Susceptibility and modifier genes in Portuguese transthyretin V30M amyloid polyneuropathy: complexity in a single-gene disease

Hereditary transthyretin amyloidosis: a myriad of factors that influence phenotypic variability

Hereditary transthyretin-related amyloidosis (ATTRv amyloidosis) is a rare and progressively debilitating disease characterized by the deposition of transthyretin (TTR) amyloid fibrils in various organs and tissues, most commonly in the heart and peripheral nerves. This pathological deposition can lead to significant organ dysfunction and, ultimately, organ failure. ATTRv amyloidosis exhibits a broad range of clinical presentations, from purely neurological symptoms to purely cardiac manifestations, as well as mixed phenotypes which result from both neurological and cardiac implications. This wide phenotypical spectrum realistically challenges disease diagnosis and prognosis, especially in individuals without or with an unknown family history. Multiple factors are thought to contribute to this variability, including genetic, epigenetic, and even environmental influences. Understanding these factors is crucial, as they can significantly affect disease expression and progression. This review aims to summarize each of these contributing factors, to help elucidate the current knowledge on the phenotypical variability of ATTRv amyloidosis.

Transthyretin mutagenesis: impact on amyloidogenesis and disease

Transthyretin (TTR), a homotetrameric protein found in plasma, cerebrospinal fluid, and the eye, plays a pivotal role in the onset of several amyloid diseases with high morbidity and mortality. Protein aggregation and fibril formation by wild-type TTR and its natural more amyloidogenic variants are hallmarks of ATTRwt and ATTRv amyloidosis, respectively. The formation of soluble amyloid aggregates and the accumulation of insoluble amyloid fibrils and deposits in multiple tissues can lead to organ dysfunction and cell death. The most frequent manifestations of ATTR are polyneuropathies and cardiomyopathies. However, clinical manifestations such as carpal tunnel syndrome, leptomeningeal, and ocular amyloidosis, among several others may also occur. This review provides an up-to-date listing of all single amino-acid mutations in TTR known to date. Of approximately 220 single-point mutations, 93% are considered pathogenic. Aspartic acid is the residue mutated with the highest frequency, whereas tryptophan is highly conserved. "Hot spot" mutation regions are mainly assigned to β-strands B, C, and D. This manuscript also reviews the protein aggregation models that have been proposed for TTR amyloid fibril formation and the transient conformational states that convert native TTR into aggregation-prone molecular species. Finally, it compiles the various in vitro TTR aggregation protocols currently in use for research and drug development purposes. In short, this article reviews and discusses TTR mutagenesis and amyloidogenesis, and their implications in disease onset.

Altered gut microbiota in Taiwanese A97S predominant transthyretin amyloidosis with polyneuropathy

Increasing evidence suggests that gut microbiota alterations are related to development and phenotypes of many neuropsychiatric diseases. Here, we evaluated the fecal microbiota and its clinical correlates in patients with hereditary transthyretin amyloidosis (ATTRv) and polyneuropathy. Fecal microbiota from 38 ATTRv patients and 39 age-matched controls was analyzed by sequencing 16S V3-V4 ribosomal RNA, and its relationships with clinical characteristics of polyneuropathy and cardiomyopathy were explored. The familial amyloidotic polyneuropathy stage was stage I, II, and III in 13, 18, and 7 patients. 99mTc-PYP SPECT showed a visual score of 2 in 15 and 3 in 21 patients. The gut microbiota of ATTRv patients showed higher alpha diversity (ASV richness and Shannon effective numbers) and dissimilar beta diversity compared to controls. Relative abundance of microbiota was dominated by Firmicutes and decreased in Bacteroidetes in ATTRv patients than in controls. Patients with more myocardial amyloid deposition were associated with increased alpha diversity, and the abundance of Clostridia was significantly correlated with pathophysiology of polyneuropathy in ATTRv patients. These findings demonstrated alterations in the gut microbiota, especially Firmicutes, in ATTRv. The association between altered microbiota and phenotypes of cardiomyopathy and polyneuropathy might suggest potential contributions of gut microbiota to ATTRv pathogenesis.

Gene Interactions in Human Disease Studies-Evidence Is Mounting

Despite monumental advances in molecular technology to generate genome sequence data at scale, there is still a considerable proportion of heritability in most complex diseases that remains unexplained. Because many of the discoveries have been single-nucleotide variants with small to moderate effects on disease, the functional implication of many of the variants is still unknown and, thus, we have limited new drug targets and therapeutics. We, and many others, posit that one primary factor that has limited our ability to identify novel drug targets from genome-wide association studies may be due to gene interactions (epistasis), gene-environment interactions, network/pathway effects, or multiomic relationships. We propose that many of these complex models explain much of the underlying genetic architecture of complex disease. In this review, we discuss the evidence from multiple research avenues, ranging from pairs of alleles to multiomic integration studies and pharmacogenomics, that supports the need for further investigation of gene interactions (or epistasis) in genetic and genomic studies of human disease. Our goal is to catalog the mounting evidence for epistasis in genetic studies and the connections between genetic interactions and human health and disease that could enable precision medicine of the future.

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.

Amyloid fibril composition type is consistent over time in patients with Val30Met (p.Val50Met) transthyretin amyloidosis

Background

We have previously shown that transthyretin (TTR) amyloidosis patients have amyloid fibrils of either of two compositions; type A fibrils consisting of large amounts of C-terminal TTR fragments in addition to full-length TTR, or type B fibrils consisting of only full-length TTR. Since type A fibrils are associated with an older age in ATTRVal30Met (p.Val50Met) amyloidosis patients, it has been discussed if the TTR fragments are derived from degradation of the amyloid deposits as the patients are aging. The present study aimed to investigate if the fibril composition type changes over time, especially if type B fibrils can shift to type A fibrils as the disease progresses.

Material and methods

Abdominal adipose tissue biopsies from 29 Swedish ATTRVal30Met amyloidosis patients were investigated. The fibril type in the patients´ initial biopsy taken for diagnostic purposes was compared to a biopsy taken several years later (ranging between 2 and 13 years). The fibril composition type was determined by western blot.

Results

All 29 patients had the same fibril composition type in both the initial and the follow-up biopsy (8 type A and 21 type B). Even patients with a disease duration of more than 12 years and an age over 75 years at the time of the follow-up biopsy had type B fibrils in both biopsies.

Discussion

The result clearly shows that the amyloid fibril composition containing large amounts of C-terminal fragments (fibril type A) is a consequence of other factors than a slow degradation process occurring over time.

Clinical Implications of the Amyloidogenic V122I Transthyretin Variant in the General Population

BACKGROUND

The V122I variant in transthyretin (TTR) is the most common amyloidogenic mutation worldwide. The aim of this study is to describe the cardiac phenotype and risk for adverse cardiovascular outcomes of young V122I TTR carriers in the general population.

