High prevalence of Arginine to Glutamine substitution at 98, 141 and 162 positions in Troponin I (TNNI3) associated with hypertrophic cardiomyopathy among Indians

Current RNA strategies in treating cardiovascular diseases

Cardiovascular disease (CVD) continues to impose a significant global health burden, necessitating the exploration of innovative treatment strategies. Ribonucleic acid (RNA)-based therapeutics have emerged as a promising avenue to address the complex molecular mechanisms underlying CVD pathogenesis. We present a comprehensive review of the current state of RNA therapeutics in the context of CVD, focusing on the diverse modalities that bring about transient or permanent modifications by targeting the different stages of the molecular biology central dogma. Considering the immense potential of RNA therapeutics, we have identified common gene targets that could serve as potential interventions for prevalent Mendelian CVD caused by single gene mutations, as well as acquired CVDs developed over time due to various factors. These gene targets offer opportunities to develop RNA-based treatments tailored to specific genetic and molecular pathways, presenting a novel and precise approach to address the complex pathogenesis of both types of cardiovascular conditions. Additionally, we discuss the challenges and opportunities associated with delivery strategies to achieve targeted delivery of RNA therapeutics to the cardiovascular system. This review highlights the immense potential of RNA-based interventions as a novel and precise approach to combat CVD, paving the way for future advancements in cardiovascular therapeutics.

Identification of variants in genes associated with hypertrophic cardiomyopathy in Mexican patients

The objective of this work was to identify genetic variants in Mexican patients diagnosed with hypertrophic cardiomyopathy (HCM). According to world literature, the genes mainly involved are MHY7 and MYBPC3, although variants have been found in more than 50 genes related to heart disease and sudden death, and to our knowledge there are no studies in the Mexican population. These variants are reported and classified in the ClinVar (PubMed) database and only some of them are recognized in the Online Mendelian Information in Men (OMIM). The present study included 37 patients, with 14 sporadic cases and 6 familial cases, with a total of 21 index cases. Next-generation sequencing was performed on a predesigned panel of 168 genes associated with heart disease and sudden death. The sequencing analysis revealed twelve (57%) pathogenic or probably pathogenic variants, 9 of them were familial cases, managing to identify pathogenic variants in relatives without symptoms of the disease. At the molecular level, nine of the 12 variants (75%) were single nucleotide changes, 2 (17%) deletions, and 1 (8%) splice site alteration. The genes involved were MYH7 (25%), MYBPC3 (25%) and ACADVL, KCNE1, TNNI3, TPM1, SLC22A5, TNNT2 (8%). In conclusion; we found five variants that were not previously reported in public databases. It is important to follow up on the reclassification of variants, especially those of uncertain significance in patients with symptoms of the condition. All patients included in the study and their relatives received family genetic counseling.

Novel MYBPC3 Mutations in Indian Population with Cardiomyopathies

Background

Mutations in Myosin Binding Protein C (MYBPC3) are one of the most frequent causes of cardiomyopathies in the world, but not much data are available in India.

Methods

We carried out targeted direct sequencing of MYBPC3 in 115 hypertrophic (HCM) and 127 dilated (DCM) cardiomyopathies against 197 ethnically matched healthy controls from India.

Results

We detected 34 single nucleotide variations in MYBPC3, of which 19 were novel. We found a splice site mutation [(IVS6+2T) T>G] and 16 missense mutations in Indian cardiomyopathies [5 in HCM; E258K, T262S, H287L, R408M, V483A: 4 in DCM; T146N, V321L, A392T, E393K and 7 in both HCM and DCM; L104M, V158M, S236G, R272C, T290A, G522E, A626V], but those were absent in 197 normal healthy controls. Interestingly, we found 7 out of 16 missense mutations (V158M, E258K, R272C, A392T, V483A, G522E, and A626V) in MYBPC3 were altering the evolutionarily conserved native amino acids, accounted for 8.7% and 6.3% in HCM and DCM, respectively. The bioinformatic tools predicted that those 7 missense mutations were pathogenic. Moreover, the co-segregation of those 7 mutations in families further confirmed their pathogenicity. Remarkably, we also identified compound mutations within the MYBPC3 gene of 6 cardiomyopathy patients (5%) with more severe disease phenotype; of which, 3 were HCM (2.6%) [(1. K244K + E258K + (IVS6+2T) T>G); (2. L104M + G522E + A626V); (3. P186P + G522E + A626V]; and 3 were DCM (2.4%) [(1. 5'UTR + A392T; 2. V158M+G522E; and 3.V158M + T262T + A626V].

