Unusual duplication mutation in a surface loop of human transthyretin leads to an aggressive drug-resistant amyloid disease.

Transthyretin (TTR) is a globular tetrameric transport protein in plasma. Nearly 140 single amino acid substitutions in TTR cause life-threatening amyloid disease. We report a one-of-a-kind pathological variant featuring a Glu51, Ser52 duplication mutation (Glu51_Ser52dup). The proband, heterozygous for the mutation, exhibited an unusually aggressive amyloidosis that was refractory to treatment with the small-molecule drug diflunisal. To understand the poor treatment response and expand therapeutic options, we explored the structure and stability of recombinant Glu51_Ser52dup. The duplication did not alter the protein secondary or tertiary structure but decreased the stability of the TTR monomer and tetramer. Diflunisal, which bound with near-micromolar affinity, partially restored tetramer stability. The duplication had no significant effect on the free energy and enthalpy of diflunisal binding, and hence on the drug-protein interactions. However, the duplication induced tryptic digestion of TTR at near-physiological conditions, releasing a C-terminal fragment 49-129 that formed amyloid fibrils under conditions in which the full-length protein did not. Such C-terminal fragments, along with the full-length TTR, comprise amyloid deposits in vivo. Bioinformatics and structural analyses suggested that increased disorder in the surface loop, which contains the Glu51_Ser52dup duplication, not only helped generate amyloid-forming fragments but also decreased structural protection in the amyloidogenic residue segment 25-34, promoting misfolding of the full-length protein. Our studies of a unique duplication mutation explain its diflunisal-resistant nature, identify misfolding pathways for amyloidogenic TTR variants, and provide therapeutic targets to inhibit amyloid fibril formation by variant TTR.

Oxidative Post-Translational Modifications of an Amyloidogenic Immunoglobulin Light Chain Protein.

Immunoglobulin light chain amyloidosis (AL) is a plasma cell disorder characterized by overproduction and deposition of monoclonal immunoglobulin (Ig) light chains (LC) or variable region fragments as amyloid fibrils in various organs and tissues. Much clinical evidence indicates that patients with AL amyloidosis sustain cardiomyocyte impairment and suffer from oxidative stress. We seek to understand the underlying biochemical pathways whose disruption or amplification during sporadic or sustained disease states leads to harmful physiological consequences and to determine the detailed structures of intermediates and products that serve as signposts for the biochemical changes and represent potential biomarkers. In this study, matrix-assisted laser desorption/ionization mass spectrometry provided extensive evidence for oxidative post-translational modifications (PTMs) of an amyloidogenic Ig LC protein from a patient with AL amyloidosis. Some of the tyrosine residues were heavily mono- or di-chlorinated. In addition, a novel oxidative conversion to a nitrile moiety was observed for many of the terminal aminomethyl groups on lysine side chains. In vitro experiments using model peptides, in-solution oxidation, and click chemistry demonstrated that hypochlorous acid produced by the myeloperoxidase - hydrogen peroxide - chloride system could be responsible for these and other, more commonly observed modifications.

Genetic variation of the transthyretin gene in wild-type transthyretin amyloidosis (ATTRwt).

Wild-type transthyretin amyloidosis (ATTRwt), typically diagnosed as congestive heart failure in elderly Caucasian men, features myocardial amyloid deposits of wild-type plasma protein transthyretin (TTR). ATTRwt is sporadic, its pathogenesis is poorly understood, and currently there are no biomarkers for diagnosis or prognosis. Genetic studies of variant-associated transthyretin amyloidosis have suggested that non-coding TTR gene variants modulate disease. We hypothesized that cis-acting regulatory elements in the TTR gene non-coding regions may modify expression, affecting ATTRwt onset and progression. We studied an ATTRwt cohort consisting of 108 Caucasian males ranging in age from 59 to 87 years with cardiomyopathy due to wild-type TTR deposition; results were compared to 118 anonymous controls matched by age, sex, and race. Four predicted non-coding regulatory regions and all exons in the TTR gene were sequenced using the Sanger method. Eleven common variants were identified; three variants were significantly associated with ATTRwt (p < 0.05), though only one, rs72922940, remained near significance (p corrected = 0.083) after multiple testing correction. Exon analyses demonstrated the occurrence of the p.G26S (G6S) polymorphism in 7 % of ATTRwt subjects and 12 % of controls; this variant was predicted to be a protective factor (p = 0.051). Four variants were significantly associated with age at onset and survival. In this first genetic study of a large, well-characterized cohort of ATTRwt, non-coding and coding variants associated with disease, age at onset, and survival were identified. Further investigation is warranted to determine the prevalence of these variants in ATTRwt, their regulatory function, and potential role in assessing disease risk.

