I'm very sorry for all you've struggled and are struggling with.
I really don't know anything about the disease. And I see that you're from the UK but if you're able to get over to the US, the top hospitals here are Johns Hopkins in Maryland, they have a great children's hospital, Children's Hospital of Philadelphia, the Mayo Clinic, and Hospital for Special Surgery in New York City.
Good luck
Hi, I am so sorry. I'm not familiar with this disease but I would say if you're not happy with the doctors and feel they are not giving you answers, start looking for other doctors. I don't know where you live but if there is a teaching hospital around, sometimes those doctors are better with knowing the latest treatments. I don't blame you for not giving up.
Please accept my condolences on the loss of your 4 yr. old.