hi. sorry i don't have any knowledge about other chromosonal disorders. my first and only child has DS. he is 6 mos. old. it sounds like your sis has had an unimaginable amount of difficulty placed on her through her children. she sounds like a strong woman. i'm sure god will pull her through this one too, although it seems to be stretching her (and her family) more than she thinks she can handle.
please let us know the results of the test and how we can help.