A new diagnostic procedure to detect unknown transthyretin (TTR) mutations in familial amyloidotic polyneuropathy (FAP)

An ultra performance liquid chromatography method for transthyretin variants screening and heart failure assisting diagnosis

BACKGROUND

Transthyretin (TTR) gene mutations are associated with hereditary amyloidosis (ATTR) caused by mutant TTR protein dissociation, misfolding, aggregation, and insoluble fibrils deposition. Herein, we reported a chromatographic approach for quantification and identification of TTR tetramer in human blood serum by ultra performance liquid chromatography (UPLC).

METHODS

TTR proteins and serum were incubated with a fluorescent TTR tetramer sensor (A2). The A2 sensor specifically reacted with tetrameric TTR and released stoichiometric fluorescence that was detected by fluorescence detector coupled to UPLC. The external standard was used for quantification, the chromatographic peak parameters were used to identification certain mutation types.

RESULTS

UPLC correctly distinguished 18 types of mutant TTR proteins from wild type. The results were consistent with follow-up analysis of two ATTR patients' blood serum samples. In addition, the tetrameric TTR of 30 heart failure (HF) patients showed strongly correlation (r = -0.63, p < 0.00) with NT-proBNP, a HF clinical biomarker.

CONCLUSIONS

UPLC method has sufficient accuracy to eliminate the necessity of sequencing for certain types of TTR mutations and allows for facile initial screening of ATTR amyloidosis patients, carriers, and healthy individuals for time-saving and economical purposes. TTR tetramer may serve as a diagnostic biomarker to evaluate the risk of HF diseases.

Long-term outcome of patients with hereditary transthyretin V30M amyloidosis with polyneuropathy after liver transplantation

BACKGROUND

Liver transplantation halts production of mutated transthyretin (TTR), and thus it is an accepted treatment, with improved survival, in patients with hereditary (familial) amyloidosis with polyneuropathy (FAP). However, the effects of transplantation on the clinical manifestations of FAP have not yet been adequately clarified. This study aimed to investigate whether liver transplantation would improve the long-term clinical manifestations in FAP patients who had undergone transplantations.

PATIENTS AND METHODS

We assessed 29 non-transplant and 36 transplant FAP V30M patients using an FAP clinical scoring system.

RESULTS

The total clinical score of the non-transplant group increased and was significantly correlated with FAP duration; that of the transplant group increased slowly after transplantation. In patients 5 years or more after FAP onset, the total clinical scores of the transplant group were significantly lower than those of the non-transplant group. In the same patients, scores for sensory, motor, autonomic and organ impairments of the transplant group were significantly lower than those of the non-transplant group.

CONCLUSIONS

Liver transplantation had beneficial effects on FAP clinical manifestations in patients with FAP TTR V30M. Liver transplantation should therefore be considered as an effective treatment in the clinical management of patients with FAP TTR V30M.

Recent advances in transthyretin amyloidosis therapy

Mutant (MT) forms of transthyretin (TTR) cause the most common type of autosomal-dominant hereditary systemic amyloidosis-familial amyloidotic polyneuropathy (FAP). Until 20 years ago, FAP was thought to be an endemic disease, but FAP is known to occur worldwide. To date, more than 130 mutations in the TTR gene have been reported. Genotype-phenotype correlations are seen in FAP, and some variation in clinical presentation is often observed in individual kindreds with the same mutation and even among family members. Of the pathogenic TTR mutations, Val30Met was the first to be identified and is the most frequent known mutation found throughout the world. Studies of patients with FAP amyloidogenic TTR (ATTR) Val30Met documented sensorimotor polyneuropathy, autonomic dysfunction, heart and kidney failure, gastrointestinal tract (GI) disorders, and other symptoms leading to death, usually within 10 years of the onset of disease. Diagnosis is sometimes delayed, especially in patients without a clear family history and typical clinical manifestations, since diagnosis requires various studies and techniques such as histopathology, genetic testing, and mass spectrometry. For treatment of FAP, liver transplantation (LT) reportedly halts the progression of clinical manifestations. Exchange of an FAP patient's diseased liver with a healthy liver causes MT TTR in the body to be replaced by wild-type (WT) TTR. Although clinical evaluations indicated that progression of other clinical symptoms such as peripheral neuropathy, GI symptoms, and renal involvement usually halted after LT in FAP ATTR Val30Met patients, recent studies suggested that LT failed to prevent progression of cardiac amyloidosis in FAP ATTR Val30Met patients after LT, with this failure reportedly being due to continued formation of amyloid that derived mainly from WT TTR secreted from the transplanted non-mutant liver graft. In recent years, many therapeutic strategies have been proposed, and several ongoing therapeutic trials involve, for example, stabilizers of TTR tetramers (tafamidis and diflunisal) and gene therapies to suppress TTR expression (antisense methods and use of small interfering RNAs). These novel therapies may prove to prevent progression of FAP.

