A new mutation (TTR Ala-47) in the transthyretin gene associated with hereditary amyloidosis

Transthyretin mutagenesis: impact on amyloidogenesis and disease

Transthyretin (TTR), a homotetrameric protein found in plasma, cerebrospinal fluid, and the eye, plays a pivotal role in the onset of several amyloid diseases with high morbidity and mortality. Protein aggregation and fibril formation by wild-type TTR and its natural more amyloidogenic variants are hallmarks of ATTRwt and ATTRv amyloidosis, respectively. The formation of soluble amyloid aggregates and the accumulation of insoluble amyloid fibrils and deposits in multiple tissues can lead to organ dysfunction and cell death. The most frequent manifestations of ATTR are polyneuropathies and cardiomyopathies. However, clinical manifestations such as carpal tunnel syndrome, leptomeningeal, and ocular amyloidosis, among several others may also occur. This review provides an up-to-date listing of all single amino-acid mutations in TTR known to date. Of approximately 220 single-point mutations, 93% are considered pathogenic. Aspartic acid is the residue mutated with the highest frequency, whereas tryptophan is highly conserved. "Hot spot" mutation regions are mainly assigned to β-strands B, C, and D. This manuscript also reviews the protein aggregation models that have been proposed for TTR amyloid fibril formation and the transient conformational states that convert native TTR into aggregation-prone molecular species. Finally, it compiles the various in vitro TTR aggregation protocols currently in use for research and drug development purposes. In short, this article reviews and discusses TTR mutagenesis and amyloidogenesis, and their implications in disease onset.

Characterization of Transthyretin Mutation G47V Associated with Hereditary Cardiac Amyloidosis

INTRODUCTION

Amyloidosis caused by TTR mutations (ATTRv) is a rare inherited and autosomal dominant disease. More than 150 mutants of TTR have been reported, whereas some of them remain to be investigated.

METHODS

A 52-year-old male presented with heart failure and clinically diagnosed ATTR cardiac amyloidosis (ATTR-CA) was recruited. Whole-exome sequencing (WES) was performed. Biochemical and biophysical experiments characterized protein stability using urea-mediated tryptophan fluorescence. Drug response was analyzed by fibril formation assay. Finally, tetramer TTR concentration in patient's serum sample was measured by ultra-performance liquid chromatography (UPLC).

RESULTS

For the proband, WES revealed a mutation (c.200G>T; p.Gly67Val and referred to as G47V) in TTR gene. Biochemical and biophysical kinetics study showed that the thermodynamic stability of G47V-TTR (Cm = 2.4 m) was significantly lower than that of WT-TTR (Cm = 3.4 m) and comparable to that of L55P-TTR (Cm = 2.3 m), an early age-of-onset mutation. G47V:WT-TTR heterozygous tetramer kinetic stability (t1/2 = 1.4 h) was further compromised compared to that of the homozygous G47V-TTR (t1/2 = 3.1 h). Among three small molecule stabilizers, AG10 exhibited the best inhibition of the fibrillation of G47V-TTR homozygous protein. Using a UPLC assay, nearly 40% of TTR in this patient was calculated to be non-tetrameric.

CONCLUSION

In this work, we reported a patient presented early onset of clinically typical ATTR-CA due to G47V-TTR mutation. Our work for the first time not only characterized the biochemical properties of G47V-TTR mutation, but also provided hints for the pathogenicity of this mutation.

Cardiac Amyloidosis: A Rare TTR Mutation Found in an Asian Female

BACKGROUND

Transthyretin cardiac amyloidosis (ATTR) is a life-threatening, debilitating disease caused by abnormal formation and deposit of transthyretin (TTR) protein in multiple tissues, including myocardial extracellular matrix. It can be challenging to diagnose due to the myriad of presenting signs and symptoms. Additionally, numerous TTR mutations exist in certain ethnicities. Interestingly, our patient was discovered to have a very rare Gly67Ala TTR mutation typically not found in individuals of Asian descent. Recent advances in cardiovascular imaging techniques have allowed for earlier recognition and, therefore, management of this disease. Although incurable, there are now new, emerging treatments that are available for symptom control of cardiac amyloidosis, making early diagnosis vital for these patients, specifically their quality of life.

CASE SUMMARY

We outline a case of a 50-year-old Asian female who was initially hospitalized for nausea and vomiting and persistent orthostatic hypotension. She underwent a multitude of laboratory and imaging tests, resulting in a diagnosis of cardiac amyloidosis, which was confirmed to be due to a rare TTR mutation via genetic testing.

CONCLUSIONS

Our objective is to describe various TTR mutations, existing diagnostic imaging modalities, and available treatments, as well as highlight the importance of early screening and awareness of cardiac amyloidosis, allowing for quicker diagnosis and treatment of this disease.