METHODS AND RESULTS

TTR genotypes were extracted from whole-exome sequence data in participants of the Dallas Heart Study. Participants with African ancestry, available V122I TTR genotypes (N = 1818) and either cardiac magnetic resonance imaging (n = 1364) or long-term follow-up (n = 1532) were included. The prevalence of V122I TTR carriers (45 ± 10 years) was 3.2% (n/N = 59/1818). The V122I TTR carriers had higher baseline left ventricular wall thickness (8.52 ± 1.82 vs 8.21 ± 1.62 mm, adjusted P = .038) than noncarriers, but no differences in other cardiac magnetic resonance imaging measures (P > .05 for all). Although carrier status was not associated with amino terminal pro-B-type natriuretic peptide (NT-proBNP) at baseline (P = .79), V122I TTR carriers had a greater increase in NT-proBNP on follow-up than noncarriers (median 28.5 pg/mL, interquartile range 11.4-104.1 pg/mL vs median 15.9 pg/mL, interquartile range 0.0-43.0 pg/mL, adjusted P = .018). V122I TTR carriers were at a higher adjusted risk of heart failure (hazard ratio 3.82, 95% confidence interval 1.80-8.13, P < .001), cardiovascular death (hazard ratio 2.65, 95% confidence interval 1.14-6.15, P = .023), and all-cause mortality (hazard ratio 1.95, 95% confidence interval 1.08-3.51, P = .026) in comparison with noncarriers.

CONCLUSIONS

V122I TTR carrier status was associated with a greater increase in NT-proBNP, slightly greater left ventricular wall thickness, and a higher risk for heart failure, cardiovascular death, and all-cause mortality. These findings suggest the need to develop amyloidosis screening strategies for V122I TTR carriers.

Are we creating a new phenotype? Physiological barriers and ethical considerations in the treatment of hereditary transthyretin-amyloidosis

Hereditary transthyretin (TTR) amyloidosis (ATTRv) is an autosomal dominant, systemic disease transmitted by amyloidogenic mutations in the TTR gene. To prevent the otherwise fatal disease course, TTR stabilizers and mRNA silencing antisense drugs are currently approved treatment options. With 90% of the amyloidogenic protein produced by the liver, disease progression including polyneuropathy and cardiomyopathy, the two most prominent manifestations, can successfully be halted by hepatic drug targeting or-formerly-liver transplantation. Certain TTR variants, however, favor disease manifestations in the central nervous system (CNS) or eyes, which is mostly associated with TTR production in the choroid plexus and retina. These compartments cannot be sufficiently reached by any of the approved medications. From liver-transplanted patients, we have learned that with longer lifespans, such CNS manifestations become more relevant over time, even if the underlying TTR mutation is not primarily associated with such. Are we therefore creating a new phenotype? Prolonging life will most likely lead to a shift in the phenotypic spectrum, enabling manifestations like blindness, dementia, and cerebral hemorrhage to come out of the disease background. To overcome the first therapeutic limitation, the blood-brain barrier, we might be able to learn from other antisense drugs currently being used in research or even being approved for primary neurodegenerative CNS diseases like spinal muscular atrophy or Alzheimer's disease. But what effects will unselective CNS TTR knock-down have considering its role in neuroprotection? A potential approach to overcome this second limitiation might be allele-specific targeting, which is, however, still far from clinical trials. Ethical standpoints underline the need for seamless data collection to enable more evidence-based decisions and for thoughtful consenting in research and clinical practice. We conclude that the current advances in treating ATTRv amyloidosis have become a meaningful example for mechanism-based treatment. With its great success in improving patient life spans, we will still have to face new challenges including shifts in the phenotype spectrum and the ongoing need for improved treatment precision. Further investigation is needed to address these closed barriers and open questions.

Current and Emerging Therapies for Hereditary Transthyretin Amyloidosis: Strides Towards a Brighter Future

The past few years have witnessed an unprecedented acceleration in the clinical development of novel therapeutic options for hereditary transthyretin amyloidosis. Recently approved agents and drugs currently under investigation not only represent a major breakthrough in this field but also provide validation of the therapeutic potential of innovative approaches, like RNA interference and CRISPR-Cas9-mediated gene editing, in rare inherited disorders. In this review, we describe the evolving therapeutic landscape for hereditary transthyretin amyloidosis and discuss how this highly disabling and fatal condition is turning into a treatable disease. We also provide an overview of the molecular mechanisms involved in transthyretin (TTR) amyloid formation and regression, to highlight how a deeper understanding of these processes has contributed to the identification of novel treatment targets. Finally, we focus on major areas of uncertainty and unmet needs that deserve further efforts to improve long-term patients' outcomes and allow for a brighter future.

Prevalence and Outcomes of p.Val142Ile TTR Amyloidosis Cardiomyopathy: A Systematic Review

BACKGROUND

The p.Val142Ile variant, predominantly found among people of African descent, is the most common cause of variant transthyretin amyloidosis and carriers predominantly develop a cardiomyopathy (variant transthyretin amyloidosis cardiomyopathy) phenotype. Yet, there are conflicting data on the prevalence and outcomes of p.Val142Ile variant carriers.

METHODS

We performed a systematic review of the prevalence and outcomes of p.Val142Ile variant transthyretin amyloidosis cardiomyopathy among subjects of African descent. We found 62 relevant articles after searching the MEDLINE databases from 1980 to 2020 that reported data for ≈150 000 subjects.

RESULTS

The reported worldwide prevalence of the p.Val142Ile variant is 0.3% to 1.6% in the general population. Among people of African descent, the reported prevalence from all studies ranges from 1.1% to 9.8%, but for studies with >1000 subjects, it is 3% to 3.5%. The prevalence of the p.Val142Ile variant in a region is dependent on the reported percentage of subjects who are of African descent in that region. p.Val142Ile variant transthyretin amyloidosis cardiomyopathy typically presents in the seventh to eighth decade of life and the majority of cases reported were male, with 25% to 38% diagnosed with atrial fibrillation. It was associated with a longitudinally worse quality of life and a lower adjusted survival compared with other types of transthyretin amyloidosis cardiomyopathy.

CONCLUSIONS

The p.Val142Ile variant is the most common variant of the transthyretin gene with most carriers being of African descent. The true penetrance is unknown but the p.Val142Ile variant is associated with increased rates of incident heart failure and portends a lower overall survival. Increased awareness could lead to earlier diagnosis and improved heart failure outcomes among those of African descent, which is of increasing importance given the advent of novel therapeutics for this disease.

Serum amyloid P component is an essential element of resistance against Aspergillus fumigatus

Serum amyloid P component (SAP, also known as Pentraxin 2; APCS gene) is a component of the humoral arm of innate immunity involved in resistance to bacterial infection and regulation of tissue remodeling. Here we investigate the role of SAP in antifungal resistance. Apcs^-/- mice show enhanced susceptibility to A. fumigatus infection. Murine and human SAP bound conidia, activate the complement cascade and enhance phagocytosis by neutrophils. Apcs^-/- mice are defective in vivo in terms of recruitment of neutrophils and phagocytosis in the lungs. Opsonic activity of SAP is dependent on the classical pathway of complement activation. In immunosuppressed mice, SAP administration protects hosts against A. fumigatus infection and death. In the context of a study of hematopoietic stem-cell transplantation, genetic variation in the human APCS gene is associated with susceptibility to invasive pulmonary aspergillosis. Thus, SAP is a fluid phase pattern recognition molecule essential for resistance against A. fumigatus.

