FDA approval of patisiran, branded Onpattro, to treat hereditary transthyretin-mediated amyloidosis (hATTR amyloidosis) represents several firsts for Alnylam Pharmaceuticals Inc., not least of which is the distinction of bringing the initial RNAI interference (RNAi) drug to market. Although the Cambridge, Mass.-based company also beat competitor Akcea Therapeutics Inc., which is developing Tegsedi (inotersen), to first approval in the hATTR indication, Alnylam now faces the challenge of wooing physicians and patients to a drug in a class without precedent.