Abnormal global longitudinal strain and reduced serum inflammatory markers in cardiac AL amyloidosis patients without significant amyloid fibril deposition.

Background: Cardiac dysfunction in AL amyloidosis is thought to be partly related to the direct impact of AL LCs on cardiomyocyte function, with the degree of dysfunction at diagnosis as a major determinant of clinical outcomes. Nonetheless, mechanisms underlying LC-induced myocardial toxicity are not well understood. Methods: We identified gene expression changes correlating with human cardiac cells exposed to a cardiomyopathy-associated κAL LC. We then sought to confirm these findings in a clinical dataset by focusing on clinical parameters associated with the pathways dysregulated at the gene expression level. Results: Upon exposure to a cardiomyopathy-associated κAL LC, cardiac cells exhibited gene expression changes related to myocardial contractile function and inflammation, leading us to hypothesize that there could be clinically detectable changes in GLS on echocardiogram and serum inflammatory markers in patients. Thus, we identified 29 patients with normal IVSd but abnormal cardiac biomarkers suggestive of LC-induced cardiac dysfunction. These patients display early cardiac biomarker staging, abnormal GLS, and significantly reduced serum inflammatory markers compared to patients with clinically evident amyloid fibril deposition. Conclusion: Collectively, our findings highlight early molecular and functional signatures of cardiac AL amyloidosis, with potential impact for developing improved patient biomarkers and novel therapeutics.

Complete variable domain sequences of monoclonal antibody light chains identified from untargeted RNA sequencing data.

Introduction: Monoclonal antibody light chain proteins secreted by clonal plasma cells cause tissue damage due to amyloid deposition and other mechanisms. The unique protein sequence associated with each case contributes to the diversity of clinical features observed in patients. Extensive work has characterized many light chains associated with multiple myeloma, light chain amyloidosis and other disorders, which we have collected in the publicly accessible database, AL-Base. However, light chain sequence diversity makes it difficult to determine the contribution of specific amino acid changes to pathology. Sequences of light chains associated with multiple myeloma provide a useful comparison to study mechanisms of light chain aggregation, but relatively few monoclonal sequences have been determined. Therefore, we sought to identify complete light chain sequences from existing high throughput sequencing data. Methods: We developed a computational approach using the MiXCR suite of tools to extract complete rearranged IGVL-IGJL sequences from untargeted RNA sequencing data. This method was applied to whole-transcriptome RNA sequencing data from 766 newly diagnosed patients in the Multiple Myeloma Research Foundation CoMMpass study. Results: Monoclonal IGVL-IGJL sequences were defined as those where >50% of assigned IGK or IGL reads from each sample mapped to a unique sequence. Clonal light chain sequences were identified in 705/766 samples from the CoMMpass study. Of these, 685 sequences covered the complete IGVL-IGJL region. The identity of the assigned sequences is consistent with their associated clinical data and with partial sequences previously determined from the same cohort of samples. Sequences have been deposited in AL-Base. Discussion: Our method allows routine identification of clonal antibody sequences from RNA sequencing data collected for gene expression studies. The sequences identified represent, to our knowledge, the largest collection of multiple myeloma-associated light chains reported to date. This work substantially increases the number of monoclonal light chains known to be associated with non-amyloid plasma cell disorders and will facilitate studies of light chain pathology.

