Normal Transthyretin Research Articles

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.

Characterization of the G-quadruplexes in the transthyretin gene and its role in silencing transthyretin mRNA transcription

Transthyretin Amyloidosis arises from the misfolding of monomers or oligomers of the normal transthyretin protein. Our investigation revealed that certain guanine-rich regions within the 5′ UTR sequence of the transthyretin gene possess the ability to form G2-quadruplex structures, as determined through analysis with QGRS mapper. We demonstrated that small molecule ligands, including TMPyP4, Braco-19, NMM, and TO, have a significant impact on the stabilization of transthyretin G-quadruplexes. The objective of this study was to confirm the effect of ligands on transthyretin gene transcription through the stabilization of G-quadruplexes. To comprehend the interaction between ligands and transthyretin G-quadruplexes, a range of analytical techniques were employed, includingUV titration, fluorescence titration assays, circular dichroism, quantitative RT-PCR and cytotoxicity tests. The results revealed the presence of four putative G2-quadruplex sequences, which formed stable anti-parallel, parallel, and hybrid G2-quadruplex structures. Notably, Ttrg 3 (5′-GGAAGGAAGGGAGGGAGGG-3′) exhibited the highest stability to form G-quadruplex. Furthermore, TmPyP4, Braco-19, NMM and TO were found to stabilize the parallel topology of Ttrg 3. After 48 h of incubation, the RT-PCR experiments revealed a significant reduction in transthyretin mRNA transcription in HepG2 cells when treated with 20 μM TmPyP4 and Braco-19, without inducing apoptosis. Our findings suggested that ligand-mediated stabilization of G-quadruplexes within the 5′-UTR can effectively silence transthyretin expression, highlighting the potential of G-quadruplex as a novel therapeutic target for Transthyretin Amyloidosis. This study might shed valuable lights for the development of innovative therapeutic approach against Transthyretin Amyloidosis.

Decreased transthyretin predicts a poor prognosis in primary myelodysplastic syndrome.

This study aims to investigate the prognostic significance of transthyretin in newly diagnosed myelodysplastic syndromes (MDS). The clinical, laboratory, and follow-up data of 280 newly diagnosed patients with MDS were collected. The relationship between serum transthyretin levels and overall survival (OS) and leukemia-free survival (LFS) were analyzed by Kaplan-Meier analysis and Cox Regression Model. In the MDS cohort, there were 121 cases in the low transthyretin group and 159 cases in the normal transthyretin group. MDS patients with decreased transthyretin had a higher risk score on the Revised International Prognostic Scoring System (IPSS-R) (p = 0.004) and on the molecular IPSS (IPSS-M) (p = 0.005), a higher frequency of TP53 mutation (p < 0.0001), a shorter OS (p < 0.0001) and LFS (p < 0.0001). Multivariate analyses showed that higher IPSS-R and IPSS-M score were adverse factors for OS (p = 0.008 and p = 0.015, respectively) and LFS (p = 0.024 and p = 0.005, respectively). Mutations of TP53 and NRAS were also poor factors for LFS (p = 0.034 and p = 0.018, respectively). Notably, decreased transthyretin was an independent adverse predictor for OS (p = 0.009, HR = 0.097, 95%CI, 0.017-0.561) but not for LFS (p = 0.167) when IPSS-R was included in the Cox regression model and an independent poor one for OS (p = 0.033, HR = 0.267, 95%CI, 0.080-0.898) and LFS (p = 0.024, HR = 0.290, 95%CI, 0.099-0.848) while IPSS-M involved. The results indicate that decreased transthyretin could be an independent adverse prognostic factor in patients with MDS and may provide a supplement to IPSS-R and IPSS-M.

Interstitial amyloidosis in sporadic inclusion body myositis.

