Early diagnosis in ATTRv amyloidosis, how early is enough? How early is possible?

Hereditary transthyretin amyloidosis (ATTRv amyloidosis) is a rare, progressive, and debilitating genetic disorder characterized by the deposition of abnormal transthyretin (TTR) protein aggregates in various tissues, leading to organ dysfunction. Early diagnosis of ATTRv amyloidosis is critical for starting timely interventions and improving patient outcomes. This review explores the concepts of "how early is enough" and "how early is possible" in the context of diagnosing ATTRv amyloidosis, highlighting the challenges and opportunities for early recognition.

Utility of Genetic Testing in Patients with Transthyretin Amyloid Cardiomyopathy: A Brief Review

Transthyretin amyloid cardiomyopathy (ATTR-CM) is an increasingly diagnosed condition. Although wild-type transthyretin amyloidosis (ATTRwt) is the most common ATTR-CM, hereditary transthyretin amyloidosis (ATTRv) may also occur. Currently, genetic testing for transthyretin pathogenic variants is recommended for patients with a confirmed clinical diagnosis of ATTR-CM. In fact, confirmation of this autosomal dominant pathogenic variant prompts genetic counselling and allows early identification of affected relatives. Additionally, in the presence of an ATTR-CM-associated polyneuropathy, specific drugs targeting transthyretin can be used. In this paper, we review the utility of genetic testing for the detection of pathogenic variants among patients harboring ATTR-CM and its impact on the natural history of the disease.

Conjunctival lymphangiectasia as a biomarker of severe systemic disease in Ser77Tyr hereditary transthyretin amyloidosis

AIMS

To investigate the relationship between the ophthalmic and systemic phenotypes in patients with hereditary transthyretin amyloidosis with the S77Y mutation (ATTRS77Y).

METHODS

In this cross-sectional study, patients with genetically confirmed ATTRS77Y amyloidosis were enrolled. All patients underwent complete neurological examination, including staging with the Neuropathy Impairment Score (NIS), Polyneuropathy Disability (PND) score; complete cardiological evaluation, including echocardiography, cardiac MRI and/or cardiac scintigraphy and complete ophthalmic evaluation, including slit lamp examination and fundus examination. Ocular ancillary tests (fluorescein and indocyanine green angiography, and anterior segment optical coherence tomography) were performed in cases with abnormal findings. The Kruskal-Wallis test was used for quantitative outcomes and Fisher's exact test for qualitative outcomes. Statistical significance was indicated by p<0.05 (two tailed).

RESULTS

The study sample was composed of 24 ATTRS77Y patients. The mean patient age was 58.4±12.4 years. None of the patients presented with amyloid deposits in the anterior chamber, secondary glaucoma or vitreous amyloidosis. Retinal angiopathy was observed in four patients, complicated with retinal ischaemia in one patient. Conjunctival lymphangiectasia (CL) was detected in 13 patients (54%), associated with perilymphatic amyloid deposits. The presence of CL was statistically associated with more severe neurological disease (NIS=43.3±31.9 vs 18.9±20.4; PND=2.6±1.0 vs 1.4±0.7 in patients with and without CL, respectively; both p<0.05) and amyloid cardiomyopathy (p=0.002).

CONCLUSION

In ATTRS77Y patients, CL is common and could serve as a potential biomarker for severe systemic disease. There were neither anterior chamber deposits, secondary glaucoma nor vitreous deposits in ATTRS77Y patients.

Prevalence of hereditary transthyretin amyloid polyneuropathy in idiopathic progressive neuropathy in conurban areas

Background

Hereditary transthyretin amyloidosis (ATTR amyloidosis) is a rare, genetically heterogenous, and clinically variable autosomal dominant disease that severely reduces life expectancy. As treatment options grow, a proper diagnostic approach is mandatory especially in non-endemic regions with diverse genetic backgrounds.

