Hey Chris, All cultivars of japanese maples are not the same. Without more info there is too many variables...a photo would help, also what cultvar you have and the planting location would help as well....AL

There may be a lot of variation between cultivars but a sick JM is a sick JM :-) If the only branch showing life is very low on the tree, then it may be only the rootstock is alive and the above-graft portion now dead. I agree a photo is necessary to determine what's going on - a close up the buds and an overall shot of the tree with the only leafy branch clearly portrayed would be helpful.

Unfortunately, I don't know much about it. Attached is a link to a picture.

Here is a link that might be useful: Photo of tree

Well I can't see a graft in the photo,if so you cannot asign any cultivar name to this tree.
I had a tree which only had life on a lower branch.General concensus was 'Pseudomonas syringae'.I've attached a photo of the dead branches for you to compare, but can't see if yours look similar,a close up would help the resident experts diagnose.The only hope for my tree was to chop it right down to healthy wood but I have to admit it will never look the same again if it survives.At least if it comes to it,your tree could still retain a decent shape,you'd just need to straighten it up afterwards.I hope though that it's not as serious as this :)

Blackened, leafless branches in spring on a Japanese maple is likely to be due to bacterial blight.

My neighbor had the same problem that didnt show up until the second year and looks the same as yours.He hired a local kid to plant the tree and the kid removed it from the landscape pot where it was totally root bound and just stuck it in a small tight hole. The reason i know that is because i was across the street watching.I didnt think it was my place to get involved. Also his was planted low and then he climbed the trunk with mulch.....just a thought, It could be the twin to yours.

This tree was planted by the professional nursery that I bought it from and they did a good job not planting it too deep. I have been keeping mulch around it (in fact there is mulch around it now), but this picture was captured before my spring mulching. I will check for a graft but the comment about blackened branches concerns me. A number of the branches have a blackened appearance.

Here's another (and simpler) possibility. If the JM is goes for several weeks w/o water during the hottest part of the summer, it may respond by selectively letting some (or most, depending on the drought severity) branches die. This may not become apparent until the following spring, when the affected branches will not leaf out. Although lack of water is the "root cause", it might result in various proliferation of various infections, e.g. verticillium, that may be present in the weakened, dying and eventually dead branch.

There's no way to know if this is the explanation in your case, but if your tree went without water for more than a week in July or August, I'd suspect something along these lines.

Unfortunately, this has been my suspicion. We have had hot/dry summers and the tree did not always get enough water. Thanks for your replies.