TTR Variants Research Articles

Rare transthyretin gene variants (p.Ala45Thr, p.Val91Ala, p.Phe53Cys, p.Ala101Val, p.Glu109Lys and p.Phe53Leu): diagnostic pitfalls and clinical characteristics of Polish patients with transthyretin cardiac amyloidosis.

The knowledge about clinical features of Polish patients with hereditary type of transthyretin cardiac amyloidosis (ATTR-CA) is scant. We present rare transthyretin (TTR) gene variants and diagnostic difficulties among patients with hereditary ATTR-CA. In 2018-2024, 252 consecutive patients with suspected cardiac amyloidosis were evaluated, including blood tests, standard 12-lead electrocardiography, transthoracic echocardiography and [99mTc]Tc-DPD scintigraphy. TTR gene sequencing was performed, if mandatory. Hereditary ATTR-CA was confirmed in 14 patients (including one female). Most of them had pathogenic or likely pathogenic TTR gene variants, which are very uncommon in the hereditary transthyretin amyloidosis population: p.Ala45Thr, p.Val91Ala, p.Phe53Cys, p.Ala101Val, p.Glu109Lys and p.Phe53Leu. Of note, patients with p.Ala101Val and p.Phe53Cys variants had inconclusive [99mTc]Tc-DPD scintigraphy results, which may be due to the low sensitivity of [99mTc]Tc-DPD bone scintigraphy for these variants. Cardiac biomarkers did not reflect the intensity of cardiac uptake on [99mTc]Tc-DPD bone scintigraphy - two patients with intense cardiac uptake of tracer had normal or borderline hs-cTnT and NT-proBNP levels. During follow-up, four patients died, two patients underwent combined heart and liver transplantation. This study enriches our knowledge regarding genotype-phenotype correlations of specific TTR variants, broadens the spectrum of identified TTR variants among Polish population, and shows limited value of [99mTc]Tc-DPD scintigraphy in some patients with hereditary ATTR-CA. In cases with strong suspicion of ATTR-CA and inconclusive [99mTc]Tc-DPD scintigraphy results, genetic testing should be considered.

Long-term all-cause and cardiovascular-related mortality in patients with ATTR-CM treated with continuous tafamidis vs placebo to tafamidis by NAC stage at baseline

Abstract Background The National Amyloidosis Centre (NAC) staging system is used to stratify patients with transthyretin amyloid cardiomyopathy (ATTR-CM) into prognostic categories.[1] Purpose This post hoc analysis evaluated all-cause and cardiovascular (CV)-related mortality in patients receiving tafamidis 80 mg or placebo by NAC stage at baseline in the phase 3 Tafamidis in Transthyretin Cardiomyopathy Clinical Trial (ATTR-ACT) and its long-term extension (LTE) study.[2,3] Methods Patients in ATTR-ACT were randomised to tafamidis meglumine 80 mg, 20 mg, or placebo for 30 months, stratified by transthyretin (TTR) genotype (wild-type or variant) and NYHA class (I or II/III). Patients with an NT-proBNP <600 ng/l or eGFR <25 ml/min/1.73m² were excluded. After completing ATTR-ACT, patients could receive tafamidis 61 mg up to 60 months in the open-label LTE study. Heart transplant and cardiac mechanical assist device implantation were treated as death in the mortality assessments. Secondary analyses were change from baseline in Kansas City Cardiomyopathy Questionnaire (KCCQ) clinical and overall summary (CS, OS) scores and frequency of all-cause and CV-related hospitalisations. Results Of 350 patients, 42%, 38% and 20% had NAC stage I, II and III at baseline, respectively. Patients at stage III tended to be older, more likely female, and with a variant TTR genotype vs those at a lower stage (Table). At the end of follow-up, all-cause mortality was consistently lower in patients continuously treated with tafamidis vs those who initially received placebo across NAC stages (I: 36% vs 61%; : 55% vs 74%; III: 69% vs 88%). The hazard ratio (HR [95% CI]) for all-cause mortality with continuous tafamidis treatment vs placebo to tafamidis was 0.43 (0.26-0.70; P<0.001), 0.51 (0.33-0.80; P=0.003) and 0.75 (0.44-1.29; P=0.298), for patients at stage I, II and III, respectively. Similar trends were observed in CV-related mortality at the end of follow-up, where HR (95% CI) for continuous tafamidis-treated patients at stage I, II and III was 0.39 (0.22-0.70; P=0.001), 0.51 (0.31-0.85; P=0.009) and 0.75 (0.42-1.33; P=0.320). The separation of survival curves was seen in the first few months of tafamidis treatment in patients at NAC stage I (Figure A). Such early separation was not seen in those at stage II or III. Starting from Month 18, statistically smaller declines in KCCQ-OS and CS scores were frequently observed in the continuous tafamidis vs placebo to tafamidis groups at stages I and II. Across NAC stages, all-cause and CV-related hospitalisations were lower in the continuous tafamidis vs placebo to tafamidis group (Figure B). Conclusions Continuous tafamidis treatment reduced mortality and hospitalisations (both all-cause and CV-related) across all NAC stages. These reductions were larger and occurred earlier in patients with NAC stage I, emphasising the importance of early disease-modifying treatment in patients with ATTR-CM.[3] NCT01994889, NCT02791230.