Methods

We examined 102 neuropathy patients at a German neuromuscular centre. Common causes of polyneuropathy were ruled out by medical history and extensive laboratory testing to define a cohort of patients with progressive polyneuropathy classified as idiopathic. Molecular genetic testing of the entire TTR gene was performed, and the detected amyloidogenic and non-amyloidogenic variants were associated with the observed clinical phenotypes and results of prior diagnostic testing.

Results

Two of 102 patients tested positive for amyloidogenic mutations (p.Ile127Val and p.Glu81Lys), while a variant of unknown significance, p.Glu26Ser, was found in 10 cases. In both positive cases, previous negative biopsy results were proved by gene sequencing to be false negative. In case of the p.Glu81Lys mutation we detected clinical presentation (combination of severe polyneuropathy and cardiomyopathy), ethnic background (patient of polish origin, mutation only reported in Japanese families before), and disease course clearly differed from well-known cases of the same mutation in the literature.

Conclusions

In conclusion, transthyretin hereditary amyloid polyneuropathy (ATTR-PN) should be considered in cases of otherwise idiopathic polyneuropathy. Sequencing of the four exons of the TTR gene should be considered the key step in diagnosis, while tissue biopsy possibly leads to false negative results.

Biophysical characterization and modulation of Transthyretin Ala97Ser

Objective

Ala97Ser (A97S) is the major transthyretin (TTR) mutation in Taiwanese patients of familial amyloid polyneuropathy (FAP), characterized by a late‐onset but rapidly deteriorated neuropathy. Tafamidis can restore the stability of some mutant TTR tetramers and slow down the progression of TTR‐FAP. However, there is little understanding of the biophysical features of A97S‐TTR mutant and the pharmacological modulation effect of tafamidis on it. This study aims to delineate the biophysical characteristics of A97S‐TTR and the pharmacological modulation effect of tafamidis on this mutant.

Method

The stability of TTR tetramers was assessed by urea denaturation and differential scanning calorimetry. Isothermal titration calorimetry (ITC) was used to measure the binding constant of tafamidis to TTR. Nuclear magnetic resonance spectroscopy (NMR) titration experiment was used to map out the tafamidis binding site.

Results

Chemical and thermal denaturation confirmed the destabilization effect of A97S. Consistent with other the amyloidogenic mutant, A97S‐TTR has slightly lower conformational stability. NMR revealed the binding site of A97S‐TTR with tafamidis is at the thyroxine binding pocket. The ITC experiments documented the high affinity of the binding which can effectively stabilize the A97S‐TTR tetramer.

Interpretation

This study confirmed the structural modulation effect of tafamidis on A97S‐TTR and implied the potential therapeutic benefit of tafamidis for A97S TTR‐FAP. This approach can be applied to investigate the modulation effect of tafamidis on other rare TTR variants and help to make individualized choices of available treatments for FAP patients.

Cause of death analysis and temporal trends in survival after liver transplantation for transthyretin familial amyloid polyneuropathy

BACKGROUND

Hereditary transthyretin amyloidosis (ATTR) is a multisystemic disease involving mainly the peripheral nervous system and the heart. Liver transplantation (LT) is the reference treatment for ATTR neuropathy and preoperative detection of high risk patients is crucial. We aimed to document the causes of death of ATTR patients after LT, their temporal trends, and to evaluate whether the available preoperative tools that predict the risk of death after LT for hereditary ATTR amyloidosis matched with these trends.

METHODS

A retrospective longitudinal cohort study was performed on 215 consecutive ATTR patients who underwent LT between January 1993 and January 2011. Each patient's death cause and timing were classified.

RESULTS

Over a median follow up of 5.9 years, 84 patients died. The rate of death was higher in the first year following LT than thereafter (13.0 vs. 4.3 ± 1.8%/year; p = .004). Cardiac events ranked as the leading cause of death (C: 38%), followed by infections (I: 24%), graft complications (G: 17%), end stage amyloidosis, stroke and others (ASO: 7% each). Deaths due to graft complications and infections (GI) occurred earlier than those due to end stage amyloidosis and stroke. Death prediction was less accurate for GI-related mortality than for other causes, which blunted the accuracy of the early-term risk prediction scores. Conclusions In ATTR amyloidosis, cardiac events were the leading cause of death after liver transplantation. Close preoperative evaluation allowed for accurate mid-term prediction of mortality, but the high rate of graft complications and infections blunted the early-term risk prediction.

