Has the soil in the root area been checked for water recently? The leaf curling and browning looks like scorch, which is a reaction to high heat and/or dry conditions. Some minor fungal diseases, like anthracnose, can also cause similar browning, though it does not require treatment (and no fungicide would cure existing infections anyway). There may also be accumulated stress like last year's drought predisposing the plant to an opportunistic infection like Botryosphaeria canker. That or similar diseases, plus winter damage from cold snaps this past season, caused dieback in many specimens of well-established trees and shrubs, including Japanese Maples. Areas that didn't die completely back may have been weakened, where the water-conducting tissues just under the bark were injured and cannot supply the canopy with enough moisture to avoid high heat damage.

For now, just monitor the tree for watering needs by feeling the soil about six inches deep; water thoroughly if the soil has become somewhat dry to the touch at that depth. No fungicide is needed or recommended (especially during this heat wave, as it would potentially cause more damage than a disease itself), though you can trim off any leafless and brittle branch tips that never leafed-out this spring (the bark on those tends to turn gray or brown rather than the reddish color of live twigs). You can also look for trunk damage (gnawing on the bark from voles, perhaps), especially if there is mulch piled against the trunk base, but we don't think that's a factor since more drastic dieback would likely have already taken place.

Miri