Hereditary gelsolin amyloidosis: a rare cause of cranial, peripheral and autonomic neuropathies linked to D187N and Y447H substitutions.

INTRODUCTION: Hereditary gelsolin (AGel) amyloidosis is a systemic disease that is characterised by neurologic, ophthalmologic, dermatologic, and other organ involvements. We describe the clinical features with a focus on neurological manifestations in a cohort of patients with AGel amyloidosis referred to the Amyloidosis Centre in the United States. METHODS: Fifteen patients with AGel amyloidosis were included in the study between 2005 and 2022 with the permission of the Institutional Review Board. Data were collected from the prospectively maintained clinical database, electronic medical records and telephone interviews. RESULTS: Neurologic manifestations were featured in 15 patients: cranial neuropathy in 93%, peripheral and autonomic neuropathy in 57% and bilateral carpal tunnel syndrome in 73% of cases. A novel p.Y474H gelsolin variant featured a unique clinical phenotype that differed from the one associated with the most common variant of AGel amyloidosis. DISCUSSION: We report high rates of cranial and peripheral neuropathy, carpal tunnel syndrome and autonomic dysfunction in patients with systemic AGel amyloidosis. The awareness of these features will enable earlier diagnosis and timely screening for end-organ dysfunction. The characterisation of pathophysiology will assist the development of therapeutic options in AGel amyloidosis.

An additive destabilising effect of compound T60I and V122I substitutions in ATTRv amyloidosis.

BACKGROUND: The amyloidogenic transthyretin (TTR) variant, V122I, occurs in 4% of the African American population and frequently presents as a restricted cardiomyopathy. While heterozygosity for TTR V122I predominates, several compound heterozygous cases have been previously described. Herein, we detail features of ATTRv amyloidosis associated with novel compound heterozygous TTR mutation, T60I/V122I and provide evidence supporting the amyloidogenecity of T60I. METHODS: A 63-year-old African American female presented with atrial fibrillation, congestive heart failure, autonomic and peripheral neuropathy. In vitro studies of TTR T60I and V122I were undertaken to compare the biophysical properties of the proteins. RESULTS: Congophilic deposits in a rectal biopsy were immunohistochemically positive for TTR. Serum screening by isoelectric focussing revealed two TTR variants in the absence of wild-type protein. DNA sequencing identified compound heterozygous TTR gene mutations, c.239C > T and c.424G > A. Adipose amyloid deposits were composed of both T60I and V122I. While kinetic stabilities of T60I and V122I variants were similar, distinct thermodynamic stabilities and amyloid growth kinetics were observed. CONCLUSIONS: This report provides clinical and experimental results supporting the amyloidogenic nature of a novel TTR T60I variant. In vitro data indicate that the destabilising effect of individual T60I and V122I variants appears to be additive rather than synergistic.

Immunoglobulin light chain, Blimp-1 and cytochrome P4501B1 peptides as potential vaccines for AL amyloidosis.

Amyloid light chain (AL) amyloidosis is a lethal disorder characterized by the pathologic deposition of clonal plasma cell-derived, fibrillogenic immunoglobulin light chains in vital organs. Current chemotherapeutic regimens are problematic in patients with compromised organ function and are not effective for all patients. Here, a platform of computer-based prediction and preclinical mouse modeling was used to begin development of a complementary, immunotherapeutic approach for AL amyloidosis. Three peptide/MHC I-binding algorithms identified immunogenic peptides from three AL plasma cell-associated proteins: (1) amyloidogenic λ6 light chains, (2) CYP1B1, a universal tumor antigen hyper-expressed in AL plasma cells and (3) B lymphocyte-induced maturation protein 1 (Blimp-1), a transcription factor required for plasma cell differentiation. The algorithms correctly predicted HLA-A(*)0201-binding native and heteroclitic peptides. In HLA-A2 transgenic mice, these peptides, given individually or in combination, induced potent CTL which kill peptide-loaded human lymphoma cells and/or lymphoma cells producing target protein. Blimp-1 peptide-immunized mice exhibited a reduced percentage of splenic, lymph node and bone marrow plasma cells and a decrease in the absolute number of splenic plasma cells demonstrating (1) presentation of target peptide by endogenous plasma cells and (2) appropriate CTL homing to lymphoid organs followed by killing of target plasma cells. These studies suggest that AL amyloidosis, with its relatively low tumor cell burden, may be an attractive target for peptide-based multivalent vaccines.

