Extending losses for the sixth straight session, the Sensex at the Bombay Stock Exchange today fell over 21 points in early trade due to sustained selling by funds and retail investors amid a weak trend in the Asian region.The 30-share index, which had lost over 778 points in the previous five sessions, fell by 21.26 points, , to 18,771.61 in early trade.The nifty at the National Stock Exchange shed 3.55 points, to 5,655.20.