The US ATTR Amyloidosis Clinical-Trial Landscape

The ATTR amyloidosis trial base divides along two axes that a commercial reader must hold at once: mechanism of action and clinical phenotype. Four mechanistic classes are now represented in registrational or late-stage trials — TTR stabilizers (tafamidis, acoramidis), TTR silencers that lower hepatic production via RNAi or antisense (patisiran, vutrisiran, inotersen, eplontersen), in-vivo CRISPR gene editing that knocks down TTR at the DNA level (nexiguran ziclumeran / NTLA-2001), and monoclonal antibodies designed to actively clear deposited amyloid from tissue (ALXN2220, coramitug). The phenotype axis splits the same programs into transthyretin amyloid cardiomyopathy (ATTR-CM) and polyneuropathy (ATTR-PN), because the trials, endpoints and regulatory labels are largely phenotype-specific even when the molecule is shared.

This division matters because it drives which trial reads across to which commercial question. The cardiomyopathy trials are powered on hard outcomes — all-cause mortality and cardiovascular hospitalization — and are the ones that expand the addressable US population, estimated at roughly 150,000 individuals with ATTR-CM. The neuropathy trials, by contrast, are powered on the modified Neuropathy Impairment Score (mNIS+7) and Norfolk quality-of-life instruments, and address the smaller hereditary (ATTRv) population. Vutrisiran is now the pivot point of the market: it is the first single molecule with pivotal trials and FDA labels on both sides of the phenotype divide (HELIOS-A in PN, HELIOS-B in CM).

Three Phase 3 trials define the approved ATTR-CM class. ATTR-ACT (NCT01994889, Pfizer, n=441) was the trial that opened the cardiac market: over 30 months, oral tafamidis reduced all-cause mortality and the frequency of cardiovascular-related hospitalizations versus placebo, analyzed by the hierarchical Finkelstein-Schoenfeld method (PMID 30145929). It supported the 2019 US approval of tafamidis (Vyndaqel / Vyndamax) and established mortality-plus-hospitalization as the endpoint standard every subsequent CM trial has had to match.

ATTRibute-CM (NCT03860935, Eidos / BridgeBio, n=632) tested the next-generation oral stabilizer acoramidis against placebo over 30 months on a four-component hierarchical endpoint (all-cause mortality, cumulative CV hospitalization, change in NT-proBNP, change in 6-minute walk distance). Acoramidis was superior, with a win ratio of approximately 1.8 favoring active treatment (PMID 38197816), and the data supported FDA approval of acoramidis (Attruby, NDA 216540) on 22 November 2024.

HELIOS-B (NCT04153149, Alnylam, n=655) extended the RNAi silencer vutrisiran into cardiomyopathy. Subcutaneous vutrisiran dosed once every three months reduced the risk of all-cause mortality and recurrent cardiovascular events by 28% versus placebo (PMID 39213194). On 20 March 2025 the FDA approved vutrisiran (Amvuttra) for ATTR-CM (sBLA/sNDA under NDA 215515), the first RNAi therapeutic in the cardiac indication and the event that turned the CM market from a two-drug stabilizer contest into a three-mechanism race.

The polyneuropathy franchise was built first and remains the proof-of-concept engine for TTR knockdown. APOLLO (NCT01960348, Alnylam, n=225) established RNAi in hereditary ATTR: patisiran improved the modified Neuropathy Impairment Score (mNIS+7) by roughly 34 points relative to placebo at 18 months, halting and in many patients reversing neuropathic progression (PMID 29972753). It supported the 2018 US approval of patisiran (Onpattro), the first-ever approved RNAi drug.

NEURO-TTR (NCT01737398, Ionis, n=173) delivered the antisense proof point in parallel: inotersen improved both co-primary endpoints — mNIS+7 and the Norfolk Quality of Life-Diabetic Neuropathy score — versus placebo over 66 weeks (PMID 29972757), supporting the 2018 approval of inotersen (Tegsedi). HELIOS-A (NCT03759379, Alnylam, n=164) then moved the franchise to a low-frequency subcutaneous silencer, vutrisiran, benchmarked against the APOLLO placebo arm and patisiran; it supported the 2022 approval of vutrisiran (Amvuttra) in PN.

NEURO-TTRansform (NCT04136184, Ionis, n=168) is the most recent PN pivotal: eplontersen, a ligand-conjugated antisense agent, reduced mNIS+7 and improved quality of life versus a historical placebo group (PMID 37768671), supporting the December 2023 US approval of eplontersen (Wainua). The strategic read is that the PN market is now crowded with four approved knockdown agents, pushing every developer's growth thesis toward the far larger cardiomyopathy pool.

The pipeline is where the competitive picture reorders. The most disruptive asset is nexiguran ziclumeran (NTLA-2001), an in-vivo CRISPR-Cas9 therapy that edits the TTR gene in hepatocytes for a potentially one-time, durable knockdown; the first-in-human Phase 1 (NCT04601051, Intellia) reported deep, sustained serum TTR reduction after a single dose (PMID 34215024). It has advanced to two Phase 3 trials: MAGNITUDE in ATTR-CM (NCT06128629, ~1,200 patients, primary completion 2027) and MAGNITUDE-2 in ATTRv-PN (NCT06672237), with a long-term follow-up study (NCT05697861) running to 2038.

On the silencer side, eplontersen is being read into cardiomyopathy through CARDIO-TTRansform (NCT04136171, Ionis, ~1,438 patients, active and not recruiting, primary completion 2026) — the antisense counterpart to HELIOS-B and the trial that could give AstraZeneca/Ionis a CM label to match Wainua's PN franchise.

The genuinely new mechanism is amyloid depletion — antibodies that clear existing TTR deposits rather than preventing new ones, potentially reversing rather than stabilizing disease. Two Phase 3 depleter programs are running: ALXN2220 in DEPLETTR-CM (NCT06183931, Alexion / AstraZeneca, ~1,181 patients, primary completion 2027), which originated from Neurimmune's NI006 Phase 1 (NCT04360434), and coramitug / NNC6019-0001 in CLEOPATTRA (NCT07207811, Novo Nordisk, ~1,280 patients, primary completion 2029). A Phase 2b combination trial (NCT07608354, AstraZeneca) is already testing eplontersen plus ALXN2220 — an explicit signal that the next commercial battleground is silencer-plus-depleter combination therapy rather than monotherapy.

The endpoint history tells the commercial story in miniature. Trials moved from functional and neuropathy scores (6MWT, mNIS+7) toward hierarchical composites and finally to recurrent-event mortality endpoints (HELIOS-B's all-cause mortality plus recurrent CV events). Each escalation raised the evidentiary bar and, with it, the payer-relevant value story — a drug that demonstrably reduces death and hospitalization commands a different reimbursement conversation than one that slows a walk-test decline.

For a US competitive-intelligence reader, three trial-driven inflection points matter. First, the March 2025 vutrisiran CM approval breaks the oral-stabilizer duopoly and forces cross-mechanism positioning. Second, the CRISPR (MAGNITUDE) and depleter (DEPLETTR-CM, CLEOPATTRA) Phase 3 readouts in 2027-2029 will decide whether the market moves from chronic suppression toward one-time or disease-reversing therapy. Third, the eplontersen-plus-ALXN2220 combination trial reframes the endgame around combinations, which reshapes both the clinical differentiation and the pricing model. Every one of these turns is anchored to a specific, verifiable trial rather than to positioning claims.