Founder effect of the Glu89Gln TTR mutation in the Bulgarian population

Hereditary transthyretin amyloidosis (ATTRv)

Hereditary transthyretin (TTR) amyloidosis (ATTRv amyloidosis) is a devastating disease characterized by broad range of clinical manifestations, including predominantly neurological, predominantly cardiac, and mixed phenotypes. This wide phenotypic variability hindered timely disease diagnosis and risk stratification in the past, especially in individuals with absent or uncharted family history. However, recent advances in noninvasive testing have led to greater awareness and earlier diagnosis. Further, medications have been discovered which proved effective in controlling the disease and improving outcomes including stabilizing TTR, silencing TTR variants, and removing TTR amyloid from affected tissues. Importantly, CRISPR gene editing, a groundbreaking technology, offers the unique potential to cure ATTRv amyloidosis, transforming lives and opening new doors in medical science. This review provides an update on ATTRv amyloidosis mechanisms, diagnosis, and management emphasizing the importance of early diagnosis as the steadfast underpinning for the capitalization of the advances in medical treatment to the benefit of the patients.

Experience of Hereditary Amyloidosis with Rare Variant in Ecuador: Case Reports

More than approximately 120 transthyretin mutations are known. Their clinical presentation is heterogeneous, as the course of disease onset depends on genetic variation and level of penetrance. They are little known in Ecuador, and some of the reported cases suggest-given analysis of family trees-that they come from a province that is possibly considered endemic. The main objective of this study is to perform a descriptive observational analysis on the presentation of transthyretin amyloidosis in families carrying the p.Ser43Asn gene of the identified index case.

The Spectrum of Disease-Associated Alleles in Countries with a Predominantly Slavic Population

There are more than 260 million people of Slavic descent worldwide, who reside mainly in Eastern Europe but also represent a noticeable share of the population in the USA and Canada. Slavic populations, particularly Eastern Slavs and some Western Slavs, demonstrate a surprisingly high degree of genetic homogeneity, and, consequently, remarkable contribution of recurrent alleles associated with hereditary diseases. Along with pan-European pathogenic variants with clearly elevated occurrence in Slavic people (e.g., ATP7B c.3207C>A and PAH c.1222C>T), there are at least 52 pan-Slavic germ-line mutations (e.g., NBN c.657_661del and BRCA1 c.5266dupC) as well as several disease-predisposing alleles characteristic of the particular Slavic communities (e.g., Polish SDHD c.33C>A and Russian ARSB c.1562G>A variants). From a clinical standpoint, Slavs have some features of a huge founder population, thus providing a unique opportunity for efficient genetic studies.

Case Report: Transthyretin Glu54Leu-a rare mutation with predominant cardiac phenotype

We report two unrelated Bulgarian families with hereditary transthyretin (ATTR) amyloidosis due to a rare p.Glu74Leu (Glu54Leu) pathogenic variant found in seven individuals-three of them symptomatic. Only one family with the same variant and with a Swedish origin has been clinically described so far. Our patients are characterized by predominant cardiac involvement, very much similar to the Swedish patients. Although the initial complaint was bilateral carpal tunnel syndrome, advanced amyloid cardiomyopathy was found in two symptomatic carriers at diagnosis with heart failure manifestations. The neurological involvement was considered as mild, with mainly sensory signs and symptoms being present. We followed a non-biopsy algorithm to confirm the diagnosis. Tafamidis 61 mg has been initiated as the only approved disease modifying treatment for ATTR cardiomyopathy. Clinical stability in the absence of adverse events has been observed at follow up.

