare genetic condition and is on life support.
Judge Nicholas Francis said the doctor should come to London to see Charlie and meet other experts. At the end of an eight-hour court hearing Thursday, Francis said ‘‘no hearing can resume’’ until that happens.
The boy’s family is locked in a legal battle with Britain’s most famous children’s hospital because they disagree on whether trying the experimental treatment is in Charlie’s best interest. The case attracted international attention after President Trump and Pope Francis weighed in.
‘‘We have a much better understanding of the data,’’ the doctor testified, saying the information has emerged in the time since judges first rejected the parents’ bid to take him to America.
Charlie suffers from mitochondrial DNA depletion syndrome, a rare genetic disease that has left him with brain damage and unable to breathe unaided.
Specialists at Great Ormond Street Hospital have fought the parent’s bid for therapy because they don’t think it will help and may cause him pain. The hospital says Charlie should be allowed to die with dignity.
A succession of courts has backed the hospital, but the case returned to the High Court on Thursday after claims of new evidence and the high-profile interventions.
The US doctor estimated the chance of ‘‘clinical meaningful success’’ for an improvement in Charlie’s muscle use to be at least 10 percent, but offered no conclusion on whether the infant’s brain function would improve.
The treatment, known as nucleoside therapy, is not a cure. The doctor said he’d be willing to travel to Britain to see the child.
The emotional toll on all involved has been clear. Two hours into the High Court hearing, questions the judge asked prompted tensions to boil over. Charlie’s mother Connie Yates shouted out, accusing Francis of misquoting her earlier statements about her son’s quality of life.
‘‘We said he’s not suffering and not in pain,’’ she yelled. ‘‘If he was we wouldn’t be up here fighting.’’ Chris Gard then slammed his water cup down and the couple left the courtroom.
The couple returned after a break. The judge offered a reassuring word, acknowledging that the situation was desperate.
‘‘I understand you walking out,’’ he said.
Earlier, Trump gave the parents new hope by offering help in a tweet, while the pope has insisted on the need to respect the wishes of the parents to ‘‘accompany and treat’’ their son to the very end.
Americans United for Life and other groups have seized upon the case, arguing the infant needs a ‘‘chance at life.’’ Petitions have circulated to offer support and others have arrived at Charlie’s bedside to pray.
‘‘We are continuing to spend every moment, working around the clock to save our dear baby Charlie,’’ the couple said in a statement before the hearing. ‘‘We’ve been requesting this specialized treatment since November, and never asked the hospital, courts or anyone for anything — except for the permission to go.’’
British judges are tasked to intervene when families and doctors disagree on the care of people unable to speak for themselves. The rights of the child take primacy, with the courts weighing issues such as whether a child is suffering and how much benefit a proposed treatment might produce.
‘‘Unlike the USA, English law is focused on the protection of children’s rights,’’ said Jonathan Montgomery, professor of health care law at University College London. ‘‘The USA is the only country in the world that is not party to the UN Convention on the Rights of the Child; it does not recognize that children have rights independent of their parents.’’