Intracellular congophilic inclusions within muscle fibers, although nonspecific, are one of the pathological hallmarks of sporadic inclusion body myositis (sIBM). Extracellular amyloid deposits in muscle, on the other hand, are the canonical findings of amyloid myopathies, which occur with or without systemic amyloidosis. We reviewed the muscle biopsy database (1998-2020) to identify sIBM patients with extracellular amyloid deposits. Clinical and laboratory data were reviewed. We identified five sIBM patients (three clinicopathologically defined and two clinically defined) with extracellular amyloid deposits in muscle. Mean age at diagnosis was 74.8y (range, 68-84 y). All patients had a typical sIBM pattern of weakness without associated sensory or autonomic symptoms. None had electrophysiological evidence of peripheral neuropathy. Only one patient had a monoclonal gammopathy (immunoglobulin M-lambda, IgM-λ) with normal bone marrow biopsy. This patient with monoclonal gammopathy and three other patients underwent abdominal fat pad aspirate and were negative for amyloid. Cardiac evaluation was unrevealing in the four patients tested. Three patients without monoclonal gammopathy had normal transthyretin gene sequencing and inconclusive mass spectrometry-based analysis. The patient with monoclonal gammopathy died of pneumosepsis 5y after diagnosis and autopsy revealed multi-organ transthyretin amyloidosis. Detection of extracellular amyloid deposition in muscle should trigger an aggressive search for systemic amyloidosis independently from other associated myopathological abnormalities. Amyloid subtyping is crucial for early therapy and mortality prevention. An isolated monoclonal gammopathy should not halt a search for non-hematological causes of systemic amyloidosis.

Advances in the treatment of hereditary transthyretin amyloidosis: A review.

IntroductionAmyloid 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.MethodsA PubMed search from 2008 to September 2018 was conducted to review the literature on ATTR.ResultsUntil 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.ConclusionsImportant 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.

Les polyneuropathies amyloïdes : aspects biochimiques et génétiques

Familial amyloid polyneuropathies (FAP) are among the most frequent hereditary amyloidoses. These are serious, most often fatal diseases with autosomal dominant inheritance. FAP can be caused by mutations in four genes, namely those encoding transthyretin, Al-apoliprotein, gelsolin, and beta-2 microglobulin. Transthyretin is a tetramer composed of four identical subunits linked by non covalent bonds and bearing binding sites for thyroxine (T4) and retinol-binding protein (RBP). More than 120 transthyretin gene sequence variations have been characterized, of which only 80% seem to be pathogenic. Gene mutations can induce tetramer destabilization, thereby generating misfolded monomers that aggregate into insoluble amyloidfibrils. The mutation spectrum is highly variable across countries. For example, while the Val30Met mutation is found in 95% of the Portuguese and Swedish patient populations, high mutational heterogeneity is observed in France. Age of onset and clinical signs are influenced by numerous factors, especially the mutation type and the country, but the mechanisms underlying this variability are not fully clear. The three-dimensional structure of the normal transthyretin protein and a dozen mutants is now known, providing insights into the deleterious effects of mutations. A better understanding of the mechanisms involved in amyloid fibril formation has led to the development of drugs that inhibit transthyretin tetramer destabilization. It is hoped that, within afew years, such drugs will replace liver transplantation, which is currently the only curative treatment.

Amyloid heart disease mimicking hypertrophic cardiomyopathy*

To investigate the importance of transthyretin (TTR) gene mutations in explaining the phenotypic expression in patients diagnosed with hypertrophic cardiomyopathy (HCM) in northern Sweden. Hypertrophic cardiomyopathy is relatively common and often caused by mutations in sarcomeric protein genes. Mutations in the TTR gene are also common, one of which causes familial amyloid polyneuropathy (FAP), with peripheral polyneuropathy and frequently, cardiac hypertrophy. These circumstances were highlighted by the finding of an index case with amyloidosis, presenting itself as HCM. Initial rectal and fat biopsies did not show amyloid deposits. Later on, the patient was shown to carry a TTR gene mutation, and cardiac amyloidosis was confirmed by myocardial biopsy. Only then was a repeated fat biopsy positive for amyloid deposits. Cross-sectional study. Cardiology tertiary referral centre. Forty-six unrelated individuals with HCM and the index case were included. Common diagnostic criteria for HCM were used. The 46 patients with HCM were previously analysed for mutations in eight sarcomeric protein genes and the TTR gene was now analysed by denaturing high-performance liquid chromatography and direct sequencing. One mutation in the TTR gene (Val30Met) was found in three individuals and the index case. Three of the 46 cases with HCM carried the Val30Met mutation, and were considered likely to have cardiac amyloidosis, like the index case. As a correct diagnosis of cardiac amyloidosis is mandatory for a potentially life-saving treatment, TTR mutation analysis should be considered in cases of HCM not explained by mutations in sarcomeric protein genes.