Targeting transthyretin - Mechanism-based treatment approaches and future perspectives in hereditary amyloidosis

The liver-derived, circulating transport protein transthyretin (TTR) is the cause of systemic hereditary (ATTRv) and wild-type (ATTRwt) amyloidosis. TTR stabilization and knockdown are approved therapies to mitigate the otherwise lethal disease course. To date, the variety in phenotypic penetrance is not fully understood. This systematic review summarizes the current literature on TTR pathophysiology with its therapeutic implications. Tetramer dissociation is the rate-limiting step of amyloidogenesis. Besides destabilizing TTR mutations, other genetic (RBP4, APCS, AR, ATX2, C1q, C3) and external (extracellular matrix, Schwann cell interaction) factors influence the type of onset and organ tropism. The approved small molecule tafamidis stabilizes the tetramer and significantly decelerates the clinical course. By sequence-specific mRNA knockdown, the approved small interfering RNA (siRNA) patisiran and antisense oligonucleotide (ASO) inotersen both significantly reduce plasma TTR levels and improve neuropathy and quality of life compared to placebo. With enhanced hepatic targeting capabilities, GalNac-conjugated siRNA and ASOs have recently entered phase III clinical trials. Bivalent TTR stabilizers occupy both binding groves in vitro, but have not been tested in trials so far. Tolcapone is another stabilizer with the potential to cross the blood-brain barrier, but its half-life is short and liver failure a potential side effect. Amyloid-directed antibodies and substances like doxycycline aim at reducing the amyloid load, however, none of the yet developed antibodies has successfully passed clinical trials. ATTR-amyloidosis has become a model disease for pathophysiology-based treatment. Further understanding of disease mechanisms will help to overcome the remaining limitations, including application burden, side effects, and blood-brain barrier permeability.

Anticipation on age at onset in kindreds with hereditary ATTRV30M amyloidosis from the Majorcan cluster

BACKGROUND

Hereditary transthyretin amyloidosis (ATTRV30M) is a rare disease caused by amyloid deposition and characterized by a heterogeneous presentation. Anticipation (AC) is described as the decrease in age at onset (AO) within each generation. Our aim was to study AC in a large number of ATTRV30M kindred from Majorca (Spain), and gain further insight into parent-of-origin effects.

METHODS

In a cohort of 262 subjects with ATTRV30M amyloidosis belonging to 51 families, we found 37 affected pairs. AO is defined as the age at the first symptom and AC (parent's age at disease onset minus that of the offspring) were calculated. Chi-square test, independent t-test and paired t-test were used for comparisons between groups. Association between AO of parents and offsprings were assessed by Pearson's correlation coefficient.

RESULTS

Offspring mean AO was 16 years lower than that of the parents (p < .001) regardless of the sex of the parents and the offspring. AC occurred in 31 out of the 37 pairs, with no differences related to the sex of parents or offspring. There was a moderate correlation (r = 0.49; p < .001) between AO of the parents and that of the offsprings.

CONCLUSION

AC was no uncommon in our cohort, and AO tended to decrease in successive generations.

Epigenetic profiling of Italian patients identified methylation sites associated with hereditary transthyretin amyloidosis

Hereditary transthyretin (TTR) amyloidosis (hATTR) is a rare life-threatening disorder caused by amyloidogenic coding mutations located in TTR gene. To understand the high phenotypic variability observed among carriers of TTR disease-causing mutations, we conducted an epigenome-wide association study (EWAS) assessing more than 700,000 methylation sites and testing epigenetic difference of TTR coding mutation carriers vs. non-carriers. We observed a significant methylation change at cg09097335 site located in Beta-secretase 2 (BACE2) gene (standardized regression coefficient = -0.60, p = 6.26 × 10-8). This gene is involved in a protein interaction network enriched for biological processes and molecular pathways related to amyloid-beta metabolism (Gene Ontology: 0050435, q = 0.007), amyloid fiber formation (Reactome HSA-977225, q = 0.008), and Alzheimer's disease (KEGG hsa05010, q = 2.2 × 10-4). Additionally, TTR and BACE2 share APP (amyloid-beta precursor protein) as a validated protein interactor. Within TTR gene region, we observed that Val30Met disrupts a methylation site, cg13139646, causing a drastic hypomethylation in carriers of this amyloidogenic mutation (standardized regression coefficient = -2.18, p = 3.34 × 10-11). Cg13139646 showed co-methylation with cg19203115 (Pearson's r2 = 0.32), which showed significant epigenetic differences between symptomatic and asymptomatic carriers of amyloidogenic mutations (standardized regression coefficient = -0.56, p = 8.6 × 10-4). In conclusion, we provide novel insights related to the molecular mechanisms involved in the complex heterogeneity of hATTR, highlighting the role of epigenetic regulation in this rare disorder.

The diagnostic challenges of cardiac amyloidosis: A practical approach to the two main types

Systemic amyloidosis of the immunoglobulin light-chain (AL) or transthyretin type (ATTR) is a multisystem protein deposition disease that often involves the heart. Delays in diagnosis are very common and can have detrimental consequences on patient outcomes. Because both major types can now be distinguished quickly and treated effectively, clear approaches are required. There have been advances in radioisotope scintigraphy, monoclonal protein testing and mass spectrometry for typing that need coordinated application. We have entered an era in which rapid diagnosis and ready therapy will save lives, therefore we must develop coherent approaches to this multisystem disease. The prognosis for AL has improved significantly with the incorporation of novel agents such as proteasome inhibitors, immunomodulators and monoclonal antibodies against plasma cells. Multiple independent studies have demonstrated the efficacy of these agents in AL, though tolerability can become an issue with dose reductions required in many cases. Median overall survival for patients achieving complete responses after stem cell transplant and consolidation exceeds a decade. The prognosis for ATTR, both age-related wild-type (ATTRwt) and hereditary due to variants of transthyretin (ATTRv), has improved as well due to the availability of the stabilizer tafamidis and the RNA-interference agents patisiran and inotersen. In both AL and ATTR, with elimination or suppression of the pathologic amyloid-forming protein, symptomatic involvement of the heart, kidneys and peripheral nervous system can improve as well. In this review, we present the current state of diagnosing and treating the two major types of systemic amyloidosis, emphasizing the coherent clinical application of the new tools and treatments. Implementation of the approaches we provide will enable rapid identification of amyloid type and rational selection of therapy.

Cellular secretion and cytotoxicity of transthyretin mutant proteins underlie late-onset amyloidosis and neurodegeneration

Transthyretin amyloidosis (ATTR) is a progressive life-threatening disease characterized by the deposition of transthyretin (TTR) amyloid fibrils. Several pathogenic variants have been shown to destabilize TTR tetramers, leading to aggregation of misfolded TTR fibrils. However, factors that underlie the differential age of disease onset amongst amyloidogenic TTR variants remain elusive. Here, we examined the biological properties of various TTR mutations and found that the cellular secretory pattern of the wild-type (WT) TTR was similar to those of the late-onset mutant (Ala97Ser, p. Ala117Ser), stable mutant (Thr119Met, p. Thr139Met), early-onset mutant (Val30Met, p. Val50Met), but not in the unstable mutant (Asp18Gly, p. Asp38Gly). Cytotoxicity assays revealed their toxicities in the order of Val30Met > Ala97Ser > WT > Thr119Met in neuroblastoma cells. Surprisingly, while early-onset amyloidogenic TTR monomers (M-TTRs) are retained by the endoplasmic reticulum quality control (ERQC), late-onset amyloidogenic M-TTRs can be secreted extracellularly. Treatment of thapsigargin (Tg) to activate the unfolded protein response (UPR) alleviates Ala97Ser M-TTR secretion. Interestingly, Ala97Ser TTR overexpression in Drosophila causes late-onset fast neurodegeneration and a relatively short lifespan, recapitulating human disease progression. Our study demonstrates that the escape of TTR monomers from the ERQC may underlie late-onset amyloidogenesis in patients and suggests that targeting ERQC could mitigate late-onset ATTR.

