Three Turkish families with different transthyretin mutations

Three patients of transthyretin amyloidosis in a Japanese family with amyloidogenic transthyretin Thr49Ser (p.Thr69Ser) variant

Transthyretin (TTR)-related hereditary amyloidosis (ATTRv) is a rare autosomal dominant disorder that is caused by pathogenic missense mutation of the TTR gene. As of today, more than 150 TTR gene variants have been reported to occur as causal mutations. Herein, we present three familial patients of ATTRv caused by the Thr49Ser (p.Thr69Ser) variant, including their phenotypes and penetrance. The first patient was a 68-year-old woman with a history of carpal tunnel syndrome, who was referred to our department with heart failure symptoms. Echocardiography, ^99mTechnetium (Tc)-pyrophosphate scintigraphy, and myocardial biopsy confirmed her diagnosis as TTR-related amyloidosis. Genetic testing for the TTR gene was performed, which confirmed the presence of a Thr49Ser (p.Thr69Ser) variant. The second patient, a 45-year-old woman, who was the niece of the first patient, presented with dyspnea on exertion. Her clinical manifestations included cardiac symptoms in addition to polyneuropathy. Similarly, myocardial biopsy showed TTR amyloid deposition within cardiac tissues, and TTR gene sequencing detected the presence of a Thr49Ser (p.Thr69Ser) variant. The final patient was a 42-year-old man, who was the nephew of the first patient, presented with numbness in his hands. Abdominal wall fat pad biopsy showed TTR amyloid deposition, and TTR gene sequencing was performed considering the familial history to confirm the presence of Thr49Ser (p.Thr69Ser) variant. No cardiac symptoms or dysfunctions have been observed yet, but imaging has detected TTR amyloid deposition in the heart. The present three patients with Thr49Ser (p.Thr69Ser) variant showed variation in phenotypes including cardiac and neurological manifestations at a fairly young age. In addition, the familial relationship in this report suggested that this variant is highly penetrant. Early genetic diagnosis due to collecting the genetic information from family medical history may be beneficial to improve patient prognosis via early therapeutic intervention.

The functional and structural evaluation of small fibers in asymptomatic carriers of p.Val50Met (Val30Met) mutation

Therapeutic advances in hereditary amyloid transthyretin (ATTRv) amyloidosis with polyneuropathy extended life expectancy and delayed symptom progression especially in patients with early disease. Thus, detection and monitoring of asymptomatic carriers gained importance. However, there is still limited consensus on genetic screening of ATTRv-PN patients' family members and diagnostic tests that must be done in the follow-up. In this study, we followed prospectively five asymptomatic carriers of a family with ATTRV30M (p.Val50Met) mutation by different diagnostic tests for three years. The carriers were followed by neurological examination, nerve conduction studies, sympathetic skin response test, heart rate variability, SFN-SIQ and DN4 questionnaires, quantitative sensory testing (QST), skin biopsy and in vivo corneal confocal microscopy. Nerve conduction studies, sympathetic skin response test and heart rate variability were normal in all for three years. Baseline QST and SFN-SIQ were normal but became abnormal during follow-up of two individuals who developed small fiber neuropathy symptoms. Baseline intraepidermal nerve fiber density was low in three carriers and decreased to below normative values in all during follow-up, while corneal sub-basal nerve density was low in all carriers compared to controls during the entire follow-up. Thus, our study showed that SFN-SIQ and QST are useful diagnostic tools to detect the transition to symptomatic ATTRv-polyneuropathy.

Different phenotypes of transthyretin-associated familial amyloid polyneuropathy due to a mutation in p.Glu109Gln in members of the same family

Transthyretin-associated familial amyloid polyneuropathy (TTR-FAP) is an unusual but life-threatening disease that is autosomal dominant inherited and involves the mutation of the transthyretin (TTR) gene. A total of 26 patients with TTR-FAP and different mutations, including the p.Glu 109Gln mutation (previously annotated p. Glu89Gln), were previously reported in Turkey. Herein, we reported two patients from the same family who had the same p.Glu 109Gln mutation but had different clinical phenotypes. The clinical picture mainly involved polyneuropathy in one patient and cardiac involvement in the other patient. This case report mentions that TTR-FAP can cause different clinical phenotypes, even due to the same mutation and even in the same family.

Hereditary transthyretin amyloidosis in multi-ethnic Malaysians

We report the clinical and genetic characteristics of hereditary transthyretin amyloidosis in the multi-ethnic Malaysian population. Subjects with genetically confirmed transthyretin amyloidosis seen between 2001 till August 2020 were included. There were 30 patients and 14 asymptomatic carriers, of which 26 (59.1%) were men. The majority (86.7%) were ethnic Chinese while two (6.7%) each were Malay and Sri Lankan Tamil ethnicity respectively. Among patients, mean age of symptom-onset was 55.9 ± 9.8 years with mean duration from symptom-onset to diagnosis of 3.2 ± 2.5 years. Common presenting symptoms were sensory symptoms of upper limbs (43.3%), symmetric sensory symptoms of both lower limbs (16.7%) and autonomic symptoms (16.7%). Nerve conduction studies showed sensorimotor polyneuropathy in 25 (83.3%) patients (22, axonal). Abnormal echocardiograms were seen in 24 (80%) patients, although 15 were asymptomatic. Of six different TTR mutations found, Ala97Ser was the commonest, and found exclusively in 84.6% of Chinese patients. Other mutations among Chinese patients were Val30Met, Ala25Thr and Asp39Val. Our Malay and Tamil patients had Glu54Lys and Gly47Val mutations respectively. In conclusion, TTR Ala97Ser is the commonest mutation among ethnic Chinese Malaysians which presented with late-onset progressive sensorimotor polyneuropathy, autonomic dysfunction and subclinical cardiac involvement.

