Brexit is a bigger worry for the UK, according to one expert, and won't ding U.S. economic growth. 'Our view is that it's a domestic issue,' said David Lebovitz, global market strategist at JPMorgan Asset Management, based in New York. 'This really matters for the UK and Europe - both economies are going to slowdown as a result.' He said the U.S. economy should be fine as we export a very small percentage of our GDP to the UK. TheStreet's Scott Gamm reports from Wall Street.