Familial amyloidotic polyneuropathy: a new transthyretin position 30 mutation (alanine for valine) in a family of German descent

Trypsin-induced aggregation of transthyretin Valine 30 variants associated with hereditary amyloidosis

Amyloid fibrils of transthyretin (TTR) consist of full-length TTR and C-terminal fragments starting near residue 50. However, the molecular mechanism underlying the production of the C-terminal fragment remains unclear. Here, we investigated trypsin-induced aggregation and urea-induced unfolding of TTR variants associated with hereditary amyloidosis. Trypsin strongly induced aggregation of variants V30G and V30A, in each of which Val30 in the hydrophobic core of the monomer was mutated to less-bulky amino acids. Variants V30L and V30M, in each of which Val30 was mutated to bulky amino acids, also exhibited trypsin-induced aggregation. On the other hand, pathogenic variant I68L as well as the nonpathogenic V30I did not exhibit trypsin-induced aggregation. The V30G variant was extremely unstable compared with the other variants. The V30G mutation caused the formation of a cavity and the rearrangement of Leu55 in the hydrophobic core of the monomer. These results suggest that highly destabilized transthyretin variants are more susceptible to trypsin digestion.

Ocular Manifestations of Familial Transthyretin Amyloidosis

PURPOSE

Among patients with familial amyloidosis, mutation in the transthyretin (TTR) protein is the most common type. Patients with TTR amyloidosis have been noted to have ocular, especially vitreous, involvement. In this report, an analysis of the types and frequency of ocular manifestations in TTR amyloidosis is presented.

DESIGN

Observational case series.

METHODS

Two hundred and sixty-three patients who presented to Mayo Clinic with TTR amyloidosis between January 1, 1970, and November 1, 2014, consented to be included in the Mayo Clinic amyloidosis database maintained by the Department of Hematology. Fifty-four patients had ocular examinations at a mean of 4.25 ± 3.93 months after systemic symptoms.

RESULTS

Of 108 examined eyes in 54 patients with TTR amyloidosis, there were 26 eyes (24%) in 13 patients with ocular involvement. Patients with ocular involvement were more likely to be women than those without ocular involvement (46% vs 15%, respectively, P = .008) and have significantly worse visual acuity (VA) at presentation (logMAR 0.24 [Snellen equivalent 20/30] vs logMAR 0.00 [Snellen equivalent 20/20], P = .017). The ophthalmic findings included vitreous amyloid (26/26, 100%), neurotrophic keratitis (2/26, 8%), glaucoma (5/26, 19%), and tortuous retinal vessels (4/26, 15%). The glaucoma was classified as open-angle (2/26), exfoliative (2/26), and neovascular following central retinal vein occlusion from amyloidosis (1/26). Ten patients underwent vitrectomy for visually significant vitreous amyloidosis, which significantly improved VA from a baseline of logMAR 0.70 (Snellen equivalent 20/100) to logMAR 0.05 (Snellen equivalent ∼20/20), P = .003. Three TTR mutations, Glu89Lys, Gly47Arg, and homozygous Gly6Ser, not previously described, were associated with vitreous amyloid.

CONCLUSION

In this large cohort of patients with TTR amyloidosis, female sex and decreased VA were associated with ocular amyloid. Three mutations that have not been previously reported to have vitreous involvement were described: Glu89Lys, Gly47Arg, and homozygous Gly6Ser.

Clinical diagnosis and typing of systemic amyloidosis in subcutaneous fat aspirates by mass spectrometry-based proteomics

Examination of abdominal subcutaneous fat aspirates is a practical, sensitive and specific method for the diagnosis of systemic amyloidosis. Here we describe the development and implementation of a clinical assay using mass spectrometry-based proteomics to type amyloidosis in subcutaneous fat aspirates. First, we validated the assay comparing amyloid-positive (n=43) and -negative (n=26) subcutaneous fat aspirates. The assay classified amyloidosis with 88% sensitivity and 96% specificity. We then implemented the assay as a clinical test, and analyzed 366 amyloid-positive subcutaneous fat aspirates in a 4-year period as part of routine clinical care. The assay had a sensitivity of 90%, and diverse amyloid types, including immunoglobulin light chain (74%), transthyretin (13%), serum amyloid A (%1), gelsolin (1%), and lysozyme (1%), were identified. Using bioinformatics, we identified a universal amyloid proteome signature, which has high sensitivity and specificity for amyloidosis similar to that of Congo red staining. We curated proteome databases which included variant proteins associated with systemic amyloidosis, and identified clonotypic immunoglobulin variable gene usage in immunoglobulin light chain amyloidosis, and the variant peptides in hereditary transthyretin amyloidosis. In conclusion, mass spectrometry-based proteomic analysis of subcutaneous fat aspirates offers a powerful tool for the diagnosis and typing of systemic amyloidosis. The assay reveals the underlying pathogenesis by identifying variable gene usage in immunoglobulin light chains and the variant peptides in hereditary amyloidosis.

