Hereditary transthyretin amyloidosis: current treatment

Quantitative sensory testing: a good tool to identify subclinical neuropathy in ATTRV30M amyloidosis patients?

BACKGROUND

Quantitative sensory testing (QST) has been one of the neurophysiological tools used for follow-up and disease progression assessment in ATTRv amyloidosis. We aimed to detect the utility of QST in identifying subclinical neuropathic involvement in ATTRV30M amyloidosis carriers.

METHODS

A cohort of ATTRV30M amyloidosis carriers were assessed with vibratory (VDT) and cooling (CDT) detection thresholds and heat pain responses. Subjects were divided into asymptomatic carriers (Group 1), paucisymptomatic carriers (Group 2) and stage 1 ATTRv-PN patients (Group 3). Nonparametric statistics were used for group comparisons.

RESULTS

A total of 207 ATTRV30M amyloidosis carriers (83 males) were included. Of these, 113 subjects were asymptomatic and 94 symptomatic carriers. In asymptomatic carriers, CDT and Heat Pain (HP 5.0 and HP 0.5) were significantly lower when compared to both group of symptomatic carriers (p ≤ 0.005). In Group 3, VDT, CDT and HP 5.0 were significantly higher, when compared to Group 2 (p < 0.05).

CONCLUSIONS

QST, in particular CDT, HP 5 and HP 0.5 modalities, seems a good tool to identify subclinical neuropathy in ATTRv amyloidosis carriers, with CDT showing a higher sensitivity to detect and early neuropathic involvement.

A novel TTR mutation (p.Ala65Val) underlying late-onset hereditary transthyretin (ATTRv) amyloidosis with mixed cardiac and neuropathic phenotype: a case report

BACKGROUND

Hereditary transthyretin (ATTRv) amyloidosis is a rare, genetically heterogeneous and phenotypically variable systemic disease characterized by deposition of misfolded transthyretin fibrils in various tissues. ATTRv cardiomyopathy and progressive axonal polyneuropathy are the most common manifestations, leading to severe disability and ultimately death within approximately ten years. As disease-modifying treatment options evolve, timely diagnosis and treatment initiation are crucial to prevent rapid disease progression.

CASE PRESENTATION

Here, we report on a 73-year old patient initially diagnosed with cardiac wild-type ATTR (ATTRwt) amyloidosis by endomyocardial biopsy. Molecular genetic analysis revealed a novel TTR sequence variant (p.Ala65Val) that is highly likely to be amyloidogenic in light of previously reported TTR mutations and the patient's clinical presentation and family history.

CONCLUSIONS

Our findings expand the spectrum of known pathogenic TTR mutations and underline the importance of a thorough diagnostic workup in amyloidosis patients including careful genetic testing to avoid misdiagnosis and missing of treatment opportunities and to enable cascade testing and tracking of carriers.

A natural history analysis of asymptomatic TTR gene carriers as they develop symptomatic transthyretin amyloidosis in the Transthyretin Amyloidosis Outcomes Survey (THAOS)

BACKGROUND

Hereditary transthyretin amyloidosis (ATTRv amyloidosis) results from pathogenic mutations in the transthyretin (TTR) gene. This analysis aimed to better understand ATTRv amyloidosis development in asymptomatic TTR gene carriers.

METHODS

The Transthyretin Amyloidosis Outcomes Survey (THAOS) is an ongoing, global, longitudinal, observational survey of patients with transthyretin amyloidosis, including both inherited and wild-type disease, and asymptomatic TTR gene carriers. Asymptomatic TTR gene carriers were assessed longitudinally to identify those who developed ATTRv amyloidosis after enrolment in THAOS (data cut-off: 1 August 2021).

RESULTS

Of 740 asymptomatic TTR gene carriers, 268 (36.2%) (Val30Met, 212/613 [34.6%]; non-Val30Met, 48/111 [43.2%]) developed ATTRv amyloidosis within a median 2.2 years after enrolment. The most common first symptoms were sensory (49.5%) and autonomic (37.3%) neuropathy in Val30Met patients, and sensory neuropathy (45.8%) and cardiac disorder (22.9%) in non-Val30Met patients. Most patients first presented with a predominantly neurologic phenotype (Val30Met, 77.8%; non-Val30Met, 70.8%).