Cardiopulmonary exercise test findings are not the same in distinct types of cardiac amyloidosis

Abstract Background Cardiopulmonary exercise testing (CPET) is a widely used tool for risk stratification and prognosis in patients with chronic heart failure. In amyloid patients, cardiac amyloid deposits are associated with poor prognosis, increased risk for arrhythmias, sudden death, and subsequent exercise limitation due to restrictive cardiomyopathy. The type of amyloidosis and its affectation of the heart are different, and little is known about the CPET parameters according to the type of cardiac amyloidosis. Purpose In this study, we aim to compare CPET data in different types of amyloidosis to determine if CPET variables evaluated could have a significant difference that could impact the follow-up or prognosis of the patients based on the type of amyloidosis. Methods We conducted a retrospective cohort study of 194 patients with a diagnosis of cardiac amyloidosis referred for CPET from February 2010 to February 2024. Patients with at least one CPET data were included in our analysis. The type of amyloidosis, comorbidities, and echocardiogram data were retrieved from medical records. Patients were divided into 3 different groups according to the type of amyloidosis: AL Amyloidosis(AL), Variant TTR Amyloidosis (vTRR), and Wild Type TTR Amyloidosis (wtTTR). Individuals with CPET studies after heart transplant were excluded from the analysis. Fisher’s exact test or chi-square was used to compare categorical variables. ANOVA and Tukey-Kramer (TK) were used to compare continuous variables. Adjustment using General Linear Models (GLM) procedure was used to identify any confounder that could affect the results. A p-value <0.05 was considered significant. Results Out of the 194 patients, 66 had AL Amyloidosis, 40 had vTTR Amyloidosis, and 88 had wtTTR Amyloidosis. Most of the patients were male, and the male predominance was higher in the wtTRR group. There were 41 (62.1%) males in the AL group, 35 (87.5%) in the vTRR group, and 83 (94.3%) in the wtTTR group (p<0.0001). Comorbidities were balanced among the groups. Additional demographic and comorbidities data are shown in Table 1. From the evaluated CPET variables, VE/VCO2 nadir and slope were significantly higher in the wtTTR group when compared to the other groups, as well as Peak VE and Peak TV(Figure A). However, after adjusting for sex, BMI, and age, VE/VCO2 nadir was still significantly higher in the wtTRR group (p=0.003) compared to the other groups, as well as Peak VE, which was higher again in vTTR patients (p=0.001), and Peak TV (Table 2). Conclusion Ventilation variables evaluated in CPET showed alterations in the wtTTR group. These findings suggest that wtTRR amyloid patients could have a severe problem in ventilation that could be of significant relevance in future prognosis.

Hereditary Transthyretin-Related Amyloidosis Ongoing Observational Study: A Baseline Report of the First 3167 Participants.

Background: Hereditary transthyretin-related amyloidosis is a clinically heterogeneous autosomal dominant disease caused by pathogenic variants in the TTR gene (hATTR amyloidosis). Objective: The current study describes the demographic, clinical, and genetic characteristics of patients with suspected hATTR amyloidosis. Methods: This study is part of the "Hereditary transthyretin-related amyloidosis and longitudinal monitoring of TTR-positive patients" (TRAMmoniTTR) study. This study included 3167 participants, along with their clinical details. Principal component (PC) analysis was used to analyze their clinical symptomatology. Next-generation sequencing of the TTR gene was performed and genotype-phenotype relationships were investigated. We compared the demographic and clinical characteristics using the principal components (PCs) and also compared participants with and without the TTR pathogenic variants. Results: We identified five main clinical phenotypes out of 22 single symptoms that explained 49% of the variation. The first two PCs referred to polyneuropathy and cardiomyopathy. We found significant differences between gender and PC-polyneuropathy and PC-cardiomyopathy, with male over-representation in the higher quantiles of PC-polyneuropathy and male under-representation in the lowest quantiles of PC-cardiomyopathy. We identified 92 participants with hATTR (3%), exhibiting 17 unique heterozygous TTR variants. The p.Val50Met variant was the most frequent. Furthermore, 503 participants (20%) were identified with ATTR and no relevant TTR variants (ATTRwt). We detected significant differences between the ATTRwt and hATTR groups, with male gender predominance in only the ATTRwt group and a positive family history of polyneuropathy and/or cardiomyopathy among the hATTR participants. Conclusions: The current clinical and genetic characterization of this cohort serves as a foundation for further longitudinal monitoring and assessment.

