Schwann cell and endothelial cell damage in transthyretin familial amyloid polyneuropathy

Age-dependent small fiber neuropathy: Mechanistic insights from animal models

Small fiber neuropathy (SFN) is a common and debilitating disease in which the terminals of small diameter sensory axons degenerate, producing sensory loss, and in many patients neuropathic pain. While a substantial number of cases are attributable to diabetes, almost 50% are idiopathic. An underappreciated aspect of the disease is its late onset in most patients. Animal models of human genetic mutations that produce SFN also display age-dependent phenotypes suggesting that aging is an important contributor to the risk of development of the disease. In this review we define how particular sensory neurons are affected in SFN and discuss how aging may drive the disease. We also evaluate how animal models of SFN can define disease mechanisms that will provide insight into early risk detection and suggest novel therapeutic interventions.

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.

Neuromuscular manifestations of wild type transthyretin amyloidosis: a review and single center's experience

Transthyretin amyloidosis (ATTR) is a condition defined by accumulation of insoluble transthyretin amyloid deposits in multiple organs, especially in the peripheral nerve and heart muscle. ATTR may result from transthyretin mutations (variant ATTR or ATTRv) or may occur with normal transthyretin genotype (wild type ATTR or ATTRwt). ATTRwt was previously known as "senile amyloidosis" and causes cardiomyopathy which may lead to heart failure with a preserved ejection fraction, affecting predominantly elderly men. The exact prevalence of ATTRwt in the general population remains unclear, but its occurrence may be underestimated in women. It was observed that a proportion of ATTRwt cardiomyopathy patients may develop slowly progressing neuropathy that is milder and indolent in comparison with typical progressive neuropathy associated with ATTRv. Furthermore, the causality of neuropathy is often uncertain in patients with ATTRwt. Neuropathy symptoms, including distal sensory loss, unsteadiness and (neuropathic) pain are common in elderly patients with multiple potential causes, and as ATTRwt patients are typically older, relatively high prevalence of peripheral neuropathy is expected with frequent comorbidities. Relatively high prevalence of ATTRwt in elderly population contrasts few documented cases of neuropathy caused by ATTRwt, and there is uncertainty whether ATTRwt neuropathy is an infrequent occurrence or a significant manifestation of multisystemic ATTRwt. We review neurologic and musculoskeletal manifestations of ATTRwt and present clinical features of a single center cohort of ATTRwt patients with suspected peripheral neuropathy.

Identification of Structures Labeled by Indocyanine Green in the Rat Choroid and Retina Can Guide Interpretation of Indocyanine Green Angiography

Purpose

Indocyanine green (ICG) is an albumin and lipoprotein binding dye absorbing in the far red used in angiography to visualize choroidal vessels (ICG angiography [ICGA]). To guide interpretation, ICG transport in the choroid, RPE, and retina of rats was studied.

Methods

Two conditions were used: RPE/choroid organoculture, incubated for 45 minutes in DMEM medium, 1% fetal bovine serum containing 0.25 mg/mL ICG and RPE/choroid and neural retina flat-mounts at 1 and 6 hours after intravenous ICG injection. Early and late sequences of ICGA were recorded until 6 hours. Ultra-deep red confocal microscope was used to localize ICG in flat-mounts and immunohistochemistry was performed for caveolin-1, tryptase (mast cell marker), and tubulin β3 (a nerve marker).

Results

In the organoculture, ICG penetrated homogeneously in the cytoplasm and stained the membranes of the RPE. At 1 hour after intravenous injection, ICG appeared in fine granules in RPE, partly labeled with caveolin-1 and decreasing at 6 hours. At 1 hour and 6 hours, ICG was found in the retinal vessels, faintly in the inner retina, and in the photoreceptor outer segments at 6 hours. In the choroid, ICG colocalized with mast cells, immunostained with tryptase, and accumulated along the large tubulin β3-labeled nerve bundles. The hypothesis was raised on the interpretation of late ICGA infrared photography in case of transthyretin amyloidosis with neuropathy.

Conclusions

Beside being a vascular dye, ICG is transported from the vessels to the RPE toward the outer retina. It stains mast cells and large choroidal nerves. These observations could help the analysis of ICGA images.

Nerve pathology of microangiopathy and thromboinflammation in hereditary transthyretin amyloidosis

OBJECTIVE

Despite amyloid deposition as a hallmark of hereditary transthyretin amyloidosis (ATTRv) with polyneuropathy, this pathology could not completely account for nerve degeneration. ATTRv patients frequently have vasomotor symptoms, but microangiopathy hypothesis in ATTRv was not systemically clarified.

METHODS

This study examined the vascular pathology of sural nerves in ATTRv patients with transthyretin (TTR) mutation of p.Ala117Ser (TTR-A97S), focusing on morphometry and patterns of molecular expression in relation to nerve degeneration. We further applied human microvascular endothelial cell (HMEC-1) culture to examine the direct effect of TTR-A97S protein on endothelial cells.

RESULTS

In ATTRv nerves, there was characteristic microangiopathy compared to controls: increased vessel wall thickness and decreased luminal area; both were correlated with the reduction of myelinated fiber density. Among the components of vascular wall, the area of collagen IV in ATTRv nerves was larger than that of controls. This finding was validated in a cell model of HMEC-1 culture in which the expression of collagen IV was upregulated after exposure to TTR-A97S. Apoptosis contributed to the endothelial cell degeneration of microvasculatures in ATTRv endoneurium. ATTRv showed prothrombotic status with intravascular fibrin deposition, which was correlated with (1) increased tissue factor and coagulation factor XIIIA and (2) reduced tissue plasminogen activator. This cascade led to intravascular thrombin deposition, which was colocalized with upregulated p-selectin and thrombomodulin, accompanied by complement deposition and macrophages infiltration, indicating thromboinflammation in ATTRv.

INTERPRETATION

Microangiopathy with thromboinflammation is characteristic of advanced-stage ATTRv nerves, which provides an add-on mechanism and therapeutic target for nerve degeneration.

Hereditary transthyretin amyloidosis: a comprehensive review with a focus on peripheral neuropathy

Amyloidoses represent a group of diseases characterized by the pathological accumulation in the extracellular area of insoluble misfolded protein material called "amyloid". The damage to the tissue organization and the direct toxicity of the amyloidogenic substrates induce progressive dysfunctions in the organs involved. They are usually multisystem diseases involving several vital organs, such as the peripheral nerves, heart, kidneys, gastrointestinal tract, liver, skin, and eyes. Transthyretin amyloidosis (ATTR) is related to abnormalities of transthyretin (TTR), a protein that acts as a transporter of thyroxine and retinol and is produced predominantly in the liver. ATTR is classified as hereditary (ATTRv) and wild type (ATTRwt). ATTRv is a severe systemic disease of adults caused by mutations in the TTR gene and transmitted in an autosomal dominant manner with incomplete penetrance. Some pathogenic variants in TTR are preferentially associated with a neurological phenotype (progressive peripheral sensorimotor polyneuropathy); others are more frequently associated with restrictive heart failure. However, many mutations express a mixed phenotype with neurological and cardiological involvement. ATTRv is now a treatable disease. A timely and definite diagnosis is essential in view of the availability of effective therapies that have revolutionized the management of affected patients. The purpose of this review is to familiarize the clinician with the disease and with the correct diagnostic pathways in order to obtain an early diagnosis and, consequently, the possibility of an adequate treatment.

Magnetic resonance neurography and diffusion tensor imaging of the sciatic nerve in hereditary transthyretin amyloidosis polyneuropathy

The therapeutic advance in hereditary transthyretin amyloidosis (ATTRv amyloidosis) requires quantitative biomarkers of nerve involvement in order to foster early diagnosis and monitor therapy response. We aimed at quantitatively assessing Magnetic Resonance Neurography (MRN) and Diffusion Tensor Imaging (DTI) properties of the sciatic nerve in subjects with ATTRv-amyloidosis-polyneuropathy (ATTRv-PN) and pre-symptomatic carriers (ATTRv-C). Twenty subjects with pathogenic variants of the TTR gene (mean age 62.20 ± 12.04 years), 13 ATTRv-PN, and 7 ATTRv-C were evaluated and compared with 20 healthy subjects (mean age 60.1 ± 8.27 years). MRN and DTI sequences were performed at the right thigh from the gluteal region to the popliteal fossa. Cross-sectional-area (CSA), normalized signal intensity (NSI), and DTI metrics, including fractional anisotropy (FA), mean (MD), axial (AD), and radial diffusivity (RD) of the right sciatic nerve were measured. Increased CSA, NSI, RD, and reduced FA of sciatic nerve differentiated ATTRv-PN from ATTRv-C and healthy subjects at all levels (p < 0.01). NSI differentiated ATTRv-C from controls at all levels (p < 0.05), RD at proximal and mid-thigh (1.04 ± 0.1 vs 0.86 ± 0.11 p < 0.01), FA at mid-thigh (0.51 ± 0.02 vs 0.58 ± 0.04 p < 0.01). According to receiver operating characteristic (ROC) curve analysis, cutoff values differentiating ATTRv-C from controls (and therefore identifying subclinical sciatic involvement) were defined for FA, RD, and NSI. Significant correlations between MRI measures, clinical involvement and neurophysiology were found. In conclusion, the combination of quantitative MRN and DTI of the sciatic nerve can reliably differentiate ATTRv-PN, ATTRv-C, and healthy controls. More important, MRN and DTI were able to non-invasively identify early subclinical microstructural changes in pre-symptomatic carriers, thus representing a potential tool for early diagnosis and disease monitoring.

