Characteristics of Patients with Late- vs. Early-Onset Val30Met Transthyretin Amyloidosis from the Transthyretin Amyloidosis Outcomes Survey (THAOS)

Amyloid Neuropathy: From Pathophysiology to Treatment in Light-Chain Amyloidosis and Hereditary Transthyretin Amyloidosis

Amyloid neuropathy is caused by deposition of insoluble β-pleated amyloid sheets in the peripheral nervous system. It is most common in: (1) light-chain amyloidosis, a clonal non-proliferative plasma cell disorder in which fragments of immunoglobulin, light or heavy chain, deposit in tissues, and (2) hereditary transthyretin (ATTRv) amyloidosis, a disorder caused by autosomal dominant mutations in the TTR gene resulting in mutated protein that has a higher tendency to misfold. Amyloid fibrils deposit in the endoneurium of peripheral nerves, often extensive in the dorsal root ganglia and sympathetic ganglia, leading to atrophy of Schwann cells in proximity to amyloid fibrils and blood-nerve barrier disruption. Clinically, amyloid neuropathy is manifested as a length-dependent sensory predominant neuropathy associated with generalized autonomic failure. Small unmyelinated nerves are involved early and prominently in early-onset Val30Met ATTRv, whereas other ATTRv and light-chain amyloidosis often present with large- and small-fiber involvement. Nerve conduction studies, quantitative sudomotor axon testing, and intraepidermal nerve fiber density are useful tools to evaluate denervation. Amyloid deposition can be demonstrated by tissue biopsy of the affected organ or surrogate site, as well as bone-avid radiotracer cardiac imaging. Treatment of light-chain amyloidosis has been revolutionized by monoclonal antibodies and stem cell transplantation with improved 5-year survival up to 77%. Novel gene therapy and transthyretin stabilizers have revolutionized treatment of ATTRv, improving the course of neuropathy (less change in the modified Neuropathy Impairment Score + 7 from baseline) and quality of life. With great progress in amyloidosis therapies, early diagnosis and presymptomatic testing for ATTRv family members has become paramount. ANN NEUROL 2024.

Hereditary transthyretin amyloidosis: a myriad of factors that influence phenotypic variability

Hereditary transthyretin-related amyloidosis (ATTRv amyloidosis) is a rare and progressively debilitating disease characterized by the deposition of transthyretin (TTR) amyloid fibrils in various organs and tissues, most commonly in the heart and peripheral nerves. This pathological deposition can lead to significant organ dysfunction and, ultimately, organ failure. ATTRv amyloidosis exhibits a broad range of clinical presentations, from purely neurological symptoms to purely cardiac manifestations, as well as mixed phenotypes which result from both neurological and cardiac implications. This wide phenotypical spectrum realistically challenges disease diagnosis and prognosis, especially in individuals without or with an unknown family history. Multiple factors are thought to contribute to this variability, including genetic, epigenetic, and even environmental influences. Understanding these factors is crucial, as they can significantly affect disease expression and progression. This review aims to summarize each of these contributing factors, to help elucidate the current knowledge on the phenotypical variability of ATTRv amyloidosis.

Silencing of ocular transthyretin, a gene responsible for hereditary transthyretin amyloidosis, by intravitreal injection of an siRNA conjugate into rabbit eyes