Monoallelic expression of the TTR gene as a contributor to the age at onset and penetrance of TTR-related amyloidosis

TTR-related amyloidosis (ATTR) is manifested in two allelic forms: familial amyloid polyneuropathy (TTR-FAP) and cardiomyopathy (TTR-FAC), both caused by mutations in the TTR gene. The most prevalent mutation in Bulgaria is p.Glu89Gln. Markedly different age at onset and disease penetrance is noticed in Bulgarian p.Glu89Gln cases even in a single family or between genetically identical twins. The present study aimed to evaluate the transcription profile of the TTR gene in order to better understand the difference in disease onset and penetrance. Six p.Glu89Gln positive families were selected from our registry, based on intrafamilial differences in disease onset and penetrance. Plasma and urine specimens were collected from 13 patients and subjected to transcription analysis. Both mutant and wild type transcripts were visualized in a mixed transcription profile, which is the traditional model of autosomal gene expression. The results from a relative quantification of the mutant versus wild type transcript showed presence of the mutant transcript between 0.14 and 1.14 times against the wild type. In addition, monoallelic expression signature was also detected. Based on our results we propose a model of natural selection, which includes age-related allele exclusion or suppression: predominant expression of a wild type (at an early age) and mutant (at the process of ageing) alleles. The intrafamilial differences in disease onset and penetrance need to be considered in genetic counselling and in follow-up of mutation carriers.

Diagnostic and Treatment Approaches Involving Transthyretin in Amyloidogenic Diseases

Transthyretin (TTR) is a thyroid hormone-binding protein which transports thyroxine from the bloodstream to the brain. The structural stability of TTR in tetrameric form is crucial for maintaining its original functions in blood or cerebrospinal fluid (CSF). The altered structure of TTR due to genetic mutations or its deposits due to aggregation could cause several deadly diseases such as cardiomyopathy and neuropathy in autonomic, motor, and sensory systems. The early diagnoses for hereditary amyloid TTR with cardiomyopathy (ATTR-CM) and wild-type amyloid TTR (ATTRwt) amyloidosis, which result from amyloid TTR (ATTR) deposition, are difficult to distinguish due to the close similarities of symptoms. Thus, many researchers investigated the role of ATTR as a biomarker, especially its potential for differential diagnosis due to its varying pathogenic involvement in hereditary ATTR-CM and ATTRwt amyloidosis. As a result, the detection of ATTR became valuable in the diagnosis and determination of the best course of treatment for ATTR amyloidoses. Assessing the extent of ATTR deposition and genetic analysis could help in determining disease progression, and thus survival rate could be improved following the determination of the appropriate course of treatment for the patient. Here, the perspectives of ATTR in various diseases were presented.

C1QA and C1QC modify age-at-onset in familial amyloid polyneuropathy patients

Objectives

Transthyretin (TTR) familial amyloid polyneuropathy (FAP) (OMIM 176300) shows a variable age‐at‐onset (AO), including within families. We hypothesized that variants in C1QA and C1QC genes, might also act as genetic modifiers of AO in TTR‐FAP Val30Met Portuguese patients.

Methods

We analyzed DNA samples of 267 patients (117 families). To search for variants, all exons and flanking regions were genotyped by automated sequencing. We used generalized estimating equations (GEEs) to take into account the non‐independency of AO among relatives. Intensive in silico analyses were performed, using various software to assess miRNAs target sites, splicing sites, transcription factor binding sites alterations, and gene–gene interactions.

Results

Two variants for C1QA gene, GA genotype of rs201693493 (P < 0.001) and CT genotype of rs149050968 (P < 0.001), were significantly associated with later AO. In silico analysis demonstrated, that rs201693493 may alter splicing activity. Regarding C1QC, we found three statistically significant results: GA genotype of rs2935537 (P = 0.003), GA genotype of rs201241346 (P < 0.001) and GA genotype of rs200952686 (P < 0.001). The first two were associated with earlier AO, whereas the third was associated with later‐onset.

Interpretation

C1QA was associated with later onset, whereas C1QC may have a double role: variants may confer earlier or later AO. As found in a study in Cyprus, we confirmed the role of complement C1Q genes (and thus of inflammation) as modulator of AO in Portuguese patients with TTR‐FAP Val30Met.

Origin of sporadic late-onset hereditary ATTR Val30Met amyloidosis in Japan

Hereditary transthyretin (ATTRm) amyloidosis, formerly known as familial amyloid polyneuropathy, is a major type of hereditary systemic amyloidosis, in which the disease is caused by mutant transthyretin (TTR). Although more than 140 different point mutations have been identified in the TTR gene, ATTRm amyloidosis patients with the TTR Val30Met mutation are most frequently found worldwide. Interestingly, the onset age of the ATTR Val30Met amyloidosis is highly varied among countries and regions. The reason for these differences in onset age and penetrance remains to be elucidated. We recently performed an epidemiological study to analyze the clinical and genetic characteristics of ATTRm amyloidosis patients in Japan. Our results led us to the following questions: Why did most of the non-endemic patients with the same TTR Val30Met mutation not have a family history of the disease, a typical autosomal dominant hereditary disorder? Why does ATTR Val30Met amyloidosis alone demonstrate foci of occurrence? Why is only this type of ATTRm amyloidosis nationally and globally distributed? In this mini-review, we discuss these unanswered questions based on recent genetic epidemiological studies on ATTR Val30Met amyloidosis.

Epistasis analysis of metabolic genes polymorphisms associated with ischemic heart disease in Yucatan

OBJECTIVE

Epistasis is a type of genetic interaction that could explain much of the phenotypic variability of complex diseases. In this work, the effect of epistasis of metabolic genes and cardiovascular risk on the susceptibility to the development of ischemic heart disease in Yucatan was determined.

METHODS

Case-control study in 79 Yucatecan patients with ischemic heart disease and 101 healthy controls matched by age and origin with cases. The polymorphisms -108CT, Q192R, L55M (paraoxonase 1; PON1), C677T, A1298C (methylenetetrahydrofolate reductase; MTHFR), and the presence/absence of the glutathione S-transferase T1 (GSTT1) gene were genotyped. Epistasis analysis was performed using the multifactorial dimensional reduction method. The best risk prediction model was selected based on precision (%), statistical significance (P<0.05), and cross-validation consistency.

RESULTS

We found an independent association of the null genotype GSTT1*0/0 (OR=3.39, CI: 1.29-8.87, P=0.017) and the null allele (OR=1.86, CI: 1.19-2.91, P=0.007) with ischemic heart disease. The GSTT1*0 deletion and the 677TT genotype (MTHFR) were identified as being at a high cardiovascular risk, whereas the GSTT1*1 wild type genotype and the CC677 variant were at low risk. The gene-environment interaction identified the GSTT1 gene, C677T polymorphism (MTHFR), and hypertension as the factors that best explain ischemic heart disease in the study population.

CONCLUSIONS

The interaction of the MTHFR, GSTT1 and hypertension may constitute a predictive model of risk for early onset ischemic heart disease in the population of Yucatan.