A novel substitution of proline (P32L) destabilises ß2-microglobulin inducing hereditary systemic amyloidosis.

BACKGROUND: ß2-microglobulin amyloidosis was first described in the 1980s as a protein deposition disease associated with long-term haemodialysis. More recently, two inherited forms resulting from separate point mutations in the ß2-microglobulin gene have been identified. In this report, we detail a novel ß2M variant, P32L, caused by a unique dinucleotide mutation that is linked to systemic hereditary ß2-microglobulin amyloidosis. METHODS: Three family members from a Portuguese kinship featured cardiomyopathy, requiring organ transplantation in one case, along with soft tissue involvement; other involvements included gastrointestinal, neuropathic and sicca syndrome. In vitro studies with recombinant P32L, P32G, D76N and wild-type ß2-microglobulin were undertaken to compare the biophysical properties of the proteins. RESULTS: The P32L variant was caused by the unique heterozygous dinucleotide mutation c.154_155delinsTT. Amyloid disease featured lowered serum ß2-microglobulin levels with near equal amounts of circulating P32L and wild-type proteins; amyloid deposits were composed exclusively of P32L variant protein. In vitro studies of P32L demonstrated thermodynamic and chemical instability and enhanced susceptibility to proteolysis with rapid formation of pre-fibrillar oligomeric structures by N- and C-terminally truncated species under physiological conditions. CONCLUSIONS: This work provides both clinical and experimental evidence supporting the critical role of P32 residue replacement in ß2M amyloid fibrillogenesis.

Amyloidogenic and associated proteins in systemic amyloidosis proteome of adipose tissue.

In systemic amyloidoses, widespread deposition of protein as amyloid causes severe organ dysfunction. It is necessary to discriminate among the different forms of amyloid to design an appropriate therapeutic strategy. We developed a proteomics methodology utilizing two-dimensional polyacrylamide gel electrophoresis followed by matrix-assisted laser desorption/ionization mass spectrometry and peptide mass fingerprinting to directly characterize amyloid deposits in abdominal subcutaneous fat obtained by fine needle aspiration from patients diagnosed as having amyloidoses typed as immunoglobulin light chain or transthyretin. Striking differences in the two-dimensional gel proteomes of adipose tissue were observed between controls and patients and between the two types of patients with distinct, additional spots present in the patient specimens that could be assigned as the amyloidogenic proteins in full-length and truncated forms. In patients heterozygotic for transthyretin mutations, wild-type peptides and peptides containing amyloidogenic transthyretin variants were isolated in roughly equal amounts from the same protein spots, indicative of incorporation of both species into the deposits. Furthermore novel spots unrelated to the amyloidogenic proteins appeared in patient samples; some of these were identified as isoforms of serum amyloid P and apolipoprotein E, proteins that have been described previously to be associated with amyloid deposits. Finally changes in the normal expression pattern of resident adipose proteins, such as down-regulation of alphaB-crystallin, peroxiredoxin 6, and aldo-keto reductase I, were observed in apparent association with the presence of amyloid, although their levels did not strictly correlate with the grade of amyloid deposition. This proteomics approach not only provides a way to detect and unambiguously type the deposits in abdominal subcutaneous fat aspirates from patients with amyloidoses but it may also have the capability to generate new insights into the mechanism of the diseases by identifying novel proteins or protein post-translational modifications associated with amyloid infiltration.