The first small interfering RNA (siRNA) therapeutic received approval for hereditary transthyretin (ATTRv) amyloidosis, and the patients' lifespan extension by specific inhibition of hepatic synthesis of transthyretin (TTR) is expected. However, ocular amyloidosis in these patients has been a crucial issue. This study aims to evaluate the efficacy and safety of intravitreal TTR siRNA conjugate injection into rabbit eyes. Rabbit (r) TTR siRNA is a screened TTR siRNA conjugate from 53 candidates. The intraocular pressure (IOP) immediately after injection was high despite the 65.9 % decrease of aqueous humor TTR protein levels in the rTTR siRNA group compared with those in the Control siRNA group 2 weeks after the 50 μL siRNA injection. The IOP spike was milder after the 30 μL siRNA injection, and aqueous humor TTR levels decreased by ∼50 % in the rTTR siRNA group, which is consistent with the mRNA levels in the retina. The parameters of dark-adapted, light-adapted, and light-adapted 30 Hz electroretinogram and the thickness of each retinal layer in histological analysis demonstrated no significant differences between the groups. In conclusion, we developed TTR siRNA conjugates for rabbit eyes, and the results indicate that intravitreal TTR siRNA conjugate injection could be a therapeutic option for ocular amyloidosis caused by ATTRv amyloidosis.

Advances in the diagnosis and treatment of transthyretin amyloid cardiomyopathy

Transthyretin amyloid cardiomyopathy (ATTR-CM) is an underrecognized cause of heart failure (HF). ATTR-CM can lead to a number of cardiovascular manifestations including HF, rhythm disturbances, and valvular disease that ultimately limit quality of life and prognosis. Due to advances in diagnostic modalities and therapeutic options, the prevalence of ATTR-CM is rising. There are several classes of medications under active investigation, though most therapies are most efficacious if instituted early on in the disease course. As such, early clinical recognition and prompt diagnosis are crucial to improving disease related outcomes. In this review, we highlight clinical manifestations of ATTR-CM as well as contemporary diagnostic and treatment approaches to the disease.

Hereditary transthyretin amyloid neuropathies: advances in pathophysiology, biomarkers, and treatment

Hereditary transthyretin (TTR) amyloid polyneuropathy is an autosomal dominant life-threatening disorder. TTR is produced mainly by the liver but also by the choroid plexus and retinal pigment epithelium. Detailed clinical characterisation, identification of clinical red flags for misdiagnosis, and use of biomarkers enable early diagnosis and treatment. In addition to liver transplantation and TTR stabilisers, three other disease-modifying therapies have regulatory approval: one antisense oligonucleotide (inotersen) and two small interfering RNAs (siRNAs; patisiran and vutrisiran). The siRNAs have been shown to stop progression of neuropathy and improve patients' quality of life. As none of the disease-modifying therapies can cross the blood-brain barrier, TTR deposition in the CNS, which can cause stroke and cognitive impairment, remains an important unaddressed issue. CRISPR-Cas9-based one-time TTR editing therapy is being investigated in a phase 1 clinical study. Identification of the earliest stages of pathogenesis in TTR variant carriers is a major challenge that needs addressing for optimal management.

Optimal practices for the management of hereditary transthyretin amyloidosis: real-world experience from Japan, Brazil, and Portugal

Hereditary transthyretin (ATTRv) amyloidosis is a rare and autosomal dominant disorder associated with mutations in the transthyretin gene. Patients present with diverse symptoms related to sensory, motor, and autonomic neuropathy, as well as gastrointestinal, ocular, cardiac, renal and orthopedic symptoms, resulting from the deposition of transthyretin amyloid fibrils in multiple organs. The progressive nature of ATTRv amyloidosis necessitates pre- and post-onset monitoring of the disease. This review article is primarily based on a collation of discussions from a medical advisory board meeting in August 2021. In this article, we summarize the best practices in amyloidosis centers in three major endemic countries for ATTRv amyloidosis (Japan, Brazil, and Portugal), where most patients carry the Val30Met mutation in the transthyretin gene and the patients' genetic background was proven to be the same. The discussions highlighted the similarities and differences in the management of asymptomatic gene mutation carriers among the three countries in terms of the use of noninvasive tests and tissue biopsies and timing of starting the investigations. In addition, this article discusses a set of practical tests and examinations for monitoring disease progression applicable to neurologists working in diverse medical settings and generalizable in non-endemic countries and areas. This set of assessments consists of periodic (every 6 to 12 months) evaluations of patients' nutritional status and autonomic, renal, cardiac, ophthalmologic, and neurological functions. Physical examinations and patient-reported outcome assessments should be also scheduled every 6 to 12 months. Programs for monitoring gene mutation carriers and robust referral networks can aid in appropriate patient management in pre- to post-onset stages. For pre- and post-symptom onset testing for ATTRv amyloidosis, various noninvasive techniques are available; however, their applicability differs depending on the medical setting in each country and region, and the optimal option should be selected in view of the clinical settings, medical environment, and available healthcare resources in each region.