Hereditary Transthyretin-Related Amyloidosis: Genetic Heterogeneity and Early Personalized Gene Therapy

Point mutations of the transthyretin (TTR) gene are related with hereditary amyloidosis (hATTR). The number of people affected by this rare disease is only partially estimated. The real impact of somatic mosaicism and other genetic factors on expressivity, complexity, progression, and transmission of the disease should be better investigated. The relevance of this rare disease is increasing and many efforts have been made to improve the time to diagnosis and to estimate the real number of cases in endemic and non-endemic areas. In this context, somatic mosaicism should be better investigated to explain the complexity of the heterogeneity of the hATTR clinical features, to better estimate the number of new cases, and to focus on early and personalized gene therapy. Gene therapy can potentially improve the living conditions of affected individuals and is one of the central goals in research on amyloidosis related to the TTR gene, with the advantage of overcoming liver transplantation as the sole treatment for hATTR disease.

Most recent common ancestor of TTR Val30Met mutation in Italian population and its potential role in genotype-phenotype correlation

INTRODUCTION

Transthyretin (TTR)-related amyloidosis is characterized by autosomal transmission of amyloidogenic mutated TTR. Val30Met is one of the most common amyloidogenic TTR mutations, showing a worldwide distribution with phenotypic heterogeneity among human populations. Multiple founder mutations for Val30Met foci have been hypothesized and the different origins may explain the phenotypic variability. The aim of our study is to determine the origin of Italian Val30Met and to analyze the genetic relationship of other Val30Met foci.

METHODS

We analyzed the origin of Italian Val30Met through 11 microsatellite markers around the TTR gene in 29 patients and 34 healthy controls.

RESULTS

Our genetic analysis showed an estimated age of origin of 34-36 generations ago for the Italian Val30Met. Comparing Italian Val30Met haplotypes with those from Sweden and Portugal highlights relevant differences that seem to be consistent with an independent origin of Italian Val30Met mutation. This genetic evidence agrees with the disease phenotypic variation in these populations.

DISCUSSION AND CONCLUSIONS

Italian Val30Met mutation should have originated before the Portuguese and Swedish Val30Met ones (which arose through independent mutational events). This indicates a genetic diversity in the surrounding regions of three different Val30Met mutations, supporting the hypothesis that TTR non-coding regions may contribute to phenotypic heterogeneity.

Description of transthyretin S50A, S52P and G47A mutations in familial amyloidosis polyneuropathy

OBJECTIVE

To describe 58 subjects with rare TTR mutations, and to compare the different biomarkers between carriers and patients.

METHODS

TTR gene sequence test was performed in 15 suspicious subjects and in their direct family. All positive subjects undertook prospective evaluations in a period of 49 months.

RESULTS

Of 95 genetic tests performed, 58 (61%) were positive for TTR mutations, Ser50Arg mutation in 38 (65%), Ser52Pro in 15 (26%) and Gly47Ala in 5 (9%). Initial symptoms were neuropathic in 19 (73%), gastrointestinal in 6 (23%) and autonomic in 1 (4%).

CONCLUSIONS

The natural history of Ser50Arg, Ser52Pro and Gly47Ala TTR mutations is similar to the Val30Met mutation described in endemic areas. The small fiber assessments were the initial tests to show abnormalities in asymptomatic subjects.

Phenotypic and genotypic heterogeneity in transthyretin-related cardiac amyloidosis: towards tailoring of therapeutic strategies?

Transthyretin-related hereditary amyloidosis (ATTR) is genotypically/phenotypically heterogeneous. We investigated myocardial involvement in ATTR in a cohort of patients with a wide range of mutations. Clinical/echocardiographic follow-up of 41 consecutive symptomatic ATTR patients from a single referral center was analyzed according to TTR mutation. Diagnosis was based on histology, immunohistochemistry and genotyping. Median follow up was 40 months (range 8-120). Among the 12 different mutations identified, Val30Met was found in 10 patients and Glu89Gln in seven. Compared with Val30Met, Glu89Gln was associated with higher LV mass index, lower left ventricular ejection fraction and shorter E-wave deceleration time. All Glu89Gln carriers had cardiomyopathy, which was more severe (for left ventricular thickness, left ventricular mass and restrictive pathophysiology) than in the six affected Val30Met patients. Glu89Gln was independently associated with higher risk of major cardiovascular events among cardiomyopathy patients. This follow-up study of ATTR patients carrying a wide range of mutations indicates that (1) cardiac involvement is a very important component of phenotypic expression; and (2) genotype is an important source of heterogeneity in myocardial involvement, with Glu89Gln being associated with a severe, heart-driven prognosis. We think that combined heart-liver transplantation could be considered for Glu89Gln carriers with established, morphologically severe cardiomyopathy.