Presence of N-glycosylated transthyretin in plasma of V30M carriers in familial amyloidotic polyneuropathy: an escape from ERAD

Familial amyloid polyneuropathy (FAP) is an autosomal dominant disease characterized by deposition of amyloid related to the presence of mutations in the transthyretin (TTR) gene. TTR is mainly synthesized in liver, choroid plexuses of brain and pancreas and secreted to plasma and cerebrospinal fluid (CSF). Although it possesses a sequon for N-glycosylation N-D-S at position 98, it is not secreted as a glycoprotein. The most common FAP-associated mutation is TTR V30M. In a screening for monoclonal antibodies developed against an amyloidogenic TTR form, we detected a distinct TTR with slower electrophoretic mobility in Western of plasma from carriers of the V30M mutation, not present in normal plasma. Mass spectrometry analyses of this slower migrating TTR (SMT) identified both wild-type and mutant V30M; SMT was undetectable upon N-glycosidase F treatment. Furthermore, SMT readily disappeared in the plasma of V30M - FAP patients after liver transplantation and appeared in plasma of transplanted domino individuals that received a V30M liver. SMT was also detected in plasma, but not in CSF of transgenic mice for the human V30M mutation. A hepatoma cell line transduced to express human V30M did not present the SMT modification in secretion media. Glycosylated TTR was absent in fibrils extracted from human kidney V30M autopsy tissue or in TTR aggregates extracted from the intestine of human TTR transgenic mice. Studies on the metabolism of this novel, glycosylated TTR secreted from FAP liver are warranted to provide new mechanisms in protein quality control and etiopathogenesis of the disease.

Identification and quantitative analysis of human transthyretin variants in human serum by Fourier transform ion-cyclotron resonance mass spectrometry

Transthyretin (TTR) is a homotetrameric protein involved in thyroid hormone transport in blood and in retinol binding in the central nervous system. More than 80 point mutations in this protein are known to be associated with the formation of amyloid deposits and systemic amyloidotic pathologies. Age at onset varies according to the mutation but considerable variations also occur for subjects carrying the same mutation. Moreover, wild-type TTR forms amyloid deposits in systemic senile amyloidosis, a geriatric disorder. An accurate diagnostic and the choice of therapeutic options depend on the identification of the specific mutation. Previous characterization of TTR variants by mass spectrometry required the use of antibodies for sample enrichment. We developed a novel assay based on ultra high-resolution mass spectrometry to identify human TTR variants. The method, requiring a very low sample amount, is based on SDS-PAGE fractionation of human serum, followed by peptide mass fingerprinting by MALDI-FTICR-MS (matrix assisted laser desorption ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry). Moreover, it is possible to perform a relative quantification of wild type and mutant TTR forms by mass spectrometry. The method was tested and validated with the V30M mutant, involved in familial amyloidotic neuropathy of Portuguese type.

A rapid and sensitive prenatal diagnosis of familial amyloidotic polyneuropathy ATTR Val30Met by mass spectrometry

OBJECTIVE

To make a prenatal diagnosis of familial amyloidotic polyneuropathy (FAP) by mass spectrometry with the amniotic fluid.

METHODS

Amniotic-fluid samples of three non-FAP pregnant women and six amniotic-fluid samples of fetal mice whose mother was a heterozygotic FAP amyloidgenic transthyretin (ATTR) Val30Met gene carrier were collected. Electro spray ionization mass spectrometry (ESI-MS) was employed to identify and quantitatively measure the molecular weight of the human transthyretin (TTR) in the amniotic fluid.

RESULTS

TTR was detected in the amniotic fluid of all the human samples. In four of the six fetuses of the transgenic mice, human TTR Val30Met was detected. The other two samples showed only mouse TTR without human TTR Val30Met. DNA analysis revealed that the four fetuses were TTR Val30Met positive, but two were negative. The data from the DNA analysis and ESI-MS showed a 100% concordance.

CONCLUSION

Mass spectrometry analysis of the amniotic fluid might be a useful tool to make a prenatal diagnosis of FAP ATTR Val30Met.

[The diagnosis and management of familial amyloid polyneuropathy]

INTRODUCTION

Familial amyloid polyneuropathy designates a group of dominantly inherited neuropathies, with extracellular deposition of amyloid substance in various tissues.