Pathological spectrum of hereditary transthyretin renal amyloidosis and clinicopathologic correlation: a French observational study

BACKGROUND

Cardiac and neurological involvements are the main clinical features of hereditary transthyretin (ATTRv) amyloidosis. Few data are available about ATTRv amyloid nephropathy (ATTRvN).

METHODS

We retrospectively included 30 patients with biopsy-proven ATTRvN [V30M (26/30) including two domino liver recipients, S77Y (2/30), V122I (1/30) and S50R (1/30) variants] from two French reference centers. We described the pathological features by comparing amyloid deposits distribution to patients with AL or AA amyloidosis, and sought to determine clinicopathological correlation with known disease-modifying factors such as TTR variant, gender and age at diagnosis.

RESULTS

In comparison with AL and AA amyloidosis, ATTRv patients had similar glomerular, arteriolar and arterial amyloid deposits, but more cortical and medullary tubulointerstitial (33%, 44%, 77%, P = .03) involvement. While the presence of glomerular deposits is associated with the range of proteinuria, some patients with abundant glomerular ATTRv amyloidosis had no significant proteinuria. V30M patients had more glomerular (100% and 25%, odds ratio = 114, 95% confidence interval 3.85-3395.00, P = .001) deposits, and higher estimated glomerular filtration rate [50 (interquartile range 44-82) and 27 (interquartile range 6-31) mL/min/1.73 m², P = .004] than non-V30M patients. We did not find difference in amyloid deposition according to gender or age at diagnosis.

CONCLUSION

ATTRvN affects all kidney compartments, but compared with AL/AA amyloidosis, ATTRvN seems to involve more frequently tubulointerstitial areas. V30M patients represents the dominant face of the disease with a higher risk of glomerular/arteriolar involvement. ATTRvN should thus be considered in patients, and potential relatives, with ATTRv amyloidosis and kidney dysfunction, regardless of proteinuria level.

A molecular basis for tetramer destabilization and aggregation of transthyretin Ala97Ser

Transthyretin (TTR)-related amyloidosis (ATTR) is a syndrome of diseases characterized by the extracellular deposition of fibrillar materials containing TTR variants. Ala97Ser (A97S) is the major mutation reported in Taiwanese ATTR patients. Here, we combine atomic resolution structural information together with the biochemical data to demonstrate that substitution of polar Ser for a small hydrophobic side chain of Ala at residue 97 of TTR largely influences the local packing density of the FG-loop, thus leading to the conformational instability of native tetramer, the increased monomeric species, and thus the enhanced amyloidogenicity of apo-A97S. Based on calorimetric studies, the tetramer destabilization of A97S can be substantially altered by interacting with native stabilizers via similarly energetic patterns compared to that of wild-type (WT) TTR; however, stabilizer binding partially rearranges the networks of hydrogen bonding in TTR variants while FG-loops of tetrameric A97S still remain relatively flexible. Moreover, TTR in complexed with holo-retinol binding protein 4 is slightly influenced by the structural and dynamic changes of FG-loop caused by A97S substitution with an approximately five-fold difference in binding affinity. Collectively, our findings suggest that the amyloidogenic A97S mutation destabilizes TTR by increasing the flexibility of the FG-loop in the monomer, thus modulating the rate of amyloid fibrillization.