Epidemiological and clinical characteristics of symptomatic hereditary transthyretin amyloid polyneuropathy: a global case series

We describe 542 cases of symptomatic hereditary transthyretin amyloid polyneuropathy (ATTR-PN) identified through a review of the literature published between 2005 and 2016. Approximately 18% of the cases were from countries where ATTR-PN is traditionally considered to be endemic (i.e., Portugal, Japan, and Sweden). East Asia (Japan, China, Taiwan, and South Korea) contributed a sizeable combined proportion (37.0%, n = 200) with Japan (n = 92) and China (n = 71) being the primary contributors. The most common genotypes among the 65 genotypes represented in the sample were Val30Met (47.6%), Ser77Tyr (10%), Ala97Ser (6.5%), and Phe64Leu (4.4%). Cases with genotypes other than the aforementioned four had the lowest ages at onset (mean 49.2 [standard deviation {SD} 21.0; inter-quartile range {IQR}14.7]) and diagnosis (mean 53.4 [SD 21.0; IQR 14.7]). Conversely, Phe64Leu mean age of onset was 67.5 (SD 8.8; IQR 5.2) and mean age of diagnosis was 71.3 (SD 8.8; IQR 5.4). The prevalence of upper and lower limb involvement at the time of diagnosis (67 and 41%) observed across all cases is consistent with the typical presentation of ATTR-PN. Other notable findings at the time of diagnosis included a high rate of impotence among the Ala97Ser cases versus all others (67% vs. 21%) and a high rate of non-motor visual symptoms (i.e., visual opacities and glaucoma) in the Ser77Tyr cases versus all others (93% vs. 16%). Though comparisons were made descriptively and were hindered by inconsistency of reporting across the cases, these findings support the notion that ATTR-PN is a more phenotypically and geographically variable disease than is typically considered.

Estimating the global prevalence of transthyretin familial amyloid polyneuropathy

INTRODUCTION

This study sought to estimate the global prevalence of transthyretin familial amyloid polyneuropathy (ATTR-FAP).

METHODS

Prevalence estimates and information supporting prevalence calculations was extracted from records yielded by reference-database searches (2005-2016), conference proceedings, and nonpeer reviewed sources. Prevalence was calculated as prevalence rate multiplied by general population size, then extrapolated to countries without prevalence estimates but with reported cases.

RESULTS

Searches returned 3,006 records; 1,001 were fully assessed and 10 retained, yielding prevalence for 10 "core" countries, then extrapolated to 32 additional countries. ATTR-FAP prevalence in core countries, extrapolated countries, and globally was 3,762 (range 3639-3884), 6424 (range, 1,887-34,584), and 10,186 (range, 5,526-38,468) persons, respectively.

DISCUSSION

The mid global prevalence estimate (10,186) approximates the maximum commonly accepted estimate (5,000-10,000). The upper limit (38,468) implies potentially higher prevalence. These estimates should be interpreted carefully because contributing evidence was heterogeneous and carried an overall moderate risk of bias. This highlights the requirement for increasing rare-disease epidemiological assessment and clinician awareness. Muscle Nerve 57: 829-837, 2018.

Understanding the Disease Course and Therapeutic Benefit of Tafamidis Across Real-World Studies of Hereditary Transthyretin Amyloidosis with Polyneuropathy: A Proof of Concept for Integrative Data Analytic Approaches

Introduction

Hereditary transthyretin (TTR) amyloidosis with polyneuropathy (hATTR-PN) is a rare, autosomal dominant amyloidosis characterized primarily by progressive ascending sensorimotor neuropathy often associated with  autonomic involvement. hATTR-PN is caused by a mutation in the TTR gene leading to protein misfolding and amyloid accumulation in peripheral nerves and vital organs. The latest global prevalence estimates point to 10,000 cases worldwide, with an upper end of about 40,000. Tafamidis has been approved in over 40 countries for delaying neurologic disease progression in early-stage hATTR-PN. Multiple observational studies have examined clinical outcomes in hATTR-PN patients treated with tafamidis in the routine clinical setting. Integrative data analysis (IDA) is a technique for optimally constructing synthetic treatment and control cohorts from multiple independent studies, which allows meta-analysis of patient-level data. Herein, we provide a proof of concept for the application of IDA to real-world and natural history hATTR-PN data. IDA permits increased understanding of outcomes in tafamidis-treated and untreated persons with hATTR-PN by optimally pooling all available information.