Biophysical analysis of normal transthyretin: Implications for fibril formation in senile systemic amyloidosis

Transthyretin (TTR) is a plasma protein that transports thyroid hormone andretinot binding protein-vitamin A complex. Eighty-four variants of TTR have been identified and seventy-four are associated with familial amyloidotic polyneuropathy. Normal TTR is the major protein found in the fibrillar deposits in the heart at time of autopsy of individuals with senile systemic amyloidosis. The mechanism by which normally soluble TTR deposits as organ-damaging, insoluble, pathological fibrils late in life is unknown. Understanding the mechanism of fibrillogenesis of normal TTR is critical to the design of clinical treatments aimed at retardation, prevention, or reversal of fibril deposition. We have employed a biophysical approach to explore the hypothesis that an instability in a particular secondary or tertiary structure plays a role in the ability of normal TTR to form fibrils at physiological pH. Using far UV circular dichroic (CD) spectroscopy as a function of temperature we have identified simultaneous, cooperative, reversible structural changes in the β-sheet and α-helical regions. The flexible short, surface-located loops undergo an irreversible conformational change at a lower temperature. Spectra before and after heating are different, particularly in the wavelength region associated with these loops, strongly suggesting that the major portion of TTR returns to its initial conformation while the loops do not. Near UV CD reveals partially reversible and irreversible changes in tertiary structure. Using calorimetry to directly measure the enthalpy associated with these changes, two peaks are observed, with further analysis suggesting conformational intermediates. Precipitates from heated samples reveal pre-fibrillar morphology by negative stain electron microscopy. These biophysical studies suggest that heat-induced conformational rearrangements enable normal TTR to assemble into prefibrils at physiological pH.

Thrombelastographic evidence of hyperfibrinolysis during liver transplantation for familial amyloidotic polyneuropathy ATTR Met 30

FAMILIAL amyloidotic polyneuropathy (FAP) ATTR Met 30 is the result of an inherited disorder of transthyretin metabolism. Both amyloid transthyretin and normal transthyretin are produced in the liver and the transplantation is a successful therapy for this disease and is performed in spite of the completely normal liver function of these patients. A high incidence of hyperfibrinolysis was reported during liver transplantation but these studies were performed in patients with previous liver insufficiency and the relative role of preoperative factors (liver disease, coagulation disorders, increased fibrinolytic activity) and intraoperative factors (surgical trauma, hypotension, and graft reperfusion) is not clearly established. As far as we know, the incidence and the severity of hyperfibrinolysis during liver transplantation in patients without preoperative liver insufficiency has not yet been studied. The aim of this study was to evaluate the incidence of hyperfibrinolysis during liver transplantation in FAP and to correlate these findings with several perioperative factors.

Tertiary structures of amyloidogenic and non-amyloidogenic transthyretin variants: new model for amyloid fibril formation

The most common form of hereditary systemic amyloidosis is familial amyloidotic poly neuropathy associated with single amino acid changes in the plasma protein transthyretin.So far, high resolution structures of only three amyloidogenic variants (Met30, Ser84, tle 122) and one non-amyloidogenic variant (Thr109) have been reported complemented by X-ray fiber diffraction studies and image reconstruction from electron micrographs of amyloid fibrilsTo investigate the role of structural factors in this disease, we extended our studies to other transthyretin variants. We report crystallization and structural investigations of three amyloidogenic (Arg10, Ala60, Tyr77) and two non-amyloidogenic variants (Ser6, Met119). The similarity oj these structures to normal transthyretin does not give direct clues to the fibril forming process. Since transthyretin amyloid fibrils contain a major fragment starting at position 49, besides the intact molecule, we calculated the solvent accessibility of residue 48. Indeed, all amyloidogenic variants show an increased main chain solvent exposure when compared to normal transthyretin and non-amyloidogenic variants, which can be postulated to result in increased susceptibility to proteolysis. Affer limited proteolysis, dimers are incapable ofreassociation to native telramersWe present a model for amyloid fibril formation based on formation of fibrils from N-terminal truncated dimers as building blocks.

