Disease-Modifying Drugs Extend Survival in Hereditary Transthyretin Amyloid Polyneuropathy.

Hereditary transthyretin (ATTRv) amyloidosis is a rare, fatal systemic disease, associated with polyneuropathy and cardiomyopathy, that is caused by mutant transthyretin (TTR). In addition to liver transplantation, several groundbreaking disease-modifying drugs (DMDs) such as tetrameric TTR stabilizers and TTR gene-silencing therapies have been developed for ATTRv amyloid polyneuropathy. They were based on a working hypothesis of the mechanisms of ATTRv amyloid formation. In this retrospective cohort study, we investigated survival of all 201 consecutive patients with ATTRv amyloidosis in our center. The effects of DMDs on survival improvements were significant not only in early-onset patients but also in late-onset patients. ANN NEUROL 2024;95:230-236.

Protease-sensitive regions in amyloid light chains: what a common pattern of fragmentation across organs suggests about aggregation.

Light-chain (AL) amyloidosis is characterized by deposition of immunoglobulin light chains (LC) as fibrils in target organs. Alongside the full-length protein, abundant LC fragments are always present in AL deposits. Herein, by combining gel-based and mass spectrometry analyses, we identified and compared the fragmentation sites of amyloid LCs from multiple organs of an AL λ amyloidosis patient (AL-55). The positions pinpointed here in kidney and subcutaneous fat, alongside those previously detected in heart of the same patient, were aligned and mapped on the LC's dimeric and fibrillar states. All tissues contain fragmented LCs along with the full-length protein; the fragment pattern is coincident across organs, although microheterogeneity exists. Multiple cleavage positions were detected; some are shared, whereas some are organ-specific, likely due to a complex of proteases. Cleavage sites are concentrated in 'proteolysis-prone' regions, common to all tissues. Several proteolytic sites are not accessible on native dimers, while they are compatible with fibrils. Overall, data suggest that the heterogeneous ensemble of LC fragments originates in tissues and is consistent with digestion of preformed fibrils, or with the hypothesis that initial proteolytic cleavage of the constant domain triggers the amyloidogenic potential of LCs, followed by subsequent proteolytic degradation. This work provides a unique set of molecular data on proteolysis from ex vivo amyloid, which allows discussing hypotheses on role and timing of proteolytic events occurring along amyloid formation and accumulation in AL patients.

Editorial focus: understanding off-target effects as the key to successful RNAi therapy.

With the first RNA interference (RNAi) drug (ONPATTRO (patisiran)) on the market, we witness the RNAi therapy field reaching a critical turning point, when further improvements in drug candidate design and delivery pipelines should enable fast delivery of novel life changing treatments to patients. Nevertheless, ignoring parallel development of RNAi dedicated in vitro pharmacological profiling aiming to identify undesirable off-target activity may slow down or halt progress in the RNAi field. Since academic research is currently fueling the RNAi development pipeline with new therapeutic options, the objective of this article is to briefly summarize the basics of RNAi therapy, as well as to discuss how to translate basic research into better understanding of related drug candidate safety profiles early in the process.

Skin nerve pathology: Biomarkers of premanifest and manifest amyloid neuropathy.

OBJECTIVE: Small-fiber sensory and autonomic symptoms are early presentations of familial amyloid polyneuropathy (FAP) with transthyretin (TTR) mutations. This study aimed to explore the potential of skin nerve pathologies as early and disease-progression biomarkers and their relationship with skin amyloid deposits. METHODS: Skin biopsies were performed in patients and carriers to measure intraepidermal nerve fiber (IENF) density, sweat gland innervation index of structural protein gene product 9.5 (SGII[PGP9.5]) and peptidergic vasoactive intestinal peptide (SGII[VIP]), and cutaneous amyloid index. These skin pathologies were analyzed with clinical disability assessed by FAP stage score (stage 0-4) and compared to neurophysiological and psychophysical tests. RESULTS: There were 70 TTR-mutant subjects (22 carriers and 48 patients), and 66 cases were TTR-A97S. Skin nerve pathologies were distinct according to stage. In carriers, both skin denervation and peptidergic sudomotor denervation were evident: (1) IENF density was gradually reduced from stage 0 through 4, and (2) SGII(VIP) was markedly reduced from stage 1 to 2. In contrast, SGII(PGP9.5) was similar between carriers and controls, but it declined in patients from stage 2. Skin amyloids were absent in carriers and became detectable from stage 1. Cutaneous amyloid index was correlated with SGII(PGP9.5) and stage in a multivariate mixed-effect model. When all tests were compared, only IENF density, SGII(PGP9.5), and cutaneous amyloid index were correlated with stage, and IENF density had the highest abnormal rate in carriers. INTERPRETATION: Biomarkers of sensory and sudomotor innervation exhibited a stage-dependent progression pattern, with sensory nerve degeneration as the early skin nerve pathology. Ann Neurol 2019;85:560-573.

Cellular clearance of circulating transthyretin decreases cell-nonautonomous proteotoxicity in Caenorhabditis elegans.

