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

His108Arg Transthyretin Amyloidosis-Shedding Light on a Distinctively Malignant Variant

Variant transthyretin amyloidosis cardiomyopathy (ATTRv-CM) is a rare form of cardiac amyloidosis associated with many possible mutations in the transthyretin gene, presenting as various distinct clinical phenotypes. Among these, the His108Arg mutation is the most prevalent TTR variant in Austria. However, data describing its clinical phenotype are lacking. This study aims to describe the characteristics, clinical manifestations, and outcomes of patients with the His108Arg variant focusing on cardiac involvement, disease progression, response to therapy, and imaging findings. Methods: Patients were enrolled from a prospective cardiac amyloidosis registry. The baseline assessment included comprehensive echocardiography, cardiac magnetic resonance imaging, a biomarker analysis, and a clinical evaluation. Patients were followed longitudinally, with outcomes such as arrhythmias, heart failure hospitalizations, and response to disease-targeted therapies recorded. Results: Between March 2012 and June 2024, a total of 20 carriers of the His108Arg variant were identified, with 12 exhibiting clear cardiac involvement and 8 remaining asymptomatic. The median age at diagnosis was 62.3 years with significant heterogeneity in the clinical presentation. Patients with ATTRv-CM had a high prevalence of atrial and ventricular arrhythmias, a reduced left ventricular ejection fraction, and elevated cardiac biomarkers. The majority received specific disease-modifying therapies, with varying tolerance and responses. A longitudinal follow-up indicated frequent arrhythmic events, heart failure exacerbations, and three cases of heart transplantation, underscoring the need for stringent monitoring and individualized management strategies. Conclusions: This study represents a unique, comprehensive analysis of the His108Arg variant in ATTR-CM, highlighting its clinical heterogeneity and significant impact on cardiac function and clinical outcomes.

Effect of alanine versus serine at position 88 of human transthyretin mutants on the protein stability

Human transthyretin (TTR) is a homo-tetrameric plasma protein associated with a high percentage of β-sheet forming amyloid fibrils. It accumulates in tissues or extracellular matrices to cause amyloid diseases. Free energy simulations with thermodynamic integration based on all-atom molecular dynamics simulations have been carried out to analyze the effects of the His88 → Ala and Ser mutations on the stability of human TTR. The calculated free energy change differences (ΔΔG) caused by the His88 → Ala and His88 → Ser mutations are -1.84 ± 0.86 and 7.56 ± 0.55 kcal/mol, respectively, which are in excellent agreement with prior reported experimental values. The simulation results show that the H88A mutant is more stable than the wild type, whereas the H88S mutant is less stable than the wild type. The free energy component analysis shows that the contribution to the free energy change difference (ΔΔG) for the His88 → Ala and His88 → Ser mutations mainly arise from electrostatic and van der Waals interactions, respectively. The electrostatic term stabilizes the H88A mutant more than the wild type, but the van der Waals interaction destabilizes the H88S mutant relative to the wild type. Individual residue contributions to the free energy change show neighboring residues exert stabilizing and destabilizing influence on the mutants. The implications of the simulation results for understanding the stabilizing and destabilizing effect and its contribution to protein stability are discussed.

Transthyretin cardiac amyloidosis in continental Western Europe: an insight through the Transthyretin Amyloidosis Outcomes Survey (THAOS)

AIMS

Transthyretin amyloidosis (ATTR amyloidosis) is a heterogeneous disorder with cardiac, neurologic, and mixed phenotypes. We describe the phenotypic and genotypic profiles of this disease in continental Western Europe as it appears from the Transthyretin Amyloidosis Survey (THAOS).