Transthyretin (TTR)-derived amyloid fibrils: Immunoelectron microscopy of fibrils formed in vivo and in vitro from synthetic peptides and normal transthyretin

The fibril forming capacity of synthetic peptides representing parts of the human TTR sequence was investigated. The in vitro formed fibrils were studied with electron microscopy and with polarized light after staining with Congo red dye and also compared with fibrils formed in vitro from normal TTR and fibrils extracted from amyloid deposits from a patient with senile systemic amyloidosis. Most of the synthetic peptides that were fibrillogenic in this study represent parts of the TTR sequence that are mostly in the β-strands in the tertiary structure of TTR. A peptide corresponding to the α-helix was also strongly fibrillogenic in vitro as was a peptide representing the DE-loop. in senile systemic amyloidosis and in familial amyloidotic polyneuropathy the fibrils contain C-terminal fragments of TTR starting just before the D strand. The cleavage of the TTR molecule thus exposes a highly fibrillogenic sequence, possibly important for in vivo fibrillogenesis.The in vitro formed fibrils from synthetic peptides and normal TTR and fibrils extracted from amyloid deposits were immunolabelled with antisera raised against synthetic TTR peptides, amyloid TTR and against normal TTR. An antiserum against TTR(II.5-124) immunoreacted with amyloid fibrils formed in vivo and fibrils formed from normal TTR in vitro but not with purified normal TTR in Western blot, ELISA or with TTR in pancreatic islet cells in immunohistochemistry.

Transthyretin gene in Alzheimer's disease patients

Amyloid β (Aβ) is known to be the main component of Alzheimer's disease (AD) senile plaques. A homologous peptide is a normal component of biological fluids and is called soluble Aβ (sAβ). Synthetic peptides homologous to Aβ form amyloid-like fibrils in vitro. This fibril formation can be inhibited by normal human cerebrospinal fluid (CSF) [Wisniewski et al., Ann. Neurol. 34 (1993)]. Furthermore, it has been proposed that normal transthyretin (TTR), which is a component of CSF, can itself bind sAβ, preventing amyloid fibril formation, and that variants of TTR could be associated with AD [Schwarzman et al., Proc. Natl. Acad. Sci. USA, 91 (1994)]. Because of this possible association, we screened for TTR mutations from 47 sporadic and 19 early-onset familial AD patients using single strand conformation polymorphism analysis. Our results show no correlation between TTR variants and Alzheimer's disease in this group of patients.

Normal and variant transthyretin in a patient with familial amyloidotic polyneuropathy: DNA, mRNA, serum, and amyloid deposits

Normal and variant transthyretin in a patient with familial amyloidotic polyneuropathy: DNA, mRNA, serum, and amyloid deposits

Structural changes in transthyretin produced by the Ile 84 Ser mutation which result in decreased affinity for retinol-binding protein

The X-ray crystal structure of the transthyretin variant Ile 84 Ser has been determined to 1.7A resolution. The functional form of normal transthyretin is a tetramer, having a cylindrical cavity which binds thyroxine and an exterior binding site for the complex of retinol with retinol-binding protein. The naturally occurring amyloidogenic variant Ile 84 Ser has reduced affinity for retinol-binding protein. The results of this study show that the overall structural homology between the C-alpha atoms of the variant and normal protein is very high with differences mainly in the loop regions, in the vicinity of the substitution, and the ligand binding areas. The known functional differences for the variant (ligand-binding) are correlated with the structural changes observed in the region of the ligand-binding site. The substitution at position 84 results in changes in the shape of the putative site for complexation with retinol binding protein. The substitution site occurs at the interface between two tetrame...

