Biochemical characterization of vitreous and cardiac amyloid in Ile84Ser transthyretin amyloidosis

The Role of Proteolysis in Amyloidosis

Amyloidoses are a group of diseases associated with deposits of amyloid fibrils in different tissues. So far, 36 different types of amyloidosis are known, each due to the misfolding and accumulation of a specific protein. Amyloid deposits can be found in several organs, including the heart, brain, kidneys, and spleen, and can affect single or multiple organs. Generally, amyloid-forming proteins become prone to aggregate due to genetic mutations, acquired environmental factors, excessive concentration, or post-translational modifications. Interestingly, amyloid aggregates are often composed of proteolytic fragments, derived from the degradation of precursor proteins by yet unidentified proteases, which display higher amyloidogenic tendency compared to precursor proteins, thus representing an important mechanism in the onset of amyloid-based diseases. In the present review, we summarize the current knowledge on the proteolytic susceptibility of three of the main human amyloidogenic proteins, i.e., transthyretin, β-amyloid precursor protein, and α-synuclein, in the onset of amyloidosis. We also highlight the role that proteolytic enzymes can play in the crosstalk between intestinal inflammation and amyloid-based diseases.

The Journey of Human Transthyretin: Synthesis, Structure Stability, and Catabolism

Transthyretin (TTR) is a homotetrameric protein mainly synthesised by the liver and the choroid plexus whose function is to carry the thyroid hormone thyroxine and the retinol-binding protein bound to retinol in plasma and cerebrospinal fluid. When the stability of the tetrameric structure is lost, it breaks down, paving the way for the aggregation of TTR monomers into insoluble fibrils leading to transthyretin (ATTR) amyloidosis, a progressive disorder mainly affecting the heart and nervous system. Several TTR gene mutations have been characterised as destabilisers of TTR structure and are associated with hereditary forms of ATTR amyloidosis. The reason why also the wild-type TTR is intrinsically amyloidogenic in some subjects is largely unknown. The aim of the review is to give an overview of the TTR biological life cycle which is largely unknown. For this purpose, the current knowledge on TTR physiological metabolism, from its synthesis to its catabolism, is described. Furthermore, a large section of the review is dedicated to examining in depth the role of mutations and physiological ligands on the stability of TTR tetramers.

Structural basis for transthyretin amyloid formation in vitreous body of the eye

Amyloid transthyretin (ATTR) amyloidosis is characterized by the abnormal accumulation of ATTR fibrils in multiple organs. However, the structure of ATTR fibrils from the eye is poorly understood. Here, we used cryo-EM to structurally characterize vitreous body ATTR fibrils. These structures were distinct from previously characterized heart fibrils, even though both have the same mutation and type A pathology. Differences were observed at several structural levels: in both the number and arrangement of protofilaments, and the conformation of the protein fibril in each layer of protofilaments. Thus, our results show that ATTR protein structure and its assembly into protofilaments in the type A fibrils can vary between patients carrying the same mutation. By analyzing and matching the interfaces between the amino acids in the ATTR fibril with those in the natively folded TTR, we are able to propose a mechanism for the structural conversion of TTR into a fibrillar form.

In Vitro and In Vivo Effects of SerpinA1 on the Modulation of Transthyretin Proteolysis

Transthyretin (TTR) proteolysis has been recognized as a complementary mechanism contributing to transthyretin-related amyloidosis (ATTR amyloidosis). Accordingly, amyloid deposits can be composed mainly of full-length TTR or contain a mixture of both cleaved and full-length TTR, particularly in the heart. The fragmentation pattern at Lys48 suggests the involvement of a serine protease, such as plasmin. The most common TTR variant, TTR V30M, is susceptible to plasmin-mediated proteolysis, and the presence of TTR fragments facilitates TTR amyloidogenesis. Recent studies revealed that the serine protease inhibitor, SerpinA1, was differentially expressed in hepatocyte-like cells (HLCs) from ATTR patients. In this work, we evaluated the effects of SerpinA1 on in vitro and in vivo modulation of TTR V30M proteolysis, aggregation, and deposition. We found that plasmin-mediated TTR proteolysis and aggregation are partially inhibited by SerpinA1. Furthermore, in vivo downregulation of SerpinA1 increased TTR levels in mice plasma and deposition in the cardiac tissue of older animals. The presence of TTR fragments was observed in the heart of young and old mice but not in other tissues following SerpinA1 knockdown. Increased proteolytic activity, particularly plasmin activity, was detected in mice plasmas. Overall, our results indicate that SerpinA1 modulates TTR proteolysis and aggregation in vitro and in vivo.