CONCLUSIONS

More than one-third of asymptomatic TTR gene carriers in THAOS developed ATTRv amyloidosis within a median 2 years of enrolment. Val30Met versus non-Val30Met patients had a lower transition rate. Given the importance of early treatment, these findings underscore the need for identification and careful monitoring of at-risk TTR gene carriers to enable prompt treatment.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00628745.

The integration of genetically-regulated transcriptomics and electronic health records highlights a pattern of medical outcomes related to increased hepatic transthyretin expression

Transthyretin (TTR) is the precursor of the fibrils that compromise organ function in hereditary and sporadic systemic amyloidoses (ATTR). RNA-interference and anti-sense therapeutics targeting TTR hepatic transcription have been shown to reduce TTR amyloid formation. In the present study, we leveraged genetic and phenotypic information from the UK Biobank and transcriptomic profiles from the Genotype-Tissue Expression project to test the association of genetically regulated TTR gene expression with 7149 traits assessed in 420,531 individuals. We conducted a multi-tissue analysis of TTR transcription and identified an association with a operational procedure related to bone fracture (p = 5.46×10^-6). Using tissue-specific TTR expression information, we demonstrated that the association is driven by the genetic regulation of TTR hepatic expression (odds ratio [OR] = 3.46, p = 9.51×10^-5). Using the UK Biobank electronic health records (EHRs), we investigated the comorbidities affecting individuals undergoing this surgical procedure. Excluding bone fracture EHRs, we identified a pattern of health outcomes previously associated with ATTR manifestations. These included osteoarthritis (OR = 3.18, p = 9.18×10^-8), carpal tunnel syndrome (OR = 2.15, p = .002), and a history of gastrointestinal diseases (OR = 2.01, p = 8.07×10^-4). In conclusion, our study supports that TTR hepatic expression can affect health outcomes linked to physiological and pathological processes presumably related to the encoded protein.

ATF6 Activation Reduces Amyloidogenic Transthyretin Secretion through Increased Interactions with Endoplasmic Reticulum Proteostasis Factors

The extracellular aggregation of destabilized transthyretin (TTR) variants is implicated in the onset and pathogenesis of familial TTR-related amyloid diseases. One strategy to reduce the toxic, extracellular aggregation of TTR is to decrease the population of aggregation-prone proteins secreted from mammalian cells. The stress-independent activation of the unfolded protein response (UPR)-associated transcription factor ATF6 preferentially decreases the secretion and subsequent aggregation of destabilized, aggregation-prone TTR variants. However, the mechanism of this reduced secretion was previously undefined. Here, we implement a mass-spectrometry-based interactomics approach to identify endoplasmic reticulum (ER) proteostasis factors involved in ATF6-dependent reductions in destabilized TTR secretion. We show that ATF6 activation reduces amyloidogenic TTR secretion and subsequent aggregation through a mechanism involving ER retention that is mediated by increased interactions with ATF6-regulated ER proteostasis factors including BiP and PDIA4. Intriguingly, the PDIA4-dependent retention of TTR is independent of both the single TTR cysteine residue and the redox activity of PDIA4, indicating that PDIA4 retains destabilized TTR in the ER through a redox-independent mechanism. Our results define a mechanistic basis to explain the ATF6 activation-dependent reduction in destabilized, amyloidogenic TTR secretion that could be therapeutically accessed to improve treatments of TTR-related amyloid diseases.

TTR Gly83Arg Mutation: Beyond Familial Vitreous Amyloidosis

BACKGROUND

Gly83Arg variation is a type of TTR mutation specific to the Chinese population. Patients of hereditary transthyretin amyloidosis (ATTR) with Gly83Arg variation predominantly present with blurred vision and most of these cases are reported by ophthalmologists. There is currently no systematic assessment of extraocular features of ATTR with Gly83Arg variation.

METHODS

Six patients and two asymptomatic carriers with molecularly confirmed Gly83Arg variation of ATTR from three unrelated families were identified by sequencing the TTR gene. The clinical, electrophysiological, ultrasonic, and pathological data were collected and analyzed.