Insights into the pharmaceuticals and mechanisms of neurological orphan diseases: Current Status and future expectations

Several rare or orphan diseases have been characterized that singly affect low numbers of people, but cumulatively reach ∼6%-10% of the population in Europe and in the United States. Human genetics has shown to be broadly effective when evaluating subjacent genetic defects such as orphan genetic diseases, but on the other hand, a modest progress has been achieved toward comprehending the molecular pathologies and designing new therapies. Chemical genetics, placed at the interface of chemistry and genetics, could be employed to understand the molecular mechanisms of subjacent illnesses and for the discovery of new remediation processes. This review debates current progress in chemical genetics, and how a variety of compounds and reaction mechanisms can be used to study and ultimately treat rare genetic diseases. We focus here on a study involving Amyotrophic lateral sclerosis (ALS), Duchenne Muscular Dystrophy (DMD), Spinal muscular atrophy (SMA) and Familial Amyloid Polyneuropathy (FAP), approaching different treatment methods and the reaction mechanisms of several compounds, trying to elucidate new routes capable of assisting in the treatment profile.

Using Molecular Tweezers to Remodel Abnormal Protein Self-Assembly and Inhibit the Toxicity of Amyloidogenic Proteins

Molecular tweezers (MTs) are broad-spectrum inhibitors of abnormal protein self-assembly, which act by binding selectively to lysine and arginine residues. Through this unique mechanism of action, MTs inhibit formation of toxic oligomers and aggregates. Their efficacy and safety have been demonstrated in vitro, in cell culture, and in animal models. Here, we discuss the application of MTs in diverse in vitro and in vivo systems, the experimental details, the scope of their use, and the limitations of the approach. We also consider methods for administration of MTs in animal models to measure efficacy, pharmacokinetic, and pharmacodynamic parameters in proteinopathies.

Management of asymptomatic gene carriers of transthyretin familial amyloid polyneuropathy

Transthyretin familial amyloid polyneuropathy (TTR‐FAP) is a rare, severe, and irreversible, adult‐onset, hereditary disorder caused by autosomal‐dominant mutations in the TTR gene that increase the intrinsic propensity of transthyretin protein to misfold and deposit systemically as insoluble amyloid fibrils in nerve tissues, the heart, and other organs. TTR‐FAP is characterized by relentless, progressively debilitating polyneuropathy, and leads to death, on average, within 10 years of symptom onset without treatment. With increased availability of disease‐modifying treatment options for a wider spectrum of patients with TTR‐FAP, timely detection of the disease may offer substantial clinical benefits. This review discusses mutation‐specific predictive genetic testing in first‐degree relatives of index patients diagnosed with TTR‐FAP and the structured clinical follow‐up of asymptomatic gene carriers for prompt diagnosis and early therapeutic intervention before accumulation of substantial damage. Muscle Nerve54: 353–360, 2016

Cardiac Dysautonomia Predicts Long-Term Survival in Hereditary Transthyretin Amyloidosis After Liver Transplantation

OBJECTIVES

This study sought to compare techniques evaluating cardiac dysautonomia and predicting the risk of death of patients with hereditary transthyretin amyloidosis (mATTR) after liver transplantation (LT).

BACKGROUND

mATTR is a multisystemic disease involving mainly the heart and the peripheral nervous system. LT is the reference treatment, and pre-operative detection of high-risk patients is critical. Cardiovascular dysautonomia is commonly encountered in ATTR and may affect patient outcome, although it is not known yet which technique should be used in the field to evaluate it.

METHODS

In a series of 215 consecutive mATTR patients who underwent LT, cardiac dysautonomia was assessed by a dedicated clinical score, time-domain heart rate variability, ¹²³-meta-iodobenzylguanidine heart/mediastinum (¹²³-MIBG H/M) ratio on scintigraphy, and heart rate response to atropine (HRRA).