Prevalence, Cardiac Phenotype, and Outcomes of Transthyretin Variants in the UK Biobank Population

The population prevalence of cardiac transthyretin amyloidosis (ATTR) caused by pathogenic variation in the TTR gene (vATTR) is unknown. To estimate the population prevalence of disease-causing TTR variants and evaluate associated phenotypes and outcomes. This population-based cohort study analyzed UK Biobank (UKB) participants with whole-exome sequencing, electrocardiogram, and cardiovascular magnetic resonance data. Participants were enrolled from 2006 to 2010, with a median follow-up of 12 (IQR, 11-13) years (cutoff date for the analysis, March 12, 2024). Sixty-two candidate TTR variants were extracted based on rarity (minor allele frequency ≤0.0001) and/or previously described associations with amyloidosis if more frequent. Carrier status for TTR variants. Associations of TTR carrier status with vATTR prevalence and cardiovascular imaging and electrocardiogram traits were explored using descriptive statistics. Associations between TTR carrier status and atrial fibrillation, conduction disease, heart failure, and all-cause mortality were evaluated using adjusted Cox proportional hazards models. Genotypic and diagnostic concordance was examined using International Statistical Classification of Diseases, Tenth Revision codes from the hospital record. The overall cohort included 469 789 UKB participants (mean [SD] age, 56.5 [8.1] years; 54.2% female and 45.8% male). A likely pathogenic/pathogenic (LP/P) TTR variant was detected in 473 (0.1%) participants, with Val142Ile being the most prevalent (367 [77.6%]); 91 individuals (0.02%) were carriers of a variant of unknown significance . The overall prevalence of LP/P variants was 0.02% (105 of 444 243) in participants with European ancestry and 4.3% (321 of 7533) in participants with African ancestry. The LP/P variants were associated with higher left ventricular mass indexed to body surface area (β = 4.66; 95% CI, 1.87-7.44), and Val142Ile was associated with a longer PR interval (β = 18.34; 95% CI, 5.41-31.27). The LP/P carrier status was associated with a higher risk of heart failure (hazard ratio [HR], 2.68; 95% CI, 1.75-4.12) and conduction disease (HR, 1.88; 95% CI, 1.25-2.83). Higher all-cause mortality risk was observed for non-Val142Ile LP/P variants (HR, 1.98; 95% CI, 1.06-3.67). Thirteen participants (2.8%) with LP/P variants had diagnostic codes compatible with cardiac or neurologic amyloidosis. Variants of unknown significance were not associated with outcomes. This study found that approximately 1 in 1000 UKB participants were LP/P TTR variant carriers, exceeding previously reported prevalence. The findings emphasize the need for clinical vigilance in identifying individuals at risk of developing vATTR and associated poor outcomes.

Emerging multisystem biomarkers in hereditary transthyretin amyloidosis: a pilot study

Hereditary transthyretin (ATTRv) amyloidosis is a rare, adult-onset, progressive, multisystemic condition caused by TTR pathogenic variants. Reliable biomarkers are needed to allow early diagnosis and to monitor disease severity and progression. We measured serum concentrations of growth differentiation factor-15 (GDF-15) and uromodulin (Umod) in ATTRv patients to evaluate correlations with standard markers of disease severity (FAP stage and PND score). Blood samples were collected from 16 patients diagnosed with ATTRv amyloidosis and a verified TTR variant and from 26 healthy controls. ATTRv patients were stratified by clinical phenotype (neurologic vs. mixed), genotype (V30M vs. non-V30M), and disease severity. We found significantly higher levels of serum GDF-15 in ATTRv patients compared with controls. Mean serum Umod levels were significantly lower in patients with ATTRv than controls. A positive correlation was found between serum Umod and estimated glomerular filtration rate (eGFR), while an inverse correlation was found with cystatin C levels. Conversely, GDF-15 showed a negative correlation with eGFR, and a direct correlation with cystatin C levels. No correlation was demonstrated between GDF-15 or Umod levels and traditional cardiac biomarkers. The results identify alteration of serum levels of GDF-15 and Umod in ATTRv amyloidosis.

Determinants of transthyretin levels and their association with adverse clinical outcomes among UK Biobank participants

Transthyretin is a transport protein whose misfolding has been implicated in the development of cardiac amyloidosis. Here, we examine the clinical correlates of transthyretin levels, the differences in transthyretin levels according to the pathogenic V142I TTR variant carrier status, and the association of transthyretin levels with outcomes among 35,206 UK Biobank participants who underwent plasma profiling and were free from prevalent cardiovascular disease and chronic renal disease. Transthyretin levels are lower in females, decrease with increasing C-reactive protein levels, and increase with body mass index, systolic blood pressure, diastolic blood pressure, total cholesterol, albumin levels, triglyceride levels, and creatinine levels. V142I non-carriers [n = 35,167, mean: −0.1 (0.3)] have higher adjusted transthyretin levels compared with the carriers [n = 39, mean: −0.5 (0.3)] (p:<0.001). A standard deviation decrease in transthyretin levels increases the risk of heart failure [HRadj: 1.17 (95% Confidence Interval = 1.08–1.26)] and all-cause mortality [HRadj: 1.18 (95% Confidence Interval = 1.14–1.24)]. This study shows that individuals with low transthyretin levels, such as those carrying the V142I variant, are at a higher risk of heart failure and mortality.