Cardiac amyloidosis in African Americans: comparison of clinical and laboratory features of transthyretin V122I amyloidosis and immunoglobulin light chain amyloidosis.

BACKGROUND: Transthyretin (TTR) mutations known to cause cardiac amyloidosis include V122I, found almost exclusively in African Americans at a prevalence of 3-3.9%. This retrospective study describes TTR V122I-associated cardiac amyloid disease (ATTR) in a major amyloid referral clinic population. METHODS: Self-identified African Americans with amyloidosis (n = 156) were screened for TTR V122I by serum isoelectric focusing; mutant TTR was confirmed by DNA sequencing or mass spectrometry. Cardiac findings in ATTR V122I and immunoglobulin light chain (AL) amyloidoses were compared. RESULTS: TTR V122I was identified in 36/156 (23.1%) of evaluated patients and included 5 homozygotes; the allele frequency was 0.013. One compound heterozygote (F44L/V122I) and 4 patients who had AL and the mutant TTR allele were characterized. In patients negative for V122I, AL was the most frequent diagnosis (86/120). Cardiomyopathy was present in 100% of patients with ATTR and 84% of patients with AL (P = .01). In patients with dominant cardiac involvement, better survival occurred in ATTR (n = 30) compared to AL (n = 31), (27 vs 5 months, P < .01) although the mean age in ATTR was higher (70.3 vs 56.2 years, P < .01). Congestive heart failure symptoms and electrocardiographic findings were similar in ATTR and AL, but significant differences in echocardiographic measurements were observed. CONCLUSIONS: ATTR V122I and AL are equally prevalent as the cause of cardiomyopathy in African Americans referred for a diagnosis of amyloidosis. Available therapy for AL underscores the need for early and accurate determination of amyloid type.

Use of Serum Transthyretin as a Prognostic Indicator and Predictor of Outcome in Cardiac Amyloid Disease Associated With Wild-Type Transthyretin.

BACKGROUND: Wild-type transthyretin amyloidosis (ATTRwt), an underappreciated cause of heart failure in older adults, is challenging to diagnose and monitor in the absence of validated, disease-specific biomarkers. We examined the prognostic use and survival association of serum TTR (transthyretin) concentration in ATTRwt. METHODS AND RESULTS: Patients with biopsy-proven ATTRwt were retrospectively identified. Serum TTR, cardiac biomarkers, and echocardiographic parameters were assessed at baseline and follow-up evaluations. Statistical analyses included Kaplan-Meier method, Cox proportional hazard survival models, and receiver-operating characteristic curve analysis. Median serum TTR concentration at presentation was 23 mg/dL (n=116). Multivariate predictors of shorter overall survival were decreased TTR, left ventricular ejection fraction and elevated cTn-I (cardiac troponin I); an inclusive model demonstrated superior accuracy in 4-year survival prediction by receiver-operating characteristic curve analysis (area under the curve, 0.77). TTR values lower than the normal limit, <18 mg/dL, were associated with shorter survival (2.8 versus 4.1 years; P=0.03). Further, TTR values at 1- and 2-year follow-ups were significantly lower (P<0.001) in untreated patients (n=23) compared with those treated with TTR stabilizer, diflunisal (n=12), after baseline evaluation. During 2-year follow-up, unchanged TTR corresponded to increased cTn-I (P=0.006) in untreated patients; conversely, the diflunisal-treated group showed increased TTR (P=0.001) and stabilized cTn-I and left ventricular ejection fraction at 1 year. CONCLUSIONS: In this series of biopsy-proven ATTRwt, lower baseline serum TTR concentration was associated with shorter survival as an independent predictor of outcome. Longitudinal analysis demonstrated that decreasing TTR corresponded to worsening cardiac function. These data suggest that TTR may be a useful prognostic marker and predictor of outcome in ATTRwt.

A new transthyretin variant (Glu61Gly) associated with cardiomyopathy.