Current Evidence Supporting the Role of Immune Response in ATTRv Amyloidosis

Hereditary transthyretin (ATTRv) amyloidosis with polyneuropathy, also known as familial amyloid polyneuropathy (FAP), represents a progressive, heterogeneous, severe, and multisystemic disease caused by pathogenic variants in the TTR gene. This autosomal-dominant neurogenetic disorder has an adult onset with variable penetrance and an inconstant phenotype, even among subjects carrying the same mutation. Historically, ATTRv amyloidosis has been viewed as a non-inflammatory disease, mainly due to the absence of any mononuclear cell infiltration in ex vivo tissues; nevertheless, a role of inflammation in its pathogenesis has been recently highlighted. The immune response may be involved in the development and progression of the disease. Fibrillary TTR species bind to the receptor for advanced glycation end products (RAGE), probably activating the nuclear factor κB (NF-κB) pathway. Moreover, peripheral blood levels of several cytokines, including interferon (IFN)-gamma, IFN-alpha, IL-6, IL-7, and IL-33, are altered in the course of the disease. This review summarizes the current evidence supporting the role of the immune response in ATTRv amyloidosis, from the pathological mechanisms to the possible therapeutic implications.

Corneal confocal microscopy identifies corneal nerve loss and increased Langerhans cells in presymptomatic carriers and patients with hereditary transthyretin amyloidosis

BACKGROUND

Hereditary transthyretin amyloidosis (ATTRv amyloidosis) is a rare, but life-threatening protein misfolding disorder due to TTR gene mutations. Cardiomyopathy (ATTRv-CM) and polyneuropathy (ATTRv-PN) with early small nerve fibre involvement are the most common manifestations. Timely diagnosis and treatment initiation are key to limiting progression of disease. Corneal confocal microscopy (CCM) is a non-invasive method to quantify corneal small nerve fibres and immune cell infiltrates in vivo.

METHODS

This cross-sectional study investigated the utility of CCM in 20 patients with ATTRv amyloidosis (ATTRv-CM, n = 6; ATTRv-PN, n = 14) and presymptomatic carriers (n = 5) compared to 20 age- and sex-matched healthy controls. Corneal nerve fibre density, corneal nerve fibre length, corneal nerve branch density, and cell infiltrates were assessed.

RESULTS

Corneal nerve fibre density and nerve fibre length were significantly lower in patients with ATTRv amyloidosis compared to healthy controls regardless of the clinical phenotype (ATTRv-CM, ATTRv-PN) and corneal nerve fibre density was significantly lower in presymptomatic carriers. Immune cell infiltrates were only evident in patients with ATTRv amyloidosis, which correlated with reduced corneal nerve fibre density.

CONCLUSIONS

CCM identifies small nerve fibre damage in presymptomatic carriers and symptomatic patients with ATTRv amyloidosis and may serve as a predictive surrogate marker to identify individuals at risk of developing symptomatic amyloidosis. Furthermore, increased corneal cell infiltration suggests an immune-mediated mechanism in the pathogenesis of amyloid neuropathy.

Human transthyretin gene expression is markedly increased in repair Schwann cells in an in vitro model of hereditary transthyretin amyloidosis

Hereditary transthyretin (TTR) amyloidosis (ATTRv) is characterized by TTR amyloid deposition in the peripheral nervous system. It remains unknown why variant TTR preferentially deposits in the peripheral nerves and dorsal root ganglia. We previously detected low levels of TTR expression in Schwann cells and established an immortalized Schwann cell line, TgS1, derived from a mouse model of ATTRv amyloidosis expressing the variant TTR gene. In the present study, the expression of TTR and Schwann cell marker genes was investigated in TgS1 cells by quantitative RT-PCR. TTR gene expression was markedly upregulated in TgS1 cells incubated in non-growth medium-Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum. The expression levels of c-Jun, Gdnf and Sox2 were increased, while Mpz was downregulated, suggesting that TgS1 cells exhibit a repair Schwann cell-like phenotype in the non-growth medium. Western blot analysis revealed that TTR protein was produced and secreted by the TgS1 cells. Furthermore, downregulation of Hsf1 with siRNA induced TTR aggregates in the TgS1 cells. These findings indicate that TTR expression is markedly increased in repair Schwann cells, likely to promote axonal regeneration. Therefore, aged dysfunctional repair Schwann cells may cause the deposition of variant TTR aggregates in the nerves of patients with ATTRv.

Inotersen to Treat Polyneuropathy Associated with Hereditary Transthyretin (hATTR) Amyloidosis

Background

Amyloidosis is a group of diseases with the common pathophysiology of protein misfolding and aberrant deposition in tissue. There are both acquired and hereditary forms of this disease, and this review focuses on the latter hereditary transthyretin-mediated (hATTR). hATTR affects about 50,000 individuals globally and mostly appears as one of three syndromes - cardiac, polyneuropathy, and oculoleptomeningeal. Polyneuropathy is the most common form, and there is usually some overlap in individual patients.

Results

Recently, novel therapeutic options emerged in the form of groundbreaking drugs, Patisiran and Inotersen, small interfering RNA molecules that target TTR and reduce the production of this protein. By targeting TTR mRNA transcripts, Inotersen decreases protein translation and production, reducing the deposition of misfolded proteins. It was shown to be both effective and safe for use and specifically formulated to concentrate in the liver - where protein production takes place.

Conclusion

hATTR is a rare, progressive, and debilitating disease. Its most common presentation is that of polyneuropathy, and it carries a very poor prognosis and a natural history conveying a median survival of < 12 years. Novel therapeutic options are groundbreaking by providing disease-modifying specific, targeted therapies against TTR production and deposition. The use of RNA interference (RNAi) opens the door to the treatment of hereditary diseases by targeting them at the genetic level.

Does Patisiran Reduce Ocular Transthyretin Synthesis? A Pilot Study of Two Cases

BACKGROUND

Variant transthyretin-mediated amyloidosis (ATTR-v) is a well-characterized disease affecting the neurologic and cardiovascular systems. Patisiran has been approved for neurologic involvement as it reduces hepatic synthesis of transthyretin (TTR). Eye involvement is a lateonset feature increasing the risk of glaucoma and cataracts in patients.

AIMS

The aim of this case series was to assess whether patisiran can effectively reduce TTR synthesis in such a barrier-protected organ as the eye.

METHODS

Two patisiran-treated ATTR-v patients underwent serum and aqueous humor sampling to measure TTR levels detected by SDS-PAGE and immunoblotting. Serum samples were compared to healthy control (HC), whereas aqueous humor samples were compared to non-amyloidotic subjects affected by cataracts and glaucoma.

RESULTS

Serum TTR levels representative of hepatic synthesis were sharply lower in treated patients if compared to the HC (-87.5% and -93.75%, respectively). Aqueous humor TTR levels showed mild-tono reduction in treated patients compared to non-amyloidotic subjects with cataracts (-34.9% and +8.1%, respectively) and glaucoma (-41.1% and -2.1%).

CONCLUSION

Patisiran does not seem to be as effective in inhibiting ocular TTR synthesis as it is in inhibiting hepatic synthesis. Re-engineering the envelope could allow the drug to target RPE cells thus avoiding any ocular involvement.

Summation of Precordial R Wave Amplitudes, a Clinical Parameter for Detecting Early TTR Amyloidosis Cardiac Involvement

There have been several reports on the identification of the stage of transthyretin amyloid cardiomyopathy (ATTR-CM); however, a staging system for ATTR-CM has not yet been established. An 83-year-old woman was referred to our department about ten years ago. Recently, she was diagnosed with ATTR-CM. The electrocardiogram showed characteristic changes that take place over the duration of ATTR-CM progression. Among these, the precordial R amplitudes abruptly decreased before the development of increased ventricular thickness. This case suggested that the decrease in the precordial R wave amplitudes may represent a new diagnostic clue reflecting early myocardial damage due to ATTR-CM.

