U.S. Congressman Steve King has said the "British courts should not be allowed to subject an innocent, eleven-month-old child to the equivalent of a death sentence when hope for a cure exists, and when his parents wish to pursue it at their own expense".
Mr Justice Francis made an order barring journalists from naming Dr Hirano or saying where he was based shortly after litigation began earlier this year.
During the proceedings on Friday, the judge clarified that he had not held Charlie's parents in any way responsible for encouraging such behaviour and spoke of his desire to be as sensitive as possible towards them.
According to hospital, the British National Health Service has the right to take Charlie's care out of the hands of his parents if doctors believe further treatment is futile. The judge is considering their claims at a hearing in the Family Division of the High Court in London.
He is due to stage further hearings later this month following next week's gathering of specialists.
Dr Hirano had spoken to the judge last on Thursday via a video link from NY.
Dr Hirano said he had clinical data which was not available in April and he still believed that the therapy was "worth trying".
But the judge said Charlie must not be transferred to the U.S. without the court's prior permission.
Opening the proceedings on Friday afternoon, Mr Justice Francis thanked the family for the appeal for calm.
Doctors treating Gard at Great Ormond Street Hospital have said they are unsure whether he is in pain and that he will die as a result of his condition. He said the possibility of improvement in muscle strength was "at least 10%", and said the proposed nucleoside therapy treatment had even allowed one patient with a similar disease to be weaned off a ventilator entirely.
On June 30, the day the Charlie's life support was initially scheduled to be disconnected, the Pope also used his Twitter account to send a clear pro-life message in the infant's favor: "To defend human life, above all when it is wounded by illness, is a duty of love that God entrusts to all".
Lawyers representing Charlie's parents objected to the meeting being staged in the absence of both parents.
Dr Hirano, a professor of neurology at the Columbia University Medical Centre in NY, is offering an experimental therapy trial for the baby's rare genetic condition.
Speaking on behalf of "the entire family and their supporters", Alasdair Seton-Marsden said that anyone wanting to help the family should demonstrate peacefully, donate to the family's fund or sign their petition, adding: "We absolutely abhor violence". Her parents, who wanted her kept alive, and her husband, who wanted to remove her feeding tube, were in a high-profile legal battle that ended when the courts sided with her husband. He's now on a ventilator from which Great Ormond Street Hospital officials want to remove him against his parents' wishes.
"We are delighted that Charlie's mother, Connie, will be present at the meeting that Prof Michio Hirano, the world's leading expert on Charlie's condition, will attend".