The search for gene-gene interactions in genome-wide association studies: challenges in abundance of methods, practical considerations, and biological interpretation

One of the primary goals in this era of precision medicine is to understand the biology of human diseases and their treatment, such that each individual patient receives the best possible treatment for their disease based on their genetic and environmental exposures. One way to work towards achieving this goal is to identify the environmental exposures and genetic variants that are relevant to each disease in question, as well as the complex interplay between genes and environment. Genome-wide association studies (GWAS) have allowed for a greater understanding of the genetic component of many complex traits. However, these genetic effects are largely small and thus, our ability to use these GWAS finding for precision medicine is limited. As more and more GWAS have been performed, rather than focusing only on common single nucleotide polymorphisms (SNPs) and additive genetic models, many researchers have begun to explore alternative heritable components of complex traits including rare variants, structural variants, epigenetics, and genetic interactions. While genetic interactions are a plausible reality that could explain some of the heritabliy that has not yet been identified, especially when one considers the identification of genetic interactions in model organisms as well as our understanding of biological complexity, still there are significant challenges and considerations in identifying these genetic interactions. Broadly, these can be summarized in three categories: abundance of methods, practical considerations, and biological interpretation. In this review, we will discuss these important elements in the search for genetic interactions along with some potential solutions. While genetic interactions are theoretically understood to be important for complex human disease, the body of evidence is still building to support this component of the underlying genetic architecture of complex human traits. Our hope is that more sophisticated modeling approaches and more robust computational techniques will enable the community to identify these important genetic interactions and improve our ability to implement precision medicine in the future.

Transthyretin Cardiac Amyloidosis in Black Americans

Transthyretin-related cardiac amyloidosis is a progressive infiltrative cardiomyopathy that mimics hypertensive and hypertrophic heart disease and often goes undiagnosed. In the United States, the hereditary form disproportionately afflicts black Americans, who when compared with whites with wild-type transthyretin amyloidosis, a phenotypically similar condition, present with more advanced disease despite having a noninvasive method for early identification (genetic testing). Although reasons for this are unclear, this begs to consider the inadequate access to care, societal factors, or a biological basis. In an effort to improve awareness and explore unique characteristics, we review the pathophysiology, epidemiology, and therapeutic strategies for transthyretin amyloidosis and highlight diagnostic pitfalls and clinical pearls for identifying patients with amyloid heart disease.

Management of asymptomatic gene carriers of transthyretin familial amyloid polyneuropathy

Transthyretin familial amyloid polyneuropathy (TTR‐FAP) is a rare, severe, and irreversible, adult‐onset, hereditary disorder caused by autosomal‐dominant mutations in the TTR gene that increase the intrinsic propensity of transthyretin protein to misfold and deposit systemically as insoluble amyloid fibrils in nerve tissues, the heart, and other organs. TTR‐FAP is characterized by relentless, progressively debilitating polyneuropathy, and leads to death, on average, within 10 years of symptom onset without treatment. With increased availability of disease‐modifying treatment options for a wider spectrum of patients with TTR‐FAP, timely detection of the disease may offer substantial clinical benefits. This review discusses mutation‐specific predictive genetic testing in first‐degree relatives of index patients diagnosed with TTR‐FAP and the structured clinical follow‐up of asymptomatic gene carriers for prompt diagnosis and early therapeutic intervention before accumulation of substantial damage. Muscle Nerve54: 353–360, 2016

Non-coding variants contribute to the clinical heterogeneity of TTR amyloidosis

Coding mutations in TTR gene cause a rare hereditary form of systemic amyloidosis, which has a complex genotype-phenotype correlation. We investigated the role of non-coding variants in regulating TTR gene expression and consequently amyloidosis symptoms. We evaluated the genotype-phenotype correlation considering the clinical information of 129 Italian patients with TTR amyloidosis. Then, we conducted a re-sequencing of TTR gene to investigate how non-coding variants affect TTR expression and, consequently, phenotypic presentation in carriers of amyloidogenic mutations. Polygenic scores for genetically determined TTR expression were constructed using data from our re-sequencing analysis and the GTEx (Genotype-Tissue Expression) project. We confirmed a strong phenotypic heterogeneity across coding mutations causing TTR amyloidosis. Considering the effects of non-coding variants on TTR expression, we identified three patient clusters with specific expression patterns associated with certain phenotypic presentations, including late onset, autonomic neurological involvement, and gastrointestinal symptoms. This study provides novel data regarding the role of non-coding variation and the gene expression profiles in patients affected by TTR amyloidosis, also putting forth an approach that could be used to investigate the mechanisms at the basis of the genotype-phenotype correlation of the disease.

Corino de Andrade disease: mechanisms and impact on reproduction

Familial amyloid polyneuropathy was first described by Corino de Andrade in 1952 in Northern Portugal. It is a fatal autosomal dominant neurodegenerative disorder characterized by a progression of neurologic symptoms, beginning early in the reproductive life. The Transthyretin gene mutation originates a mutated protein that precipitates in the connective tissue as amyloid deposits. This disease is presently named Transthyretin-related hereditary amyloidosis. We performed an extensive review on this disease based on searches in Medical databases and in paper references. In this review, we briefly summarize the epidemiology and the mechanisms involved on amyloid deposition; we detailed how to evaluate the mechanisms implicated on the development of the major signs and symptoms associated with reproductive dysfunction; and we discuss the mechanisms involved in secondary sexual dysfunction after psychological treatments. Treatment of the disease is directed towards relieving specific symptoms in association with liver transplant, and molecular and genetic therapeutics. Although the current clinical trials indicate symptoms relief, no data on the reproductive function was reported. Thus, preimplantation genetic diagnosis is presently the only available technique that eradicates the disease as it avoids the birth of new patients.

One mutation, two distinct disease variants: unravelling the impact of transthyretin amyloid fibril composition

Although hereditary transthyretin (h-ATTR) amyloidosis is a monogenetic disease, a large variation in its phenotype has been observed. The common hypothesis of amyloid fibril formation involves dissociation of the transthyretin (TTR) tetramer into monomers that after misfolding reassemble into amyloid fibrils. This notion is partly challenged by the finding of two distinct types of amyloid fibrils. One of these, type A, consists of C-terminal ATTR fragments and full-length TTR, whereas the other, type B, consists only of full-length TTR. All organs of an individual patient contain ATTR deposits of either type A or type B fibrils, and the composition in each individual remains unchanged over time. The finding of two distinct types of ATTR fibrils suggests that there are at least two different pathways in operation for ATTR fibril formation. For the most common European mutation, TTR Val30Met, ATTR fibril composition is related to the outcome of liver transplantation, which is the first successful treatment for the disease, and the penetrance of the trait. In addition, the presence of C-terminal ATTR fragments has an impact on the affinity for various tracers used for noninvasive imaging of amyloid depositions such as 99 m-technetium-diphosphono-propanodicarboxylic acid scintigraphy and positron emission tomography utilizing Pittsburgh component B, and even for the gold standard diagnostic procedure, tissue biopsy stained by Congo red and examined under polarized light. The importance of amyloid fibril composition needs to be taken into consideration when designing clinical trials of treatment modalities, and also in the evaluation of diagnostic methods such as imaging techniques.

Transthyretin V122I (pV142I)* cardiac amyloidosis: an age-dependent autosomal dominant cardiomyopathy too common to be overlooked as a cause of significant heart disease in elderly African Americans

Since the identification of a valine-to-isoleucine substitution at position 122 (TTR V122I; pV142I) in the transthyretin (TTR)-derived fibrils extracted from the heart of a patient with late-onset cardiac amyloidosis, it has become clear that the amyloidogenic mutation and the disease occur almost exclusively in individuals of identifiable African descent. In the United States, the amyloidogenic allele frequency is 0.0173 and is carried by 3.5% of community-dwelling African Americans. Genotyping across Africa indicates that the origin of the allele is in the West African countries that were the major source of the slave trade to North America. At autopsy, the allele was found to be associated with cardiac TTR amyloid deposition in all the carriers after age 65 years; however, the clinical penetrance varies, resulting in substantial heart disease in some carriers and few symptoms in others. The allele has been found in 10% of African Americans older than age 65 with severe congestive heart failure. At this time there are potential forms of therapy in clinical trials. The combination of a highly accurate genetic test and the potential for specific therapy demands a greater awareness of this autosomal dominant, age-dependent cardiac disease in the cardiology community.Genet Med advance online publication 19 January 2017.

