Wall Street futures lower on Brexit concerns

U.S. stock index futures eased slightly in early trading on Sunday after Britain's vote to leave the European Union sparked a sharp sell-off in global markets on Friday, wiping out over $2 trillion from world equities. Investors were blindsided by Thursday's vote, having bid up equity markets in the days leading up to it. U.S. stock indexes had been in striking distance of all-time highs, with some expecting a sharp rally to new highs in the coming days.