Transthyretin monomers: a new plasma biomarker for pre-symptomatic transthyretin-related amyloidosis

Background Genotyping and amyloid fibril detection in tissues are generally considered the diagnostic gold standard in transthyretin-related amyloidosis. Patients carry less stable TTR homotetramers prone to dissociation into non-native monomers, which rapidly self-assemble into oligomers and, ultimately, amyloid fibrils. Thus, the initial event of the amyloid cascade produces the smallest transthyretin species: the monomers. This creates engineering opportunities for diagnosis that remain unexplored. Methods We hypothesise that molecular sieving represents a promising method for isolating and concentrating trace TTR monomers from the tetramers present in plasma samples. Subsequently, immunodetection can be utilised to distinguish monomeric TTR from other low molecular weight proteins within the adsorbed fraction. A two-step assay was devised (ImmunoSieve assay), combining molecular sieving and immunodetection for sensing monomeric transthyretin. This assay was employed to analyse plasma microsamples from 10 individuals, including 5 pre-symptomatic carriers of TTR-V30M, the most prevalent amyloidosis-associated TTR variant worldwide, and 5 healthy controls. Results The ImmunoSieve assay enable sensitive detection of monomeric transthyretin in plasma microsamples. Moreover, the circulating monomeric TTR levels were significantly higher in carriers of amyloidogenic TTR mutation. Conclusions Monomeric TTR can function as a biomarker for evaluating disease progression and assessing responses to therapies targeted at stabilising native TTR.

Structural and thermodynamic characterization of a highly amyloidogenic dimer of transthyretin involved in a severe cardiomyopathy

Transthyretin (TTR) is a homotetrameric protein involved in the transport of thyroxine. More than 150 different mutations have been described in the TTR gene, several of them associated with familial amyloid cardiomyopathy (FAC). Recently, our group described a new variant of TTR in Brazil, namely A39D-TTR, which causes a severe cardiac condition. Position 39 is in the AB loop, a region of the protein that is located within the thyroxine-binding channels and is involved in tetramer formation. In the present study we solved the structure and characterize the thermodynamic stability of this new variant of TTR using urea and high hydrostatic pressure (HHP). Interestingly, during the process of purification, A39D-TTR turned out to be a dimer and not a tetramer, a variation that might be explained by the close contact of the four aspartic acids at position 39, where they face each other inside the thyroxine channel. In the presence of sub-denaturing concentrations of urea, bis-ANS binding and dynamic light scattering revealed A39D-TTR in the form of a molten-globule dimer. Co-expression of A39D and WT isoforms in the same bacterial cell did not produce heterodimers or heterotetramers, suggesting that somehow a negative charge at the AB loop precludes tetramer formation. A39D-TTR proved to be highly amyloidogenic, even at mildly acidic pH values where WT-TTR does not aggregate. Interestingly, despite being a dimer, aggregation of A39D-TTR was inhibited by diclofenac, which binds to the thyroxine channel in the tetramer, suggesting the existence of other pockets in A39D-TTR able to accommodate this molecule.

Cardiovascular autonomic failure in hereditary transthyretin amyloidosis and TTR carriers is an early and progressive disease marker.

The cardiomyopathic and neuropathic phenotype of hereditary transthyretin amyloidosis are well recognized. Cardiovascular autonomic dysfunction is less systematically and objectively assessed. Autonomic and clinical features, quantitative cardiovascular autonomic function, and potential autonomic prognostic markers of disease progression were recorded in a cohort of individuals with hereditary transthyretin amyloidosis and in asymptomatic carriers of TTR variants at disease onset (T0) and at the time of the first quantitative autonomic assessment (T1). The severity of peripheral neuropathy and its progression was stratified with the polyneuropathy disability score. A total of 124 individuals were included (111 with a confirmed diagnosis of hereditary transthyretin amyloidosis, and 13 asymptomatic carriers of TTR variants). Symptoms of autonomic dysfunction were reported by 27% individuals at T0. Disease duration was 4.5 ± 4.0years [mean ± standard deviation (SD)] at autonomic testing (T1). Symptoms of autonomic dysfunction were reported by 78% individuals at T1. Cardiovascular autonomic failure was detected by functional testing in 75% individuals and in 64% of TTR carriers. Progression rate from polyneuropathy disability stages I/II to III/IV seemed to be shorter for individuals with autonomic symptoms at onset [2.33 ± 0.56 versus 4.00 ± 0.69years (mean ± SD)]. Cardiovascular autonomic dysfunction occurs early and frequently in individuals with hereditary transthyretin amyloidosis within 4.5years from disease onset. Cardiovascular autonomic failure can be subclinical in individuals and asymptomatic carriers, and only detected with autonomic function testing, which should be considered a potential biomarker for early diagnosis and disease progression.