Orthotopic liver transplantation for familial amyloidotic polyneuropathy

Orthotopic liver transplantation for inborn errors of metabolism has become a standard indication for transplantation in pediatric and adult patients with alpha‐1 antitrypsin deficiency, Wilson's disease and tyrosinemia, amongst several less common diseases. Familal amyloidotic polyneuropathy (FAP) is a rare autosomal dominant disease whose metabolic origin lies in an abnormal protein synthesized primarily in the liver. FAP, also discussed as the autosomal dominant form of amyloidosis, is characterized as a hereditary form of amyloidosis. It is the rarest form of amyloidosis affecting kindreds of specific ethnic backgrounds. The true incidence of this disease in the United States is not known. The mutant protein, called transthyretin or prealbumin, forms amyloid fibrils which accumulate in vital tissues ultimately leading to the patient's death. Liver transplantation for this inherited disease leads to the production of normal transthyretin protein. This theoretically should arrest the disease process. The first 5 patients in the United States with FAP who have undergone transplantation are presented.

Alteration in molecular structure which results in disease: the Met-30 variant of human plasma transthyretin

The structure of a variant transthyretin has been determined by X-ray crystallography at 2.3 Å resolution in order to investigate those changes which lead to amyloid formation. This variant transthyretin, in which the internal valyl residue at position 30 is replaced by methionyl, is associated with the most common form of familial amyloidotic polyneuropathy (FAP). Comparison to the known structure of the normal transthyretin tetramer shows that the bulkier methionine residue 30 which lies between the nearly orthogonal beta sheets of the dimer, results in the sheets being displaced an average of 0.4 Å. The internal structure of the sheets and of the monomer-monomer interface is maintained. Such global changes may affect the metabolic properties and the tendency towards polymerization of the mutant protein. These findings may form a basis for understanding other amyloid-deposition diseases.

Preparation and crystallization of human transthyretin (prealbumin) variants

Naturally occurring variants of human serum transthyretin (prealbumin) have been prepared by recombinant DNA methods and crystallized from ammonium sulfate solutions to give crystals suitable for x-ray crystallographic analysis. Included are variants which are known to be associated with familial amyloidotic polyneuropathy. Dyes which have been used as histochemical stains to identify amyloid tissue deposits: Congo Red, Methylene Blue and Bromophenol Blue, have been co-crystallized with the transthyretin variants. Congo Red was found to be very selective while Methylene Blue actually assisted in the formation of crystals. All crystal forms which were examined were isomorphous to the structure of normal transthyretin.

Normal transthyretin and synthetic transthyretin fragments from amyloid-like fibrils in vitro

In two general forms of amyloidosis, senile systemic amyloidosis and several familial amyloidoses the amyloid fibrils are built up by transthyretin and fragments of the molecule. It has previously been demonstrated that other amyloid fibril proteins e.g. atrial natriuretic factor and islet amyloid polypeptide form amyloid-like fibrils in vitro. In this study we used normal transthyretin and synthetic polypeptides corresponding to segments of the transthyretin molecule. We show that normal transthyretin and two of our tested polypeptides, which corresponded to the β-strands A and G, easily form amyloid-like fibrils in vitro.

A new transthyretin variant from a patient with familial amyloidotic polyneuropathy has asparagine substituted for histidine at position 90

A new transthyretin variant which lost an Sph I cleavage site within exon 3 has been characterized. A 260 bp sequence containing exon 3 was amplified using the polymerase chain reaction, and the variant was found to possess a Bsm I cleavage site not present in normal transthyretin. This led to the conclusion that the histidine at position 90 was replaced by asparagine, and amino acid analysis supported the conclusion. The discovery of this mutation suggests that intermolecular binding between hydrophobic polypeptide loops on the surface of transthyretin can lead to familial amyloidotic polyneuropathy.

Fibril in senile systemic amyloidosis is derived from normal transthyretin.

The amyloid fibril in senile systemic amyloidosis (SSA), like that of familial amyloidotic polyneuropathy, is derived from transthyretin (TTR). SSA, however, is a common disease, affecting to some degree 25% of the population greater than 80 years old. In familial amyloidotic polyneuropathy, the amyloidogenesis has been considered to depend on point mutations leading to TTR variants. We show that the TTR molecule in SSA, on the other hand, has a normal primary structure. Factors other than the primary structure of TTR must therefore be important in the pathogenesis of TTR-derived amyloid.