RESULTS

This study included six patients and two carriers with TTR Gly83Arg mutation, all of whom came from the Han nationality of China. The average age of onset for the six patients was 39 years, and the course of disease ranged from 5 to 19 years. All the patients started with blurred vision, which was diagnosed as vitreous opacity (VO). Most of the patients developed sensory-motor polyneuropathies over years or even more than a decade (4-15 years) after VO. However, the heterogeneity of peripheral neuropathies among these patients remained large between families. Autonomic impairment also occurred after VO, with varying degrees of abnormalities seen in the associated autonomic assessments. None of the patients had any symptoms of cardiac impairment, but abnormal results were found in examinations. A combined biopsy of the sural nerve and muscle was also performed. Nerve pathology revealed the moderately reduced myelinated nerve fiber density and muscle pathology showed predominant neurogenic impairment accompanied by possible myogenic impairment.

CONCLUSIONS

This is a detailed account of Gly83Arg mutation-related ATTR, focusing on the extraocular presentations of this special variant in Chinese. Clinical features of this variant are early-onset, ocular involvement predominance, neurological, and cardiac involvement along with the disease, and relatively long survival.

Muscle MRI as a Useful Biomarker in Hereditary Transthyretin Amyloidosis: A Pilot Study

Hereditary transthyretin amyloidosis (ATTRv, v for variant) is a severe and heterogeneous multisystem condition with a prevalent peripheral nervous system impairment, due to mutations in the transthyretin gene. Considering the introduction of different disease-modifying therapies in the last few years, a need of reliable biomarkers is emerging. In this study, we evaluated muscle MRI in a cohort of ATTRv patients in order to establish if the severity of muscle involvement correlated with disease severity. Linear regression analysis showed a significant positive correlation between the total fatty infiltration score and NIS, NIS-LL, and Norfolk, and an inverse correlation with Sudoscan registered from feet. In conclusion, we demonstrated the role of muscle MRI in ATTRv as possible disease biomarker, both for diagnostic purposes and for assessing the severity of the disease.

Phenotypic Differences of Glu89Gln Genotype in ATTR Amyloidosis From Endemic Loci: Update From THAOS

INTRODUCTION

Transthyretin amyloidosis (ATTR amyloidosis) is a progressive, clinically heterogeneous disease with spontaneous (wild-type) and hereditary (ATTRv) forms. The Glu89Gln variant is primarily associated with cardiomyopathy and prevalent in Italy and Bulgaria. The objective of this analysis was to better understand the profile of patients with ATTRv Glu89Gln amyloidosis in the Transthyretin Amyloidosis Outcomes Survey (THAOS).

METHODS

THAOS is an ongoing, global, longitudinal, observational survey of patients with ATTR amyloidosis, including both inherited and wild-type disease, and asymptomatic carriers with mutations in the transthyretin gene. Demographic and clinical characteristics of all symptomatic patients with the ATTRv Glu89Gln variant enrolled in THAOS are described (data cutoff, January 6, 2020).

RESULTS

There were 91 patients with ATTRv Glu89Gln amyloidosis with the majority from Bulgaria (n = 53) or Italy (n = 29). All patients were Caucasian and 50.5% were male. Patients from Bulgaria had a mean (standard deviation) age at enrollment of 57.1 (8.2) years, and duration of symptoms of 8.6 (9.6) years, compared with 54.8 (8.6) and 5.0 (4.1) years in Italy. In Bulgaria, 39.6% of patients were of a predominantly cardiac phenotype, 18.9% predominantly neurologic, and 41.5% mixed. In Italy, 3.4% of patients were predominantly cardiac, 62.1% predominantly neurologic, and 34.5% mixed.

CONCLUSIONS

The majority of patients with ATTRv Glu89Gln amyloidosis in THAOS are from Bulgaria or Italy. There were notable phenotypic differences, with the cardiac phenotype more common in Bulgaria and the neurologic phenotype more common in Italy. Over one-third of patients had a mixed phenotype, suggesting a potential role of multiple genetic and/or environmental factors and the need for comprehensive assessment of all patients.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00628745.