TAFAMIDIS FOR TREATMENT OF TRANSTHYRETIN CARDIAC AMYLOIDOSIS: A REAL WORLD EXPERIENCE

Abstract Background A regional network for cardiac amyloidosis (CA) was created in 2019 with the aim of enhancing disease awareness among physicians and favoring appropriate access to innovative diagnostic tools/therapies. The network includes all 14 Cardiology Departments and outpatient clinics from 5 Local Health Units. Therapies for variant (ATTR–v) and wild–type (ATTR–wt) CA have recently become available in Italy. Selected centres with expertise in cardiomyopathies were identified to prescribe new modifying disease drugs. Tafamidis is the first medication approved for the treatment of ATTR–C. The landmark ATTRACT trial showed a reduction in cardiovascular mortality and cardiovascular–related hospitalization in patients treated with tafamidis compared to placebo. From October 2021 tafamidis can be prescribed in Italy according to AIFA criteria (only NYHA I/II patients eligible). The aim of our study is to present the experience of our Network in prescribing tafamidis and to compare the clinical baselibe characteristics of our population and the ATTRACT trial population. Methods Thanks to our network , 189 patients with ATTR–CA were referred to our Center. 58 ATTR patients were treated with tafamidis according to AIFA criteria, while 5 patients with variant–TTR and neuropathy received patisiran iv. The causes of exclusion from tafamidis therapy are shown in figure 1. We prospectively collected all the patientst treated with tafamidis from January 2022 until November 2023. All the data about clinical characteristics, laboratoy findings ECG, echo, bone scintigraphy and concomitant treatment were collected during routin follow–up visits anc compared to those of ATTRACT trial population. Results The main findings of our study are summarized in Table (fig,2) The age of our population was similar to that of the patients enrolled in the ATTR–ACT trial (75,94 ± 11.4 vs. 74,5±7.2, P = 0.21). Of note, our population does not include patients in NYHA class III as the AIFA prescriptive criteria exclude these patients from treatment in Italy. this implies a substantial difference in the distribution of the NYHA class compared to the attract population (p = 0.001). The outcome of our patient was excellent, the drug was well tolerated. Conclusions: Implementing specific clinical network provided excellent results, allowing a precise phenotype/genotype characterization and favoring appropriate access to specific disease–modifying drugs.

Multinational experience with next-generation sequencing: opportunity to identify transthyretin cardiac amyloidosis and Fabry disease.

Sarcomeric hypertrophic cardiomyopathy (HCM) must be differentiated from phenotypically similar conditions because clinical management and prognosis may greatly differ. Patients with unexplained left ventricular hypertrophy require an early, confirmed genetic diagnosis through diagnostic or predictive genetic testing. We tested the feasibility and practicality of the application of a 17-gene next-generation sequencing (NGS) panel to detect the most common genetic causes of HCM and HCM phenocopies, including treatable phenocopies, and report detection rates. Identification of transthyretin cardiac amyloidosis (ATTR-CA) and Fabry disease (FD) is essential because of the availability of disease-specific therapy. Early initiation of these treatments may lead to better clinical outcomes. In this international, multicenter, cross-sectional pilot study, peripheral dried blood spot samples from patients of cardiology clinics with an unexplained increased left ventricular wall thickness (LVWT) of ≥13 mm in one or more left ventricular myocardial segments (measured by imaging methods) were analyzed at a central laboratory. NGS included the detection of known splice regions and flanking regions of 17 genes using the Illumina NextSeq 500 and NovaSeq 6000 sequencing systems. Samples for NGS screening were collected between May 2019 and October 2020 at cardiology clinics in Colombia, Brazil, Mexico, Turkey, Israel, and Saudi Arabia. Out of 535 samples, 128 (23.9%) samples tested positive for pathogenic/likely pathogenic genetic variants associated with HCM or HCM phenocopies with double pathogenic/likely pathogenic variants detected in four samples. Among the 132 (24.7%) detected variants, 115 (21.5%) variants were associated with HCM and 17 (3.2%) variants with HCM phenocopies. Variants in MYH7 (n=60, 11.2%) and MYBPC3 (n=41, 7.7%) were the most common HCM variants. The HCM phenocopy variants included variants in the TTR (n=7, 1.3%) and GLA (n=2, 0.4%) genes. The mean (standard deviation) ages of patients with HCM or HCM phenocopy variants, including TTR and GLA variants, were 42.8 (17.9), 54.6 (17.0), and 69.0 (1.4) years, respectively. The overall diagnostic yield of 24.7% indicates that the screening strategy effectively identified the most common forms of HCM and HCM phenocopies among geographically dispersed patients. The results underscore the importance of including ATTR-CA (TTR variants) and FD (GLA variants), which are treatable disorders, in the differential diagnosis of patients with increased LVWT of unknown etiology.