Investigation on the high recurrence of the ATTRv-causing transthyretin variant Val142Ile in central Italy

The p.Val142Ile variant in transthyretin (encoded by the TTR gene) is the most common genetic cause of transthyretin-related amyloidosis. This allele is particularly prevalent in communities ofAfrican descent compared with populations of different ancestries, where its frequency is two orders of magnitude lower. For this reason, p.Val142Ile has always been considered an "African" variant, with limited studies performed on individuals of European descent. However, recent reports of higher-than-expected prevalence in European-ancestry populations question the African specificity of this allele. Here we show that the high recurrence of p.Val142Ile in central Italy is due to a founder effect and not to recent admixture from African populations, highlighting how this may be the case in other communities. This suggests a probable underestimate of the global prevalence of p.Val142Ile, and further emphasizes the importance of routine inclusion of TTR in gene panels used for clinical genetic testing in hypertrophic cardiomyopathy (independently of the patient's geographical origin), that transthyretin-related amyloidosis can mimic.

Phenotype and clinical outcomes of Glu89Lys hereditary transthyretin amyloidosis: a new endemic variant in Spain

BACKGROUND

The p.Glu109Lys variant (Glu89Lys) is a rare cause of hereditary transthyretin amyloidosis (ATTRv) for which clinical spectrum remains unresolved. We sought to describe the clinical characteristics and outcomes of ATTR Glu89Lys amyloidosis and assess a potential founder effect in Spain.

METHODS

Patients with the p.Glu109Lys ATTRv variant from 14 families were recruited at 7 centres. Demographics, complementary tests and clinical course were analysed. Haplotype analysis was performed in 7 unrelated individuals.

RESULTS

Thirty-eight individuals (13 probands, mean age 40.4 ± 13.1 years) were studied. After median follow-up of 5.1 years (IQR 1.7-9.6), 7 patients died and 7 required heart transplantation (median age at transplantation 50.5 years). Onset of cardiac and neurological manifestations occurred at a mean age of 48.4 and 46.8 years, respectively. Median survival from birth was 61.6 years and no individual survived beyond 65 years. Patients treated with disease-modifying therapies exhibited better prognosis (p < 0.001). Haplotype analysis revealed a common origin from an ancestor who lived ∼500 years ago in southeast Spain.

CONCLUSIONS

Glu89Lys ATTRv is a TTR variant with a founder effect in Spain. It is associated with near complete penetrance, early onset and mixed cardiac and neurologic phenotype. Patients have poor prognosis, particularly if not treated with disease-modifying therapies.

Hereditary Transthyretin-Related Amyloidosis: Genetic Heterogeneity and Early Personalized Gene Therapy

Point mutations of the transthyretin (TTR) gene are related with hereditary amyloidosis (hATTR). The number of people affected by this rare disease is only partially estimated. The real impact of somatic mosaicism and other genetic factors on expressivity, complexity, progression, and transmission of the disease should be better investigated. The relevance of this rare disease is increasing and many efforts have been made to improve the time to diagnosis and to estimate the real number of cases in endemic and non-endemic areas. In this context, somatic mosaicism should be better investigated to explain the complexity of the heterogeneity of the hATTR clinical features, to better estimate the number of new cases, and to focus on early and personalized gene therapy. Gene therapy can potentially improve the living conditions of affected individuals and is one of the central goals in research on amyloidosis related to the TTR gene, with the advantage of overcoming liver transplantation as the sole treatment for hATTR disease.

Seven Years of Selective Genetic Screening Program and Follow-Up of Asymptomatic Carriers With Hereditary Transthyretin Amyloidosis in Bulgaria

Hereditary transthyretin amyloidosis (ATTRv amyloidosis) is a rare, autosomal-dominant (AD) multisystem disorder resulting from the extracellular deposition of amyloid fibrils formed by a destabilized mutant form of transthyretin (TTR), a transport protein predominantly produced by the liver.