Familial amyloid polyneuropathy in Portugal: New genes modulating age-at-onset

Objectives

Familial amyloid polyneuropathy (FAP ATTRV30M) shows a wide variation in age‐at‐onset (AO) between clusters, families, and among generations. We will now explore some candidate genes involved in altered disease pathways in order to assess their role as genetic modifiers of AO, using a family‐centered approach.

Methods

We analyzed 62 tagging SNPs from nine genes‐NGAL,MMP‐9,BGN,MEK1,MEK2,ERK1,ERK2,HSP27, and YWHAZ – in a sample of 318 V30M Portuguese patients (106 families), currently under follow‐up. A generalized estimating equation analysis was used to take into account nonindependency of AO between relatives. Also, an in silico analysis was performed in order to assess the functional impact of significant variants associated with AO.

Results

We found for the first time variants from six genes (NGAL,BGN (in the female group), MEK1,MEK2,HSP27, and YWHAZ) that were significantly associated with early‐ and/or late‐onset. Then, we confirmed a strong synergistic interaction between NGAL and MMP‐9 genes. Additionally, by an in silico analysis, we found some variants for MEK1 gene that may alter binding of the transcription factors and that influence the regulation of gene expression regarding microRNA binding sites and splicing regulatory factors.

Interpretation

These findings showed that different genetic factors can modulate differently the onset of disease's symptoms and revealed new mechanisms with clinical implications in the genetic counseling and follow‐up of mutation carriers and could contribute for development of potential therapeutical targets.

Genetic background modifies amyloidosis in a mouse model of ATTR neuropathy

Penetrance and age of onset of ATTRV30M amyloidotic neuropathy varies significantly among different populations. This variability has been attributed to both genetic and environmental modifiers. We studied the effect of genetic background on phenotype in two lines of transgenic mice bearing the same ATTRV30M transgene. Amyloid deposition, transthyretin (TTR), megalin, clusterin and disease markers of endoplasmic reticulum stress, the ubiquitin-proteasome system, apoptosis, and complement activation were assessed with WB and immunohistochemistry in donor and recipient tissue. Our results indicate that genetic background modulates amyloid deposition by influencing TTR handling in recipient tissue and may partly account for the marked variability in penetrance observed in various world populations.

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Genetic background modulates ATTR amyloid deposition.

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Genetic background affects pathogenic cascades involved in amyloidogenesis.

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Megalin and clustering possibly involved in the handing of TTR monomers.

The prevalence and distribution of the amyloidogenic transthyretin (TTR) V122I allele in Africa

Background

Transthyretin (TTR) pV142I (rs76992529‐A) is one of the 113 variants in the human TTR gene associated with systemic amyloidosis. It results from a G to A transition at a CG dinucleotide in the codon for amino acid 122 of the mature protein (TTR V122I). The allele frequency is 0.0173 in African Americans.

Methods

PCR‐based assays to genotype 2767 DNA samples obtained from participants in genetic studies from various African populations supplemented with sequencing data from 529 samples within the 1000 Genomes Project.

Results

The rs76992529‐A variant allele was most prevalent (allele frequency 0.0253) in the contiguous West African countries of Sierra Leone, Guinea, Ivory Coast, Burkina Faso, Ghana, and Nigeria. In other African countries, the mean allele frequency was 0.011.

Conclusions

Our data are consistent with a small number of founder carriers of the amyloidogenic TTR V122I (p.Val142Ile) allele in southern West Africa, with no apparent advantage or disadvantage of an allele carrying newborn reaching adulthood. In U.S. African Americans, the allele represents a significant risk for congestive heart failure late in life. If clinical penetrance is similar in African countries with high allele frequencies, then cardiac amyloidosis could also represent a significant cause of heart disease in the elderly in those populations.

Variants in RBP4 and AR genes modulate age at onset in familial amyloid polyneuropathy (FAP ATTRV30M)

Familial amyloid polyneuropathy (FAP) ATTRV30M is a neurodegenerative disorder due to point mutations in the transthyretin gene, with V30M being the commonest. FAP ATTRV30M shows a wide variation in age at onset (AO) between clusters, families and generations. Portuguese patients also show remarkable AO differences between genders. Genes found to be associated with FAP ATTRV30M pathways may act as AO modifiers. Our aim was to further explore the role of APCS and RBP4 genes and to study for the first time the involvement of sex-linked genetic modifiers - AR and HSD17B1 genes - in AO variation in Portuguese families. We collected DNA from a sample of 318 patients, currently under follow-up. A total of 18 tagging SNPs from APCS, RBP4, AR and HSD17B1 and 5 additional SNPs from APCS and RBP4 previously studied were genotyped. To account for nonindependency of AO between members of the same family, we used generalized estimating equations (GEEs). We found that APCS and RBP4 were associated with late AO. In addition, rs11187545 of the RBP4 was associated with an early AO. For the AR, in the male group three SNPs were associated with an early AO, whereas in the female group four were associated with both an early and later AO. These results strengthened the role of APCS and RBP4 genes and revealed for the first time the contribution of AR genes as an AO modifier in both males and females. These findings may have important implications in genetic counseling and for new therapeutic strategies.

A roadmap to multifactor dimensionality reduction methods

Complex diseases are defined to be determined by multiple genetic and environmental factors alone as well as in interactions. To analyze interactions in genetic data, many statistical methods have been suggested, with most of them relying on statistical regression models. Given the known limitations of classical methods, approaches from the machine-learning community have also become attractive. From this latter family, a fast-growing collection of methods emerged that are based on the Multifactor Dimensionality Reduction (MDR) approach. Since its first introduction, MDR has enjoyed great popularity in applications and has been extended and modified multiple times. Based on a literature search, we here provide a systematic and comprehensive overview of these suggested methods. The methods are described in detail, and the availability of implementations is listed. Most recent approaches offer to deal with large-scale data sets and rare variants, which is why we expect these methods to even gain in popularity.

Most recent common ancestor of TTR Val30Met mutation in Italian population and its potential role in genotype-phenotype correlation

INTRODUCTION

Transthyretin (TTR)-related amyloidosis is characterized by autosomal transmission of amyloidogenic mutated TTR. Val30Met is one of the most common amyloidogenic TTR mutations, showing a worldwide distribution with phenotypic heterogeneity among human populations. Multiple founder mutations for Val30Met foci have been hypothesized and the different origins may explain the phenotypic variability. The aim of our study is to determine the origin of Italian Val30Met and to analyze the genetic relationship of other Val30Met foci.

METHODS

We analyzed the origin of Italian Val30Met through 11 microsatellite markers around the TTR gene in 29 patients and 34 healthy controls.

RESULTS

Our genetic analysis showed an estimated age of origin of 34-36 generations ago for the Italian Val30Met. Comparing Italian Val30Met haplotypes with those from Sweden and Portugal highlights relevant differences that seem to be consistent with an independent origin of Italian Val30Met mutation. This genetic evidence agrees with the disease phenotypic variation in these populations.

DISCUSSION AND CONCLUSIONS

Italian Val30Met mutation should have originated before the Portuguese and Swedish Val30Met ones (which arose through independent mutational events). This indicates a genetic diversity in the surrounding regions of three different Val30Met mutations, supporting the hypothesis that TTR non-coding regions may contribute to phenotypic heterogeneity.