Conclusion

The present comprehensive study on MYBPC3 has revealed both single and compound mutations in MYBPC3 and their association with disease in Indian Population with Cardiomyopathies. Our findings may perhaps help in initiating diagnostic strategies and eventually recognizing the targets for therapeutic interventions.

Sarcomeric gene variants among Indians with hypertrophic cardiomyopathy: A scoping review

Hypertrophic cardiomyopathy (HCM) is a genetic heart muscle disease that frequently causes sudden cardiac death (SCD) among young adults. Several pathogenic mutations in genes encoding the cardiac sarcomere have been identified as diagnostic factors for HCM and proposed as prognostic markers for SCD. The objective of this review was to determine the scope of available literature on the variants encoding sarcomere proteins associated with SCD reported among Indian patients with HCM. The eligibility criteria for the scoping review included full text articles that reported the results of genetic screening for sarcomeric gene mutations in HCM patients of Indian south Asian ancestry. We systematically reviewed studies from the databases of Medline, Scopus, Web of Science core collection and Google Scholar. The electronic search strategy included a combination of generic terms related to genetics, disease and population. The protocol of the study was registered with Open Science Framework (https://osf.io/53gde/). A total of 19 articles were identified that reported pathogenic or likely pathogenic (P/LP) variants within MYH7, MYBPC3, TNNT2, TNNI3 and TPM1 genes, that included 16 singletons, one de novo and one digenic mutation (MYH7/ TPM1) associated with SCD among Indian patients. Evidence from functional studies and familial segregation implied a plausible mechanistic role of these P/LP variants in HCM pathology. This scoping review has compiled all the P/LP variants reported to-date among Indian patients and summarized their association with SCD. Single homozygous, de novo and digenic mutations were observed to be associated with severe phenotypes compared to single heterozygous mutations. The abstracted genetic information was updated with reference sequence ID (rsIDs) and compiled into freely accessible HCMvar database, available at https://hcmvar.heartfailure.org.in/. This can be used as a population specific genetic database for reference by clinicians and researchers involved in the identification of diagnostic and prognostic markers for HCM.

Novel Mutations in β-MYH7 Gene in Indian Patients With Dilated Cardiomyopathy

Background

Methods

Results

Conclusions

Analysis of the Exonic Single Nucleotide Polymorphism rs182428269 of the NRF2 Gene in Patients with Diabetic Foot Ulcer

BACKGROUND

The pivotal role of Nuclear factor erythroid-2-related factor 2 (NRF2) in redox homeostasis and wound healing has been well documented. However, the genetic mechanisms that regulate NRF2 in type 2 diabetes and diabetic foot ulcers remain unexplored. The present study investigated the association of single nucleotide polymorphism rs182428269 (-127 C/T) in subjects with type 2 diabetes and diabetic foot ulcers.

METHODS

This cross-sectional study comprised 400 participants that included group I: normal glucose tolerant subjects (NGT, n = 150), group II: type 2 diabetes mellitus subjects (T2DM, n = 150) and group III: infected diabetic foot ulcer subjects (DFU, n = 100). The non-synonymous SNP rs182428269 was selected based on in silico analysis and genotyped by PCR-restriction fragment length polymorphism (RFLP) followed by bidirectional Sanger sequencing. In addition, the gene expression of NRF2 in patients with polymorphism was analyzed by qPCR to evaluate the functional impact of the SNP.