Patterns of myelinated nerve fibers loss in transthyretin amyloid polyneuropathy and mimics

Objective

The present study was intended to analyze the characteristics of myelinated nerve fibers density (MFD) of transthyretin amyloid polyneuropathy (ATTR‐PN) and other similar neuropathies.

Methods

A total of 41 patients with ATTR‐PN, 58 patients of other common peripheral neuropathies, and 17 age‐and gender‐matched controls who visited the First Hospital of Peking University and performed sural nerve biopsy between June 2007 and August 2021 were included for analysis of MFD.

Results

Except the vasculitic neuropathy group, the total and small MFD of patients in the ATTR‐PN group were significantly lower than those of other disease groups. There was an obvious negative correlation between the total MFD and the disease course in the ATTR‐PN group. The disease course of early‐onset and late‐onset symptoms was similar, but the loss of large myelinated nerve fibers (MF) was more severe for the latter. In addition, all late‐onset and most early‐onset patients had severely reduced MFD after a 2 years' disease course. The MFD in ATTR‐PN patients was negatively correlated with Neuropathy Impairment Score (NIS) and Norfolk Quality of life‐diabetic neuropathy (Norfolk QOL‐DN) score.

Conclusion

MF is lost differently in ATTR‐PN and in other common peripheral neuropathies. The late‐onset and early‐onset ATTR‐PN patients have different patterns of loss of large and small MF.

Skeletal Muscle Involvement Pattern of Hereditary Transthyretin Amyloidosis: A Study Based on Muscle MRI

Objects

This study was intended to explore the characteristics of muscle magnetic resonance imaging (MRI) of patients with hereditary transthyretin amyloidosis (ATTRv amyloidosis) prospectively.

Methods

The clinical data of 20 patients with ATTRv amyloidosis at our hospital between July 2020 and August 2021 were analyzed. MRI of lower limbs including calf muscles was performed in all these 20 patients and MRI of thigh muscles was performed in 16 of them.

Results

The mean age of the 20 patients with ATTRv amyloidosis was 44.2 years (ranging from 26 to 60) whose mean duration of weakness was 23.3 ± 23.0 (ranging from 0 to 84) months. All the patients presented with polyneuropathy, and 18 of them with weakness in their lower limbs. Muscle involvement was selective in these patients with ATTRv amyloidosis. The posterior group of muscles was heavily fatty, and the soleus muscle was the most heavily involved. The proportion of fatty infiltration scores at the calf level was higher than at the thigh level with paired comparison for most patients. Three of these patients had more severely fatty infiltration of muscles at the thigh level. The fatty infiltration of posterior compartments at the calf level was highly consistent with neuropathy impairment scores of lower limbs (weakness), the strength of ankle plantar flexion muscles, and the amplitude of the compound muscle action potential of the tibial nerve.

Conclusions

It was found that the pattern of muscle fatty infiltration was consistent with a distal-to-proximal gradient on the whole and that proximal involvements in MRI of lower limbs in some patients could also be observed. Selective fatty infiltration of muscles of posterior compartments and fatty infiltration of the soleus muscle might be typical of ATTRv amyloidosis.

Corneal confocal microscopy to detect early immune-mediated small nerve fibre loss in AL amyloidosis

Objective

Light chain (AL) amyloidosis is a life‐threatening disorder characterised by extracellular deposition of amyloid leading to dysfunction of multiple organs. Peripheral nerve involvement, particularly small fibre neuropathy, may be associated with poorer survival. Corneal confocal microscopy (CCM) is a rapid and non‐invasive imaging technique to quantify corneal small nerve fibres and immune cells in vivo. We aimed to evaluate CCM as a tool for early diagnosis of peripheral nerve involvement in AL amyloidosis.

Methods

CCM and nerve conduction studies (NCS) were undertaken in 21 newly diagnosed, treatment‐naïve AL amyloidosis patients and 21 age‐ and sex‐matched healthy controls. Corneal nerve fibre density (CNFD), corneal nerve branch density and fibre length, and cell infiltrates were quantified in the sub‐basal layer of the cornea.

Results

There was a significant reduction in CNFD and nerve fibre length, even without large fibre affection and an increase in cell density, particularly around corneal nerve fibres in patients with AL amyloidosis compared to controls. Additionally, cell infiltration correlated with reduced nerve fibre density in patients with AL amyloidosis, but reduced CNFD did not correlate with laboratory parameters of organ dysfunction.

Interpretation

Our study is the first to show that CCM allows rapid non‐invasive identification of early small nerve fibre damage associated with immune cell infiltration in patients with AL amyloidosis. CCM detects peripheral nerve involvement more sensitively than NCS.

Distinct Patterns of Amyloid Pathology in Autopsies of Transthyretin S77Y and A97S Amyloidosis: Significance of Symptomatology and Cell Biology

Hereditary transthyretin (ATTRv) amyloidosis is a systemic disease with amyloid deposition in the peripheral and autonomic nervous systems caused by mutation of transthyretin (TTR) gene. The mutant TTR S77Y is the second prevalent mutation in many countries. In Taiwan, A97S mutant accounts for more than 90% of cases. Although distinct clinical manifestations such as dysphagia, carpal tunnel syndrome, and sudden cardiac death occur, the underlying pathology has not been elucidated. Here, we report the first autopsy cases of ATTRv S77Y and A97S and comprehensively compare the pathology underlying the unique clinical manifestations. This study demonstrated the following: (1) distinct spatial patterns of amyloid deposits in peripheral nerves, with a tendency toward more amyloid deposition in the large peripheral nerves, particularly the median nerves, and scarcely in the sural nerves, and different amyloid distribution in different genotypes; (2) amyloid deposits in the conduction system of the heart in addition to surrounding cardiomyocytes; (3) extensive amyloid deposits in the larynx and gastrointestinal tract, contributing to the unique clinical symptom of dysphagia; and (4) characteristic TTR intracytoplasmic inclusions in the hepatocytes of A97S. The pathology of the first autopsied cases of ATTRv S77Y and A97S provides pathology and mechanisms underlying unique clinical manifestations.

Recovery of sinus rhythm by tafamidis in patients with wild-type transthyretin amyloid cardiomyopathy with atrial arrhythmias

Transthyretin amyloid cardiomyopathy (ATTR-CM) is a life-threatening infiltrative disease in elderly patients. Atrial arrhythmias (AAr) are common in patients with ATTR-CM. However, AAr treatment in these patients is challenging. In this case, a patient diagnosed with wild-type ATTR-CM suffered atrial fibrillation (AF) for ~1 year, according to the data of his self-monitoring and regular electrocardiogram. This AF reverted to normal sinus rhythm a few months after the initiation of tafamidis without administering an antiarrhythmic drug. Tafamidis may be beneficial as alternative antiarrhythmic therapy in patients with ATTR-CM.

OCULAR MANIFESTATIONS OF ASP38ALA AND THR59LYS FAMILIAL TRANSTHYRETIN AMYLOIDOSIS

PURPOSE

To describe the ophthalmic manifestations of familial transthyretin amyloidosis (FTA) mutations, including Asp38Ala and Thr59Lys, which have not been previously reported to have ocular involvement.

METHODS

This is an observational case series of prospectively collected data of 16 patients with FTA who were taking tafamidis for mild peripheral neuropathy and underwent a comprehensive ophthalmic examination at a single tertiary center, between January 2013 and March 2020. The ocular involvement of each FTA mutation type and the specific manifestations were the main outcome measures.

RESULTS

Six of 16 patients with FTA manifested ocular involvement. Ocular involvement was noted in two of three patients with Glu89Lys mutations having retinal deposits, retinal hemorrhages, and corneal opacity. Three of nine patients with Asp38Ala mutations and one of two patients with Thr59Lys mutations showed ocular involvement that had not been previously described. The ophthalmic findings included glaucoma, anterior lens capsule opacity, vitreous opacity, and retinal deposits. The decrease in vascular flow due to perivascular cuffing of the amyloid deposits was detected by optical coherence tomography angiography.

CONCLUSION

The current study newly described that two transthyretin mutation types of FTA, Asp38Ala and Thr59Lys, may manifest with ocular findings such as anterior lens capsule opacity and retinal deposits.