Cell-autonomous and cell-nonautonomous mechanisms of neurodegeneration appear to occur in the proteinopathies, including Alzheimer's and Parkinson's diseases. However, how neuronal toxicity is generated from misfolding-prone proteins secreted by nonneuronal tissues and whether modulating protein aggregate levels at distal locales affects the degeneration of postmitotic neurons remains unknown. We generated and characterized animal models of the transthyretin (TTR) amyloidoses that faithfully recapitulate cell-nonautonomous neuronal proteotoxicity by expressing human TTR in the Caenorhabditis elegans muscle. We identified sensory neurons with affected morphological and behavioral nociception-sensing impairments. Nonnative TTR oligomer load and neurotoxicity increased following inhibition of TTR degradation in distal macrophage-like nonaffected cells. Moreover, reducing TTR levels by RNAi or by kinetically stabilizing natively folded TTR pharmacologically decreased TTR aggregate load and attenuated neuronal dysfunction. These findings reveal a critical role for in trans modulation of aggregation-prone degradation that directly affects postmitotic tissue degeneration observed in the proteinopathies.

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.

Amyloid polyneuropathy caused by wild-type transthyretin.

INTRODUCTION: Amyloidosis derived from transthyretin (TTR) molecules is typically caused by mutations of the TTR gene. METHODS: We describe an elderly patient with a severe length-dependent polyneuropathy that unexpectedly proved to be caused by wild-type transthyretin amyloidosis. RESULTS: The diagnosis was made by muscle biopsy, because no amyloid deposits were found in the biopsied nerve segment. Most cases of wild-type transthyretin amyloidosis occur in elderly patients with cardiomyopathy, but a few cases of polyneuropathy have been reported. CONCLUSIONS: This entity is especially noteworthy in light of emerging treatment options for hereditary transthyretin amyloidosis, which are likely to also be beneficial in wild-type disease.

Current and future treatment of amyloid neuropathies.

Amyloid neuropathies of acquired or genetic origin are disabling and life-threatening, until recently there were few treatment options available. Poor prognosis is related to progressive neuropathy and associated, although often underdiagnosed, cardiac involvement in specific transthyretin (TTR) gene mutations. Recent progress has modified prognosis and management of amyloid neuropathies. In TTR-familial amyloidosis with polyneuropathy, major changes have occurred over the last 30 years: better knowledge concerning genetics, phenotypes and epidemiology, and the advent of possible treatments. Liver transplantation, first performed in 1990, stopped disease progression, thus doubling survival in early onset V30M patients. More recently tetramer stabilizers (Tafamidis and Diflunisal) showed a significant reduction of progression of neuropathic scores; Tafamidis is now recommended in Stage I patients. Two multicentric clinical trials are now ongoing to evaluate TTR gene silencing by antisense Oligonucleotides (ASO) or siRNA. In the near future we should have new therapeutical options for patients with amyloid neuropathy.

Hereditary amyloid polyneuropathy in a family from North West India: phenotypic, MRI and pathologic study.

Hereditary amyloid polyneuropathies are rare, heterogeneous group of autosomal dominant disorders and deserve special attention because of its rare presentation, multisystem involvement and significant therapeutic implications if diagnosed early. We report a male patient of hereditary amyloid polyneuropathy from North West India with peripheral nerve, autonomic nervous system, vitreous and cardiac involvement.

TTR-related amyloid neuropathy: clinical, electrophysiological and pathological findings in 15 unrelated patients.

Familial amyloid polyneuropathy (FAP) is a rare condition caused by mutations of the transthyretin (TTR) gene and it is generally characterized by a length-dependent polyneuropathy affecting prevalently the small fibers. We reviewed clinical, electrophysiological and pathological findings of 15 unrelated patients with genetically confirmed TTR-FAP. All patients presented a progressive sensory-motor polyneuropathy. Pathological findings were negative for amyloid deposits in about half of the cases. Sequence analysis of TTR gene revealed the presence of three different mutations (p.Val30Met, p.Phe64Leu, and p.Ala120Ser). The p.Val30Met was the most frequently identified mutation and it often occurred in apparently sporadic cases. Conversely, the p.Phe64Leu generally presented in a high percentage of familial cases in patients coming from Southern Italy. Clinicians should consider, to avoid misdiagnosis, the screening for TTR mutations in patients presenting with progressive axonal polyneuropathy of undetermined etiology, including apparently sporadic cases with pathological examinations negative for amyloid deposition.

Amyloid neuropathies.

PURPOSE OF REVIEW: As amyloid neuropathies have benefited from recent major progress, this review is timely and relevant. RECENT FINDINGS: The main recent articles on amyloid neuropathy cover its description, methods for diagnosis and therapies. Varied clinical presentations are described in transthyretin (TTR)-familial amyloidosis with polyneuropathy (FAP) and light chain amyloid neuropathy. Mass spectrometry is able to identify the biochemical nature of amyloidogenic protein in nerve biopsy and skin biopsy samples for diagnosis of small fiber polyneuropathy. Both nerve biopsy and TTR gene sequencing are important to identify sporadic cases of amyloid neuropathy. Nerve biopsy is useful in demonstrating the amyloid origin of neuropathies developing after domino liver transplant recipients. Liver transplantation improves long-term survival in Met30 TTR-FAP. Factors recognized as leading to cardiomyopathy progression or heart involvement after liver transplantation are late disease onset and fibril composition. Combined heart and liver transplantation is recommended in severe restrictive cardiomyopathy. Antiamyloid drugs are emerging: tafamidis, a TTR stabilizer, showed in a phase III controlled study its ability to slow stage 1 FAP progression. Other strategies are emerging for TTR-FAP (combination doxycycline-tauroursodeoxycholic acid, small interfering RNA, antisense oligonucleotide, monoclonal antibody antiserum amyloid P component). For light chain neuropathy, intensive chemotherapy may be helpful. SUMMARY: There is better recognition of amyloid neuropathies, and hope for enrolling patients with FAP in future clinical trials testing new antiamyloid drugs.