BACKGROUND

The 3 main precursor proteins encountered in these disorders are transthyretin, apolipoprotein A1 or gelsolin. Among them, transthyretin neuropathies are by far the most frequent type with a severe sensori-motor and autonomic neuropathy as the hallmark of the disease, most often associated with cardiac manifestations. First described in Portugal, the affection was subsequently reported across the world, although Portugal, Japan and Sweden are the 3 main areas of prevalence. In the past years, an increasing number of mutations have been identified in the TTR gene, along with a larger clinical spectrum than initially thought. Variable age of onset and penetrance are also largely reported with unclear phenotypic-genotypic correlations. Indeed, the contribution of the molecular genetics is important to ensure the diagnosis at an early stage, but also for predictive diagnosis, in the setting of genetic counselling.

PERSPECTIVES

Over the last 15 years, liver transplantation (LT) has enabled improved prognosis of this devastating condition.

FUTURE PROSPECTS

at present, such procedure should be performed in Val30Met patients, as early as possible in the course of the disease. Experience with such procedure in patients with other TTR variants remains scarce. Other therapeutic strategies are awaited.

CONCLUSION

This review summarizes the recent data on the diagnosis and management of patients and families affected with TTR amyloid neuropathy.

Immunoaffinity chromatographic and immunoprecipitation methods combined with mass spectrometry for characterization of circulating transthyretin

Transthyretin (TTR) is a small serum protein that is involved in distinct phenotypes of amyloidosis with different tissue localization, age of onset, and rate of progression. Some types of TTR-amyloidosis (such as familial amyloid polyneuropathy) are associated with various amino acid point mutations, while cardiac amyloid myopathy may also be associated with precipitation of the wild-type molecules, e.g., in senile systemic amyloidosis. Because of the unsettled relationship between circulating and precipitated TTR we here explore on-line immunoaffinity (IA) chromatography-MS and immunoprecipitation (IP)-MS methods for characterizing the circulating TTR population in normal individuals and in patients with known TTR-amyloidosis. It was found necessary to reduce the samples, e.g., with DTT, prior to ESI-TOF-MS. This reversed oxidative modifications to sufficiently resolve the two mass peaks isolated from sera of heterozygous patients. A simple IP technique without the use of centrifugal filtration was found to be convenient for the assessment of the TTR population in serum as demonstrated for both normal and variant (the Met111Leu mutation) TTR. This approach also readily allowed the identification of oxidation, S-sulfation, and S-cysteinylation in unreduced samples, while these modifications were less well resolved in the on-line IA chromatography-MS approach.

Definition of organ involvement and treatment response in immunoglobulin light chain amyloidosis (AL): a consensus opinion from the 10th International Symposium on Amyloid and Amyloidosis, Tours, France, 18-22 April 2004

We undertook this study to develop uniformly accepted criteria for the definition of organ involvement and response for patients on treatment protocols for immunoglobulin light-chain amyloidosis (AL). A consensus panel was convened comprising 13 specialists actively involved in the treatment of patients with amyloidosis. Institutional criteria were submitted from each, and a consensus was developed defining each organ involved and the criteria for response. Specific criteria have been developed with agreed on definitions of organ and hematologic response as a result of discussions at the 10th International Symposium on Amyloid and Amyloidosis held in Tours, France, April 2004. These criteria now form the working definition of involvement and response for the purposes of future data collection and reporting. We report criteria that centers can now use to define organ involvement and uniform response criteria for reporting outcomes in patients with light-chain AL.

Identification of Transthyretin Variants by Sequential Proteomic and Genomic Analysis

Background: Transthyretin-associated hereditary amyloidosis (ATTR) is an inherited disease in which variants in the primary structure of transthyretin (TTR; prealbumin) lead to the extracellular polymerization of insoluble protein fibrils, causing organ failure and ultimately death when major organs are involved. We have developed an integrated approach to molecular diagnosis with initial analysis of intact plasma TTR by electrospray ionization mass spectrometry (MS) and referral of positive samples for DNA sequence analysis and real-time PCR to confirm the common Gly6Ser polymorphism.

Methods: Samples from 6 patients previously diagnosed with ATTR and from 25 controls with (n = 15) or without (n = 10) polyneuropathy were analyzed in a blinded fashion for the presence of variant TTR. TTR protein was extracted with an immunoaffinity resin from 20 μL of archived plasma samples. The purified TTR was reduced with tris(2-carboxyethyl)phosphine and analyzed by MS. The appearance of two peaks (or a single peak shifted in mass indicative of a homozygous variant), including the wild-type mass of 13 761 Da, was indicative of the presence of a variant, and the individual was referred for DNA sequence analysis.

Results: MS analysis of intact reduced TTR correctly identified each of six samples known to contain variant TTR. These results were corroborated by subsequent DNA sequence analysis. Additionally, all Gly6Ser polymorphisms were correctly called based on the +30 mass shift and an equal relative abundance of the +30 polymorphism relative to wild-type TTR. No false-positive results were seen.