Longitudinal analysis of serum neurofilament light chain levels as marker for neuronal damage in hereditary transthyretin amyloidosis

Objective To evaluate serum neurofilament light chain (sNfL) as biomarker of disease onset, progression and treatment effect in hereditary transthyretin (ATTRv) amyloidosis patients and TTR variant (TTRv) carriers. Methods sNfL levels were assessed longitudinally in persistently asymptomatic TTRv carriers (N = 12), persistently asymptomatic ATTRv amyloidosis patients (defined as asymptomatic patients but with amyloid detectable in subcutaneous abdominal fat tissue) (N = 8), in TTRv carriers who developed polyneuropathy (N = 7) and in ATTRv amyloidosis patients with polyneuropathy on treatment (TTR-stabiliser (N = 20) or TTR-silencer (N = 18)). Polyneuropathy was confirmed by nerve conduction studies or quantitative sensory testing. sNfL was analysed using a single-molecule array assay. Results sNfL increased over 2 years in persistently asymptomatic ATTRv amyloidosis patients, but did not change in persistently asymptomatic TTRv carriers. In all TTRv carriers who developed polyneuropathy, sNfL increased from 8.4 to 49.8 pg/mL before the onset of symptoms and before polyneuropathy could be confirmed neurophysiologically. In symptomatic ATTRv amyloidosis patients on a TTR-stabiliser, sNfL remained stable over 2 years. In patients on a TTR-silencer, sNfL decreased after 1 year of treatment. Conclusion sNfL is a biomarker of early neuronal damage in ATTRv amyloidosis already before the onset of polyneuropathy. Current data support the use of sNfL in screening asymptomatic TTRv carriers and in monitoring of disease progression and treatment effect.

Eplontersen: First Approval.

Eplontersen (Wainua™) is a ligand-conjugated antisense oligonucleotide directed to TTR, which is being developed by Ionis Pharmaceuticals and AstraZeneca for the treatment of TTR-mediated amyloidosis (ATTR). Eplontersen, which is targeted to the liver by a ligand containing three N-acetyl galactosamine residues, binds to wild-type and variant TTR mRNA, thus reducing the levels of circulating TTR protein and amyloid deposition. Subcutaneous eplontersen reduced serum TTR levels, inhibited neuropathy progression and improved health-related quality of life in patients with polyneuropathy of hereditary ATTR (ATTRv-PN; v for variant) in a phase III trial. Based on these results, eplontersen was approved in the USA for the treatment of ATTRv-PN on 21 December 2023 and is currently undergoing regulatory review for a similar indication in the EU, the UK, Switzerland and Canada. Eplontersen is also undergoing phase III development for ATTR cardiomyopathy. This article summarizes the milestones in the development of eplontersen leading to this first approval for ATTRv-PN.

Trypsin-induced aggregation of transthyretin Valine 30 variants associated with hereditary amyloidosis.

Amyloid fibrils of transthyretin (TTR) consist of full-length TTR and C-terminal fragments starting near residue 50. However, the molecular mechanism underlying the production of the C-terminal fragment remains unclear. Here, we investigated trypsin-induced aggregation and urea-induced unfolding of TTR variants associated with hereditary amyloidosis. Trypsin strongly induced aggregation of variants V30G and V30A, in each of which Val30 in the hydrophobic core of the monomer was mutated to less-bulky amino acids. Variants V30L and V30M, in each of which Val30 was mutated to bulky amino acids, also exhibited trypsin-induced aggregation. On the other hand, pathogenic variant I68L as well as the nonpathogenic V30I did not exhibit trypsin-induced aggregation. The V30G variant was extremely unstable compared with the other variants. The V30G mutation caused the formation of a cavity and the rearrangement of Leu55 in the hydrophobic core of the monomer. These results suggest that highly destabilized transthyretin variants are more susceptible to trypsin digestion.

The clinical significance of transthyretin gene variant homozygosity in variant ATTR-CM

Abstract Background Transthyretin Amyloid Cardiomyopathy (ATTR-CM) is a progressive condition characterised by the infiltration of the myocardial extracellular space resulting in progressive heart failure and mortality. Owing to advances in imaging and diagnostics, ATTR-CM is an increasingly recognised form of heart failure worldwide. ATTR-CM can be hereditary (hATTR) and associated with a pathogenic TTR gene variant which exhibits an autosomal dominant pattern of inheritance. Studies have shown that homozygosity in Mendelian diseases confers a more severe clinical phenotype. This has yet to be determined for hATTR-CM. Purpose To determine the clinical significance of TTR gene variant homozygosity in hATTR-CM. Methods All patients whom were diagnosed with hATTR-CM at a single UK national referral centre for amyloidosis were identified retrospectively. TTR gene zygosity, clinical, biochemical and echocardiographic parameters were obtained from patient clinical records. Results Only patients that were homozygous for the V122I TTR gene variant were identified in sufficient numbers for meaningful analysis. Twenty three patients with hATTR-CM whom were homozygous for the V122I variant were identified. Three hundred and ninety heterozygous V122I hATTR-CM patients were identified as a control group. There were no statistically significant differences in echocardiographic parameters (heterozygous vs homozygous means were as follows: IVSd 16.9mm v 16.6mm, LVEF 43.8% v 44.8%, stroke volume 30.7ml v 34.4ml, TAPSE 14.4mm v 15.3mm and GLS -9.7% vs -9.0%). Median NT-proBNP was lower in the homozygotes compared to heterozygotes (2480ng/L v 3179ng/L, p&amp;lt;0.05). Median survival from baseline was similar between the two groups (Figure 1), with homozygous and heterozygous patients having median survivals of 28.7 months and 24.5 months, respectively. However, homozygous patients were significantly younger at baseline diagnosis (mean age 66.4 years v 76.3 years, p&amp;lt;0.01) and therefore died at a much younger age (mean age at death 72.5 years v 79.9 years, p&amp;lt;0.01). Conclusions To our knowledge, this is the first study reporting outcomes in hATTR-CM patients whom are homozygous TTR gene variant carriers. Whilst the cardiac phenotype, natural history and length of survival were not substantially different between heterozygotes and homozygotes, the mean age at first diagnosis was substantially younger. Given the natural course of the disease was relatively similar between the groups, this resulted in a significantly younger age at death in hATTR patients whom are homozygous TTR variant carriers. Larger studies are required to confirm if this is applicable across all TTR variants. Nonetheless our study suggests that hATTR patients whom are homozygous carriers of TTR variants should be afforded closer clinical surveillance from a younger age than their heterozygous counterparts.Figure 1