RESULTS

NRF2 expression was significantly decreased among the T2DM and DFU subjects when compared to the NGT subjects. Of particular interest, the homozygous mutant (TT) genotype of rs182428269 polymorphism was significantly associated with an increased risk for the development of T2DM (OR = 1.95 (1.02-3.72), p = 0.04) and DFU (OR = 5.66 (2.98-10.76), p = 0.0001). Furthermore, a progressive decline in NRF2 expression was observed among the T2DM and DFU subjects with "TT" genotype compared to the "CC" and "CT" genotypes.

CONCLUSION

NRF2 polymorphism rs182428269 is associated with the pathogenesis of T2DM and DFU.

Identification of a lncRNA-miRNA-mRNA network based on competitive endogenous RNA theory reveals functional lncRNAs in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease that affects 1 in every 200 people in the general population, leading to cardiac ischemia, heart failure and increased risk of sudden death. Recently, accumulating evidence has suggested that long noncoding RNAs (lncRNAs) may serve specific roles in various biological processes and participate in the pathology of various diseases, including HCM. Although a large number of lncRNAs have been detected, the functions of lncRNAs in HCM are still unknown. In the present study, a global triple network based on competitive endogenous RNA (ceRNA) theory was constructed using data from the National Center for Biotechnology Information Gene Expression Omnibus. Furthermore, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses of mRNAs in the lncRNA-microRNA (miRNA)-mRNA network were performed using the Cytoscape plugins, BiNGO and Database. The lncRNA-miRNA-mRNA network was composed of 30 lncRNA nodes, 94 mRNA nodes and 8 miRNA nodes. Subsequently, hub nodes and the number of relationship pairs were analyzed and showed that 5 lncRNAs (ENST00000597346.1, ENST00000458178.1, ENST00000544461.1, ENST00000567093.1 and ENST00000571219.1) were closely related to HCM. Cluster module analysis and Random Walk with Restart of the ceRNA network further confirmed the potential role of two lncRNAs (ENST00000458178.1 and ENST00000567093.1) in HCM. The present study provides a new strategy for identifying potential pathways associated with HCM or other diseases. Furthermore, lncRNA-miRNA pairs may be regarded as candidate diagnostic biomarkers or potential therapeutic targets for HCM.

Neonatal Severe Hyperparathyroidism: Novel Insights From Calcium, PTH, and the CASR Gene

CONTEXT

Neonatal severe hyperparathyroidism (NSHPT) is rare and potentially lethal. It is usually from homozygous or heterozygous germline-inactivating CASR variant(s). NSHPT shows a puzzling range of serum calcium and parathyroid hormone (PTH) levels. Optimal therapy is unclear.

EVIDENCE ACQUISITION

We categorized genotype/phenotype pairings related to CASRs. For the 2 pairings in NSHPT, each of 57 cases of neonatal severe hyperparathyroidism required calcium, PTH, upper normal PTH, and dosage of a germline pathogenic CASR variant.

EVIDENCE SYNTHESIS

Homozygous and heterozygous NSHPT are 2 among a spectrum of 9 genotype/phenotype pairings relating to CASRs and NSHPT. For the 2 NSHPT pairings, expressions differ in CASR allelic dosage, CASR variant severity, and sufficiency of maternofetal calcium fluxes. Homozygous dosage of CASR variants was generally more aggressive than heterozygous. Among heterozygotes, high-grade CASR variants in vitro were more pathogenic in vivo than low-grade variants. Fetal calcium insufficiency as from maternal hypoparathyroidism caused fetal secondary hyperparathyroidism, which persisted and was reversible in neonates. Among NSHPT pairings, calcium and PTH were higher in CASR homozygotes than in heterozygotes. Extreme hypercalcemia (above 4.5 mM; normal 2.2-2.6 mM) is a robust biomarker, occurring only in homozygotes (83% of that pairing). It could occur during the first week.

CONCLUSIONS

In NSHPT pairings, the homozygotes for pathogenic CASR variants show higher calcium and PTH levels than heterozygotes. Calcium levels above 4.5 mM among NSHPT are frequent and unique only to most homozygotes. This cutoff supports early and robust diagnosis of CASR dosage. Thereby, it promotes definitive total parathyroidectomy in most homozygotes.

