The coroner has indicated she is likely to give a narrative verdict on the death of seven-week-old Axel Peanberg King.
Dr Shirley Radcliffe told the inquest that she had been unable to find any evidence to suggest a "clear cause" of death.
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Charlie Gard will "inevitably" die shortly after being moved to a hospice and having life-support treatment withdrawn.
The service has 1,366 people rammed into a dozen carriages designed for just 640.
The deadline for Charlie Gard's parents to reach an agreement with doctors on arrangements for his death has passed.