Conclusions: This referral method eliminates the necessity of sequencing most samples and allows screening for the familial forms of amyloidosis in a broad patient population in a timely fashion. This method correctly identified all previously known variants and also identified a novel variant, Val94Ala.

Detection of Genetic Variants of Transthyretin by Liquid Chromatography–Dual Electrospray Ionization Fourier-Transform Ion-Cyclotron-Resonance Mass Spectrometry

Background: One of the numerous proteins causing amyloidosis is transthyretin (TTR), a protein usually responsible for the transport of thyroxine and retinol-binding protein. Variants within TTR cause it to aggregate and form insoluble fibers that accumulate in tissue, leading to organ dysfunction.

Methods: TTR was immunoprecipitated from serum by use of a polyclonal antibody and subsequently reduced with tris(2-carboxyethyl)phosphine. The purified TTR was then analyzed by fast-gradient liquid chromatography–dual-electrospray ionization Fourier-transform ion-cyclotron-resonance (FT-ICR) mass spectrometry. DNA sequencing was performed on all samples used in this study.

Results: Because of the inherent limitations in achieving high mass measurement accuracy based on the most abundant isotopic mass, we applied a fitting procedure that allowed determination of monoisotopic mass. Wild-type TTR (mean molecular mass, 13 761 Da) and its associated variant forms could be distinguished because of the high molecular mass accuracy afforded by FT-ICR (≤3 ppm) except for instances involving isobaric species or when isotopic distributions overlapped significantly. The [M + 11 H+]11+ charge state for all samples was used to determine the mass accuracies for both wild-type and variant forms of the protein. We correctly assigned seven of seven TTR variants. Moreover, using a combination of proteomic and genomic technologies, we discovered and characterized a previously unreported cis double mutation with a mass only 2 Da different from wild-type TTR. Furthermore, DNA sequencing of the TTR gene for all individuals in this study completely agreed with the intact protein measurements.

Conclusions: FT-ICR mass spectrometry has sufficient mass accuracy to identify genetic variants of immunoaffinity-purified TTR. We believe that 91% of known TTR variants could be detected by this technique.

Muscular amyloid angiopathy with amyloidgenic transthyretin Ser50Ile and Tyr114Cys

Among patients with familial amyloid polyneuropathy (FAP), those with transthyretin Val30Met mainly show distally predominant weakness and atrophy, whereas some FAP patients, including those with transthyretin Ser50Ile and Tyr114Cys, show muscle weakness and atrophy that is dominant proximally, simulating myopathy. To clarify the cause of proximally dominant muscular atrophy in patients with FAP transthyretin Ser50Ile and Tyr114Cys, we investigated the distinctive features of muscle specimens of patients with FAP, 3 of who had Val30Met, 2 Ser50Ile, and 2 Tyr114Cys transthyretin. All specimens showed transthyretin amyloid around blood vessels and perimysium, and neurogenic denervation patterns. The amount of amyloid around the vessels was much greater in patients with FAP Ser50Ile and Tyr114Cys than in Val30Met patients. Muscular amyloid angiopathy may contribute to motor nerve injury that, in turn, may lead to amyotropic changes in patients with FAP Ser50Ile and Tyr114Cys.

An on-line assay for clinical detection of amyloidogenic transthyretin variants directly from serum

We report here for the first time the on-line analysis of transthyretin genetic variants by mass spectral analysis. The use of mass spectrometry to analyze immunoprecipitated transthyretin has been previously described. However, the on-line analysis of TTR directly from serum reported here will allow for a fully automated high throughput analysis. Mutations in the plasma transport protein TTR are readily observed and distinguished from normal TTR. Free TTR as well as TTR-cysteine and TTR-cysteinylglycine adducts are clearly evident. The resulting assay from serum to final interpretation requires less than twenty minutes. The assay should be an effective first line discriminator of patients who are being considered to have Familial Amyloidotic Polyneuropathy (FAP) and an adjunct to definitive diagnosis by sequencing of the TTR gene or protein.

Transthyretin related familial amyloid polyneuropathy

Familial amyloid polyneuropathy (FAP) applies to a group of dominantly inherited severe diseases with endoneurial and polyvisceral deposition of amyloidosis. The transthyretin, essentially produced by the liver, is the main protein involved in FAP. Up to 80 different mutations of the transthyretin gene are identified, many of them being associated with small fibres sensory-motor and autonomic polyneuropathy and/or cardiomyopathy. Variable age of onset, clinical expression and penetrance are largely reported. However, phenotypic-genotypic correlations remain unclear and the genetic or environmental modifying factors are unknown. The liver transplantation is proposed as a curative treatment of FAP resulting in an improvement of the general condition and a stabilization of the neuropathy, in a majority of patients. At present, the ratio benefit/risk seems acceptable when the procedure is performed early in the course of the disease.