Modulation of the Mechanisms Driving Transthyretin Amyloidosis

Transthyretin (TTR) amyloidoses are systemic diseases associated with TTR aggregation and extracellular deposition in tissues as amyloid. The most frequent and severe forms of the disease are hereditary and associated with amino acid substitutions in the protein due to single point mutations in the TTR gene (ATTRv amyloidosis). However, the wild type TTR (TTR wt) has an intrinsic amyloidogenic potential that, in particular altered physiologic conditions and aging, leads to TTR aggregation in people over 80 years old being responsible for the non-hereditary ATTRwt amyloidosis. In normal physiologic conditions TTR wt occurs as a tetramer of identical subunits forming a central hydrophobic channel where small molecules can bind as is the case of the natural ligand thyroxine (T₄). However, the TTR amyloidogenic variants present decreased stability, and in particular conditions, dissociate into partially misfolded monomers that aggregate and polymerize as amyloid fibrils. Therefore, therapeutic strategies for these amyloidoses may target different steps in the disease process such as decrease of variant TTR (TTRv) in plasma, stabilization of TTR, inhibition of TTR aggregation and polymerization or disruption of the preformed fibrils. While strategies aiming decrease of the mutated TTR involve mainly genetic approaches, either by liver transplant or the more recent technologies using specific oligonucleotides or silencing RNA, the other steps of the amyloidogenic cascade might be impaired by pharmacologic compounds, namely, TTR stabilizers, inhibitors of aggregation and amyloid disruptors. Modulation of different steps involved in the mechanism of ATTR amyloidosis and compounds proposed as pharmacologic agents to treat TTR amyloidosis will be reviewed and discussed.

TTRMDB: A database for structural and functional analysis on the impact of SNPs over transthyretin (TTR) using bioinformatic tools

Hereditary Transthyretin-associated amyloidosis (ATTR) is an autosomal dominant protein-folding disorder with adult-onset caused by mutation of transthyretin (TTR). TTR is characterized by extracellular deposition of amyloid, leading to loss of autonomy and finally, death. More than 100 distinct mutations in TTR gene have been reported from variable age of onset, clinical expression and penetrance data. Besides, the cure for the disease remains still obscure. Further, the prioritizing of mutations concerning the characteristic features governing the stability and pathogenicity of TTR mutant proteins remains unanswered, to date and thus, a complex state of study for researchers. Herein, we provide a full report encompassing the effects of every reported mutant model of TTR protein about the stability, functionality and pathogenicity using various computational tools. In addition, the results obtained from our study were used to create TTRMDB (Transthyretin mutant database), which could be easy access to researchers at http://vit.ac.in/ttrmdb.

Transthyretin Glu54Leu - an unknown mutation within the Swedish population associated with amyloid cardiomyopathy and a unique fibril type

For the first time, we report of a Swedish family of five individuals with a TTR Glu54Leu (p. Glu74Leu) mutation in the transthyretin gene. This mutation has been previously described a few times in the literature, but no phenotypic or clinical description has been done before. The most common mutation in the Swedish population is TTRVal30Met and is mostly found in the Northern part of Sweden. Interestingly, the TTRGlu54Leu mutation was found in the same endemic area. The main phenotype of the TTR Glu54Leu patients is severe cardiomyopathy, which resulted in heart transplantation for the index person. As previously seen for ATTR amyloidosis patients with mainly cardiomyopathy, the amyloid fibrils consisted of a mixture of full-length and fragmented TTR species. However, western blot analyses detected a previously unrecognized band, indicating that these patients may have a third, so far unrecognized, fibril composition type that is distinct from the usual type A band pattern.

Vitreous amyloidosis with autonomic neuropathy of the digestive tract associated with a novel transthyretin p.Gly87Arg variant in a Bangladeshi patient: a case report

BACKGROUND

Hereditary transthyretin amyloidosis is an autosomal dominant inherited disorder, first described in families with sensorimotor and autonomic neuropathy. Since its first description, more than 120 amyloidogenic transthyretin mutations have been reported with various geographic distributions and associated with a wide range of phenotypes involving the peripheral nerve, the heart, the gastrointestinal tract, the eyes, the central nervous system, or the kidneys. In some cases of transthyretin amyloidosis, the first clinical manifestation is vitreous opacity.