RESULTS

Patient median age was 43 years, 62% were male and 69% carried the Val30Met mutation. Cardiac dysautonomia was documented by at least 1 technique for all patients but 6 (97%). In univariate analysis, clinical score, ¹²³-MIBG H/M ratio and HRRA were associated with mortality but not heart rate variability. The ¹²³-MIBG H/M ratio and HRRA had greater area under the curve (AUC) of receiver-operating characteristic curves than clinical score and heart rate variability (AUC: 0.787, 0.748, 0.656, and 0.523, respectively). Multivariate score models were then built using the following variables: New York Heart Association functional class, interventricular septum thickness, and either ^123-MIBG H/M ratio (S_MIBG) or HRRA (S_atropine). AUC of S_MIBG and S_atropine were greater than AUC of univariate models, although nonsignificantly (AUC: 0.798 and 0.799, respectively). Predictive powers of S_MIBG, S_atropine, and a reference clinical model (AUC: 0.785) were similar.

CONCLUSIONS

Evaluation of cardiac dysautonomia is a valuable addition for predicting survival of mATTR patients following LT. Among the different techniques that evaluate cardiac dysautonomia, ¹²³-MIBG scintigraphy and heart rate response to atropine had better prognostic accuracy. Multivariate models did not improve significantly prediction of outcome.

First European consensus for diagnosis, management, and treatment of transthyretin familial amyloid polyneuropathy

Purpose of review

Early and accurate diagnosis of transthyretin familial amyloid polyneuropathy (TTR-FAP) represents one of the major challenges faced by physicians when caring for patients with idiopathic progressive neuropathy. There is little consensus in diagnostic and management approaches across Europe.

Recent findings

The low prevalence of TTR-FAP across Europe and the high variation in both genotype and phenotypic expression of the disease means that recognizing symptoms can be difficult outside of a specialized diagnostic environment. The resulting delay in diagnosis and the possibility of misdiagnosis can misguide clinical decision-making and negatively impact subsequent treatment approaches and outcomes.

Summary

This review summarizes the findings from two meetings of the European Network for TTR-FAP (ATTReuNET). This is an emerging group comprising representatives from 10 European countries with expertise in the diagnosis and management of TTR-FAP, including nine National Reference Centres. The current review presents management strategies and a consensus on the gold standard for diagnosis of TTR-FAP as well as a structured approach to ongoing multidisciplinary care for the patient. Greater communication, not just between members of an individual patient's treatment team, but also between regional and national centres of expertise, is the key to the effective management of TTR-FAP.

Recommendations for presymptomatic genetic testing and management of individuals at risk for hereditary transthyretin amyloidosis

PURPOSE OF REVIEW

These recommendations highlight recent experience in genetic counselling for the severe autosomal-dominant, late-onset transthyretin familial amyloid polyneuropathy (TTR-FAP) disease, and present a structured approach towards identification and monitoring of asymptomatic carriers of the mutated gene.

RECENT FINDINGS

The effectiveness of current treatment options is still limited in patients with TTR-FAP beyond stage I. Diagnosis in the early stages of TTR-FAP is essential to prevent or delay the progression of disease. Existing legal and cultural issues differ among countries within Europe. Experts of the European Network for TTR-FAP (ATTReuNET) concluded that genetic counselling for diagnosed individuals and at-risk family members is mostly beneficial and should be carried out with care by trained professionals. Systematic and regular monitoring of an asymptomatic carrier is necessary to detect early signs of TTR-FAP and maximize the effectiveness of treatment. This includes five areas of assessment: history/clinical examination, sensorimotor function, autonomic dysfunction, cardiac function, and renal function. At least two related symptoms and positive biopsy findings are required to confirm diagnosis of TTR-FAP.

SUMMARY

Early detection of TTR-FAP is essential to improve the prognosis of TTR-FAP. ATTReuNET recommends genetic counselling and routine monitoring for asymptomatic carriers of TTR-FAP.