In silico analysis of TTR gene (coding and non-coding regions, and interactive network) and its implications in transthyretin-related amyloidosis

INTRODUCTION

Transthyretin (TTR)-related amyloidosis is a life-threatening disease. Currently, several questions about the pathogenic mechanisms of TTR-related amyloidosis remain unanswered.

METHODS

We have investigated various TTR-related issues using different in silico approaches.

RESULTS

Using an amino acid similarity-based analysis, we have indicated the most relevant TTR secondary structures in determining mutation impact. Our amyloidogenic propensity analysis of TTR missense substitutions has highlighted a similar pattern for wild-type and mutated TTR amino β acid sequences. However, some mutations present differences with respect to the general distribution. We have identified non-coding variants in cis-regulatory elements of the TTR gene, and our analysis on V122I-related haplotypes has indicated differences in non-coding regulatory variants, suggesting differences among V122I carriers. The analysis of methylation status indicated CpG sites that may affect TTR expression. Finally, our interactive network analysis revealed functional partners of TTR that may play a modifier role in the pathogenesis of TTR-related amyloidosis.

DISCUSSION AND CONCLUSION

Our data provided new insights into the pathogenesis of TTR-related amyloidosis that, if they were to be confirmed through experimental investigations, could significantly improve our understanding of the disease.

Diagnostic hallmarks and pitfalls in late-onset progressive transthyretin-related amyloid-neuropathy

Familial amyloid polyneuropathy (FAP) is a progressive systemic autosomal dominant disease caused by pathogenic mutations in the transthyretin (TTR) gene. We studied clinical, electrophysiological, histopathological, and genetic characteristics in 15 (13 late-onset and two early-onset) patients belonging to 14 families with polyneuropathy and mutations in TTR. In comparison, we analysed the features of nine unrelated patients with an idiopathic polyneuropathy, in whom TTR mutations have been excluded. Disease occurrence was familial in 36 % of the patients with TTR-associated polyneuropathy and the late-onset type was observed in 86 % (mean age at onset 65.5 years). Clinically, all late-onset TTR-mutant patients presented with distal weakness, pansensory loss, absence of deep tendon reflexes, and sensorimotor hand involvement. Afferent-ataxic gait was present in 92 % leading to wheelchair dependence in 60 % after a mean duration of 4.6 years. Autonomic involvement was observed in 60 %, and ankle edema in 92 %. The sensorimotor polyneuropathy was from an axonal type in 82 %, demyelinating or mixed type in 9 % each. Compared to the TTR-unmutated idiopathic polyneuropathy patients, we identified rapid progression, early ambulatory loss, and autonomic disturbances, associated with a severe polyneuropathy as red flags for TTR-FAP. In 18 % of the late-onset TTR-FAP patients, no amyloid was found in nerve biopsies. Further diagnostic pitfalls were unspecific electrophysiology, and coincident diabetes mellitus (23 %) or monoclonal gammopathy (7 %). We conclude that a rapid disease course, severely ataxic gait, hand involvement, and autonomic dysfunction are diagnostic hallmarks of late-onset TTR-FAP. Genetic analysis should be performed even when amyloid deposits are lacking or when polyneuropathy-causing comorbidities are concomitant.

Where genotype is not predictive of phenotype: towards an understanding of the molecular basis of reduced penetrance in human inherited disease

Some individuals with a particular disease-causing mutation or genotype fail to express most if not all features of the disease in question, a phenomenon that is known as 'reduced (or incomplete) penetrance'. Reduced penetrance is not uncommon; indeed, there are many known examples of 'disease-causing mutations' that fail to cause disease in at least a proportion of the individuals who carry them. Reduced penetrance may therefore explain not only why genetic diseases are occasionally transmitted through unaffected parents, but also why healthy individuals can harbour quite large numbers of potentially disadvantageous variants in their genomes without suffering any obvious ill effects. Reduced penetrance can be a function of the specific mutation(s) involved or of allele dosage. It may also result from differential allelic expression, copy number variation or the modulating influence of additional genetic variants in cis or in trans. The penetrance of some pathogenic genotypes is known to be age- and/or sex-dependent. Variable penetrance may also reflect the action of unlinked modifier genes, epigenetic changes or environmental factors. At least in some cases, complete penetrance appears to require the presence of one or more genetic variants at other loci. In this review, we summarize the evidence for reduced penetrance being a widespread phenomenon in human genetics and explore some of the molecular mechanisms that may help to explain this enigmatic characteristic of human inherited disease.

Amyloid fibrils containing fragmented ATTR may be the standard fibril composition in ATTR amyloidosis

Abstract The clinical phenotype of familial ATTR amyloidosis depends to some extent on the particular mutation, but differences exist also within mutations. We have previously described that two types of amyloid fibril compositions exist among Swedish ATTRV30M amyloidosis patients, one consisting of a mixture of intact and fragmented ATTR (type A) and one consisting of mainly intact ATTR (type B). The fibril types are correlated to phenotypic differences. Patients with ATTR fragments have a late onset and develop cardiomyopathy, while patients without fragments have an early onset and less myocardial involvement. The present study aimed to determine whether this correlation between fibril type and phenotype is valid for familial ATTR amyloidosis in general. Cardiac or adipose tissues from 63 patients carrying 29 different TTR non-V30M mutations as well as 13 Japanese ATTRV30M patients were examined. Fibril type was determined by western blotting and compared to the patients' age of onset and degree of cardiomyopathy. All ATTR non-V30M patients had a fibril composition with ATTR fragments, except two ATTRY114C patients. No clear conclusions could be drawn about a phenotype to fibril type correlation among ATTR non-V30M patients. In contrast, Japanese ATTRV30M patients showed a similar correlation as previously described for Swedish ATTRV30M patients. This study shows that a fibril composition with fragmented ATTR is very common in ATTR amyloidosis, and suggests that fibrils composed of only full-length ATTR is an exception found only in a subset of patients.

Possible anticipation associated with a novel splice site mutation in episodic ataxia type 2

Anticipation is a phenomenon characterized by decreasing age at onset and increasing severity of symptoms of a disease in successive generations within a pedigree. Anticipation mostly occurs in neurodegenerative diseases with expansion of unstable trinucleotide repeats. However, it has not been previously pointed out in episodic ataxia type 2 (EA2). Clinical and genetic analyses were performed in nine members from three consecutive generations of a Korean family with EA2. We performed a polymerase chain reaction (PCR)-based direct sequence analysis of all coding regions of CACNA1A using genomic DNA. The clinically affected family members showed recurrent vertigo, interictal nystagmus, and childhood epilepsy. There is a decrease in the age onset (possible genetic anticipation) in three succeeding generations of the family. Genetic analysis identified a splice site mutation (p.Val1465Glyfs13X) and normal trinucleotide repeats in CACNA1A in all clinically affected and one unaffected members. Recognizing anticipation would aid in genetic counseling in EA2.

Familial amyloidosis with polyneuropathy associated with TTR Ser50Arg mutation

BACKGROUND

The phenotypic heterogeneity of transthyretin amyloidosis (ATTR) familial polyneuropathy may be linked to the type of mutation and to the environmental factors. A gender difference in relation to the severity of the disease has been suspected. More than 100 different pathogenic variants of hereditary transthyretin (TTR) mutations have been reported.

OBJECTIVE

To describe 32 patients with confirmed TTR Ser50Arg mutation from the same geographical origin.

