Stephanie, you say your son was scheduled for ATG before they found the trisomy 8. I'm guessing he must have originally been diagnosed AA. Do I understand correctly that those plans were cancelled once the new diagnosis was made? Did they say why?
I ask because my husband's situation is very similar. His diagnosis was officially changed from SAA to hypocellular MDS once they found a trisomy 8 clone in his third BMB, but none of that has significantly changed his course of treatment. He has had 2 ATGs and responded well to them. The only impact from the chromosomal mutation has been that it seems to mean he will have to continue immune suppressants as long as it is present. His first attempt at tapering the cyclosporine resulted in relapse, necessitating a second round of ATG. At that point I found an article citing an apparent relationship between secondary onset trisomy 8 and continued CsA dependency. I showed it to his doctor, and we haven't attempted any more tapers since then.
We don't actually know if the trisomy 8 clone was there all along (and was just so small it didn't show in the first 2 BMBs) or not. It's possible that it was, and that's what triggered the autoimmune attack in the first place (which would explain why continued immune suppression is needed). The 3rd BMB showed a 25% clone, but since then it's been only 5%, i.e. one cell out of the 20 they look at. At any rate, ATG/cyclo has been an effective treatment. He has a sibling match, but at his age we don't want to go that route unless we have to. His counts have continued to improve and he's doing very well, so that's good enough for us right now.
Obviously the prospect of spending the rest of one's life taking immune suppressants has much greater ramifications for a young child than it does for a middle-aged adult, and if a good match can be found for your son, he would be a much better candidate because of his age. If there is not a good match, however, I'm just wondering why ATG seems to be off the table as a fall-back option now. If that was the original plan, I'm assuming his marrow is hypoplastic as well, is that correct? Did they say how big his clone is? You might want to take a look at the article below and discuss it with his doctor.
http://www3.interscience.wiley.com/j...TRY=1&SRETRY=0