Characterization of population genetic structure of hereditary transthyretin amyloidosis in Bulgaria

The hereditary transthyretin amyloidosis (ATTRv amyloidosis) is an autosomal dominant genetic disease characterized by amyloid formation in different tissues due to pathogenic variants in the TTR gene. Great heterogeneity in the penetrance and manifestation of ATTRv amyloidosis is observed. In Bulgaria, the most common TTR pathogenic variant is Glu89Gln. Other TTR pathogenic variants are also found - Val30Met, Ser77Phe, Gly47Glu and Ser52Pro. There is a proven founder effect for the Glu89Gln variant, thus the aim of the present study is to investigate the founder effect for the other TTR pathogenic variants in Bulgaria. Haplotype analysis was performed by using microsatellite markers close to the TTR gene. DNA samples from ATTRv amyloidosis patients and their healthy relatives were analyzed. Theoretical haplotype reconstruction was done with Arlequin v.3.01 software. The age of the most recent common ancestor (hypothetical founder) for the studied variants was calculated with the DMLE 2.2 software. In addition, DBS screening among 100 Roma newborns was done for the Gly47Glu TTR variant via direct Sanger sequencing. The reconstructed haplotypes of the patients were compared to their healthy relatives and to a control group of 40 healthy individuals. The results showed a possible founder effect for each of the studied variants. The Val30Met haplotype was compared to published haplotype data for this variant and no similarity was found. The result from the DBS screening showed no pathogenic TTR variants in exon 2 of the gene, so we considered the presence of the Gly47Glu variant in our population a sporadic event. With this study, we succeeded to gain a more complete picture of the population genetics of ATTRv amyloidosis in Bulgaria and made another step towards a more detailed understanding of the disease epidemiology.

Variant transthyretin amyloidosis (ATTRv) polyneuropathy in Greece: a broad overview with a focus on non-endemic unexplored regions of the country

Comprehensive data on variant transthyretin amyloidosis polyneuropathy (ATTRv-PN) in Greece are lacking. We presently provide an overview of ATTRv-PN in Greece, focusing on unexplored non-endemic regions of the country. In total, we identified 57 cases of ATTRv-PN diagnosed over the past 25 years, including 30 from the island of Crete, an apparent endemic region. Patients carried 10 different TTR mutations (C10R; P24S; V30M; R34G; R34T; I68L; A81T; E89Q; E89K and V94A). Carriers of the common V30M mutation constituted 54.3 % of the cohort. A known founder effect for the V30M mutation was present on the island of Crete. Non-endemic cases identified outside the island of Crete are presently reported in more detail. The age of onset ranged from 25 to 77 years, with a mean of 51.1 years. A mean diagnostic delay of 3.2 years was observed. V30M patients had earlier onset and less cardiac involvement than patients carrying other mutations. Genotype-phenotype correlations were largely consistent with published data. We conclude that, with the exception of the Cretan cluster, ATTRv-PN is not endemic in the Greek population. This makes timely diagnosis more challenging, yet absolutely essential given the availability of therapies that can alter the long-term course of the disease.

Molecular characterization of mucopolysaccharidosis type IVA patients in the Andean region of Colombia

Colombia has a high prevalence of mucopolysaccharidosis (MPS) type IVA. Nevertheless, data regarding the mutation spectrum for MPS IVA in this population have not been completely characterized. Forty-seven families and 53 patients from seven different Colombian regions were tested for MPS IVA mutations. We compared the sequences with the N-acetylgalactosamine-6-sulfatase (GALNS) reference sequence NM_000512.4, and gene variants were reported. Bioinformatics analysis was performed using SWISS-MODEL. The mutant proteins were generated by homology from the wild-type GALNS 4FDJ template obtained from the PDB database, and visualization was performed using Swiss-PDBViewer and UCSF Chimera. The predictive analysis was run using different bioinformatic tools, and the deleterious annotation of genetic variants was performed using a neural network. We found that 79% and 21% of the cohort was homozygous and compound heterozygous, respectively. The most frequent mutation observed was p.Gly301Cys (78.3% of alleles), followed by p.Arg386Cys (10.4% of alleles). A novel mutation (p.Phe72Ile) was described and classified in silico as a pathogenic variant. This study reveals the mutation spectrum of MPS IVA in Colombia. The high prevalence of the p.Gly301Cys mutation suggests a founder effect of this variant in the Colombian population that causes diseases in the Andean region (via migration). These data can facilitate genetic counseling, prenatal diagnosis, and the design of therapeutic interventions.