Eyes on amyloidosis: microvascular retinal dysfunction in cardiac amyloidosis

Aims

Methods and results

Conclusions

Dissecting the Crosstalk between Endothelial Mitochondrial Damage, Vascular Inflammation, and Neurodegeneration in Cerebral Amyloid Angiopathy and Alzheimer's Disease

Alzheimer’s disease (AD) is the most prevalent cause of dementia and is pathologically characterized by the presence of parenchymal senile plaques composed of amyloid β (Aβ) and intraneuronal neurofibrillary tangles of hyperphosphorylated tau protein. The accumulation of Aβ also occurs within the cerebral vasculature in over 80% of AD patients and in non-demented individuals, a condition called cerebral amyloid angiopathy (CAA). The development of CAA is associated with neurovascular dysfunction, blood–brain barrier (BBB) leakage, and persistent vascular- and neuro-inflammation, eventually leading to neurodegeneration. Although pathologically AD and CAA are well characterized diseases, the chronology of molecular changes that lead to their development is still unclear. Substantial evidence demonstrates defects in mitochondrial function in various cells of the neurovascular unit as well as in the brain parenchyma during the early stages of AD and CAA. Dysfunctional mitochondria release danger-associated molecular patterns (DAMPs) that activate a wide range of inflammatory pathways. In this review, we gather evidence to postulate a crucial role of the mitochondria, specifically of cerebral endothelial cells, as sensors and initiators of Aβ-induced vascular inflammation. The activated vasculature recruits circulating immune cells into the brain parenchyma, leading to the development of neuroinflammation and neurodegeneration in AD and CAA.

The Effect of Tafamidis on Circulating Endothelial Progenitor Cells in Patients with Transthyretin Cardiac Amyloidosis

AIMS

Endothelial microvascular dysfunction is a known mechanism of vascular pathology in cardiac amyloidosis (CA). Scientific evidence regarding the possible protective role of the amyloid transthyretin (ATTR) stabilizer, tafamidis, is lacking. Circulating endothelial progenitor cells (cEPCs) have an important role in the process of vascular repair. We aimed to examine the effect of tafamidis on cEPCs.

METHODS AND RESULTS

Study population included patients with ATTR-CA. cEPCs were assessed using flow cytometry by the expression of CD34⁽⁺⁾/CD133⁽⁺⁾ and vascular endothelial growth factor receptor (VEGFR)-2⁽⁺⁾ and by the formation of colony-forming units (CFUs) and production of VEGF. Tests were repeated at pre-specified time-points up to 12 months following the initiation of tafamidis. Included were 18 ATTR-CA patients at a median age of 77 (IQR 71, 85) years and male predominance (n = 15, 83%). Following the initiation of tafamidis and during 12 months of drug treatment, there was a gradual increase in the levels of CD34⁽⁺⁾/VEGFR-2⁽⁺⁾ (0.43 to 2.42% (IQR 1.53, 2.91)%, p = 0.002) and CD133⁽⁺⁾/VEGFR-2⁽⁺⁾ (0.49 to 1.64% (IQR 0.97, 2.90)%, p = 0.004). Functionally, increase in EPCs-CFUs was microscopically evident following treatment with tafamidis (from 0.5 CFUs (IQR 0.0, 1.0) to 3.0 (IQR 1.3, 3.8) p < 0.001) with a concomitant increase in EPC's viability as demonstrated by an MTT assay (from 0.12 (IQR 0.03, 0.16) to 0.30 (IQR 0.18, 0.33), p < 0.001). VEGF levels increased following treatment (from 54 (IQR 52, 72) to 107 (IQR 62, 129) pg/ml, p = 0.039).

CONCLUSIONS

Tafamidis induced the activation of the cEPCs pathway, possibly promoting endothelial repair in ATTR-CA.

Current Review of Leptomeningeal Amyloidosis Associated With Transthyretin Mutations

INTRODUCTION

Leptomeningeal amyloidosis (LA) represents a rare subtype of familial transthyretin (TTR) amyloidosis, characterized by deposition of amyloid in cranial and spinal leptomeninges. Of >120 TTR mutations identified, few have been associated with LA.

CASE REPORT

A 27-year-old male presented with a 2-year history of progressive symptoms including cognitive decline and right-sided weakness and numbness. Cerebrospinal fluid (CSF) analyses demonstrated high protein level. Gadolinium-enhanced magnetic resonance imaging (MRI) revealed extensive leptomeningeal enhancement over the surface of the brain and spinal cord. Pathologic analyses revealed a TTR mutation c.113A>G (p.D38G).

REVIEW SUMMARY

Fifteen mutations and genotype-phenotype correlation of 72 LA patients have been summarized to provide an overview of LA associated with transthyretin mutations. The mean age of clinical onset was 44.9 years and the neurological symptoms primarily included cognitive impairment, headache, ataxia seizures and hearing, visual loss. CSF analysis showed elevated high CSF protein level and MRI revealed extensive leptomeningeal enhancement.

CONCLUSION

Clinicians should be aware of this rare form of familial transthyretin amyloidosis as well as its typical MRI enhancement and high CSF protein. The important role of biopsy, genetic testing and the potential early diagnosis value of contrast MRI were suggested. Early recognition of these characteristics is important to provide misdiagnosis and shorten the time before correct diagnosis. These findings expand the phenotypic spectrum of TTR gene and have implications for the diagnosis, treatment, and systematic study of LA.

The role of transthyretin in cell biology: impact on human pathophysiology

Transthyretin (TTR) is an extracellular protein mainly produced in the liver and choroid plexus, with a well-stablished role in the transport of thyroxin and retinol throughout the body and brain. TTR is prone to aggregation, as both wild-type and mutated forms of the protein can lead to the accumulation of amyloid deposits, resulting in a disease called TTR amyloidosis. Recently, novel activities for TTR in cell biology have emerged, ranging from neuronal health preservation in both central and peripheral nervous systems, to cellular fate determination, regulation of proliferation and metabolism. Here, we review the novel literature regarding TTR new cellular effects. We pinpoint TTR as major player on brain health and nerve biology, activities that might impact on nervous systems pathologies, and assign a new link between TTR and angiogenesis and cancer. We also explore the molecular mechanisms underlying TTR activities at the cellular level, and suggest that these might go beyond its most acknowledged carrier functions and include interaction with receptors and activation of intracellular signaling pathways.

Significance of Oligomeric and Fibrillar Species in Amyloidosis: Insights into Pathophysiology and Treatment

Amyloidosis is a term referring to a group of various protein-misfolding diseases wherein normally soluble proteins form aggregates as insoluble amyloid fibrils. How, or whether, amyloid fibrils contribute to tissue damage in amyloidosis has been the topic of debate. In vitro studies have demonstrated the appearance of small globular oligomeric species during the incubation of amyloid beta peptide (Aβ). Nerve biopsy specimens from patients with systemic amyloidosis have suggested that globular structures similar to Aβ oligomers were generated from amorphous electron-dense materials and later developed into mature amyloid fibrils. Schwann cells adjacent to amyloid fibrils become atrophic and degenerative, suggesting that the direct tissue damage induced by amyloid fibrils plays an important role in systemic amyloidosis. In contrast, there is increasing evidence that oligomers, rather than amyloid fibrils, are responsible for cell death in neurodegenerative diseases, particularly Alzheimer’s disease. Disease-modifying therapies based on the pathophysiology of amyloidosis have now become available. Aducanumab, a human monoclonal antibody against the aggregated form of Aβ, was recently approved for Alzheimer’s disease, and other monoclonal antibodies, including gantenerumab, solanezumab, and lecanemab, could also be up for approval. As many other agents for amyloidosis will be developed in the future, studies to develop sensitive clinical scales for identifying improvement and markers that can act as surrogates for clinical scales should be conducted.

The Ultrastructure of Tissue Damage by Amyloid Fibrils

Amyloidosis is a group of diseases that includes Alzheimer’s disease, prion diseases, transthyretin (ATTR) amyloidosis, and immunoglobulin light chain (AL) amyloidosis. The mechanism of organ dysfunction resulting from amyloidosis has been a topic of debate. This review focuses on the ultrastructure of tissue damage resulting from amyloid deposition and therapeutic insights based on the pathophysiology of amyloidosis. Studies of nerve biopsy or cardiac autopsy specimens from patients with ATTR and AL amyloidoses show atrophy of cells near amyloid fibril aggregates. In addition to the stress or toxicity attributable to amyloid fibrils themselves, the toxicity of non-fibrillar states of amyloidogenic proteins, particularly oligomers, may also participate in the mechanisms of tissue damage. The obscuration of the basement and cytoplasmic membranes of cells near amyloid fibrils attributable to an affinity of components constituting these membranes to those of amyloid fibrils may also play an important role in tissue damage. Possible major therapeutic strategies based on pathophysiology of amyloidosis consist of the following: (1) reducing or preventing the production of causative proteins; (2) preventing the causative proteins from participating in the process of amyloid fibril formation; and/or (3) eliminating already-deposited amyloid fibrils. As the development of novel disease-modifying therapies such as short interfering RNA, antisense oligonucleotide, and monoclonal antibodies is remarkable, early diagnosis and appropriate selection of treatment is becoming more and more important for patients with amyloidosis.

