It could be a number of things......Does it need watering......has it been windy....is it in a position where it gets the sun early in the day. Acers don't like windy sites...if it has been frosty and then the sun gets on it ...the leaves could burn.....It needs to be in a position where it gets good light, but out of direct sunlight in late morning.early afternoon...and not subject to strong wind.

Thanks Amblealice, it is just out side the patio doors which is also next to a fence, we only got it last year so is only 1ft n half tall, we have another one next to it that is about 6ft tall and that one is beautiful, so very confused

I would suggest wind damage and lack of watering if it has been windy. Japanese acers really do not like wind and need a semi-shaded protected site.

If its in a pot WATER WATER WATER!!

Oh and take it out of full sun.

Are they very thirsty plants then? I've noticed that the tips of mine have been turning white and wasn't sure what was causing - could that be lack of water?

I believe leaves turning white is associated with leaf burn. I had a very small acer planted in a fairly exposed west facing position-- bottom line: it didn't like it. Too much wind, too much direct sun & not enough water will produce an unhappy acer. So... ditto what everyone else has said. :)

An established acer can cope with wind and lack of water better than one only planted a year.

Hi i had a lovely Acer could not figer out how it died seems some thing got into the roots some insect a killed it you dont know it's there until Acer has died.

Vine weevil probably Dantina