Structure-based analysis of A19D, a variant of transthyretin involved in familial amyloid cardiomyopathy

Transthyretin (TTR) is a tetrameric beta-sheet-rich protein. Its deposits have been implicated in four different amyloid diseases. Although aggregation of the wild-type sequence is responsible for the senile form of the disease, more than one hundred variants have been described thus far, most of which confer a more amyloidogenic character to TTR, mainly because they compromise the stability of the protein in relation to monomer formation, which upon misfolding is intrinsically aggregation-prone. We report the case of a Brazilian patient suffering from a severe cardiomyopathy who carries a rare mutation in exon 2 of the TTR gene that results in an Ala to Asp substitution at position 19 (A19D). The putative pathogenic mechanisms of this variant were analyzed in silico. We constructed a structural model for the A19D tetramer from which its thermodynamic stability was compared to that displayed by the V30M (more amyloidogenic than WT-TTR) and T119M (non-amyloidogenic) variants. The FoldX force field predicted that A19D and V30M are 10.88 and 8.07 kCal/mol less stable than the WT-TTR, while T119M is 5.15 kCal/mol more stable, which is consistent with the aggregation propensities exhibited by these variants. We analyzed the step in which the tetramer-dimer-monomer-unfolded monomer equilibrium might contribute the most to the increased or decreased amyloidogenicity in each variant. Our results suggest that the concentration of four non-native negative charges occur inside thyroxine-binding channels, and the loss of contacts at both the tetrameric and dimeric interfaces would account for an overall decreased stability of the tetramer and the consequent enhanced amyloidogenicity of the A19D variant. As far as we know, this is the first description of a non-V30M mutation in Brazil.

Effects of chronic stress on prefrontal cortex transcriptome in mice displaying different genetic backgrounds

There is increasing evidence that depression derives from the impact of environmental pressure on genetically susceptible individuals. We analyzed the effects of chronic mild stress (CMS) on prefrontal cortex transcriptome of two strains of mice bred for high (HA)and low (LA) swim stress-induced analgesia that differ in basal transcriptomic profiles and depression-like behaviors. We found that CMS affected 96 and 92 genes in HA and LA mice, respectively. Among genes with the same expression pattern in both strains after CMS, we observed robust upregulation of Ttr gene coding transthyretin involved in amyloidosis, seizures, stroke-like episodes, or dementia. Strain-specific HA transcriptome affected by CMS was associated with deregulation of genes involved in insulin secretion (Acvr1c, Nnat, and Pfkm), neuropeptide hormone activity (Nts and Trh), and dopamine receptor mediated signaling pathway (Clic6, Drd1a, and Ppp1r1b). LA transcriptome affected by CMS was associated with genes involved in behavioral response to stimulus (Fcer1g, Rasd2, S100a8, S100a9, Crhr1, Grm5, and Prkcc), immune effector processes (Fcer1g, Mpo, and Igh-VJ558), diacylglycerol binding (Rasgrp1, Dgke, Dgkg, and Prkcc), and long-term depression (Crhr1, Grm5, and Prkcc) and/or coding elements of dendrites (Crmp1, Cntnap4, and Prkcc) and myelin proteins (Gpm6a, Mal, and Mog). The results indicate significant contribution of genetic background to differences in stress response gene expression in the mouse prefrontal cortex.