CASE PRESENTATION

A 46-year-old Bangladeshi woman presented with vitreous amyloidosis and progressive autonomic neuropathy of the digestive tract as initial clinical manifestations, with no clinical evidence of cardiac, renal, central nervous system, or peripheral nerve dysfunction. A novel transthyretin mutation, p.Gly87Arg, was identified in the heterozygous state in this proband of Bangladeshi origin. Histological examination of accessory salivary glands and gastric biopsies revealed Congo-red-positive deposits. Laser microdissection of salivary gland Congo-red deposits and tandem mass spectrometry-based proteomic analysis identified the mutated transthyretin peptide containing the arginine residue at position 87 of the mature protein.

CONCLUSIONS

Vitreous amyloidosis should be considered a differential diagnosis of uveitis, in particular transthyretin amyloidosis. Proteomics data from our case, consistent with the genetic findings, highly suggests that this new p.Gly87Arg variant is amyloidogenic. Here, we described the second case of transthyretin amyloidosis reported in a Bangladeshi patient.

Marked biochemical difference in amyloid proportion between intra- and extraocular tissues in a liver-transplanted patient with hereditary ATTR amyloidosis

In order to elucidate the pathomechanism of ocular amyloid formation in a liver-transplanted patient with hereditary ATTR amyloidosis, we investigated detailed biochemical features of ocular amyloid. The patient was a 49-year-old woman with V30M transthyretin (TTR) variant (p.TTRV50M), who underwent ophthalmectomy due to corneal rupture 10 years after liver transplantation (LT). The amyloid was selectively isolated from several portions in intra- and extraocular tissues using a laser microdissection (LMD) system and analyzed by liquid chromatography-tandem mass spectrometry to determine the composition percentage of wild-type and variant TTR in the isolated amyloid. Biochemical analysis revealed that the amyloid consisted mainly of variant TTR in intraocular tissues with a percentage > 80%. On the contrary in the extraocular muscles, wild-type TTR was the main component of the amyloid with a percentage of ∼70%. Our data indicate that intraocular amyloid formation strongly depends on locally synthesized variant TTR and the contribution of wild-type TTR to amyloid formation is quite limited.

Hereditary systemic immunoglobulin light-chain amyloidosis

Protein and DNA analyses reveal that mutation in the immunoglobulin κ light-chain constant region gene may cause hereditary amyloidosis. Sequencing of immunoglobulin light-chain constant region genes is indicated for patients with AL amyloidosis and no evidence of a plasma cell dyscrasia.

A genealogical and clinical study of the phenotypical variation within the Swedish transthyretin His88Arg (p. His108Arg) amyloidosis family

In 2005 we reported the first case of transthyretin His88Arg (p. His108Arg) amyloidosis, a mutation characterised by cardiomyopathy. Six additional gene carriers of whom five have clinical symptoms of disease have now been identified in Sweden, and we have been able to identify a possible founder and to characterise the Swedish phenotype of the transthyretin (TTR) His88Arg mutation. Genealogical studies of church records were used to identify the individuals with the disease and their families. Routine clinical investigations of neurological and heart manifestation of the disease were utilised. We found that genealogically all seven individuals were related and originated from the same region in Sweden. Amyloid deposits were demonstrated in biopsies and the TTR His88Arg mutation was identified in all patients. Patients had a late onset disease (≥ 50 years of age) and all exhibited a severe amyloid cardiomyopathy. A pronounced peripheral axonal neuropathy was with certainty demonstrated in one patient only, who also was operated for a magnetic resonance confirmed spinal stenosis, however, without any effect on his neurological symptoms. Five of the patients had carpal tunnel syndrome. The first reported case is now deceased from cardiac failure. One patient has had a sequential heart and liver transplantation. One gene carrier had no symptoms or findings of disease on latest evaluation at the age of 44.

IN CONCLUSION

the Swedish TTRHis88Arg patients all have a common Swedish founder. Cardiomyopathy with heart failure, as well as carpal tunnel syndrome and spinal stenosis were early signs of disease; but peripheral neuropathy was present in one patient before symptoms of cardiomyopathy so the phenotypical presentation of this mutation is variable.

