A couple who want to take their sick baby son to the USA for treatment are preparing to mount a fight in the Supreme Court at a hearing overseen by the most senior female judge in British legal history.
Chris Gard and Connie Yates want 10-month-old Charlie Gard, who suffers from a rare genetic condition and has brain damage, to undergo a therapy trial.
Specialists at Great Ormond Street Hospital in London, where Charlie is being cared for, say therapy proposed by a doctor in America is experimental and will not help.
They say life support treatment should stop.
A High Court judge in April ruled against a trip to America and in favour of Great Ormond Street doctors.
Mr Justice Francis concluded that life support treatment should end and said Charlie should be allowed to die with dignity.
Three Court of Appeal judges upheld that ruling in May.
A panel of three Supreme Court justices - headed by Lady Hale, the Deputy President of the Supreme Court and most senior female judge in British legal history - is scheduled to consider the couple's latest appeal at a hearing in London on Thursday.
Supreme Court officials say justices will consider preliminary arguments before deciding whether to give permission for a full appeal hearing.
A spokesman said if permission was granted, a date for a full hearing would be set.
Doctors at Great Ormond Street are continuing to provide treatment pending decisions by Supreme Court justices.
Mr Justice Francis had made a ruling on April 11 after a trial in the Family Division of the High Court in London.
He heard that Charlie, who was born on August 4 last year, had a form of mitochondrial disease, a condition which causes progressive muscle weakness and brain damage.
Specialists in the USA have offered a therapy called nucleoside.
Charlie's parents, who are in their 30s and come from Bedfont, west London, have appealed for money on a GoFundMe page to cover doctors' bills in America.
They reached a £1.2 million target before the High Court trial.
People are continuing to donate and the fund has now topped £1.3 million.
Mr Justice Francis said Great Ormond Street doctors had considered the experimental treatment, but decided it would not help Charlie.
He said the case had never been ''about money''.