Identification of a novel TTR Gly67Glu mutant and the first case series of familial transthyretin amyloidosis in Hong Kong Chinese

Familial transthyretin amyloidosis (ATTR), caused by mutant transthyretin deposition, is mainly characterized by peripheral neuropathy, autonomic dysfunction, and cardiomyopathy. There are few reports among the Chinese population. We previously described the TTR mutation (Val30Ala) in the first Hong Kong Chinese family with ATTR. In this study, we report the progress of this family and describe another three unrelated Chinese kinships newly diagnosed with ATTR. The second proband presented mainly with peripheral neuropathy, and genetic analysis of the TTR gene showed alanine-to-serine substitution at amino acid 97. The third proband complained of autonomic dysfunction, and a novel missense mutation of glycine-to-glutamate substitution at amino acid 67 was found. The fourth patient presented with peripheral neuropathy and diastolic cardiomyopathy with the mutation threonine-to-lysine at codon 59. Diagnosis was delayed for more than 2 years. We performed DNA analysis in 46 subjects and detected a total of 21 patients, including the four probands, affected with ATTR, 15 of whom were still at a symptom-free stage at the time of writing. We conclude that ATTR remains largely underdiagnosed in the Chinese population. A high clinical suspicion is crucial for a timely diagnosis and can thus lead to a significant decrease in morbidity and mortality.

Genetics of familial amyloidotic polyneuropathy in a Hong Kong Chinese kindred

Familial amyloidotic polyneuropathy type 1 (FAP1, MIM176300) is an autosomal dominant disease caused by mutations in the transthyretin (TTR) gene. An extended Chinese kindred of FAP1 was first reported in Hong Kong in 1989, three of the four histologically proven subjects have deceased. TTR gene mutations were not studied then. A DNA-based diagnosis was performed on FAP1 by restriction analysis and direct DNA sequencing was carried out on a symptomatic member of this family who had undergone a liver transplantation. It showed a substitution of thymine by cytosine in the second base of codon 30 in exon 2 of the TTR gene, with the creation of a novel HhaI restriction endonuclease site. Valine is substituted by alanine (V30A) in the mutant TTR. Both restriction analysis and direct sequencing revealed the same mutation in one of the two asymptomatic siblings. This mutation was first reported in a FAP1 family of German descent.

A new transthyretin variant Leu55Gln in a patient with systemic amyloidosis

We report a 40-year-old woman with a new transthyretin (TTR) variant, glutamine replacing leucine at residue 55 (Leu55Gln), who showed progressive somatic and autonomic neuropathy, glaucoma, and vitreous opacities. Symptoms of glaucoma appeared prior to the onset of the neuropathy. Sural nerve biopsy revealed amyloid deposition in the endoneurium, and immunohistochemical analysis was positive with anti-human TTR. Sequencing of the patient's DNA revealed the substitution of A for T at the second position of codon 55 of the TTR gene indicating an amino acid change from leucine to glutamine.

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.

Familial amyloid polyneuropathy related to transthyretin mutation Val30 to Leu in a Japanese family

A rare variant transthyretin that has a leucine-for-valine substitution at position 30 was reported in a sporadic case of type 1 familial amyloid polyneuropathy (FAP). We found the same substitution in members of a Japanese family with FAP. Three individuals in this family had a guanine-to-cytosine mutation at the first base of codon 30 in exon 2. This family shows a direct link between a valine-to-leucine substitution at position 30 and type 1 FAP.

Endoscopic and pathological manifestations of the gastrointestinal tract in familial amyloidotic polyneuropathy type I (Met30)

OBJECTIVES

To evaluate the characteristic changes in the gastrointestinal tract in familial amyloidotic polyneuropathy (FAP) (Met30), both fibre gastroscopy and colonoscopy studies were performed in FAP (Met30) patients. Microscopic changes were also examined in autopsied and biopsied materials from patients with FAP, and compared with data from autopsied samples from patients with AL amyloidosis, and secondary amyloidosis patients.

DESIGN

Endoscopic and histopathological study.

SETTING

Kumamoto University Hospital, Kumamoto, Japan.

SUBJECTS

Nine patients with FAP (Met30) underwent fibre gastroscopy and colonoscopy. Six autopsied and 23 biopsied gastrointestinal samples from FAP patients, four from autopsied amyloidosis (including two myeloma associated form), and two from autopsied secondary amyloidosis patients were examined for histopathological study.

MAIN OUTCOME MEASURES

Fibre gastroscopy and colonoscopy were employed for macroscopic study. Congo red and H-E staining were performed for histopathological study. Macroscopic changes in the gastrointestinal tract and microscopic differences in the amyloid distribution pattern were compared between the different types of amyloidosis.