RNA Targeting and Gene Editing Strategies for Transthyretin Amyloidosis

Transthyretin (TTR) is a tetrameric protein synthesized primarily by the liver. TTR can misfold into pathogenic ATTR amyloid fibrils that deposit in the nerves and heart, causing a progressive and debilitating polyneuropathy (PN) and life-threatening cardiomyopathy (CM). Therapeutic strategies, which are aimed at reducing ongoing ATTR amyloid fibrillogenesis, include stabilization of the circulating TTR tetramer or reduction of TTR synthesis. Small interfering RNA (siRNA) or antisense oligonucleotide (ASO) drugs are highly effective at disrupting the complementary mRNA and inhibiting TTR synthesis. Since their development, patisiran (siRNA), vutrisiran (siRNA) and inotersen (ASO) have all been licensed for treatment of ATTR-PN, and early data suggest these drugs may have efficacy in treating ATTR-CM. An ongoing phase 3 clinical trial will evaluate the efficacy of eplontersen (ASO) in the treatment of both ATTR-PN and ATTR-CM, and a recent phase 1 trial demonstrated the safety of novel in vivo CRISPR-Cas9 gene-editing therapy in patients with ATTR amyloidosis. Recent results from trials of gene silencer and gene-editing therapies suggest these novel therapeutic agents have the potential to substantially alter the landscape of treatment for ATTR amyloidosis. Their success has already changed the perception of ATTR amyloidosis from a universally progressive and fatal disease to one that is treatable through availability of highly specific and effective disease-modifying therapies. However, important questions remain including long-term safety of these drugs, potential for off-target gene editing, and how best to monitor the cardiac response to treatment.Kindly check and confirm the processed running title.This is correct.

Neuropathic pain experience in symptomatic and presymptomatic subjects carrying a transthyretin gene mutation

Introduction

Pain is a common symptom of hereditary transthyretin amyloidosis (ATTRv), however, its occurrence in late-onset ATTRv has not been investigated thoroughly. Our aim was to describe the pain experience and its impact on quality of life (QoL) in symptomatic patients and presymptomatic carriers harboring a transthyretin (TTR) gene mutation with a late-onset phenotype.

Materials and methods

Study participants (aged ≥18 years) were consecutively recruited from four Italian centers. Clinical disability was assessed using the Familial Amyloid Polyneuropathy (FAP) stage and Neuropathy Impairment Score (NIS). The Norfolk questionnaire evaluated QoL and the Compound Autonomic Dysfunction Test assessed autonomic involvement. Neuropathic pain was screened using the Douleur Neuropathique 4 (DN4) questionnaire, and pain intensity and its impact on daily activity were assessed using the Brief Pain Inventory severity and interference subscores. Data on the type of TTR mutation, presence of cardiomyopathy, treatment, and Body Mass Index (BMI) were collected.

Results

Overall, 102 subjects with TTR mutations (mean age ± SD 63.6 ± 13.5 years) were recruited, including 78 symptomatic patients (68.1 ± 10.9 years) and 24 presymptomatic carriers (49 ± 10.3 years). Pain was reported by 75.5% of all subjects, but was more frequent in symptomatic patients than in presymptomatic carriers (85.9 vs. 41.6%, respectively). Pain exhibited neuropathic features (DN4≥4) in 69.2% of symptomatic patients and in 8.3% of presymptomatic carriers. Subjects with neuropathic pain were older (p = 0.015) had worse FAP stage (p < 0.001), higher NIS scores (p < 0.001), greater autonomic involvement (p = 0.003), and a lower QoL (p < 0.001) than those without neuropathic pain. Neuropathic pain was associated with higher pain severity (p < 0.001) and had a significant negative impact on daily activities (p < 0.001) Neuropathic pain was not associated with gender, mutation type, TTR therapy, or BMI.

Conclusion

Approximately 70% of late-onset ATTRv patients complained of neuropathic pain (DN4≥4) that worsened as peripheral neuropathy progressed and increasingly interfered with daily activities and QoL. Notably, 8% of presymptomatic carriers complained of neuropathic pain. These results suggest that assessment of neuropathic pain may be useful to monitor disease progression and identify early manifestations of ATTRv.

