** Drugmaker Biohaven's BHVN.N shares fall 11.6% to $17.39 premarket

** Co says the US FDA has extended review period of its marketing application for its genetic disease drug, troriluzole, by three months

** FDA's decision is now expected in fourth quarter of the year, co says

** No new safety concerns were raised by the FDA - BHVN

** FDA planning to hold an advisory committee meeting to discuss the application, but no date has been scheduled, co says

** Earlier this month, the FDA extended review date of Cytokinetics's CYTK.O heart disease drug aficamten by 3 months, as well

** The Trump administration's mass firings at the FDA, totaling 3,500 employees, have raised concerns about the agency's ability to review new medicines

** As of last close, stock down 47.4% YTD

(Reporting by Kamal Choudhury in Bengaluru)

((Kamal.Choudhury@thomsonreuters.com))