Genetic variants in cardiac calcification in Northern Sweden

Extensive coronary calcification without significant stenosis, described as calcific coronary artery disease (CCAD) may cause abnormal myocardial perfusion and hence generalized ischemia. There is a discrepancy in the expression pattern of CCAD compared to the well-known atherosclerotic disease which raises questions about the exact pathophysiology of coronary calcification and whether there is a genetic etiology for it.In this pilot study we studied 3 candidate genes, ectonucleotide pyrophosphatase/phosphodiesterase (ENPP1), ATP Binding Cassette Subfamily C Member 6 (ABCC6), and 5'-Nucleotidase Ecto (NT5E) involved in pyrophosphate (PPi) and inorganic phosphate (Pi) metabolism, which may predispose to coronary arterial or valvular calcification. We studied 70 patients with calcific cardiac disease; 65 with CCAD (age 43-83 years) and 5 with calcific aortic valve disease (CAVD) (age 76-82 years).Five DNA variants potentially affecting protein function were found in 6 patients. One variant is a known disease-causing mutation in the ABCC6 gene. Our findings support that disturbances in the PPi and Pi metabolism might influence the development of CCAD and CAVD. However, segregation in the families must first be performed to ascertain any damaging effect of these variants we have found.We report 4 new genetic variants potentially related to coronary calcification, through the disturbed Pi and PPi metabolism. The search for direct causative genetic variants in coronary artery and aortic valve calcification must be broadened with other genes particularly those involved with Pi and PPi metabolism.

A Complete Absence of Missense Mutation in Myosin Regulatory and Essential Light Chain Genes of South Indian Hypertrophic and Dilated Cardiomyopathies

BACKGROUND

Myosin is a hexameric contractile protein composed of 2 heavy chains associated with 4 light chains of 2 distinct classes - 2 regulatory light chains (MYL2) and 2 essential light chains (MYL3). The myosin light chains stabilize the long alpha helical neck of the myosin head and regulate the myosin ATPase activities.

OBJECTIVES

Mutations in MYL2 and MYL3 are reported to be associated with cardiomyopathies. However, there is no study available on these genes in Indian cardiomyopathies, and therefore we planned to study them.

METHOD

For the first time we sequenced MYL2 and MYL3 genes in a total of 248 clinically well-characterized cardiomyopathies consisting of 101 hypertrophic and 147 dilated cases along with 207 healthy controls from south India.

RESULTS

Our study revealed a total of 10 variations - 7 in MYL2 and 3 in MYL3, of which 3 are novel variations observed exclusively in cases. However, the 15 causative missense mutations previously reported are totally absent in our study, which showed that the sequences of MYL2 and MYL3 are highly conserved in Indian cases/controls.

CONCLUSIONS

MYL2 and MYL3 mutations are rare and the least cause of cardiomyopathies in Indians.

Recent Advances in the Molecular Genetics of Familial Hypertrophic Cardiomyopathy in South Asian Descendants

The South Asian population, numbered at 1.8 billion, is estimated to comprise around 20% of the global population and 1% of the American population, and has one of the highest rates of cardiovascular disease. While South Asians show increased classical risk factors for developing heart failure, the role of population-specific genetic risk factors has not yet been examined for this group. Hypertrophic cardiomyopathy (HCM) is one of the major cardiac genetic disorders among South Asians, leading to contractile dysfunction, heart failure, and sudden cardiac death. This disease displays autosomal dominant inheritance, and it is associated with a large number of variants in both sarcomeric and non-sarcomeric proteins. The South Asians, a population with large ethnic diversity, potentially carries region-specific polymorphisms. There is high variability in disease penetrance and phenotypic expression of variants associated with HCM. Thus, extensive studies are required to decipher pathogenicity and the physiological mechanisms of these variants, as well as the contribution of modifier genes and environmental factors to disease phenotypes. Conducting genotype-phenotype correlation studies will lead to improved understanding of HCM and, consequently, improved treatment options for this high-risk population. The objective of this review is to report the history of cardiovascular disease and HCM in South Asians, present previously published pathogenic variants, and introduce current efforts to study HCM using induced pluripotent stem cell-derived cardiomyocytes, next-generation sequencing, and gene editing technologies. The authors ultimately hope that this review will stimulate further research, drive novel discoveries, and contribute to the development of personalized medicine with the aim of expanding therapeutic strategies for HCM.