RESULTS

Fibre gastroscopy and colonoscopy for nine FAP patients revealed that four showed a fine granular appearance in the duodenum, three showed lack of lustre, and two showed mucosal friability in the gastrointestinal tract; however, no macroscopic abnormality was observed in four other FAP patients. Histopathological examination of tissue from FAP patients revealed that, although a small amount of amyloid was recognized in the submucosa perivascular layer, a significant amount of amyloid was seen in and around the nerves of the gastrointestinal tract, but very little in Auerbach's nerve plexus. In total, the amount of deposited amyloid in the tissues was small compared with that in other types of systemic amyloidosis, such as AL and secondary amyloidosis.

CONCLUSION

These results suggest that the major reason why FAP patients show such severe gastrointestinal symptoms, compared with other types of systemic amyloidosis, may be because of the deposition of a significant amount of amyloid in the nerves in the gastrointestinal tract.

Transthyretin amyloidosis: a new mutation associated with dementia

Familial transthyretin (TTR) amyloidosis commonly presents with peripheral neuropathy and involvement of visceral organs. In contrast, signs of central nervous system (CNS) involvement are exceptional. We report that members of a kindred affected by a slowly progressive dementia, seizures, ataxia, hemiparesis, and decreased vision without neuropathy have TTR amyloid deposits in the leptomeninges, the brain parenchyma, and the eye. This condition, previously labeled oculoleptomeningeal amyloidosis, is linked to a mutation at codon 30 of TTR gene, resulting in the substitution of valine with glycine in this family, TTR amyloid deposits were present in the leptomeninges, especially the leptomeningeal vessels, and in the subependymal regions of the ventricular system where they disrupted the ependymal lining and resulted in amyloid-glial formations protruding into and narrowing the ventricular system. Hydrocephalus and atrophy and infarction of cerebral and cerebellar cortexes were also present. Review of the literature shows that amyloid deposition in the leptomeninges is not uncommon in TTR amyloidoses clinically characterized by peripheral neuropathy and lack of CNS signs. The present kindred, which presented exclusively with signs of CNS involvement, expands the phenotype of TTR amyloidosis and raises questions concerning the mechanisms determining phenotypic expression in TTR familial amyloidosis.

The evolution of gene expression, structure and function of transthyretin

Thyroxine, the most abundant thyroid hormone in blood, partitions into lipid membranes. In a network-like system, thyroxine-binding plasma proteins counteract this partitioning and establish intravascular, protein-bound thyroxine pools. These are far larger than the free thyroxine pools. In larger eutherians, proteins specifically binding thyroxine are albumin, transthyretin, and thyroxine-binding globulin. Some binding of thyroxine can also occur to lipoproteins. During evolution, transthyretin synthesis first appeared in the choroid plexus of the stem reptiles, about 300 million years ago. Transthretin synthesis in the liver evolved much later, independently, in birds, eutherians and some marsupial species. Analysis of 57 human transthyretin variants suggests that most mutations in transthyretin are not compatible with its normal metabolism and lead to its deposition as amyloid. Analysis of transthyretin or its gene in 20 different species shows that evolutionary changes of transthyretin predominantly occurred near the N-termini. A change in RNA splicing between exon 1 and exon 2 led to a decrease in hydrophobicity and length of the N-termini. It is proposed that the selection pressure producing these changes was the need for a more effective prevention of thyroxine partitioning into lipids. Lipid pools increased during evolution with the increases in relative sizes of brains and internal organs and changes in lipid composition of membranes in ectothermic and endothermic species.

Transthyretin mutations in health and disease

To date, over 40 different mutations in transthyretin (TTR) have been associated with amyloid deposition. The major unresolved problem is the correlation between the clinical heterogeneity and the genetic heterogeneity. For instance, whereas some mutations produce neuropathy and some give rise to cardiomyopathy, others produce vitreous opacities, the vast majority being neuropathic. Moreover, some mutations are not amyloidogenic but are responsible to hyperthyroxinemias (by virtue of the protein function in thyroid transport), whereas others are apparently nonpathogenic. The study of TTR variants is very important to the understanding of the amyloid formation process and to establish a relationship between the structure and function of the molecule. The results of current TTR mutation screening programs and their characterization are summarized.

