REGENXBIO Inc. (RGNX), a biotechnology company, saw its shares drop 17.75 percent or $2.38, closing at$11.03 on Wednesday. This decline followed the company's disclosure that the U.S. Food and Drug Administration had placed clinical holds on two of its investigational gene therapy programs.The FDA imposed the hold on RGX-111, which was being studied for the treatment of MPS I or Hurler syndrome, after a preliminary review of a single case of neoplasm involving an intraventricular central nervous system tu ...