Left ventricular speckle-tracking-derived mechanical dispersion in patients with transthyretin amyloidosis and their first-degree relatives

Abstract Background Mechanical dispersion has shown to predict ventricular (LV) arrhythmias and sudden cardiac death in populations with established cardiac diseases, such as cardiomyopathies and heart failure. Transthyretin amyloid (ATTR) cardiomyopathy arises from deposition of misfolded, insoluble transthyretin (TTR) in extracellular matrix. The disease impacts profoundly cardiac tissue architecture and its mechanical properties. Purpose The aim of this prospective study was assessment of LV speckle-tracking-derived mechanical dispersion in patients with ATTR cardiomyopathy and their first-degree relatives. Methods We present data based on evaluation of 85 patients, including 34 (group 1) index patients with ATTR and 51 (group 2) first-degree relatives who were studied between June 2020 and January 2023. Study protocol included clinical data, free light chain blood immunoglobulins and urine immunofixation, transthoracic echocardiography (TTE) with global longitudinal strain (GLS) analysis, hybrid technique single-photon emission computed tomography and computed tomography (SPECT/CT) with [99mTc] Tc 3,3-disphono-1,2-propanodicarboxylic acid (DPD), genetic testing by an amplicon-based next-generation TTR sequencing approach, and in selected cases cardiac or soft tissue biopsy. Mechanical dispersion was calculated manually from GLS measurements and defined as the standard deviation (SD) of contraction duration from R on the electrocardiogram (ECG) to peak negative longitudinal strain of all LV segments. Results In group 1 patients were older (66.6±11 vs. 50.7±14) and presented with higher New York Heart Association (NYHA) class (2.4± 1 vs. 1.1± 0.6) (p&amp;lt;0.05). Overall, there were detected following types of TTR variants - Phe53Leu, Ala101Val, Glu112Lys, Glu109Lys, Glu122Lys, Glu82Lys. Compared to group 2, group 1 presented with higher N-terminal (NT)-pro hormone BNP (NT-proBNP) value (5859±7320 vs. 281±990 pg/ml), greater intraventricular septum thickness (19±4 vs. 12±3 mm) and LV mass index values (199±69 vs.111±42 g/m2), impaired LV ejection fraction (44±13 vs. 59±10 %) and GLS (-12.7±6 vs. -18.7±4 %) (p&amp;lt;0.05). Moreover, patients with ATTR cardiomyopathy had significantly higher value of LV speckle-tracking-derived mechanical dispersion compared to their first-degree relatives (96.2±22.3 vs. 77.9±23.3 ms, p=0.0007). Conclusions Patients with ATTR cardiomyopathy present with significantly higher LV mass index value, impaired GLS and higher value of LV speckle-tracking-derived mechanical dispersion compared to their first-degree relatives (p&amp;lt;0.05). Assessment of LV speckle-tracking-derived mechanical dispersion may in future translate into further enhancement of disease evaluation and improving prognosis in the group of patients.

Acoramidis produces near-complete TTR stabilization in blood samples from patients with variant transthyretin amyloidosis that is greater than that achieved with tafamidis