Unifying features of systemic and cerebral amyloidosis

Amyloidosis is a generic term for a group of clinically and biochemically diverse diseases that are characterized by the deposition of an insoluble fibrillar protein in the extracellular space. Over 16 biochemically distinct amyloids are known. Despite this diversity, all amyloids have a particular ultrastructural and tinctorial appearance, a beta-pleated sheet structure, and are codeposited with a group of amyloid-associated proteins. The most common amyloidosis is Alzheimer's disease (AD), where A beta is the main component of the amyloid. Recently it has been found that A beta exists as a normal soluble protein (sA beta) in biological fluids. This links AD more closely to some of the systemic amyloidoses, where the amyloid precursor is found in the circulation normally. Numerous mutations have been found in the A beta precursor (beta PP) gene, associated with familial AD. Many mutations are also found in some of the hereditary systemic amyloidoses. For example, over 40 mutations in the transthyretin (TTR) gene are associated with amyloid. However, both A beta and TTR related amyloid deposition can occur with no mutation. The pathogenesis of amyloid is complex, and appears to be associated with genetic and environmental risk factors that can be similar in the systemic and cerebral amyloidoses.

Familial amyloidotic polyneuropathy with late-onset and well-preserved autonomic function: a Japanese kindred with novel mutant transthyretin (Ala97 to Gly)

We report the characteristics of one patient and two asymptomatic carriers from a Japanese family with familial amyloidotic polyneuropathy (FAP). The clinical features were somatic sensory and motor neuropathy with well-preserved autonomic function and late onset with slow insidious progression. These symptoms and signs are different from those of type 1 FAP. There were massive amyloid deposits with transthyretin (TTR) in the myocardium and the sural nerve. DNA sequencing of the TTR gene and amino acid sequence analysis of serum TTR revealed a new mutation in which Gly97 was substituted for Ala. We suggest that patients with somatic sensory and motor neuropathy of unknown origin without apparent autonomic dysfunction should be further studied for TTR mutation.

Immunoassay for transthyretin variants associated with amyloid neuropathy

An anti-transthyretin (TTR) mouse monoclonal antibody (88.6.FD6) of IgG1 subclass, obtained using as immunogen TTR from the serum of a patient with familial amyloidotic polyneuropathy, was found to bind to sera from carriers of several amyloidogenic TTR variants associated with peripheral neuropathy, but not to normal sera or sera from carriers of non-pathogenic or cardiomyopathic variants, in an ELISA performed under special conditions. Further characterization suggests that it recognizes an epitope near the N-terminal side of the TTR monomer. We propose that this epitope is exposed in amyloid and could be implicated in fibril deposition in the peripheral nervous system.

A novel transthyretin mutation at position 30 (Leu for Val) associated with familial amyloidotic polyneuropathy

A novel transthyretin (TTR) mutation associated with familial amyloidotic polyneuropathy was detected in a Japanese patient. Single-strand conformation polymorphism analysis and sequence analysis of polymerase chain reaction (PCR)-amplified exons of the patient's TTR gene revealed a point mutation resulting in a substitution of leucine for valine at position 30. As the mutation creates a Cfr13I site, it was confirmed by PCR and restriction analysis. Our finding indicates the importance of position 30 in TTR-derived amyloid fibril formation.

Identification of a novel transthyretin variant (Val30----Leu) associated with familial amyloidotic polyneuropathy

A novel variant transthyretin which contains a leucine-for-valine substitution at position 30 was isolated and identified in the serum of a patient with familial amyloidotic polyneuropathy (FAP). The amino acid substitution was proven to result from a guanine-to-cytosine change at the first base of codon 30 located in exon 2 in the mutated transthyretin gene by restriction fragment length analysis on the amplified transthyretin gene using Cfr13 I. The study indicates that the point mutation of the transthyretin gene is a cause of the disorder.

Two transthyretin variants (TTR Ala-49 and TTR Gln-89) in two Sicilian kindreds with hereditary amyloidosis

We report the biochemical and molecular characterization of two new transthyretin (TTR) variants in two Italian families with hereditary amyloidosis. Both families presented neuropathy and cardiomyopathy but they differ in other clinical features. These TTR variants were previously detected by isoelectric focusing (IEF); one is a neutral TTR variant and the other one is basic. By protein and DNA analysis the neutral variant was found to have a substitution of an alanine for a threonine residue at position 49 (TTR Ala-49) of the polypeptide chain. The basic variant has a glutamine residue replacing glutamate at position 89 (TTR Gln-89).