Screening for hereditary transthyretin amyloidosis in Bulgaria

Transthyretin amyloid (ATTR) amyloidosis is a rare disorder with an adult-onset defined by the accumulation of misfolded fibrils predominantly in peripheral nerves, the heart, and the digestive tract. The disease is characterized by two forms - hereditary (ATTRv) or acquired (ATTRwt). Various point mutations in the transthyretin gene induce the hereditary form of the disease. For finding new cases of ATTR amyloidosis and proper screening, the establishment of a multidisciplinary team and a Centre of Excellence (CoE) is essential. CoE provides regular education and training for better diagnosis and treatment. In the current review, we focus on the importance of having a multidisciplinary team and CoE, the screening strategy for ATTR amyloidosis in Bulgaria, and assessments performed when a patient is first suspected of having this rare disease.

Phenotypic Differences of Glu89Gln Genotype in ATTR Amyloidosis From Endemic Loci: Update From THAOS

INTRODUCTION

Transthyretin amyloidosis (ATTR amyloidosis) is a progressive, clinically heterogeneous disease with spontaneous (wild-type) and hereditary (ATTRv) forms. The Glu89Gln variant is primarily associated with cardiomyopathy and prevalent in Italy and Bulgaria. The objective of this analysis was to better understand the profile of patients with ATTRv Glu89Gln amyloidosis in the Transthyretin Amyloidosis Outcomes Survey (THAOS).

METHODS

THAOS is an ongoing, global, longitudinal, observational survey of patients with ATTR amyloidosis, including both inherited and wild-type disease, and asymptomatic carriers with mutations in the transthyretin gene. Demographic and clinical characteristics of all symptomatic patients with the ATTRv Glu89Gln variant enrolled in THAOS are described (data cutoff, January 6, 2020).

RESULTS

There were 91 patients with ATTRv Glu89Gln amyloidosis with the majority from Bulgaria (n = 53) or Italy (n = 29). All patients were Caucasian and 50.5% were male. Patients from Bulgaria had a mean (standard deviation) age at enrollment of 57.1 (8.2) years, and duration of symptoms of 8.6 (9.6) years, compared with 54.8 (8.6) and 5.0 (4.1) years in Italy. In Bulgaria, 39.6% of patients were of a predominantly cardiac phenotype, 18.9% predominantly neurologic, and 41.5% mixed. In Italy, 3.4% of patients were predominantly cardiac, 62.1% predominantly neurologic, and 34.5% mixed.

CONCLUSIONS

The majority of patients with ATTRv Glu89Gln amyloidosis in THAOS are from Bulgaria or Italy. There were notable phenotypic differences, with the cardiac phenotype more common in Bulgaria and the neurologic phenotype more common in Italy. Over one-third of patients had a mixed phenotype, suggesting a potential role of multiple genetic and/or environmental factors and the need for comprehensive assessment of all patients.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00628745.

Very Early Onset of ATTRE89Q Amyloidosis in a Homozygous Patient

Case Presentarion:

Hereditary transthyretin amyloidosis is a progressive, fatal disease that generally involves the peripheral nervous system, the autonomic nervous system, and the heart. It is autosomal dominant with different penetrance depending on the mutation and the genetic background. Many other missense mutations of the TTR gene may cause the disease. Being an overall rare disease is very rare to observe the condition of homozygosity. In particular, cases of homozygosity have been described in patients with ATTRV30M and ATTRV122I amyloidosis. In the former, the phenotype does not seem to be aggravated, having an age of onset and disease course that does not appear to differ from those of heterozygotes, while in the latter, the onset appears to be earlier.

Conclusion:

We report the first case of ATTRE89Q amyloidosis in a patient that was homozygous for the E89Q mutation in the TTR gene. The clinical phenotype resulted in the earlier disease onset reported in this form of amyloidosis, suggesting that the homozygous condition may be prognostically negative.

