Mizuho analyst Peter Lawson downgraded Intrexon (XON) to Underperform from Neutral with the stock well above his $45 price target. Underperform is equivalent to a sell rating at Mizuho. Shares of the synthetic biology company closed yesterday down $1.92 to $57.59. Additional clinical data or significant company updates need to be seen in order to justify a higher price target, Lawson tells investors in a research note. He cites valuation for the downgrade and recommends biotech investors consider TESARO (TSRO), Clovis (CLVS) or Verastem (VSTM). All three companies have better risk/reward profiles relative to Intrexon, Lawson believes.