Let me first start by saying how sorry I am that this happened to your son and for what you are all going through. I can only imagine the stress and worry this has caused.
I can understand that you would like to take civil action against the hospital/doctor responsible, particularly facing what must be insurmountable medical expenses.
The only difficulty that arises here is the fact that there is a 2 year statute of limitation on civil actions, meaning that a person only has 2 years from the date of the event which caused the loss, or from when it was "discoverable" meaning the point at which it was realized that the wrong had occurred.
If you only recently learned about this condition in the last two years, then you'd still be able to make a claim, however if you knew this from birth or early on in your son's life, then your window for filing a claim has closed.
I know this isn't what you wanted to hear, however the courts are clear on this as they don't want the potential for civil actions to be left hanging over people indefinitely, thus the reason for statutes of limitations.
The only positive spin that could be put on it is that given that it's been 22 years, the staff and personnel that you dealt with when this occurred are likely no longer there and we would hope that they'd provide proper care for your son were he able to get in for the transplant.
I really wish I had better news for you, however there's no point in sugar coating it, better to get right to the point so that you can examine what other options are available for you.
Please let me know if you require any clarification or have further questions as I am happy to continue chatting.