Recommendations for the diagnosis and management of transthyretin amyloidosis with gastrointestinal manifestations

Transthyretin amyloid (ATTR) amyloidosis is an adult-onset, rare systemic disorder characterized by the accumulation of misfolded fibrils in the body, including the peripheral nerves, the heart and the gastrointestinal tract. Gastrointestinal manifestations are common in hereditary (ATTRv) amyloidosis and are present even before the onset of the polyneuropathy in some cases. Delays in diagnosis of ATTRv amyloidosis with gastrointestinal manifestations commonly occur because of fragmented knowledge among gastroenterologists and general practitioners, as well as a shortage of centers of excellence and specialists dedicated to disease management. Although the disease is becoming well-recognized in the societies of Neurology and Cardiology, it is still unknown for most gastroenterologists. This review presents the recommendations for ATTRv amyloidosis with gastrointestinal manifestations elaborated by a working group of European gastroenterologists and neurologists, and aims to provide digestive health specialists with an overview of crucial aspects of ATTRv amyloidosis diagnosis to help facilitate rapid and accurate identification of the disease by focusing on disease presentation, misdiagnosis and management of gastrointestinal symptoms.

Cardiac involvement, morbidity and mortality in hereditary transthyretin amyloidosis because of p.Glu89Gln mutation

BACKGROUND

Hereditary transthyretin amyloidosis is a systemic infiltrative disease, caused by a mutation in the transthyretin gene. p.Glu89Gln is the most common mutation in the Balkan countries.

METHODS

We evaluated the clinical manifestations, cardiac involvement, morbidity and mortality in 78 patients with p.Glu89Gln mutation, verified through a DNA analysis. Clinical assessment, electrocardiogram and echocardiography were performed at the time of diagnosis. The patients have been followed for 30 months.

RESULTS

All included patients were Caucasian, 39 (50%) - men, with median age at diagnosis of 56 years (42-73), median age at onset -- 53 years (35-69), starting significantly earlier in men (4.36, P = 0.004). Cardiac and neurological involvement was found in 74 (95%) patients. Pathological ECG was present in 65 (84%) patients, infarct pattern in 43 (56%), low voltage in 24 (31%). Echocardiography revealed an infiltrative cardiomyopathy with restrictive filling in 31 (40%) and ejection fraction less than 50% in 20 (27%) patients. Twenty-two patients (28%) died: 14 (64%) because of advanced heart failure, 6 (27%) died suddenly, 2 (9%) from an ischemic stroke. The median age at death was 58.5 years (52-72). No statistically significant sex difference in survival was observed; a significant difference in survival was found for the New York Heart Association class, familial amyloidotic polyneuropathy stage, ejection fraction, filling pattern and tafamidis treatment.

CONCLUSION

Cardiac involvement is common and has significant prognostic implications in the evaluated patients with p.Glu89Gln mutation. Heart failure and rhythm disturbances are the main causes of death. An earlier identification of the disease is crucial to improve prognosis.

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.

Transthyretin amyloidosis: Testing strategies and model for center of excellence support

Appropriate testing strategies and strict model for Center Of Excellence (CoE) support are essential for the correct diagnosis, follow-up strategy and treatment plan for transthyretin (ATTR) amyloidosis. CoE is defined as a programme within a healthcare institution established to provide an exceptionally high concentration of expertise and related resources centred on a particular area of medicine, delivering associated care in a comprehensive, interdisciplinary fashion to afford the best patient outcome. Ideally, CoEs provide regular education and training for healthcare professionals and share knowledge and learning with other CoEs and specialists to ensure the highest standards of care. CoEs and testing strategies are of significant value to those with rare diseases and their families, as there is naturally low awareness among healthcare professionals, a phenomenon that potentially delays diagnosis and treatment. In this review, we focus on the importance of performing the most appropriate testing strategies for ATTR amyloidosis and establishing a CoE for this rare disease. We highlight our experience in establishing a CoE in Sofia, Bulgaria and define the fundamental steps needed to successfully launch a programme.