METHODS AND RESULTS

THAOS is an ongoing, worldwide, longitudinal, observational survey established to study differences in presentation, diagnosis, and natural history in ATTR amyloidosis subjects. At data cut-off, 1411 symptomatic subjects from nine continental Western European countries were enrolled in THAOS [1286 hereditary (ATTRm) amyloidosis; 125 wild-type ATTR (ATTRwt) amyloidosis]. Genotypes and phenotypes varied notably by country. Four mutations (Val122Ile, Leu111Met, Thr60Ala, and Ile68Leu), and ATTRwt, were associated with a mainly cardiac phenotype showing symmetric left ventricular (LV) hypertrophy, normal diastolic LV dimensions and volume, and mildly depressed LV ejection fraction (LVEF). Morphologic and functional abnormalities on echocardiogram were significantly more severe in subjects with cardiac (n'= 210), compared with a mixed (n = 298), phenotype: higher median (Q1-Q3) interventricular septal thickness [18 (16-21) vs. 16 (13-20) mm; P = 0.0006]; and more frequent incidence of LVEF <50% (38.1 vs. 17.5%; P = 0.0008). Subjects with cardiac mutations or ATTRwt (or cardiac or mixed phenotype) had a lower survival rate than subjects in other genotype (or the neurologic phenotype) categories (P < 0.0001, for both).

CONCLUSION

ATTR amyloidosis genotypes and phenotypes are highly heterogeneous in continental Western Europe. A geographic map of the different disease profiles and awareness that a subset of subjects have a dominant cardiac phenotype, mimicking hypertrophic cardiomyopathy, at presentation can facilitate the clinical recognition of this underdiagnosed disease.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00628745.

Variant Transthyretin Amyloidosis (ATTRv) in Hungary: First Data on Epidemiology and Clinical Features

Background: Variant transthyretin amyloidosis (ATTRv) is an autosomal dominant inherited disease, where the mutation of the transthyretin gene (TTR) results in the deposition of pathogenic protein fibrils in various tissues. The mutation type influences the clinical course. Until now, no data were available on the genotype, phenotype, and prevalence of Hungarian ATTRv patients. The aim of our study was to assess the prevalence, regional distribution, genotypes, and phenotypes of Hungarian patients with ATTRv. Methods: With the collaboration of Hungarian regional and university centers, we identified patients diagnosed with ATTRv. We also searched prior publications for case studies of Hungarian ATTRv patients. Results: 40 individuals in 23 families with ATTRv were identified within the borders of Hungary. At the time of the diagnosis, 24 of them were symptomatic. The two most common mutations were ATTRHis88Arg (nine families) and ATTRIle107Val (8 families). ATTRVal30Met was demonstrated in 2 families, and ATTRVal122del, ATTRPhe33Leu, ATTRIle84Ser, and ATTRAsp18Gly in one family each. The median age of the symptomatic patients at the time of clinical diagnosis was 65 years. The most common clinically significant organ involvement was restrictive cardiomyopathy, found in 24 patients. Polyneuropathy was diagnosed in 20 patients. A total of 19 patients showed a mixed phenotype. The leading symptom was heart failure in 8 cases (3 of them had only cardiac symptoms), polyneuropathy in 11 cases (all of them also had cardiac symptoms), and equally severe cardiac and neuropathy symptoms were present in 3 cases. Out of 24 symptomatic patients, 10 received targeted pharmacological therapy. The follow-up period ranged from 1 to 195 months. At the time of the retrospective analysis, 12 patients had already died, and 1 patient underwent heart transplantation. Conclusions: As TTR genotype influences the phenotype and clinical course of ATTRv, it is important to know the regional data. In Hungary, ATTRHis88Arg and ATTRIle107Val are the most common mutations in ATTRv, both presenting with mixed phenotype, but the median age at the time of the diagnosis is 9 years lower in patients with ATTRHis88Arg than in patients with ATTRIle107Val.

Hereditary ATTR Amyloidosis in Austria: Prevalence and Epidemiological Hot Spots

BACKGROUND

Hereditary transthyretin amyloidosis (hATTR) is an autosomal dominantly inherited disorder caused by an accumulation of amyloid fibrils in tissues due to mutations in the transthyretin (TTR) gene. The prevalence of hATTR is still unclear and likely underestimated in many countries. In order to apply new therapies in a targeted manner, early diagnosis and knowledge of phenotype-genotype correlations are mandatory. This study aimed to assess the prevalence and phenotypic spectrum of hATTR in Austria.