Disease Modifying Treatments for Transthyretin Amyloidosis

ABSTRACT

The transthyretin (TTR) amyloidoses result from misfolding of the protein leading to fibril formation and aggregation as amyloid deposits in predominantly the cardiovascular and nervous systems. Cardiac involvement can manifest as heart failure, arrhythmias, and valvular disease. Neurologic involvement can cause sensorimotor polyneuropathies, mononeuropathies, and dysautonomia. Previously, treatment has focused on management of these symptoms and disease sequelae, with a high rate of mortality due to the absence of disease modifying therapies. In this manuscript, we review novel treatments focusing on three mechanistic pathways: (1) silencing of the TTR gene to suppress production, (2) stabilizing of TTR tetramers to prevent misfolding, or (3) disrupting of existing TTR amyloid fibrils to promote reabsorption.

Multidisciplinary Approaches for Transthyretin Amyloidosis

Amyloidosis caused by systemic deposition of transthyretin (TTR) is called ATTR amyloidosis and mainly includes hereditary ATTR (ATTRv) amyloidosis and wild-type ATTR (ATTRwt) amyloidosis. Until recently, ATTRv amyloidosis had been considered a disease in the field of neurology because neuropathic symptoms predominated in patients described in early reports, whereas advances in diagnostic techniques and increased recognition of this disease revealed the presence of patients with cardiomyopathy as a predominant feature. In contrast, ATTRwt amyloidosis has been considered a disease in the field of cardiology. However, recent studies have suggested that some of the patients with ATTRwt amyloidosis present tenosynovial tissue complications, particularly carpal tunnel syndrome, as an initial manifestation of amyloidosis, necessitating an awareness of this disease among neurologists and orthopedists. Although histopathological confirmation of amyloid deposits has traditionally been considered mandatory for the diagnosis of ATTR amyloidosis, the development of noninvasive imaging techniques in the field of cardiology, such as echocardiography, magnetic resonance imaging, and nuclear imaging, enabled nonbiopsy diagnosis of this disease. The mechanisms underlying characteristic cardiac imaging findings have been deciphered by histopathological studies. Novel disease-modifying therapies for ATTR amyloidosis, such as TTR stabilizers, short interfering RNA, and antisense oligonucleotides, were initially approved for ATTRv amyloidosis patients with polyneuropathy. However, the indications for the use of these disease-modifying therapies gradually widened to include ATTRv and ATTRwt amyloidosis patients with cardiomyopathy. Since the coronavirus disease 2019 (COVID-19) pandemic, which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, occurred, the minimization of hospital visits and telemedicine have become increasingly important. As older age and cardiovascular disease are major factors associated with increased disease severity and mortality of COVID-19, many ATTR amyloidosis patients are at increased risk of disease aggravation when they are infected with SARS-CoV-2. From this viewpoint, close interspecialty communication to determine the optimal interval of evaluation is needed for the management of patients with ATTR amyloidosis.

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

INTRODUCTION

Hereditary transthyretin amyloidosis (ATTRv amyloidosis) is a clinically heterogeneous disease caused by mutations in the transthyretin (TTR) gene. The most common mutation, Val30Met, can manifest as an early- or late-onset disease.

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 patients with TTR mutations. This is a descriptive analysis of symptomatic patients with ATTRv Val30Met amyloidosis with late- (age at least 50 years) vs. early-onset (age less than 50 years) disease in THAOS (data cutoff August 1, 2019).

RESULTS

Of 1389 patients with ATTRv Val30Met amyloidosis, 491 (35.3%) had late-onset disease. Compared with early-onset, patients with late-onset were more likely to be male (66.2% vs. 53.6%) and have a longer mean (standard deviation [SD]) time from onset to diagnosis (3.8 [3.4] vs. 2.7 [4.1] years). Late-onset disease was associated with more severe neurological impairment at enrollment (median [10th, 90th percentile] derived Neuropathy Impairment Score in the Lower Limbs, 25.0 [4.0, 69.3] vs. 8.0 [0, 54.8]; Neurologic Composite Score, 42.0 [2.0, 155.0] vs. 21.0 [0, 102.0]). Cardiac findings were more prominent in late-onset disease. An overall interpretation of electrocardiogram as abnormal was reported in 72.1% of late-onset patients (vs. 44.3% early-onset). A left-ventricular septal thickness of at least 12 mm was reported in 69.7% of late-onset patients (vs. 14.6% early-onset). All differences were statistically significant (p < 0.001).

CONCLUSION

In THAOS, late-onset ATTRv Val30Met amyloidosis is common, presenting with more severe neurologic and cardiac findings at enrollment. Heterogeneity of disease may make it more difficult to diagnose. Increased recognition of late-onset ATTRv Val30Met amyloidosis could lead to more timely diagnosis and improve patient outcomes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00628745.

The neuropathy in hereditary transthyretin amyloidosis: A narrative review

Hereditary transthyretin amyloidosis (ATTRv) is a condition with adult onset, caused by mutation of the transthyretin (TTR) gene and characterized by extracellular deposition of amyloid fibrils in tissue, especially in the peripheral nervous system (PNS) and heart. PNS involvement leads to a rapidly progressive and disabling sensory‐motor axonal neuropathy. Although awareness among neurologists increased in recent years thanks to new treatment options, ATTRv is frequently misdiagnosed, and thus a correct diagnosis can be delayed by several years. This review aims to draw the history and features of polyneuropathy in ATTRv based on pathological and electrophysiological correlates. We assessed original articles and case reports based on their relevance to ATTRv neuropathy and we included those appropriate for the scheme of this narrative review. Amyloid fibrils initially deposit in ganglia, causing an axonal neuropathy without amyloid deposits in distal segments (eg, sural nerve biopsy). Over time, amyloid fibrils spread along the nerves, leading to some demyelinating features in the context of severe axonal loss. This review highlights how the features of neuropathy change based on type of ATTRv (early vs late onset) and stage of disease.

ASSOCIATION BETWEEN CHOROIDAL CHARACTERISTICS AND SYSTEMIC SEVERITY IN AMYLOIDOSIS

PURPOSE

This study aimed to describe the choroidal features of ocular amyloidosis using multimodal imaging, to correlate these findings with systemic involvement, and to propose a choroidal grading system.

METHODS

Eleven patients with systemic amyloidosis were reviewed retrospectively. Each case was assigned a grade according to the severity of choroidal findings as determined by both enhanced depth imaging optical coherence tomography and indocyanine green angiography. The severity of systemic amyloidosis was then correlated with the choroidal involvement.

RESULTS

On indocyanine green angiography, all patients exhibited hyperfluorescent spots in the late stage and were classified according to preexisting criteria. On enhanced depth imaging optical coherence tomography, hyperreflective foci were seen in the choriocapillaris and Sattler's layer in Grade 1, partial loss of Sattler's layer was additionally seen in Grade 2, and a dense hyperreflective Haller's layer was seen in Grade 3. Choroidal grading scores were significantly correlated with the systemic severity score (P = 0.0014, Pearson's correlation coefficient; ρ = 0.83).

CONCLUSION

With ocular amyloidosis, evaluation of choroidal characteristics using multimodal imaging may serve as a biomarker for systemic involvement.

Feasibility of assessing progression of transthyretin amyloid polyneuropathy using nerve conduction studies: Findings from the Transthyretin Amyloidosis Outcomes Survey (THAOS)

Patients with transthyretin amyloid polyneuropathy (ATTR‐PN) show decreased motor and sensory nerve amplitudes and conduction. Electrophysiological changes over time may be sensitive indicators of progression. This analysis from the Transthyretin Amyloidosis Outcomes Survey (THAOS) assessed longitudinal changes in nerve conduction as signals of neurologic disease progression in patients with hereditary ATTR (ATTRv) amyloidosis. Patients with ATTRv in THAOS with recorded nerve conduction values were included (data cut‐off: January 6, 2020); changes in nerve amplitude and velocity over time were assessed. Patients (n = 1389) were 45.0% male; 80.4% were the Val30Met (p.Val50Met) genotype. Mean (SD) age at enrollment was 43.6 (14.5) years; duration of symptoms was 9.3 (6.4) years. Median (10th, 90th percentile) sural nerve amplitude and velocity was 18.0 (4.9, 35.0) μV and 50.7 (41.0, 57.9) m/s; peroneal conduction was 13.0 (4.4, 27.0) μV and 51.0 (41.7, 59.7) m/s, respectively. Median (10th, 90th percentile) percentage change from baseline in sural nerve amplitude was variable, but generally decreased over time from −7.4 (−43.2, 52.4) at year 1 to −14.4 (−76.9, 46.7) at year 8. Percent change from baseline in sural nerve velocity declined similarly: −0.1 (−14.5, 15.3) at year 1 and − 6.4 (−21.3, 10.5) at year 8. The decline was more pronounced in patients with greater disability at baseline. Similar patterns were observed for the peroneal nerve. These data show an association between nerve amplitudes and velocities and disease severity, suggesting progressive deterioration in nerve conduction may be an indicator of ATTRv amyloidosis disease progression.