Transthyretin cardiac amyloidosis: pathogenesis, treatments, and emerging role in heart failure with preserved ejection fraction

Transthyretin (TTR) amyloidosis causes heart failure from cardiac deposition of TTR amyloid fibrils, the by-product of TTR homotetramer disassembly. Wild-type (WT) TTR deposition leads to senile amyloidosis, predominantly manifesting with cardiomyopathy. Missense mutations in the TTR gene result in familial TTR amyloidosis. Certain mutations are more likely to affect the heart, while others cause more neurologic involvement. Extracellular fibril deposition triggers intracellular stress response, upregulation of the inflammatory cascades, apoptosis, and organ dysfunction. Recent studies suggest that TTR cardiac amyloid may be a significant contributor to the pathogenesis of heart failure with preserved ejection fraction (HFpEF). Summarized in this review are the molecular pathways underlying the cellular toxicity of TTR amyloid fibrils and the emerging therapies aimed at TTR tetramer stabilization, abrogation of TTR synthesis in the liver, or inhibition of amyloidogenesis.

Mass spectrometry analysis reveals non-mutated apolipoprotein A1 lumbosacral radiculoplexus amyloidoma

INTRODUCTION

In rare instances, amyloidosis presents as a focal, macroscopic lesion involving peripheral neural tissues (amyloidoma). In all known reported cases, peripheral nerve amyloidomas have had immunoglobulin light-chain fibril composition and occurred in the context of paraproteinemia.

METHODS

A 46-year-old man presented with progressive insidious-onset right lumbosacral radiculoplexus neuropathy without paraproteinemia. MRI-targeted fascicular nerve biopsy was performed on an enlarged sciatic nerve after earlier distal fibular nerve biopsy was nondiagnostic. Laser dissected mass spectroscopy of the discovered amyloid protein was performed after immunohistochemistry failed to identify the specific amyloid protein. Complete gene sequencing of apolipoprotein A1 (ApoA1) was performed.

RESULTS

Only wild-type ApoA1 amyloid was found in the congophilic component in the nerve.

CONCLUSIONS

This case highlights the utility of MRI-guided fascicular nerve biopsy combined with laser-dissected mass spectrometric analysis. Importantly, the case expands the known causes of amyloidomas to include wild-type ApoA1.

Pathogenesis of transthyretin amyloidosis

Current dogma for transthyretin (TTR) pathogenesis is that mutations in TTR alter its structure such that the tetramer becomes unstable and prone to release of monomer which then becomes the putative building block of the fibril. This hypothesis is supported by thermodynamic data showing decreased stability of mutant TTR tetrameric proteins and accelerated fibril formation under acidic conditions in vitro. There are, however, a number of questions that are not readily answered by this simplistic model of a very complex disease. Worrisome questions still to be answered include: 1. If the monomer is the precursor of the fibril, why do fibril deposits contain large amounts of wild-type TTR and not just variant? 2. If destabilized tetramers can form fibrils in vitro, why do we consistently find partial proteolysis of fibril subunit proteins? If enzymatic proteolysis is a required step in fibril formation, are the findings of in vitro fibril formation relevant to the true pathogenesis? 3. With some TTR mutations (e.g. 122ΔVal), it would appear that very little TTR is present in the blood (probably due to degradation prior to hepatic secretion). Enough mutant TTR circulates to the heart and nerves to cause pathology but, if the mutant only serves to initiate fibril deposition, why are not the deposits mainly wild-type TTR?4. Since mutated TTR is present from birth, why is TTR amyloidosis of such delayed onset? What is the role of aging factors?5. Do the variations in biochemical analyses of heart and nerve versus choroid and leptomeningeal fibrils tell us something about pathogenesis? These are questions we need to address. Do not expect quick and easy answers. Hopefully, they will generate thought and discussion.

Variation in amount of wild-type transthyretin in different fibril and tissue types in ATTR amyloidosis

Familial transthyretin (TTR) amyloidosis is caused by a mutation in the TTR gene, although wild-type (wt) TTR is also incorporated into the amyloid fibrils. Liver transplantation (LT) is the prevailing treatment of the disease and is performed in order to eliminate the mutant TTR from plasma. The outcome of the procedure is varied; especially problematic is a progressive cardiomyopathy seen in some patients, presumably caused by continued incorporation of wtTTR. What determines the discrepancy in outcome is not clear. We have previously shown that two structurally distinct amyloid fibrils (with or without fragmented ATTR) are found among ATTRV30M patients. In this study, we investigated the proportion of wtATTR in cardiac and adipose amyloid from patients having either fibril type. It was found that cardiac amyloid more easily incorporates wtTTR than adipose amyloid, offering a potential explanation for the vulnerability of cardiac tissue for continued amyloidosis after LT. In cardiac tissue, fibrils with fragmented ATTR contained a higher wt proportion than fibrils without, suggesting that continued incorporation of wtTTR after LT, perhaps, can take place more easily in these patients. In adipose tissue, a rapid increase in wt proportion after LT indicates that a rather fast turnover of the deposits must occur. A difference in wt proportion between the fibril types was seen post-LT but not pre-LT, possibly caused by differences in turnover rate. Conclusively, this study further establishes the basic dissimilarities between the two fibril types and demonstrates that their role in LT outcome needs to be further investigated.

