You mentioned in your first post that all the tests were normal except for the VER. You say your son has been ill for about 6 months. Has he become progressively worse over time or up and down with same symptoms. I wonder if you remember anything unusual around the time he became ill. e.g. did he get the flu, or a viral illness or have any immunizations or such? I guess they've ruled out he may have something like Guillain Barre [edited to add - although I just went and re-read one of your other posts and you say he's OK 90% of the time which would rule out GBS and lots of other things].

This must all be so worrying for you. I'd be beside myself with worry. The fact he's now needing to be carried is just awful. Let us know when the porphyria tests come back. It's good they're testing for that. I hope you find some answers soon and that your son recovers very fast from whatever is going on at the moment.