METHODS

Seven families with up to four affected generations underwent genetic testing and prospective clinical and laboratory evaluations.

RESULTS

The mutation was confirmed in seven patients from different families with clinical symptoms compatible with ATTR amyloidosis, and in 25 (62%) of the 40 direct relatives tested. Of the 32 patients with positive test results, 18 (56%) were men. Only 5 (16%) subjects were disease-free at the time of the genetic test (mean age: 20, range: 18-30-year-old). The rest developed symptoms at a young age, between ages 36 and 41. Symptomatic, histologically positive patients were older than carriers and symptomatic patients without a confirmatory biopsy. The later generation displayed symptoms at a younger age. Initial manifestations in the 27 symptomatic patients were neuropathic in 19 (70%), gastrointestinal in 6 (22%) and autonomic in 1 (4%). Significant differences were demonstrated among genders, where men had a considerably worse outcome.

CONCLUSION

ATTR Ser50Arg mutation was associated with an early onset, an unbalanced male to female ratio, a more aggressive course in males and possibly displayed anticipation.

Transthyretin amyloidosis and the kidney

The amyloidoses are protein-misfolding disorders associated with progressive organ dysfunction. Immunoglobulin light chain is the most common, amyloid A the longest recognized, and transthyretin-associated amyloidosis (ATTR) the most frequent inherited systemic form. Although ATTR, an autosomal-dominant disease, is associated with at least 100 different transthyretin (TTR) mutations, the single amino-acid substitution of methionine for valine at position 30 is the most common mutation. Each variant has a different organ involvement, although clinical differences attributed to environmental and genetic factors exist within the same mutation. Peripheral neuropathy and cardiomyopathy are broadly described, and insights into disease reveal that kidney impairment and proteinuria are also clinical features. This review combines clinical and laboratory findings of renal involvement from the main geographic regions of disease occurrence and for different mutations of TTR. Fifteen nephropathic variants have been described, but the TTR V30M mutation is the best documented. Nephropathy affects patients with late-onset neuropathy, low penetrance in the family, and cardiac dysrhythmias. Microalbuminuria can be the disorder's first presentation, even before the onset of neuropathy. Amyloid renal deposits commonly occur, even in the absence of urinary abnormalities. The experience with renal replacement therapy is based on hemodialysis, which is associated with poor survival. Because TTR is synthesized mainly in the liver, liver transplantation has been considered an acceptable treatment; simultaneous liver-kidney transplantation is recommended to avoid recurrence of nephropathy. In addition, the kidney-safety profile of new drugs in development may soon be available.

Gene-gene and gene-environmental interactions of childhood asthma: a multifactor dimension reduction approach

Background

The importance of gene-gene and gene-environment interactions on asthma is well documented in literature, but a systematic analysis on the interaction between various genetic and environmental factors is still lacking.

Methodology/Principal Findings

We conducted a population-based, case-control study comprised of seventh-grade children from 14 Taiwanese communities. A total of 235 asthmatic cases and 1,310 non-asthmatic controls were selected for DNA collection and genotyping. We examined the gene-gene and gene-environment interactions between 17 single-nucleotide polymorphisms in antioxidative, inflammatory and obesity-related genes, and childhood asthma. Environmental exposures and disease status were obtained from parental questionnaires. The model-free and non-parametrical multifactor dimensionality reduction (MDR) method was used for the analysis. A three-way gene-gene interaction was elucidated between the gene coding glutathione S-transferase P (GSTP1), the gene coding interleukin-4 receptor alpha chain (IL4Ra) and the gene coding insulin induced gene 2 (INSIG2) on the risk of lifetime asthma. The testing-balanced accuracy on asthma was 57.83% with a cross-validation consistency of 10 out of 10. The interaction of preterm birth and indoor dampness had the highest training-balanced accuracy at 59.09%. Indoor dampness also interacted with many genes, including IL13, beta-2 adrenergic receptor (ADRB2), signal transducer and activator of transcription 6 (STAT6). We also used likelihood ratio tests for interaction and chi-square tests to validate our results and all tests showed statistical significance.

Conclusions/Significance

The results of this study suggest that GSTP1, INSIG2 and IL4Ra may influence the lifetime asthma susceptibility through gene-gene interactions in schoolchildren. Home dampness combined with each one of the genes STAT6, IL13 and ADRB2 could raise the asthma risk.

Relation of clinical, echocardiographic and electrocardiographic features of cardiac amyloidosis to the presence of the transthyretin V122I allele in older African-American men

Previous studies have shown that 3% to 4% of African Americans carry an amyloidogenic allele of the human serum protein transthyretin (TTR V122I). The allele appears to have an absolute anatomic risk for cardiac amyloid deposition after 65 years of age. In this study, a case-control comparison was performed of clinical, echocardiographic, and electrocardiographic characteristics of 23 age at risk carriers of the amyloidogenic allele and 46 age-, gender-, and ethnically matched noncarriers being evaluated for cardiac disease using standard clinical testing. The 2 groups were matched for blood pressure and the cardiac ejection fraction. None of the subjects had a prestudy diagnosis of cardiac amyloidosis. Carriers of the amyloidogenic allele were found to have statistically significant increases in the occurrence of many of the echocardiographic features of cardiac amyloidosis relative to the noncarriers and a higher frequency of congestive heart failure and atrial fibrillation. The observations suggest that TTR V122I represents a substantial risk for clinically significant cardiac amyloidosis in elderly African American men, behaving as an age-dependent autosomal dominant disease-associated allele. The diagnosis is difficult to make but can be suspected in African Americans aged >60 years on the basis of age, echocardiographic evidence of diastolic dysfunction, and interventricular septal thickening, even in the absence of more recently available sophisticated echocardiographic techniques for evaluating long-axis function and cardiac magnetic resonance imaging. Positive results for the amyloidogenic TTR V122I allele support the diagnosis and define the origin of the disease, which can be confirmed by endomyocardial biopsy.

Bioinformatics challenges for personalized medicine

MOTIVATION

Widespread availability of low-cost, full genome sequencing will introduce new challenges for bioinformatics.

RESULTS

This review outlines recent developments in sequencing technologies and genome analysis methods for application in personalized medicine. New methods are needed in four areas to realize the potential of personalized medicine: (i) processing large-scale robust genomic data; (ii) interpreting the functional effect and the impact of genomic variation; (iii) integrating systems data to relate complex genetic interactions with phenotypes; and (iv) translating these discoveries into medical practice.

CONTACT

russ.altman@stanford.edu

Using biological knowledge to uncover the mystery in the search for epistasis in genome-wide association studies

The search for the missing heritability in genome-wide association studies (GWAS) has become an important focus for the human genetics community. One suspected location of these genetic effects is in gene-gene interactions, or epistasis. The computational burden of exploring gene-gene interactions in the wealth of data generated in GWAS, along with small to moderate sample sizes, have led to epistasis being an afterthought, rather than a primary focus of GWAS analyses. In this review, I discuss some potential approaches to filter a GWAS dataset to a smaller, more manageable dataset where searching for epistasis is considerably more feasible. I describe a number of alternative approaches, but primarily focus on the use of prior biological knowledge from databases in the public domain to guide the search for epistasis. The manner in which prior knowledge is incorporated into a GWA study can be many and these data can be extracted from a variety of database sources. I discuss a number of these approaches and propose that a comprehensive approach will likely be most fruitful for searching for epistasis in large-scale genomic studies of the current state-of-the-art and into the future.