[Sleepingpopman]

Hi Everyone. 
 Today we visited my other halves step mum & she showed us her acer tree in the front garden, she said it was about 6years old & in past it had just shed it's leaves at this time of year but still looked healthy but this year it looks dead. She doesn't know what type it is & said she doesn't think it should grow any bigger, it's about 4ft tall. 1st thought was the tall hedge sheltering it but as it's been in the same position all this time & doing fine that probable isn't the reason.
Any ideas to pass on would be gratefully received.
Keith 

[allotmentann]

Are you saying that the branches look dead or that the leaves shrivelled and looked horrible and like the tree was diseased before they fell off?
I ask because some acers (especially brilliantissimum), need to be planted in exactly the right spot and conditions to get good autumn colour. I have had three of these trees now in various gardens and all are horrible before their leaves drop. There is no autumn colour, they go a sludgy brown, shrivel and then drop off.
The first tree it happened to, I thought the tree had some dreadful disease as it looks so ugly. I have since heard the question being discussed on a recording of GQT I attended. I had not realised they were so fussy about location. The biggest thing I think they said was some sort of wind burn. I wish that I could remember the explanation now. I do know that ultimately it was not anything serious, it just looks ugly.
It makes up for its ugly autumn by being beautiful for the rest of the year!
The thing I am not sure about with your partner's, step mum's tree is that it sounds as if it has been okay in the past, or maybe it has not been that brilliant as you don't mention it looking spectacular before the leaves drop. I have three more acers in my garden of different varieties and all of them are absolutely stunning in the autumn. So, it might be that the tree is just not in the best location for it.
If it was my tree I certainly wouldn't do anything drastic to it until I had seen what happened to it in the spring.
They can also get diseases though, many years ago, I lost a potted one in the autumn, the leaves did the same thing but when I looked closely at the tree, under the bark it appeared to have growths all over it. This was before the internet was a mine of readily available information, so I have no idea what it was, but it might be worth having a good close up look at the bark.   

[Goosegirl]

Some of this year's new growth can die off due to wind or whatever, but best way to see if it is dying is to gently scrape a bit of bark off a top stem and if it's brown, then try a lower one. Continue like this until you see green beneath the bark on the stem or branch - ths means that it is still alive.

[JayG]

It took me 3 "dig up and move" operations over 3 years to find a location where my long-suffering purple Acer palmatum dissectum was happy, which turned out to be a fairly shady, but in particular the most sheltered part of the garden, wind clearly being the thing which burns the very delicate leaves and eventually could cause it to give up, although being woodland plants they probably don't like too much sunshine either.

That doesn't seem to be the problem with your OH's step-mum's tree given that it's been quite happy for several years. Like Allotmentann I'm not clear why you think you have a problem - there aren't really any signs of life until spring once they've lost their leaves.

Goosegirl's tip will help, as will checking whether the thinner stems are still flexible. Hope it's OK, but sometimes these things just happen to individual plants and you never really get to find out the reason why.