Difficult to say without a picture but a common problem with redcurrants is the redcurrant blister mite. This affects the ends of the branches and makes all the leaves at the tips of the branches look screwed up as though you'd scrunched them up in your hand. If this sounds like yours what I do is to shorten the branches as it usually only affects the end few inches. Just cut off the damaged parts and burn or otherwise safely dispose of them. The bushes need pruning anyway so no harm done. Next years crops seem unaffected.
Next year keep a lookout early on in the season and remove affected leaves of sprays as you see them.

I have never known this affect blackcurrants which explains why yours is untouched by it.