We report the identification of a new transthyretin (TTR) gene mutation and variant protein, Glu61Gly, in a 55-year-old man with progressive cardiomyopathy, mild peripheral neuropathy and bilateral carpal tunnel syndrome. A diagnosis of TTR-associated familial amyloidosis (ATTR) was considered after an endomyocardial biopsy revealed amyloid deposits in the heart of a patient who had no family history of amyloidosis and no evidence of a plasma cell dyscrasia. Serum screening for a TTR variant by isoelectric focusing (IEF) was positive and prompted further studies to identify the genetic abnormality and to characterize the amyloidogenic protein. Direct DNA sequence analysis of all four coding regions in the TTR gene demonstrated heterozygosity in exon 3. Near equal amounts of guanine (G) and adenine (A) were observed at the second base position of codon 61. The wild-type (GAG) and mutated (GGG) sequences found in codon 61 correspond to glutamic acid (Glu) and glycine (Gly) residues, amino acids which differ in mass by -72 Da. Mass spectrometric analyses of TTR immunoprecipitated from serum showed the presence of both wild-type and variant proteins. The observed mass results for the wild-type and variant proteins were consistent with the predicted values calculated from the genetic analysis data.

In vitro co-expression of human amyloidogenic immunoglobulin light and heavy chain proteins: a relevant cell-based model of AL amyloidosis.

Immunoglobulin (Ig) light chain (LC) amyloidosis (AL) is characterized by the overproduction and tissue deposition of monoclonal LC in various organs and tissues. The plasma circulating monoclonal LC is believed to be the precursor of the deposited protein and in vitro studies aimed at understanding AL pathobiology have mainly focused on LC and its variable domain. While 33% of patients have free circulating monoclonal LC, ∼40% feature LC complexed to heavy chain (HC) forming a monoclonal intact Ig; the significance of free vs. bound LC in the amyloid forming pathway is unknown. To address this issue, we developed a cell-based model using stable mouse plasmacytoma Sp2/0 cells that co-express patient-derived amyloidogenic LC and HC proteins. The system was designed using amyloidogenic kappa and lambda LC, and gamma HC sequences; stable production and secretion of either free LC and/or intact Ig were accomplished by varying the LC to HC ratios. This novel cell-based system provides a relevant tool to systematically investigate LC and HC interactions, and the molecular events leading to the development of AL amyloidosis.

Immunoglobulin heavy light chain test quantifies clonal disease in patients with AL amyloidosis and normal serum free light chain ratio.

BACKGROUND: Serum and urine immunofixation electrophoreses (SIFE/UIFE) are used for clonal detection in plasma cell dyscrasias, while serum free light chain (sFLC) testing provides quantitation of clonal disease. Up to 20% of patients with light chain (AL) amyloidosis may present with normal FLC ratio (FLCr). METHODS: We assessed the diagnostic, quantitative and prognostic potential of serum heavy light chain ratio (HLCr) in 199 untreated patients at initial evaluation. RESULTS: An abnormal HLCr was found in 37.2%, abnormal FLCr in 81.9% and positivity by SIFE/UIFE in 94% of patients. HLCr together with SIFE/UIFE identified clonality in 94% patients; the combination with FLCr yielded 100% sensitivity. An HLCr abnormality was significantly over-represented in normal compared to abnormal FLCr group (63.9% versus 31.3%). HLCr did not predict overall survival (OS) (log rank, p = 0.09), while an abnormal FLCr was associated with decreased OS (log rank, p = 0.03). The combined use of both ratios trended toward increased OS in the abnormal HLCr/normal FLCr group (log rank, p = 0.11; Wilcoxon, p = 0.04). On multivariate analysis, HLCr was not predictive of OS, whereas an abnormal FLCr was associated with shorter OS (HR = 1.7, p = 0.04). CONCLUSIONS: The HLC assay has potential as a supplemental test to quantify monoclonal protein in patients with normal FLCr results.

Identification of S-sulfonation and S-thiolation of a novel transthyretin Phe33Cys variant from a patient diagnosed with familial transthyretin amyloidosis.

