We are and have been working on potty training with John for a about 6 months now off and on. It is easy for us to loose interest when he looses interest and doesn't respond that way we think he should. It is difficult enough with a child without any delays but it is more difficult with a delayed child.
But we are learning that no matter how much we push, John has his own timetable and we are probably not there. Yes, he knows how to hold his bladder and he goes when we take him (most of the time), but he will not ask to go. And when we tell him to tell us when he needs to go and to not go in his diaper, it doesn't seem to phase him. It doesn't really bother him to wear a wet diaper. So we keep sitting him on his little potty chair and keeping it fresh in his mind so he can associate the two. And when he is ready, he will learn to initiate going to the potty. Until then, we have a 4 year old who in content in wearing diapers which is more difficult for us than for him.
I guess if we were to honest with ourselves, that is really the issue - having a 4 year old wearing dieapers. Looking back, it was easy to grow impatient as our other children met the different milestones. But I believe it is more difficult with John because John plays by his own rules. Children with Down syndrome are on a different schedule about reaching milestones and that schedule usually is slower than what we think it should be.
So that lesson that we have and are learning is that we need to be patient, but yet continue teaching and challenging him to learn new skills. Keep challenging their minds and abilities, but do not give up when they don't get it easily. Hang in there with them. What and how they learn from us as parents in their younger years are the building blocks of what lies ahead for them.