Progression of transthyretin amyloid neuropathy after liver transplantation

OBJECTIVE

To biochemically characterize peripheral nerve amyloid in subjects with transthyretin (TTR) amyloidosis and assess effect of orthotopic liver transplantation (OLT) on progression of neuropathy.

METHODS

Amyloid fibrils were isolated from peripheral nerve tissues of 6 patients with TTR amyloidosis who were heterozygous for an amyloid-associated TTR mutation. Ratio of variant to wild-type TTR in the fibrils was determined by amino acid sequencing of tryptic peptides containing either the variant amino acid residue or the corresponding normal amino acid.

RESULTS

Amyloid fibrils from 3 subjects who died without having received a liver transplant were composed of 60%-65% variant TTR and 35%-40% wild-type. Amyloid fibrils from a subject who died 5 years after liver transplantation contained 25% variant and 75% wild-type TTR.

CONCLUSION

Ratios of variant to wild-type TTR in amyloid patients heterozygous for an amyloid-associated TTR mutation are similar to published ratios for amyloid fibrils in cardiac tissue. Survival after liver transplantation for TTR amyloidosis may be associated with progression of neuropathy due to continued deposition of amyloid derived from wild-type TTR.

A case of familial amyloid polyneuropathy due to Phe33Val TTR with vitreous involvement as the initial manifestation

We report a 61-year-old Japanese woman with transthyretin (TTR) Val33-related familial amyloid polyneuropathy (FAP). She presented with late-onset, vitreous involvement as the initial manifestation, slow development of polyneuropathy, cardiomyopathy, and severe autonomic failure without carpal tunnel syndrome. Liver transplantation was performed and her postoperative course was stable. Taken together with previous reports, vitreous opacities seem to be common to Val33 FAP. Vitreous amyloidosis is usually seen in combination with the involvement of other visceral organs. The findings in the present case emphasize that vitreous opacities could be the first manifestation of FAP.

Genetics and molecular pathogenesis of sporadic and hereditary cerebral amyloid angiopathies

In cerebral amyloid angiopathy (CAA), amyloid fibrils deposit in walls of arteries, arterioles and less frequently in veins and capillaries of the central nervous system, often resulting in secondary degenerative vascular changes. Although the amyloid-beta peptide is by far the commonest amyloid subunit implicated in sporadic and rarely in hereditary forms of CAA, a number of other proteins may also be involved in rare familial diseases in which CAA is also a characteristic morphological feature. These latter proteins include the ABri and ADan subunits in familial British dementia and familial Danish dementia, respectively, which are also known under the umbrella term BRI2 gene-related dementias, variant cystatin C in hereditary cerebral haemorrhage with amyloidosis of Icelandic-type, variant transthyretins in meningo-vascular amyloidosis, disease-associated prion protein (PrP(Sc)) in hereditary prion disease with premature stop codon mutations and mutated gelsolin (AGel) in familial amyloidosis of Finnish type. In this review, the characteristic morphological features of the different CAAs is described and the implication of the biochemical, genetic and transgenic animal data for the pathogenesis of CAA is discussed.

Amyloid fibril composition is related to the phenotype of hereditary transthyretin V30M amyloidosis