Abstract Introduction Transthyretin (TTR) amyloidosis (ATTR) is a progressive, fatal disease caused by destabilizing TTR variants (TTRv) and age-related factors. Dissociation of tetrameric TTR initiates protein misfolding, aggregation, and tissue deposition which constitutes the mechanism of disease. More destabilizing variants drive more severe clinical phenotypes. TTR stabilizers have demonstrated clinical benefits for neuropathic and cardiovascular outcomes correlated with the extent of TTR stabilization. Acoramidis (AG10) is a novel TTR stabilizer in development for the treatment of TTR amyloid cardiomyopathy. Hypothesis: Acoramidis achieves near-complete in vitro TTR stabilization, exceeding levels achieved with clinically relevant concentrations of tafamidis (a TTR stabilizer in clinical use), when added to blood samples from ATTRv patients across a spectrum of destabilizing TTR variants. Methods Two established assays assessed TTR stabilization: fluorescent probe exclusion (FPE; measures binding site occupancy), and Western blot (WB; quantifies tetrameric TTR persistence under conditions of accelerated dissociation). Over 60 individual patient samples representing 18 unique TTRv across a spectrum of intrinsic instability and clinical phenotypes were assayed. Acoramidis was added at its target clinical trough concentration (10 µM) and compared to tafamidis added at its clinical peak (26 µM) and trough (16 µM) concentrations reported for its maximal approved dose. Results Acoramidis bound serum TTR to a greater extent (103 ± 13%) than either peak (87 ± 14%) or trough (71 ± 14%) concentrations of tafamidis. WB assays showed that addition of acoramidis resulted in significantly greater and more durable TTR stabilization (93 ± 14%) than adding tafamidis (peak: 49 ± 14%, trough: 36 ± 13%) in all paired individual patient plasma samples tested (Figure 1, p &amp;lt; 0.0001). Rare variants (A97S, D38A, F64L, L58H, P24S, Y114C) also demonstrated near complete stabilization upon in vitro addition of acoramidis. Conclusions At its target therapeutic trough concentration, acoramidis achieved near-complete TTR stabilization across 18 unique genotypes; in the subset of paired samples, the stabilization was significantly greater for acoramidis than for tafamidis even at its peak clinical concentration. This observation held across a range of destabilizing mutations, including a∼2-fold greater stabilization than tafamidis for the prevalent cardiomyopathic V122I variant. Based on the mechanism of disease and the association between TTR destabilization and severity of clinical outcomes, these data suggest that acoramidis has the potential to be a clinically differentiated and efficacious treatment option for patients with ATTRv, independent of variant genotype.

Detailed clinical, physiological and pathological phenotyping can impact access to disease-modifying treatments in ATTR carriers

BackgroundHereditary transthyretin amyloidosis is a life-threatening autosomal dominant systemic disease due to pathogenic TTR variants (ATTRv), mostly affecting the peripheral nerves and heart. The disease is characterised by a combination...

Eplontersen for Hereditary Transthyretin Amyloidosis With Polyneuropathy

Transthyretin gene silencing is an emerging treatment strategy for hereditary transthyretin (ATTRv) amyloidosis. To evaluate eplontersen, an investigational ligand-conjugated antisense oligonucleotide, in ATTRv polyneuropathy. NEURO-TTRansform was an open-label, single-group, phase 3 trial conducted at 40 sites across 15 countries (December 2019-April 2023) in 168 adults with Coutinho stage 1 or 2 ATTRv polyneuropathy, Neuropathy Impairment Score 10-130, and a documented TTR variant. Patients treated with placebo from NEURO-TTR (NCT01737398; March 2013-November 2017), an inotersen trial with similar eligibility criteria and end points, served as a historical placebo ("placebo") group. Subcutaneous eplontersen (45 mg every 4 weeks; n = 144); a small reference group received subcutaneous inotersen (300 mg weekly; n = 24); subcutaneous placebo weekly (in NEURO-TTR; n = 60). Primary efficacy end points at week 65/66 were changes from baseline in serum transthyretin concentration, modified Neuropathy Impairment Score +7 (mNIS+7) composite score (scoring range, -22.3 to 346.3; higher scores indicate poorer function), and Norfolk Quality of Life Questionnaire-Diabetic Neuropathy (Norfolk QoL-DN) total score (scoring range, -4 to 136; higher scores indicate poorer quality of life). Analyses of efficacy end points were based on a mixed-effects model with repeated measures adjusted by propensity score weights. Among 144 eplontersen-treated patients (mean age, 53.0 years; 69% male), 136 (94.4%) completed week-66 follow-up; among 60 placebo patients (mean age, 59.5 years; 68% male), 52 (86.7%) completed week-66 follow-up. At week 65, adjusted mean percentage reduction in serum transthyretin was -81.7% with eplontersen and -11.2% with placebo (difference, -70.4% [95% CI, -75.2% to -65.7%]; P < .001). Adjusted mean change from baseline to week 66 was lower (better) with eplontersen vs placebo for mNIS+7 composite score (0.3 vs 25.1; difference, -24.8 [95% CI, -31.0 to -18.6; P < .001) and for Norfolk QoL-DN (-5.5 vs 14.2; difference, -19.7 [95% CI, -25.6 to -13.8]; P < .001). Adverse events by week 66 that led to study drug discontinuation occurred in 6 patients (4%) in the eplontersen group vs 2 (3%) in the placebo group. Through week 66, there were 2 deaths in the eplontersen group consistent with known disease-related sequelae (cardiac arrhythmia; intracerebral hemorrhage); there were no deaths in the placebo group. In patients with ATTRv polyneuropathy, the eplontersen treatment group demonstrated changes consistent with significantly lowered serum transthyretin concentration, less neuropathy impairment, and better quality of life compared with a historical placebo. ClinicalTrials.gov Identifier: NCT04136184; EU Clinical Trials Register: EudraCT 2019-001698-10.