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Transthyretin‐mediated amyloidosis (ATTR) is a rare, under‐recognized, progressively debilitating, fatal disease caused by the aggregation and extracellular deposition of amyloid transthyretin (TTR) fibrils in multiple organs and tissues throughout the body. TTR is predominantly synthesized by the liver and normally circulates as a homotetramer, while misfolded monomers aggregate to form amyloid fibrils. One strategy to treat ATTR amyloidosis is to reduce the amount of TTR produced by the liver using drugs that directly target the TTR mRNA or gene. This narrative review focuses on how TTR gene silencing tools act to reduce TTR production, describing strategies for improved targeted delivery of these agents to hepatocytes where TTR is preferentially expressed. Antisense oligonucleotides (ASOs) and small interfering RNAs (siRNAs), termed RNA silencers, cause selective degradation of TTR mRNA, while a TTR gene editing tool reduces TTR expression by introducing nonsense mutations into the TTR gene. Two strategies to facilitate tissue‐specific delivery of these nucleic acid‐based drugs employ endogenous receptors expressed by hepatocytes. Lipid nanoparticles (LNPs) that recruit apolipoprotein E support low‐density lipoprotein receptor‐mediated uptake of unconjugated siRNA and are now used for CRISPR gene editing tools. Additionally, conjugating N‐acetylgalactosamine (GalNAc) moieties to ASOs or siRNAs facilitates receptor‐mediated uptake by the asialoglycoprotein receptor. In summary, ATTR is a progressive disease with various clinical manifestations due to TTR aggregation, deposition, and amyloid formation. Receptor‐targeted ligands (eg, GalNAc) and nanoparticle encapsulation (eg, LNPs) are technologies to deliver ASOs, siRNAs, and gene editing tools to hepatocytes, the primary location of TTR synthesis. [ABSTRACT FROM AUTHOR]

Transthyretin amyloid cardiomyopathy (ATTR‐CM) is a life‐threatening condition with a heterogeneous clinical presentation. The recent availability of treatment for ATTR‐CM has stimulated increased awareness of the disease and patient identification. Stratification of patients with ATTR‐CM is critical for optimal management and treatment; however, monitoring disease progression is challenging and currently lacks best‐practice guidance. In this report, experts with experience in treating amyloidosis and ATTR‐CM developed consensus recommendations for monitoring the course of patients with ATTR‐CM and proposed meaningful thresholds and frequency for specific parameters. A set of 11 measurable features across three separate domains were evaluated: (i) clinical and functional endpoints, (ii) biomarkers and laboratory markers, and (iii) imaging and electrocardiographic parameters. Experts recommended that one marker from each of the three domains provides the minimum requirements for assessing disease progression. Assessment of cardiac disease status should be part of a multiparametric evaluation in which progression, stability or improvement of other involved systems in transthyretin amyloidosis should also be considered. Additional data from placebo arms of clinical trials and future studies assessing ATTR‐CM will help to elucidate, refine and define these and other measurements. [ABSTRACT FROM AUTHOR]

Background: Because transthyretin amyloid cardiomyopathy (ATTR-CM) poses unique diagnostic and therapeutic challenges, referral of patients with known or suspected disease to specialized amyloidosis centers is recommended. These centers have developed strategic practices to provide multidisciplinary comprehensive care, but their best practices have not yet been well studied as a group. Methods: A qualitative survey was conducted by telephone/email from October 2019 to February 2020 among eligible healthcare providers with experience in the management of ATTR-CM at US amyloidosis centers, patients with ATTR-CM treated at amyloidosis centers, and patient advocates from amyloidosis patient support groups. Results: Fifteen cardiologists and 9 nurse practitioners/nurses from 15 selected amyloidosis centers participated in the survey, with 16 patients and 4 patient advocates. Among participating healthcare providers, the most frequently cited center best practices were diagnostic capability, multidisciplinary care, and time spent on patient care; the greatest challenges involved coordination of patient care. Patients described the "ideal" amyloidosis program as one that provides physicians with expertise in ATTR-CM, sufficient time with patients, comprehensive patient care, and opportunities to participate in research/clinical trials. The majority of centers host patient support group meetings, and patient advocacy groups provide support for centers with physician/patient education and research. Conclusions: Amyloidosis centers offer comprehensive care based on staff expertise in ATTR-CM, a multidisciplinary approach, advanced diagnostics, and time dedicated to patient care and education. Raising awareness of amyloidosis centers' best practices among healthcare providers can reinforce the benefits of early referral and comprehensive care for patients with ATTR-CM. [ABSTRACT FROM AUTHOR]

