Shares of Ionis Pharmaceuticals Inc. (NASDAQ:IONS) were pummeled Thursday, sinking to a three-year low of $21.09, after the company clarified that “less than a handful of patients” enrolled in its phase III NEURO-TTR study evaluating IONIS-TTRRx in transthyretin (TTR) familial amyloid polyneuropathy (FAP) experienced a serious decline in platelets. The small number of events, in seriously ill patients often taking other medications, might have been a minor blip on the radar screen except that partner Glaxosmithkline plc (GSK), which holds an option to license IONIS-TTRRx exclusively, decided to postpone a phase III cardiovascular study, CARDIO-TTR, that was planned to evaluate IONIS-TTRRx in patients with TTR amyloid cardiomyopathy.