Gerald Cox, chief medical officer of Editas Medicine (NASDAQ: [[ticker:EDIT]]), will step down at the end of 2018, the gene editing company announced Monday, after the markets closed. Cambridge, MA-based Editas gave no reason for Cox’s departure, but said that a search for his successor is underway. Cox joined Editas in 2016, a few months after the company went public. Editas is working to advance its lead program, an experimental treatment for a rare, inherited form of blindness called Leber congenital amaurosis, into clinical testing.