Alnylam’s stock tumbled after management trimmed its full-year forecast for ATTR franchise revenues, citing normalization of early launch dynamics. Following disappointing Amvuttra sales and guidance adjustments, the company reduced its expected total ATTR revenue range to $4.2 billion–$4.5 billion, with a $200 million cut at both ends. Alnylam framed the dip as a post–pent-up demand adjustment rather than a fundamental loss of momentum, pointing to strong U.S. underlying demand growth and first-line pull-through. The guidance shift still underscored how quickly investor expectations can reprice when real-world uptake and second-line trajectory diverge. For the RNAi-heavy portfolio, the episode highlights the market’s sensitivity to quarterly launches—particularly in competitive TTR cardiomyopathy landscapes.