Cardiomyopathy is a manifestation of transthyretin amyloidosis (ATTR), which is an underrecognized systemic disease whereby the transthyretin protein misfolds to form fibrils that deposit in various tissues and organs. ATTR amyloidosis is debilitating and associated with poor life expectancy, especially in those with cardiac dysfunction, but a variety of treatment options have recently become available. Considered a rare disease, ATTR amyloidosis may be more prevalent than thought, particularly in older persons. Diagnosis is often delayed because of a lack of disease awareness and the heterogeneity of symptoms at presentation. Given the recent availability of effective treatments, early recognition and diagnosis are especially critical because treatment is likely more effective earlier in the disease course. The Amyloidosis Research Consortium recently convened a group of experts in ATTR amyloidosis who, through an iterative process, agreed on best practices for suspicion, diagnosis, and characterization of disease. This review describes these consensus recommendations for ATTR associated with cardiomyopathy as a resource to aid cardiologists and others in the recognition and diagnosis of ATTR associated with cardiomyopathy. Included in this review is an overview of red flag signs and symptoms and a recommended diagnostic approach, including testing for monoclonal protein, scintigraphy, or biopsy and, if ATTR associated with cardiomyopathy is identified, TTR genotyping. [ABSTRACT FROM AUTHOR]

Transthyretin (TTR) amyloidosis is an underdiagnosed disease caused by destabilization of TTR due to pathogenic mutations or aging. Both pathogenic and protective mutations illuminate mechanisms of disease and potential interventions. AG10 is a selective, oral TTR stabilizer under development for transthyretin amyloidosis cardiomyopathy (ATTR-CM) that mimics a protective TTR mutation. This randomized, double-blind, placebo-controlled study evaluated safety, tolerability, pharmacokinetics, and pharmacodynamics of AG10 in ATTR-CM patients with symptomatic, chronic heart failure. ATTR-CM, New York Heart Association functional class II to III subjects (n = 49, mutant or wild-type) were randomized 1:1:1 to AG10 400 mg, AG10 800 mg, or placebo twice daily for 28 days. Safety and tolerability were assessed by clinical and laboratory criteria. AG10 plasma levels were measured. TTR stability was assessed by changes in serum TTR, and 2 established ex vivo assays (fluorescent probe exclusion and Western blot). AG10 treatment was well-tolerated, achieved target plasma concentrations and demonstrated near-complete stabilization of TTR. TTR stabilization was more complete and less variable at the higher dose with stabilization by fluorescent probe exclusion of 92 ± 10% (mean ± SD) at trough and 96 ± 9% at peak (both p < 10−12 vs. placebo). Average serum TTR increased by 36 ± 21% and 51 ± 38% at 400 and 800 mg, respectively (both p < 0.0001 vs. placebo). Baseline serum TTR in treated subjects was below normal in 80% of mutant and 33% of wild-type subjects. AG10 treatment restored serum TTR to the normal range in all subjects. AG10 has the potential to be a safe and effective treatment for patients with ATTR-CM. A phase 3 trial is ongoing. (Study of AG10 in Amyloid Cardiomyopathy; NCT03458130) [ABSTRACT FROM AUTHOR]