Hereditary transthyretin amyloidosis in mainland China: a unicentric retrospective study

OBJECTIVE

This study aims to report the genotypes and phenotypes of hereditary transthyretin amyloidosis (ATTR) in a large Chinese cohort, yet the clinical and genetic profiles of ATTR remain elusive in mainland China.

METHODS

Fifty-four patients with molecularly confirmed ATTR from 39 unrelated families were identified by sequencing the TTR gene. Sural nerve biopsies were performed in 40 of these cases. The clinical and electrophysiological data were retrospectively collected and analyzed.

RESULTS

The male/female ratio was 42:12. The average age of patients at the onset of the disease was 47.8 ± 13.0 years. The late-onset type occurred in 29 cases (53.7%). Twenty-two probands (56.4%) had a family history with ATTR. The initial symptoms were limb paresthesia in 33 cases (61.1%), autonomic dysfunction in 15 cases (27.8%), and blurred vision in 6 cases (11.1%). A total of 22 different TTR mutations were identified, including Val30Met (25.6%) in 10 families in North China and Ala97Ser in 4 families (10.3%) in South China. Electrophysiological studies revealed general sensorimotor axonal polyneuropathy in 33/44 cases (75.0%), mixed neuropathy with axonal and demyelinating impairment features in 9/44 cases (20.5%) and isolated carpal tunnel syndrome in two cases. Sural nerve biopsies revealed positive Congo red staining in 16/40 cases (40.0%).

CONCLUSION

Chinese patients with ATTR exhibited heterogeneous TTR genotypes and clinical phenotypes. Val30Met remains the most common mutation type in mainland China.

Unusual Pain Disorders - What Can Be Learned from Them?

Pain is common in many different disorders and leads to a significant reduction in quality of life in the affected patients. Current treatment options are limited and often result in insufficient pain relief, partly due to the incomplete understanding of the underlying pathophysiological mechanisms. The identification of these pathomechanisms is therefore a central object of current research. There are also a number of rare pain diseases, that are generally little known and often undiagnosed, but whose correct diagnosis and examination can help to improve the management of pain disorders in general. In some of these unusual pain disorders like sodium-channelopathies or sensory modulation disorder the underlying pathophysiological mechanisms have only recently been unravelled. These mechanisms might serve as pharmacological targets that may also play a role in subgroups of other, more common pain diseases. In other unusual pain disorders, the identification of pathomechanisms has already led to the development of new drugs. A completely new therapeutic approach, the gene silencing, can even stop progression in hereditary transthyretin amyloidosis and porphyria, ie in pain diseases that would otherwise be rapidly fatal if left untreated. Thus, pain therapists and researchers should be aware of these rare and unusual pain disorders as they offer the unique opportunity to study mechanisms, identify new druggable targets and finally because early diagnosis might save many patient lives.

Early changes of nerve integrity in preclinical carriers of hereditary transthyretin Ala117Ser amyloidosis with polyneuropathy

BACKGROUND AND PURPOSE

Disease-modifying therapies provide new horizons for hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN) to slow neuropathic progression. Initiating treatment at the earliest time requires biomarkers reflecting both small- and large-fiber degeneration in carriers.

METHODS

This study included examinations of pathology (intraepidermal nerve fiber [IENF] density), physiology (nerve conduction studies, autonomic function test, and nerve excitability), and psychophysics (thermal thresholds) in carriers to compare to healthy controls and asymptomatic diabetic patients.

RESULTS

There were 43 carriers (44.2 ± 11.4 years, p.Ala117Ser in 42 carriers), 43 controls (43.4 ± 12.7 years) including 26 noncarrier families, and 50 asymptomatic diabetic patients (58.1 ± 9.5 years). Carriers had lower IENF densities than controls and similar densities as diabetic patients. Median nerve conduction parameters, especially distal motor latency, were the most frequent neurophysiological abnormality in carriers, could differentiate carriers from controls and diabetic patients, were correlated with IENF densities in carriers but not in controls and diabetic patients, and were correlated with nerve excitability parameters in carriers but not in controls. Fifteen carriers (34.9%) with electrophysiological evidence of median nerve entrapment at the wrist had lower IENF densities and more abnormal conduction parameters than carriers without. We defined nerve dysfunction index-the ratio of median distal motor latency to IENF density-which differentiated carriers from controls.

CONCLUSIONS

In late-onset ATTRv-PN carriers with predominant p.Ala117Ser, median conduction parameters were the most common neurophysiological abnormalities and served as surrogate signatures of small- and large-fiber impairment. Combination of median distal motor latency and IENF density can reflect early neuropathy in carriers.

Two distinct mechanisms of neuropathy in immunoglobulin light chain (AL) amyloidosis

INTRODUCTION

Although polyneuropathy in patients with immunoglobulin light chain (AL) amyloidosis has been considered to be attributable to axonal degeneration resulting from amyloid deposition, patients with nerve conduction parameters indicating demyelination that mimics chronic inflammatory demyelinating polyneuropathy (CIDP) have also been reported anecdotally.

METHODS

We evaluated the electrophysiological and pathological features of 8 consecutive patients with AL amyloidosis who were referred for sural nerve biopsy.

RESULTS

Although findings of axonal neuropathy predominantly in the lower limbs were the cardinal feature, all patients showed one or more abnormalities of nerve conduction velocities or distal motor latencies. In particular, 2 of these patients fulfilled the definite electrophysiological for CIDP defined by the European Federation of Neurological Societies/Peripheral Nerve Society (EFNS/PNS). On electron microscopic examination of sural nerve biopsy specimens, Schwann cells apposed to amyloid fibrils became atrophic in all patients, suggesting that amyloid deposits directly affect neighboring tissues. Additionally, detachment of the neurilemma from the outermost compacted myelin lamella was seen where amyloid fibrils were absent in 4 patients. Electrophysiological findings suggestive of demyelination were more conspicuous in these patients compared with the other patients. The detachment of the neurilemma from the outermost compacted myelin lamella was particularly conspicuous in patients who fulfilled the definite EFNS/PNS electrophysiological criteria for CIDP.

CONCLUSION

Abnormalities of myelinated fibers unrelated to amyloid deposition may frequently occur in AL amyloidosis. Disjunction between myelin and the neurilemma may induce nerve conduction abnormalities suggestive of demyelination.

Targeting transthyretin - Mechanism-based treatment approaches and future perspectives in hereditary amyloidosis

The liver-derived, circulating transport protein transthyretin (TTR) is the cause of systemic hereditary (ATTRv) and wild-type (ATTRwt) amyloidosis. TTR stabilization and knockdown are approved therapies to mitigate the otherwise lethal disease course. To date, the variety in phenotypic penetrance is not fully understood. This systematic review summarizes the current literature on TTR pathophysiology with its therapeutic implications. Tetramer dissociation is the rate-limiting step of amyloidogenesis. Besides destabilizing TTR mutations, other genetic (RBP4, APCS, AR, ATX2, C1q, C3) and external (extracellular matrix, Schwann cell interaction) factors influence the type of onset and organ tropism. The approved small molecule tafamidis stabilizes the tetramer and significantly decelerates the clinical course. By sequence-specific mRNA knockdown, the approved small interfering RNA (siRNA) patisiran and antisense oligonucleotide (ASO) inotersen both significantly reduce plasma TTR levels and improve neuropathy and quality of life compared to placebo. With enhanced hepatic targeting capabilities, GalNac-conjugated siRNA and ASOs have recently entered phase III clinical trials. Bivalent TTR stabilizers occupy both binding groves in vitro, but have not been tested in trials so far. Tolcapone is another stabilizer with the potential to cross the blood-brain barrier, but its half-life is short and liver failure a potential side effect. Amyloid-directed antibodies and substances like doxycycline aim at reducing the amyloid load, however, none of the yet developed antibodies has successfully passed clinical trials. ATTR-amyloidosis has become a model disease for pathophysiology-based treatment. Further understanding of disease mechanisms will help to overcome the remaining limitations, including application burden, side effects, and blood-brain barrier permeability.

Chronic inflammatory demyelinating polyneuropathy associated with diabetes: a European multicentre comparative reappraisal

INTRODUCTION

The association between chronic inflammatory demyelinating polyneuropathy (CIDP) and diabetes is uncertain despite important diagnostic and management implications.

METHODS

We retrospectively analysed two European cohorts, totaling 257 patients with 'definite' or 'probable' CIDP, from Serbia and Birmingham, UK.