Sixty years of transthyretin familial amyloid polyneuropathy (TTR-FAP) in Europe: where are we now? A European network approach to defining the epidemiology and management patterns for TTR-FAP

Purpose of review

Transthyretin familial amyloid polyneuropathy (TTR-FAP) is a highly disabling, life-threatening disease characterized by progressive sensorimotor and autonomic neuropathy. The profile of the disease across Europe is inadequately understood at present.

Recent findings

The incidence and clinical presentation of TTR-FAP varies widely within Europe, with early and late-onset disease subtypes. In those regions in which the disease is endemic (Portugal, Sweden, Cyprus, and Majorca), a Val30Met substitution in the TTR gene is the predominant genetic cause, whereas in the rest of Europe, cases of TTR-FAP are mainly sporadic with genetic heterogeneity. Current management strategies lack cohesion and patients can experience years of misdiagnosis and suboptimal treatment.

Summary

The article aims to disseminate the findings and recommendations from two recent meetings of the European Network for TTR-FAP (ATTReuNET), a panel comprising representatives from 10 European countries (Bulgaria, Cyprus, France, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, and Turkey) with expertise in the diagnosis and management of TTR-FAP. We explore the epidemiology and genetic mark of TTR-FAP across Europe and assess current management strategies, with a view to developing an alternative framework – a networked approach to disease management with an emphasis on collaboration and sharing of best practice.

Tissue remodeling after interference RNA mediated knockdown of transthyretin in a familial amyloidotic polyneuropathy mouse model

Transthyretin (TTR) deposition in the peripheral nervous system is the hallmark of familial amyloidotic polyneuropathy (FAP). Currently, liver transplantation is the only available treatment to halt the progression of clinical symptoms; however, due to the limitations of this procedure, development of alternative therapeutic strategies is of utmost importance. In this regard, interference RNA (RNAi) targeting TTR is currently in phase III clinical development. To dissect molecular changes occurring in dorsal root ganglia (DRG) upon RNAi-mediated knockdown of TTR, we treated both chronically and acutely an FAP mouse model, in different stages of disease. Our data show that inhibition of TTR expression by the liver with RNAi reverse TTR deposition in DRG, decrease matrix metalloproteinase-2 (MMP-2) protein levels in plasma, inhibit Mmp-2 gene expression and downregulate MMP-9 activity in DRG, indicating extracellular matrix remodeling. Furthermore, protein levels of MMP-2 were found upregulated in plasma samples from FAP patients indicating that MMP-2 might be a novel potential biomarker for FAP diagnosis. Collectively, our data show that silencing TTR liver synthesis in vivo can modulate TTR-induced pathology in the peripheral nervous system and highlight the potential of MMP-2 as a novel disease biomarker.

Bioengineered non-coding RNA agent (BERA) in action

Non-coding RNAs (ncRNAs) including microRNAs (miRNAs) and small interfering RNAs (siRNAs) are important players in the control of gene regulation and represent novel promising therapeutic targets or agents for the treatment of various diseases. While synthetic ncRNAs are predominately utilized, the effects of excessive artificial modifications on higher-order structures, activities and toxicities of ncRNAs remain uncertain. Inspired by recombinant protein technology allowing large-scale bioengineering of proteins for research and therapy, efforts have been made to develop practical and effective means to bioengineer ncRNA agents. The fermentation-based approaches shall offer biological ncRNA agents with natural modifications and proper folding critical for ncRNA structure, function and safety. In this article, we will summarize current recombinant RNA platforms to the production of ncRNA agents including siRNAs and miRNAs. The applications of bioengineered ncRNA agents for basic research and potential therapeutics are also discussed.