Cardiac troponin structure-function and the influence of hypertrophic cardiomyopathy associated mutations on modulation of contractility

Cardiac troponin (cTn) acts as a pivotal regulator of muscle contraction and relaxation and is composed of three distinct subunits (cTnC: a highly conserved Ca(2+) binding subunit, cTnI: an actomyosin ATPase inhibitory subunit, and cTnT: a tropomyosin binding subunit). In this mini-review, we briefly summarize the structure-function relationship of cTn and its subunits, its modulation by PKA-mediated phosphorylation of cTnI, and what is known about how these properties are altered by hypertrophic cardiomyopathy (HCM) associated mutations of cTnI. This includes recent work using computational modeling approaches to understand the atomic-based structural level basis of disease-associated mutations. We propose a viewpoint that it is alteration of cTnC-cTnI interaction (rather than the Ca(2+) binding properties of cTn) per se that disrupt the ability of PKA-mediated phosphorylation at cTnI Ser-23/24 to alter contraction and relaxation in at least some HCM-associated mutations. The combination of state of the art biophysical approaches can provide new insight on the structure-function mechanisms of contractile dysfunction resulting cTnI mutations and exciting new avenues for the diagnosis, prevention, and even treatment of heart diseases.

A Systematic Review of Phenotypic Features Associated With Cardiac Troponin I Mutations in Hereditary Cardiomyopathies

BACKGROUND

Genetic investigations have established that mutations in proteins of the contractile unit of the myocardium, known as the sarcomere, may be associated with hypertrophic cardiomyopathy (HCM), restrictive cardiomyopathy (RCM), and dilated cardiomyopathy (DCM). It has become clinical practice to offer genetic testing in affected individuals to identify causative mutations, which provides the basis for presymptomatic testing of relatives who are at risk of disease development. This ensures adequate clinical follow-up of mutation carriers, whereas noncarriers can be discharged. However, before genetic testing can be used for individual risk assessment and prediction of prognosis, it is important to investigate if there is a relation between the clinical disease expression (phenotype) of the condition and mutations in specific disease genes (genotype).

METHODS

We reviewed the literature in relation to phenotypic features reported to be associated with mutations in cardiac troponin I (cTnI; TNNI3), which is a recognized sarcomeric disease gene in all 3 cardiomyopathies.

RESULTS

The results of this review did not identify specific genotype-phenotype relations in HCM or DCM, and cTnI appeared to be the most frequent disease gene in RCM.

CONCLUSIONS

To further explore if there is a genotype-phenotype relation, long-term follow-up studies are needed. It is essential to investigate the natural history of the condition among affected individuals and to provide clinical follow-up on disease development among healthy mutation carriers. Such information is required to provide evidence-based counselling for affected families and to elucidate if knowledge about specific genotypes can be used in future risk prediction models.

Coexistence of Digenic Mutations in Both Thin (TPM1) and Thick (MYH7) Filaments of Sarcomeric Genes Leads to Severe Hypertrophic Cardiomyopathy in a South Indian FHCM