RESULTS

Diabetes was present at CIDP diagnosis in 25/139 (18%) subjects in the Serbian cohort and in 23/118 (19.5%) in the UK cohort. In both cohorts, diabetes prevalence was higher than local general population prevalence rates (RR: 2.09; 95% CI 1.39 to 2.95 and RR: 2.22; 95% CI 1.46 to 3.17, respectively). Considering typical CIDP only, diabetes prevalence was greater than expected in both cohorts (RR: 2.58; 95% CI 1.60 to 3.82 and RR: 2.68; 95% CI 1.71 to 3.87, respectively). CIDP with diabetes occurred later in life than CIDP without diabetes (58.96 years, SD: 11.09 vs 51.71 years, SD: 16.02; p=0.003) and presented more frequently in the typical form than in patients without diabetes (79.2% vs 61.2%; p=0.02). Baseline Inflammatory Neuropathy Cause and Treatment disability scores were similar in patients with and without diabetes (p=0.90). Proportions of treatment responders were similar in both groups (70% vs 74.9%; p=0.65), as were response amplitudes (p=0.87).

DISCUSSION

Our results, both for all CIDP and typical CIDP presentations, support a twofold increased relative risk of diabetes compared with the general population. CIDP with diabetes appears to present older and more frequently in the typical form, as compared with CIDP without diabetes. CIDP with diabetes appears similar to CIDP without diabetes in disability levels at diagnosis and probability, as well as amplitude of treatment response.

A low amyloidogenic E61K transthyretin mutation may cause familial amyloid polyneuropathy

Patients with transthyretin (TTR)-type familial amyloid polyneuropathy (FAP) typically exhibit sensory dominant polyneuropathy and autonomic neuropathy. However, the molecular pathogenesis of the neuropathy remains unclear. In this study, we characterize the features of FAP TTR the substitution of lysine for glutamic acid at position 61 (E61K). This FAP was late-onset, with sensory dominant polyneuropathy, autonomic neuropathy, and cardiac amyloidosis. Interestingly, no amyloid deposits were found in the endoneurium of the four nerve specimens examined. Therefore, we examined the amyloidogenic properties of E61K TTR in vitro. Recombinant wild-type TTR, the substitution of methionine for valine at position 30 (V30M) TTR, and E61K TTR proteins were incubated at 37°C for 72 hr, and amyloid fibril formation was assessed using the thioflavin-T binding assay. Amyloid fibril formation by E61K TTR was less than that by V30M TTR, and similar to that by wild-type TTR. E61K TTR did not have an inhibitory effect on neurite outgrowth from adult rat dorsal root ganglion (DRG) neurons, but V30M TTR did. Furthermore, we studied the sural nerve of our patient by terminal deoxynucleotidyl transferase dUTP nick end labeling and electron microscopy. A number of apoptotic cells were observed in the endoneurium of the nerve by transferase dUTP nick end labeling. Chromatin condensation was confirmed in the nucleus of non-myelinating Schwann cells by electron microscopy. These findings suggest that E61K TTR is low amyloidogenic, in vitro and in vivo. However, TTR aggregates and amyloid fibrils in the DRG may cause sensory impairments in FAP because the DRG has no blood-nerve barrier. Moreover, Schwann cell apoptosis may contribute to the neurodegeneration.

Transthyretin Amyloidosis: Update on the Clinical Spectrum, Pathogenesis, and Disease-Modifying Therapies

ATTR amyloidosis is caused by systemic deposition of transthyretin (TTR) and comprises ATTRwt (wt for wild-type) amyloidosis, ATTRv (v for variant) amyloidosis, and acquired ATTR amyloidosis after domino liver transplantation. ATTRwt amyloidosis has classically been regarded as cardiomyopathy found in the elderly, whereas carpal tunnel syndrome has also become a major initial manifestation. The phenotypes of ATTRv amyloidosis are diverse and include neuropathy, cardiomyopathy, and oculoleptomeningeal involvement as the predominant features, depending on the mutation and age of onset. In addition to variant TTR, the deposition of wild-type TTR plays a significant role, even in patients with ATTRv amyloidosis. The formation of amyloid fibrils tends to occur in association with the basement membrane. The thickening or reduplication of the basement membrane surrounding endoneurial microvessels, which is similar to diabetic neuropathy, is observed in ATTRv amyloidosis, suggesting that common mechanisms, such as an accumulation of advanced glycation end products, may participate in the disease process. In addition to direct damage caused by amyloid fibrils, recent studies have suggested that the toxicity of nonfibrillar TTRs, such as TTR oligomers, participates in the process of tissue damage. Although liver transplantation has been performed for patients with ATTRv amyloidosis since 1990, late-onset patients were not eligible for this treatment. However, as the efficacy of orally administered tafamidis and diflunisal, which stabilize TTR tetramers, was suggested in the early 2010s, such late-onset patients have also become targets for disease-modifying therapies. Additionally, recent studies of small interfering RNA (patisiran) and antisense oligonucleotide (inotersen) therapies have demonstrated the efficacy of these gene-silencing agents. A strategy for monitoring patients that enables the choice of an appropriate treatment from comprehensive and long-term viewpoints should be established. As many patients with ATTR amyloidosis are aged and have heart failure, they are at increased risk of aggravation if they are infected by SARS-CoV2. The optimal interval of evaluation should also be considered, particularly in this COVID-19 era.

Amyloid Proteins and Peripheral Neuropathy

Painful peripheral neuropathy affects millions of people worldwide. Peripheral neuropathy develops in patients with various diseases, including rare familial or acquired amyloid polyneuropathies, as well as some common diseases, including type 2 diabetes mellitus and several chronic inflammatory diseases. Intriguingly, these diseases share a histopathological feature-deposits of amyloid-forming proteins in tissues. Amyloid-forming proteins may cause tissue dysregulation and damage, including damage to nerves, and may be a common cause of neuropathy in these, and potentially other, diseases. Here, we will discuss how amyloid proteins contribute to peripheral neuropathy by reviewing the current understanding of pathogenic mechanisms in known inherited and acquired (usually rare) amyloid neuropathies. In addition, we will discuss the potential role of amyloid proteins in peripheral neuropathy in some common diseases, which are not (yet) considered as amyloid neuropathies. We conclude that there are many similarities in the molecular and cell biological defects caused by aggregation of the various amyloid proteins in these different diseases and propose a common pathogenic pathway for "peripheral amyloid neuropathies".

Cellular secretion and cytotoxicity of transthyretin mutant proteins underlie late-onset amyloidosis and neurodegeneration

Transthyretin amyloidosis (ATTR) is a progressive life-threatening disease characterized by the deposition of transthyretin (TTR) amyloid fibrils. Several pathogenic variants have been shown to destabilize TTR tetramers, leading to aggregation of misfolded TTR fibrils. However, factors that underlie the differential age of disease onset amongst amyloidogenic TTR variants remain elusive. Here, we examined the biological properties of various TTR mutations and found that the cellular secretory pattern of the wild-type (WT) TTR was similar to those of the late-onset mutant (Ala97Ser, p. Ala117Ser), stable mutant (Thr119Met, p. Thr139Met), early-onset mutant (Val30Met, p. Val50Met), but not in the unstable mutant (Asp18Gly, p. Asp38Gly). Cytotoxicity assays revealed their toxicities in the order of Val30Met > Ala97Ser > WT > Thr119Met in neuroblastoma cells. Surprisingly, while early-onset amyloidogenic TTR monomers (M-TTRs) are retained by the endoplasmic reticulum quality control (ERQC), late-onset amyloidogenic M-TTRs can be secreted extracellularly. Treatment of thapsigargin (Tg) to activate the unfolded protein response (UPR) alleviates Ala97Ser M-TTR secretion. Interestingly, Ala97Ser TTR overexpression in Drosophila causes late-onset fast neurodegeneration and a relatively short lifespan, recapitulating human disease progression. Our study demonstrates that the escape of TTR monomers from the ERQC may underlie late-onset amyloidogenesis in patients and suggests that targeting ERQC could mitigate late-onset ATTR.

Hereditary Transthyretin Amyloidosis: Clinical Presentation and Management Updates

Hereditary transthyretin amyloidosis, once a rare progressive neuropathy and/or cardiomyopathy, is now recognized with increasing worldwide frequency, various phenotypes, and over 130 gene mutations identified to date. This inherited disorder develops as a result of mutated transthyretin amyloid aggregation and systematic deposition throughout the body. With increasing knowledge about the pathophysiology of this disease, new disease-modifying therapies are being developed. In addition to slowing progression, these new agents were found to improve quality of life and reduce the severity of neuropathic symptoms. Two new gene-modifying therapies recently received Food and Drug Administration approval following the positive results from phase III trials. These include an antisense oligonucleotide, inotersen, and small interfering RNA, patisiran, which were reported to reduce the production of transthyretin and had promising safety profiles. Additional novel therapies are being explored with hopes to prolong survival. Therefore, early diagnosis of this treatable disorder has become increasingly important in clinical practice.

