Metabolic Support UK chief executive Kirsty Hoyle told the BBC that Grayson is the only patient with the disease the charity “has come across” and is believed to be the only known case in the UK.
She said only a small number of all rare diseases have a specific treatment and there were “huge unmet” needs across patient groups.
“Grayson really evidences how often parents and families need to fill that gap in care and advocate for access to treatment,” Ms Hoyle added.
South Tyneside and Sunderland NHS Foundation Trust said it has “current plans to ensure this treatment is in place as we continue to care for Grayson and support his family”.
A spokesperson said “discussions with them” had continued throughout as “we [and the family] work together on this”.
They added talks were “ongoing with the wider NHS” about how this treatment could be offered to others.
Meanwhile, the NHS North East and North Cumbria Integrated Care Board said it was “pleased that this issue has been resolved”.