Pupillometric findings in ATTRv patients and carriers: results from a single-centre experience

INTRODUCTION

Hereditary transthyretin amyloidosis (ATTRv) is a treatable multisystemic disease with great phenotypic heterogeneity. Among extra-neurological features, pupillary abnormalities have been reported, either related to amyloid deposition in the eye or to a progressive autonomic neuropathy.

OBJECTIVE

To evaluate the role of automated pupillometry, a non-invasive and rapid test able to provide objective and reproducible data on pupil size and reactivity, as a marker of disease severity in late-onset ATTRv patients.

PATIENTS AND METHODS

We performed automated pupillometry on a cohort of ATTRv patients and pre-symptomatic TTR mutation carriers and compared results to healthy controls. An exhaustive clinical and instrumental evaluation was performed on all enrolled subjects.

RESULTS

A statistically significant difference in most pupillometry parameters was found in ATTRv patients as compared to both carriers and healthy controls. Moreover, in ATTRv patients, we found a significant correlation between many pupillometry findings and disease duration, as well as widely accepted clinical scales and investigations (NIS, Sudoscan from feet, and Norfolk QoL-DN questionnaire).

CONCLUSIONS

We suggest pupillometry may play a role as a reliable and non-invasive biomarker to evaluate ATTRv disease severity and monitor its progression.

Quantitative Sensory Testing in Late-Onset ATTRv Presymptomatic Subjects: A Single Center Experience

Backgrounds Hereditary transthyretin amyloidosis (ATTRv) presymptomatic subjects undergo multidisciplinary evaluation to detect, as early as possible, a subclinical involvement of multisystem disease. Quantitative sensory testing (QST) that investigates and discriminates the function of C, Aδ and Aβ fibers is included as an instrumental test to monitor nerve fiber function. The purpose of this study was to evaluate the role of QST in the context of the multidisciplinary evaluation in late onset carriers. Methods Four-teen presymptomatic (namely carriers) were enrolled. Subjects underwent thermal [cold and warm detection threshold (CDT, WDT), cold and heat pain (CP and HP)] and tactile QST in four body sites: foot dorsum, distal lateral leg, distal thigh, hand dorsum. Results Overall, presymptomatic subject showed a significant difference in all thermal QST findings compared to the control group. All subjects had at least one altered thermal QST finding; the sites more frequently altered were foot and leg, whilst the thermal modalities which were more frequently abnormal were CDT, WDT and CP. Conclusions Our study highlights the importance of performing thermal QST in subjects carrying TTR mutation, given the high frequency of abnormal findings. Notably, performing both innocuous and painful stimulation in foot and/or leg increases the chance of detecting nerve fiber dysfunction. Moreover, the investigation of the hand may provide useful information in monitoring disease progression before the Predicted Age of Disease Onset (PADO).

Transthyretin: Its function and amyloid formation

Transthyretin (TTR), which is one of the major amyloidogenic proteins in systemic amyloidosis, forms extracellular amyloid deposits in the systemic organs such as nerves, ligaments, heart, and arterioles, and causes two kinds of systemic amyloidosis, hereditary ATTR (ATTRv) amyloidosis induced by variant TTR and aging-related wild-type ATTR (ATTRwt) amyloidosis. More than 150 different mutations, most of which are amyloidogenic, have been reported in the TTR gene. Since most disease-associated mutations affect TTR tetramer dissociation rates, destabilization of TTR tetramers is widely believed to be a critical step in TTR amyloid formation. Recently, effective disease-modifying therapies such as TTR tetramer stabilizers and TTR gene silencing therapies have been developed for ATTR amyloidosis. This study reviews the clinical phenotypes of ATTR amyloidosis, TTR features, and recent progress in promising therapies for ATTR amyloidosis.