Alnylam’s stock dropped sharply after the company lowered sales guidance for Amvuttra and adjusted outlook for its transthyretin amyloidosis franchise. In reporting, Alnylam said Amvuttra’s earlier launch spike reflected “pent-up demand” that has since normalized, lowering expectations for the remainder of 2026. The company revised total ATTR revenue to $4.2 billion–$4.5 billion, reflecting a $200 million reduction at both ends. Alnylam emphasized that patient demand in first-line settings remains strong and that access and adherence in the U.S. continue to track above internal expectations. The update matters for the competitive TTR cardiomyopathy market, where investor confidence often hinges on whether growth sustains after launch timing effects fade.