METHODS

Within the period of 2014-2019, patients with ATTR-associated cardiomyopathy and/or unexplained progressive polyneuropathies were screened for mutations in the TTR gene.

RESULTS

We identified 43 cases from 22 families carrying 10 different TTR missense mutations and confirmed two mutational hot spots at c.323A>G (p.His108Arg) and c.337G>C (p.Val113Leu). Two further patients with late onset ATTR carried TTR variants of unknown significance. The majority of patients initially presented with heart failure symptoms that were subsequently accompanied by progressive polyneuropathy in most cases. A total of 55% had a history of carpal tunnel syndrome before the onset of other organ manifestations.

CONCLUSIONS

Our study underlined the relevance of hATTR in the pathogenesis of amyloid-driven cardiomyopathy and axonal polyneuropathy and indicated considerable genetic heterogeneity of this disease in the Austrian population. The estimated prevalence of hATTR in Austria based on this study is 1:200,000 but a potentially higher number of unknown cases must be taken into account. With respect to new therapeutic approaches, we strongly propose genetic testing of the TTR gene in an extended cohort of patients with unexplained heart failure and progressive polyneuropathy.

Spinal Stenosis in Familial Transthyretin Amyloidosis

Here we describe a patient with genetically confirmed ATTR, a family history of the disease and histological confirmation following carpal tunnel release surgery but no other manifestations. The first major neurological or systemic manifestation was cauda equina syndrome with ATTR deposits contributing to lumbar spinal stenosis. Recent gene therapy trials showed improvement in the neuropathy in TTR amyloidosis. This case highlights the need for awareness of the heterogeneous neurological phenotype seen in ATTR to aid earlier diagnosis especially now that disease modifying therapies are available.

Coronary ectasia in amyloid cardiomyopathy and neuropathy due to the transthyretin mutation c.323A>G

BACKGROUND

atrial fibrillation(AF) is a frequent manifestation of cardiac involvement in genetic and wild-type transthyretin-related familial amyloidosis(TTR-FA). However, ectasia of coronary arteries and ablation for AF have not been reported in TTR-FA.

METHODS AND RESULTS

A 65yo male developed progressive sensori-motor polyneuropathy since age 59y. At age 60y bifascicular block and myocardial thickening were recognised. At age 62y heart failure developed and work-up with cardiac MRI suggested amyloidosis but biopsy was non-informative. Coronary angiography revealed ectasias of the coronary arteries. At age 65y AF developed, neither responding to electrical cardioversion nor ablation. Work-up for polyneuropathy revealed the point mutation c.323A>G (p.His108Arg) in the TTR-gene. Tafamidis was started but did not exhibit a beneficial effect after 7 months.

CONCLUSIONS

TTR-FA may manifest in the coronary arteries with ectasia. Ablation for AF in TTR-FA may be unsuccessful. Tafamidis has been unsuccessful for cardiac or nerve involvement after the first seven months.

Stability and crystal structures of His88 mutant human transthyretins

Destabilization of human transthyretin (TTR) has been implicated in its misfolding and aggregation. A previous study on the neutron crystal structure of TTR suggested that a large hydrogen bond network around H88 which includes water molecules is significantly involved in the stability of wild-type TTR (WT-TTR). Here, we demonstrate that the H88R mutant associated with amyloid cardiomyopathy is substantially destabilized compared with WT-TTR. In order to clarify the role of H88 and the hydrogen bond network in the stability of TTR, we determined the thermodynamic stability and the crystal structure of H88 mutants (H88A, H88F, H88Y, and H88S). Our results suggest that in some cases TTR is destabilized due to alterations in bound water molecules as well as structural changes in TTR itself.