Transthyretin mutation (TTRGly47Ala) associated with familial amyloid polyneuropathy in a French family

A French family in which three individuals had familial amyloid polyneuropathy (FAP) was investigated. The proband presented cardiomyopathy with atrial arrhythmia and then developed axonal polyneuropathy, carpal tunnel syndrome, and sclerodactyly. Nucleotide sequencing of exons 2, 3 and 4 of the transthyretin (TTR) gene revealed heterozygosity for a single base change in the second position of codon 47. This G to C transversion predicts replacement of a glycine by an alanine at position 47 in the mature protein. This mutation (G47A) was previously identified in two different families of Italian origin both of which had FAP and cardiomyopathy. Here we report the first identification of this mutation in a non-Italian family.

Familial amyloid polyneuropathy with genetic anticipation associated to a gly47glu transthyretin variant in an Italian kindred

The most frequent localization of amyloid in transthyretin (TTR) mutations is in the peripheral nerve, causing familial amyloidpolyneuropathy (FAP). It is generally accompanied by involvement of other organs such as the myocardium and kidney. To date, over 70 TTR point mutations have been reported in literature, with different phenotypes depending on the location of the mutation in the TTR gene. This paper deals with a point mutation in exon 2 position 47 of the TTR gene, encoding the substitution of glycine with glutamate. The mutation was found in an Italian family with 5 patients over 3 generations. The phenotype was characterised by peripheral neuropathy and autonomic dysfunction, associated in some patients with cardiomyopathy and renal involvement. The symptoms were very severe and the patients did not survive long, thus suggesting the aggressive nature of the pathological process. Moreover, in the succeeding generations of this family, there was genetic anticipation in the age of onset of the disease.

Transthyretin mutations in hyperthyroxinemia and amyloid diseases

Over 80 different disease-causing mutations in transthyretin (TTR) have been reported. The vast majority are inherited in an autosomal dominant manner and are related to amyloid deposition, affecting predominantly peripheral nerve and/or the heart. A small portion of TTR mutations are apparently non-amyloidogenic. Among these are mutations responsible for hyperthyroxinemia, presenting high affinity for thyroxine (a TTR ligand). Compound heterozygotic individuals for TTR mutants have been described; noteworthy is the clinically protective effect exerted by a non-pathogenic over a pathogenic mutation. Current TTR mutations and their significance are briefly reviewed here.

Mutation and transcription analysis of transthyretin gene in Italian families with hereditary amyloidosis: a putative novel hot spot' in codon 47

Transthyretin gene mutations are associated with autosomal dominant familial amyloidosis. The commonest phenotype in the patients is peripheral neuropathy, but restrictive cardiomyopathy is also a frequent sign. More than 70 different mutations in the gene have been described. Although these mutations are randomly distributed, some hot spots have also been reported notably at position 6, 30, 33, 58, 109, 119 and 122. A few of these codons contain a CpG dinucleotide. We describe an additional 'hot spot' occurring at codon 47, in which we report one novel and two previously described mutations. This codon, however, does not contain a CpG dinucleotide, suggesting that other mechanisms might be responsible for the allelic heterogeneity. All the reported mutations in codon 47 are located in the exon 2 consensus sequence and are potentially involved in splicing. We performed transcription analysis on two livers obtained from transplanted patients carrying the Ala47 mutation. These livers showed a normally spliced message, indicating that this mutation does not affect splicing.

An Italian family with Ala-47 transthyretin mutation associated with cardiomyopathy and polyneuropathy

We describe two Italian first cousins with familial amyloidotic polyneuropathy associated with transthyretin variant consisting of the substitution of alanine for glycine at codon 47 (TTR Ala-47), from a family with a history of cardiac failure. The 40-year-old patient presented with autonomic dysfunction and the 44-year-old cousin with congestive heart failure. Both developed sensorimotor and autonomic polyneuropathy. Since a similar clinical picture has been described in another Italian family, the cardiac involvement must be regarded as a salient and early feature of the TTR Ala-47 mutation.

Homozygosity and heterozygosity for the transthyretin Leu64 mutation: clinical, biochemical and molecular findings

Transthyretin gene point mutations cause hereditary amyloidosis with an autosomal dominant pattern of inheritance. The disease usually manifests itself in heterozygous patients, although a few homozygotes have been reported. We describe two unrelated patients carrying the Leu64 mutation, one of whom presents a homozygous genotype (Family B). Homozygosity was confirmed by sequence analysis, RG-PCR and double one-dimensional electrophoresis of the plasma protein. Although the clinical picture of the homozygous patient of Family B was more severe than that shown by the heterozygous members of Family A, the variability often displayed by FAP patients does not allow any firm conclusion about the role of homozygosity in the seriousness of the disease.

Molecular diagnosis of transthyretin Met30 mutation in an Italian family with familial amyloidotic polyneuropathy

We report the molecular analysis of the transthyretin gene in a large Italian pedigree with familial amyloidotic polyneuropathy and demonstrate the presence of a Met30 mutation. The usefulness of the genetic analysis in the identification of presymptomatic persons and the diagnosis of individuals with partial symptoms is discussed.