Mutations in sarcomeric genes are the leading cause for cardiomyopathies. However, not many genetic studies have been carried out on Indian cardiomyopathy patients. We performed sequence analyses of a thin filament sarcomeric gene, α-tropomyosin (TPM1), in 101 hypertrophic cardiomyopathy (HCM) patients and 147 dilated cardiomyopathy (DCM) patients against 207 ethnically matched healthy controls, revealing 13 single nucleotide polymorphisms (SNPs). Of these, one mutant, S215L, was identified in two unrelated HCM cases-patient #1, aged 44, and patient #2, aged 65-and was cosegregating with disease in these families as an autosomal dominant trait. In contrast, S215L was completely absent in 147 DCM and 207 controls. Patient #1 showed a more severe disease phenotype, with poor prognosis and a family history of sudden cardiac death, than patient #2. Therefore, these two patients and the family members positive for S215L were further screened for variations in MYH7, MYBPC3, TNNT2, TNNI3, MYL2, MYL3, and ACTC. Interestingly, two novel thick filaments, D896N (homozygous) and I524K (heterozygous) mutations, in the MYH7 gene were identified exclusively in patient #1 and his family members. Thus, we strongly suggest that the coexistence of these digenic mutations is rare, but leads to severe hypertrophy in a South Indian familial hypertrophic cardiomyopathy (FHCM).

A novel arginine to tryptophan (R144W) mutation in troponin T (cTnT) gene in an indian multigenerational family with dilated cardiomyopathy (FDCM)

Cardiomyopathy is a major cause of heart failure and sudden cardiac death; several mutations in sarcomeric protein genes have been associated with this disease. Our aim in the present study is to investigate the genetic variations in Troponin T (cTnT) gene and its association with dilated cardiomyopathy (DCM) in south-Indian patients. Analyses of all the exons and exon-intron boundaries of cTnT in 147 DCM and in 207 healthy controls had revealed a total of 15 SNPs and a 5 bp INDEL; of which, polymorphic SNPs were compared with the HapMap population data. Interestingly, a novel R144W mutation, that substitutes polar-neutral tryptophan for a highly conserved basic arginine in cTnT, altering the charge drastically, was identified in a DCM, with a family history of sudden-cardiac death (SCD). This mutation was found within the tropomyosin (TPM1) binding domain, and was evolutionarily conserved across species, therefore it is expected to have a significant impact on the structure and function of the protein. Family studies had revealed that the R144W is co-segregating with disease in the family as an autosomal dominant trait, but it was completely absent in 207 healthy controls and in 162 previously studied HCM patients. Further screening of the proband and three of his family members (positive for R144W mutant) with eight other genes β-MYH7, MYBPC3, TPM1, TNNI3, TTN, ACTC, MYL2 and MYL3, did not reveal any disease causing mutation, proposing the absence of compound heterozygosity. Therefore, we strongly suggest that the novel R144W unique/private mutant identified in this study is associated with FDCM. This is furthermore signifying the unique genetic architecture of Indian population.

An in silico analysis of troponin I mutations in hypertrophic cardiomyopathy of Indian origin

Hypertrophic Cardiomyopathy (HCM) is an autosomal dominant disorder of the myocardium which is hypertrophied resulting in arrhythmias and heart failure leading to sudden cardiac death (SCD). Several sarcomeric proteins and modifier genes have been implicated in this disease. Troponin I, being a part of the Troponin complex (troponin I, troponin C, troponin T), is an important gene for sarcomeric function. Four mutations (1 novel) were identified in Indian HCM cases, namely, Pro82Ser, Arg98Gln, Arg141Gln and Arg162Gln in Troponin I protein, which are in functionally significant domains. In order to analyse the effect of the mutations on protein stability and protein-protein interactions within the Troponin complex, an in silico study was carried out. The freely available X-ray crystal structure (PDB ID: 1JIE) was used as the template to model the protein followed by loop generation and development of troponin complex for both the troponin I wild type and four mutants (NCBI ID: PRJNA194382). The structural study was carried out to determine the effect of mutation on the structural stability and protein-protein interactions between three subunits in the complex. These mutations, especially the arginine to glutamine substitutions were found to result in local perturbations within the troponin complex by creating/removing inter/intra molecular hydrogen bonds with troponin T and troponin C. This has led to a decrease in the protein stability and loss of important interactions between the three subunits. It could have a significant impact on the disease progression when coupled with allelic heterogeneity which was observed in the cases carrying these mutations. However, this can be further confirmed by functional studies on protein levels in the identified cases.