Bioengineering of noncoding RNAs for research agents and therapeutics

The discovery of functional small noncoding RNAs (ncRNAs), such as microRNAs and small interfering RNAs, in the control of human cellular processes has opened new avenues to develop RNA-based therapies for various diseases including viral infections and cancers. However, studying ncRNA functions and developing RNA-based therapeutics relies on access to large quantities of affordable ncRNA agents. Currently, synthetic RNAs account for the major source of agents for RNA research and development, yet carry artificial modifications on the ribose ring and phosphate backbone in sharp contrast to posttranscriptional modifications present on the nucleobases or unmodified natural RNA molecules produced within cells. Therefore, large efforts have been made in recent years to develop recombinant RNA techniques to cost-effectively produce biological RNA agents that may better capture the structure, function, and safety properties of natural RNAs. In this article, we summarize and compare current in vitro and in vivo methods for the production of RNA agents including chemical synthesis, in vitro transcription, and bioengineering approaches. We highlight the latest recombinant RNA approaches using transfer RNA (tRNA), ribosomal RNA (rRNA), and optimal ncRNA scaffold (OnRS), and discuss the applications of bioengineered ncRNA agents (BERAs) that should facilitate RNA research and development.

Drugs for the treatment of peripheral neuropathies

Peripheral neuropathies are frequent in association with systemic diseases as well as isolated disorders. Recent advances in the therapy of specific neuropathies led to the approval of new drugs/treatments. This review selected those peripheral neuropathies where the most recent approvals were provided and revised the potential future developments in diabetic and toxic-induced neuropathies, although they do not have a currently available causal therapy in view of their epidemiological and social relevance. Data have been extracted from the most important published trials and from clinical experience. In addition, data from the Food and Drug Administration and European Medicine Agency indications on the treatment of the selected peripheral neuropathies and from recently updated international guidelines have also been included. The website of the U.S. National Institutes of Health www.clinicaltrials.gov registry has been used as the reference database for phase III clinical trials not yet published or ongoing. This review gives a general overview of the most recent advances in the treatment of amyloid, inflammatory, and paraproteinemic peripheral neuropathies. Moreover, it briefly describes the unmet medical need in disabling and frequent conditions, such as diabetic and chemotherapy-induced neuropathy, highlighting the most promising therapeutic approaches to their treatment.

A Review of Tafamidis for the Treatment of Transthyretin-Related Amyloidosis

Transthyretin (TTR)-related amyloidosis (ATTR) is a devastating disease which affects a combination of organs including the heart and the peripheral nerves, and which has a fatal outcome if not treated within a average of 10 years. Tafamidis, or 2-(3,5-dichloro-phenyl)-benzoxazole-6-carboxylic acid, selectively binds to TTR with negative cooperativity and kinetically stabilizes wild-type native TTR and mutant TTR; tafamidis therefore has the potential to halt the amyloidogenic cascade initiated by TTR tetramer dissociation, monomer misfolding, and aggregation. The first tafamidis trial, Fx-005, evaluated the effect of 18 months of tafamidis treatment (20 mg once daily) on disease progression, as well as assessing its safety in TTR-FAP Val30Met patients. The secondary objective of this trial was to study the pharmacodynamic stabilization of mutated TTR. Tafamidis proved effective in reducing the progress of neuropathy, and in maintaining the nutritional status and quality of life of stage 1 (able to walk without support) Val3OMet TTR-FAP patients. Furthermore, TTR stabilization was achieved in more than 90% of patients. An extension study, Fx-006, was conducted to determine the long-term safety and tolerability of tafamidis and to assess the efficacy of the drug on slowing disease progression. No significant safety or tolerability issues were noticed. Taken together, the results from both trials indicated that the beneficial effects of tafamidis were sustained over a 30-month period and that starting treatment early is desirable. Results are expected from an extended open-label study but data that have already been presented show that long-term use of tafamidis in Val30Met patients is associated with reduced progression in polyneuropathy. Tafamidis was initially approved for commercial use in Europe in 2011 and has since been approved for use in Japan, Mexico, and Argentina where it is used as a first-line treatment option for patients with early-stage TTR-FAP. Patients should be carefully followed at referral centers to ascertain the individual response to treatment. In cases of discontinuation, liver transplantation and enrollment in clinical trials of novel drugs aimed mostly toward suppression of TTR production are options.