Methods

Summary statistics corresponding to the Neuropathy Impairment Score-Lower Limb (NIS-LL) from five published studies were pooled, converted to change from baseline means and variances, and analyzed using IDA. IDA-based synthetic cohorts were generated by averaging across studies stratified on treatment versus control cohort. Trends in change from baseline in each study and the corresponding synthetic cohorts were plotted. Patient-level data were simulated from the synthetic cohort trends in a Monte Carlo simulation to highlight the ability to contrast synthetic cohort trends using the mixed model for repeated measures (MMRM).

Results

The average sample size among the five studies was 71 (37–128) patients. The average NIS-LL trends indicated that tafamidis-treated patients experienced slower progression in neuropathy compared to untreated patients. Synthetic cohort trends reflected the trends observed in the contributing studies, while simultaneously shrinking the width of corresponding confidence bands. Monte Carlo simulation results demonstrated precise recovery of the synthetic cohort and time-dependent simulated NIS-LL means by the MMRM.

Discussion

This proof of concept demonstrates the utility of IDA-based synthetic cohorts for increased precision in characterizing and testing hypotheses about treatment outcomes and prognosis in hATTR-PN.

Funding

Pfizer.

Plain Language Summary

Plain language summary available for this article.

Hereditary transthyretin (TTR) amyloidosis with polyneuropathy (hATTR-PN) is a rare inherited disease. It is caused by genetic mutations that change the structure of TTR proteins, causing an abnormal buildup of amyloid protein deposits (amyloidosis) in your body’s nerves and organs. This damages your nerves and organs and causes weakness, numbness, and pain. The drug tafamidis stabilizes TTR proteins and slows the disease’s progression. Tafamidis has been approved in over 40 countries based on clinical trial results. However, researchers and doctors are still studying how it works for patients in the real world. Over the past few years, researchers have published multiple real-world studies about tafamidis, but it is difficult to get a full, uniform picture of how well tafamidis works, because the studies are too different. hATTR-PN is a rare disease, so the number of patients per study is small; small sample sizes can make it more difficult to tell true effects from statistical noise, whereas large samples can be more precise. Integrative data analysis (IDA) is a technique that allows researchers to combine the results of multiple studies into a large pool of data and analyze the larger data set (or “synthetic cohort”) instead. This makes optimal use of each study’s information and creates a fuller picture of the treatment’s real-world results. This manuscript is a “proof of concept” to demonstrate how the IDA statistical method can be used to build synthetic cohorts from real-world hATTR-PN data, improving our understanding of hATTR-PN patients’ outcomes.

Mechanistic basis for the recognition of a misfolded protein by the molecular chaperone Hsp90

The critical toxic species in over 40 human diseases are misfolded proteins. Their interaction with molecular chaperones such as Hsp90, which preferentially interacts with metastable proteins, is essential for the blocking of disease progression. Here we used nuclear magnetic resonance (NMR) spectroscopy to determine the three-dimensional structure of the misfolded cytotoxic monomer of the amyloidogenic human protein transthyretin, which is characterized by the release of the C-terminal β-strand and perturbations of the A-B loop. The misfolded transthyretin monomer, but not the wild-type protein, binds to human Hsp90. In the bound state, the Hsp90 dimer predominantly populates an open conformation, and transthyretin retains its globular structure. The interaction surface for the transthyretin monomer comprises the N-terminal and middle domains of Hsp90 and overlaps with that of the Alzheimer's-disease-related protein tau. Taken together, the data suggest that Hsp90 uses a mechanism for the recognition of aggregation-prone proteins that is largely distinct from those of other Hsp90 clients.

Genotypic and phenotypic presentation of transthyretin-related familial amyloid polyneuropathy (TTR-FAP) in Turkey

Transthyretin-related familial amyloid polyneuropathy (TTR-FAP) is an autosomal dominant disorder caused by mutations of the transthyretin (TTR) gene. The mutant amyloidogenic transthyretin protein causes the systemic accumulation of amyloid fibrils that result in organ dysfunction. TTR-associated FAP is a progressive and fatal disease, if left untreated, and should be considered in the differential diagnosis of any person presenting with a progressive polyneuropathy, particularly with accompanying autonomic involvement. The clinical, electrophysiological, histopathological, and genetic characteristics of 17 patients from Turkey (5 female, 13 male) from nine families with polyneuropathy and mutations in TTR were evaluated. Sequence analysis of the TTR gene revealed five mutations (Val30Met, Glu89Gln, Gly53Glu, Glu54Gly and Gly47Glu). Mean age at disease onset was 40.4 ± 13.9 years (range 21-66 years). The most commonly reported initial complaint was paresthesia in the feet (asymmetric in three patients). Three patients (2 male) with the Glu89Gln mutation presented with carpal tunnel syndrome. Two patients with the Gly53Glu mutation showed episodes of dysarthria and hemiparesis, consistent with this genotype. Seven patients died during the period of follow-up as a result of systemic involvement. Our study suggests that a cohort of patients from Turkey with TTR-FAP exhibits clinical and genetic heterogeneity.