Familial transthyretin amyloidosis (ATTR) is an autosomal dominant disorder associated with a variant form of the plasma carrier protein transthyretin (TTR). Amyloid fibrils consisting of variant TTR, wild-type TTR, and TTR fragments deposit in tissues and organs. The diagnosis of ATTR relies on the identification of pathologic TTR variants in plasma of symptomatic individuals who have biopsy proven amyloid disease. Previously, we have developed a mass spectrometry-based approach, in combination with direct DNA sequence analysis, to fully identify TTR variants. Our methodology uses immunoprecipitation to isolate TTR from serum, and electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry (MS) peptide mapping to identify TTR variants and posttranslational modifications. Unambiguous identification of the amino acid substitution is performed using tandem MS (MS/MS) analysis and confirmed by direct DNA sequence analysis. The MS and MS/MS analyses also yield information about posttranslational modifications. Using this approach, we have recently identified a novel pathologic TTR variant. This variant has an amino acid substitution (Phe --> Cys) at position 33. In addition, like the Cys10 present in the wild type and in this variant, the Cys33 residue was both S-sulfonated and S-thiolated (conjugated to cysteine, cysteinylglycine, and glutathione). These adducts may play a role in the TTR fibrillogenesis.

Identification of a novel transthyretin Thr59Lys/Arg104His. A case of compound heterozygosity in a Chinese patient diagnosed with familial transthyretin amyloidosis.

Transthyretin (TTR) is a 127-amino acid residue protein synthesized mainly in the liver and in several minor sites, including the choroid plexus and the eye. In plasma, TTR circulates as a homotetramer and transports the hormone thyroxine and the retinol-binding protein-vitamin A complex. It is hypothesized that amino acid substitutions in TTR destabilize the tetramer by causing each subunit toform intermediates that may self-associate into amyloid fibrils. Deposition of wild type TTR, its variants and/or fragments as amyloid fibrils in tissues and organs is associated with familial transthyretin amyloidosis (ATTR). Reported herein is the characterization of a novel TTR Thr59Lys/Arg104His in a patient of Chinese ancestry, who was diagnosed with ATTR. The two variant proteins and the double gene mutations in this compound heterozygous case were detected and identified using a multifaceted approach consisting of isoelectric focusing, electrospray ionization mass spectrometry (MS), matrix-assisted laser desorption/ionization time-of-flight MS in combination with enzymatic digestion, and direct DNA sequence analysis. Previous studies have shown that the TTR Arg104His variant is non-pathologic. It appeared to provide a protective effect in another compound heterozygous case (TTR Val30Met/Arg104His). However, the TTR Arg104His variant when presented with the TTR Thr59Lys variant did not seem to have any protective role.

A new lysozyme tyr54asn mutation causing amyloidosis in a family of Swedish ancestry with gastrointestinal symptoms.

Familial amyloidoses are a group of inherited disorders that cause deposition of misfolded amyloidogenic proteins in various tissues, resulting in organ dysfunction. Point mutations in the coding region of seven different genes are known to cause clinically significant systemic amyloid disease. We describe a new mutation in exon 2 of the lysozyme gene associated with amyloidosis (ALys) in a 61-year-old woman with a 7-year history of non-bloody, watery diarrhea, and weight loss. Biopsies of the duodenum and stomach were positive for amyloid deposits in the lamina propria and blood vessels. Direct DNA sequencing of the lysozyme gene revealed a single base nucleotide transversion from T to A at the first position of codon 54, resulting in replacement of Tyr by Asn in the mature lysozyme protein (pTyr54Asn). Immunoblot analysis of amyloid fibrils extracted from a fat tissue sample confirmed lysozyme as the amyloid protein. Clinically, the phenotype associated with this lysozyme mutation featured chronic abdominal pain, diarrhea, weight loss, malabsorption, and sicca syndrome. There was no associated nephropathy as has been reported for other ALys mutations. We describe a new mutant lysozyme that presents with abdominal discomfort, diarrhea, weight loss, and sicca syndrome.