Swedish familial systemic amyloidosis with polyneuropathy (FAP) depends on a mutation leading to a methionine-for-valine substitution in transthyretin. The disease appears with different clinical manifestations, including age of onset and involvement of the heart. Liver transplantation is currently the only curative treatment, but progressive cardiomyopathy may occur post-transplant. Two amyloid deposition patterns have previously been described in the heart. In one, the amyloid consists partially of transthyretin fragments and is weakly stainable by Congo red, while in the other, only full-length molecules are found and the fibrils have a strong affinity for Congo red. The present study aimed to see whether these morphological and biochemical variations have clinical implications. Subcutaneous adipose tissue biopsies were taken from 33 patients with Val30Met FAP and examined by microscopy, electrophoresis and western blot. Clinical data included age, sex, duration of disease and echocardiographic determination of the interventricular septum (IVS) thickness. It was found that fibrils composed of only full-length transthyretin were associated with early age of onset (44.8 +/- 12.9 years), no clinical cardiac involvement and a strong affinity for Congo red. In contrast, presence of transthyretin fragments in the amyloid was associated with late age of onset (67.3 +/- 7.0 years), signs of cardiac involvement and weak Congo red staining. For each individual, the same molecular type of amyloid was found in different organs. This is the first report showing that variations in clinical appearance of familial ATTR amyloidosis are associated with specific structural differences in the amyloid fibrils, and therefore may have a molecular cause. The molecular type of amyloid can be determined from a subcutaneous fat tissue biopsy.

Marked regression of abdominal fat amyloid in patients with familial amyloid polyneuropathy during long-term follow-up after liver transplantation

To elucidate whether the amount of tissue-deposited amyloid in familial amyloid polyneuropathy (FAP) patients decreases or increases over the long-term course after liver transplantation (LT), we examined changes in histopathological and biochemical characteristics of abdominal fat amyloid in the transplanted patients with a postoperative history of more than 10 years. Using a series of aspirated abdominal fat tissues from 6 FAP patients with transthyretin (TTR) Val30Met variant, the severity of amyloid deposits was examined and the composition ratio of wild type-to-variant TTR in fat amyloid was assayed by liquid chromatography-ion trap mass spectrometry (LC-MS/MS). Histopathological examination of abdominal fat tissues demonstrated a significant decrease or disappearance of amyloid deposits in all 6 patients. On LC-MS/MS analysis, the contribution of wild-type TTR to the composition ratio in amyloid fibrils was markedly increased in all patients after LT. This is the first report showing pathological evidence that deposited amyloid in FAP patients with long posttransplantation courses can gradually regress or disappear.

Progression of cardiac amyloid deposition in hereditary transthyretin amyloidosis patients after liver transplantation

It has been hypothesized that transthyretin (TTR) amyloidosis may progress after orthotopic liver transplantation (OLT) as a result of continued amyloid fibril synthesis and deposition from normal TTR. To test this hypothesis amyloid fibrils were isolated from cardiac tissues of three patients who died 1(1/2) to 5(1/2) years after OLT: two with Val30Met and one with Thr60Ala TTR. The ratio of variant to normal TTR in each case was determined and compared with the ratio of variant to normal in cardiac tissues from seven patients who died with TTR amyloidosis but who had not had liver transplantation. Tissues from patients with TTR amyloidosis without OLT included three with Val30Met, two with Thr60Ala, one with deltaVal122, and one with Val122Ile. All tissues from patients without OLT had greater amounts of variant TTR than normal TTR except for the Val122Ile in which the ratio was 50:50. The overall median variant to normal ratio was 60:40 with a range of 50-70% variant. In contrast, the mean percentage of variant TTR in the three tissues from patients after OLT was 25% (range 20-35). These data are consistent with the continued deposition of normal TTR in cardiac tissue after liver transplantation.

The molecular biology and clinical features of amyloid neuropathy

Neuropathy is often a major manifestation of systemic amyloidosis. It is most frequently seen in patients with hereditary transthyretin (TTR) amyloidosis, but is also present in 20% of patients with systemic immunoglobulin light chain (primary) amyloidosis. Familial amyloid polyneuropathy (FAP) is the most common form of inherited amyloidotic polyneuropathy, with clinical and electrophysiologic findings similar to neuropathies with differing etiologies (e.g., diabetes mellitus). Hereditary amyloidosis is an adult-onset autosomal-dominant disease with varying degrees of penetrance. It is caused by specific gene mutations, but demonstration that a patient has one such mutation does not confirm the diagnosis of amyloidosis. Diagnosis requires tissue biopsy with demonstration of amyloid deposits either by special histochemical stains or electron microscopy. Transthyretin amyloidosis is treated by liver transplantation, which eliminates the mutated transthyretin from the blood, but for some patients continued amyloid deposition can occur from wild-type (normal) transthyretin. Presently, a study is ongoing to determine whether amyloid deposition can be inhibited by small organic molecules that are hypothesized to affect the fibril-forming ability of transthyretin. Proposed gene therapy with antisense oligonucleotides (ASOs) to suppress hepatic transthyretin synthesis is effective in a transgenic mouse model but has not yet been tested in humans.