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.

Exploration of the Misfolding Mechanism of Transthyretin Monomer: Insights from Hybrid-Resolution Simulations and Markov State Model Analysis

Misfolding and aggregation of transthyretin (TTR) is widely known to be responsible for a progressive systemic disorder called amyloid transthyretin (ATTR) amyloidosis. Studies suggest that TTR aggregation is initiated by a rate-limiting dissociation of the homo-tetramer into its monomers, which can rapidly misfold and self-assemble into amyloid fibril. Thus, exploring conformational change involved in TTR monomer misfolding is of vital importance for understanding the pathogenesis of ATTR amyloidosis. In this work, microsecond timescale hybrid-resolution molecular dynamics (MD) simulations combined with Markov state model (MSM) analysis were performed to investigate the misfolding mechanism of the TTR monomer. The results indicate that a macrostate with partially unfolded conformations may serve as the misfolded state of the TTR monomer. This misfolded state was extremely stable with a very large equilibrium probability of about 85.28%. With secondary structure analysis, we found the DAGH sheet in this state to be significantly destroyed. The CBEF sheet was relatively stable and sheet structure was maintained. However, the F-strand in this sheet was likely to move away from E-strand and reform a new β-sheet with the H-strand. This observation is consistent with experimental finding that F and H strands in the outer edge drive the misfolding of TTR. Finally, transition pathways from a near native state to this misfolded macrostate showed that the conformational transition can occur either through a native-like β-sheet intermediates or through partially unfolded intermediates, while the later appears to be the main pathway. As a whole, we identified a potential misfolded state of the TTR monomer and elucidated the misfolding pathway for its conformational transition. This work can provide a valuable theoretical basis for understanding of TTR aggregation and the pathogenesis of ATTR amyloidosis at the atomic level.

Association between hearing loss and hereditary ATTR amyloidosis

Background: Hereditary transthyretin (TTR) related amyloidosis (ATTRv) is a life-threatening condition, which can potentially affect all organs. The objective was to identify the hearing status of patients with cardiac ATTRv and describe their audiological pattern. Methods: Nineteen patients with confirmed diagnosis of ATTRv cardiac amyloidosis (CA) underwent otoscopy and audiological tests, including pure tone and speech audiometry. Results: 74% were male, with a mean age of 72 ± 1.8 years. The main mutations were Val122Ile (n = 7) and Val30Met (n = 6). Objective hearing loss was detected in 17 patients (89%), whereas only 37% complained of hearing loss. ATTRv patients presented a different audiometric profile compared to patients of the same age with presbycusis: a higher prevalence and worse hearing thresholds compared to age-related expectations (ISO). Hearing loss affected all frequencies with, unexpectedly, mixed or conductive hearing loss (35%). According to the type of mutation, there was an increased rate of sensorineural or mixed/conductive hearing loss. Conclusions: the present study indicates that hearing loss is more prevalent and worse in patients with ATTRv amyloidosis than in the general population, while mostly clinically under-estimated. It suggests that ATTRv deposits could infiltrate the various anatomical structures of the inner and mild ear.

Clinicopathological correlations of sural nerve biopsies in TTR Val30Met familial amyloid polyneuropathy

Familial amyloid polyneuropathy with the substitution of methionine for valine at position 30 in the TTR gene is the most common type of hereditary transthyretin amyloidosis. Although several authors have previously reported a size-dependent fibre loss, predominantly involving unmyelinated and small-diameter myelinated fibres, the mechanisms of nerve fibre loss have not been fully understood. In this study, we establish the morphometric pattern of peripheral neuropathy in patients with familial amyloid polyneuropathy and asymptomatic mutation carriers in the biopsies from our archive and correlated the pathological findings with clinical features. A total of 98 patients with familial amyloid polyneuropathy and 37 asymptomatic mutation carriers (TTR Val30Met mutation), aged between 17 and 84 years, who underwent sural nerve biopsy between 1981 and 2017 at Centro Hospitalar Universitário do Porto were studied. Thirty-one controls were included for comparison. The median age at nerve biopsy was 26.0 [interquartile range = 23.5–39.5] years for asymptomatic mutation carriers, 45.0 [35.0–60.0] years for patients with familial amyloid polyneuropathy and 44.0 [30.0–63.0] years for controls. The median duration between nerve biopsy and symptoms’ onset was 7.0 [3.3–11.8] years (range: 1–27 years) in the asymptomatic carriers. Most patients were in an earlier disease stage (93% with a polyneuropathy disability scale ≤2). Patients had loss of small and myelinated fibres compared with both asymptomatic carriers and controls (P < 0.001), whereas asymptomatic carriers showed loss of small myelinated fibres when compared with controls (P < 0.05). The loss of myelinated fibres increased with disease progression (P < 0.001), and patients in more advanced clinical stage showed more frequent amyloid deposition in the nerve (P = 0.001). There was a positive correlation between large myelinated fibre density and time to symptoms’ onset in the asymptomatic carriers that developed early-onset form of the disease (r = 0.52, P < 0.01). In addition, asymptomatic carriers with amyloid deposition already present in sural nerve biopsies developed symptoms earlier than those with no amyloid (P < 0.01). In conclusion, this study confirms that the loss of small fibre size is an initial event in familial amyloid polyneuropathy, already present in asymptomatic gene carriers, starting several years before the onset of symptoms. We show for the first time that large myelinated fibres’ loss and amyloid deposition are pathological features that correlate independently with short period to the onset of symptoms for asymptomatic carriers that developed early-onset form of the disease. These findings are therapeutically relevant, as it would allow for a better interpretation of the role of disease-modifying agents in transthyretin familial amyloid polyneuropathy.

Advances in the treatment of hereditary transthyretin amyloidosis: A review

INTRODUCTION

Amyloid transthyretin amyloidosis (ATTR) is a progressive and often fatal disease caused by the buildup of mutated (hereditary ATTR [hATTR]; also known as ATTR variant [ATTRv]) or normal transthyretin (wild-type ATTR) throughout the body. Two new therapies-inotersen, an antisense oligonucleotide therapy, and patisiran, an RNA interference therapy-received marketing authorization and represent a significant advance in the treatment of amyloidosis. Herein, we describe the clinical presentation of ATTR, commonly used procedures in its diagnosis, and current treatment landscape for ATTR, with a focus on hATTR.

METHODS

A PubMed search from 2008 to September 2018 was conducted to review the literature on ATTR.

RESULTS

Until recently, there have been few treatment options for polyneuropathy of hATTR. Inotersen and patisiran substantially reduce the amyloidogenic precursor protein transthyretin and have demonstrated efficacy in patients with early- and late-stage disease and in slowing or improving neuropathy progression. In contrast, established therapies, such as liver transplantation, typically reserved for patients with early-stage disease, and tafamidis, indicated for the treatment of early-stage disease in Europe, or diflunisal, a nonsteroidal anti-inflammatory drug that is used off-label, are associated with side effects and/or unclear efficacy in certain patient populations. Thus, inotersen and patisiran are positioned to be the preferred therapeutic modalities.

CONCLUSIONS

Important differences between inotersen and patisiran, including formulation, dosing, requirements for premedications, and safety monitoring, require an understanding and knowledge of each treatment for informed decision making.

Tafamidis for autonomic neuropathy in hereditary transthyretin (ATTR) amyloidosis: a review

Purpose

Autonomic dysfunction is a very common, early and distressing aspect of hereditary transthyretin (ATTR) amyloidosis leading to significant loss of quality of life and morbidity for patients. Although the clinical variability of ATTR has been well characterized as neuropathic, cardiac or mixed phenotype, the extent of autonomic involvement remains poorly understood. Despite the fact that the autonomic nervous system has not been specifically evaluated in any of the clinical trials of tafamidis, and that, for some primary and secondary endpoints used in these trials, the behavior cannot be separated from non-autonomic items, an attempt was made to use published material to indirectly access the efficacy of tafamidis in treating dysautonomia.

Methods

Literature review summarizing the results of primary and secondary endpoints related to the autonomic features used in the original tafamidis trials, the post hoc publications, and real-world data, on the effect of tafamidis on autonomic dysfunction in patients with ATTR amyloidosis.

Results

There is some evidence that indirectly demonstrates that tafamidis is safe and could slow or arrest the progression of autonomic neuropathy in patients with ATTR amyloidosis, in addition to its well-described effects to ameliorate sensory-motor peripheral neuropathy.

Conclusion

Although the current evidence is scarce, tafamidis might be effective in arresting the progression of autonomic neuropathy in patients with ATTR amyloidosis. Tafamidis might be more effective at the early stage of the disease; however, individual responses must be monitored.