Alnylam cuts TTR franchise guidance, market cap loses $10.8B as shares tumble 28%

Alnylam announced a reduction in its full-year revenue outlook for its transthyretin (TTR) franchise, trimming the midpoint by $200 million.

The company now projects TTR therapy sales of $4.2 billion to $4.5 billion for the year, down from the previous $4.4 billion‑$4.7 billion range. The forecast covers Onpattro for ATTR‑PN and Amvuttra for ATTR‑PN and ATTR‑CM.

Analysts at Stifel said the surprise cut could create a near-term credibility overhang and raise questions about peak sales potential, even though the competitive landscape remains favorable.

Following the announcement, Alnylam's shares fell more than 28% at market close, wiping roughly $10.8 billion from its market capitalization.