TTN-related hereditary myopathy with early respiratory failure presented with elevated hemoglobin initially: A case report and literature review

Background

As common abnormal conditions in clinical practice, hypoxemia and respiratory failure are mainly caused by various respiratory diseases. However, other causes are easily overlooked but deserve more attention from doctors.

Case presentation

A 44-year-old man presented with dyspnea for 10 years. In the early stage, his dyspnea was mild without hypoxemia, and he was misdiagnosed with polycythemia vera due to elevated hemoglobin level. He later developed to respiratory failure but he did not have weakness in his extremities. The positional difference in pulmonary function tests and arterial blood gas analysis led us to identify the respiratory muscle dysfunction. Fatty infiltration of the thigh muscle found by magnetic resonance imaging and muscle biopsies gave us more clues to the causes of diaphragmatic dysfunction. Finally, in combination with his family history and the results of whole exome sequencing, he was diagnosed with hereditary myopathy with early respiratory failure (HMERF, OMIM 603689) caused by a variant in the titin gene (TTN).

Conclusions

We have identified a Chinese family with HMERF due to genetic variants in TTN NM_001256850.1: c.90272C > T, p. Pro30091Leu, located at g.179410829A > G on chromosome 2 (GRCh37), which may be specifically associated with the diagrammatic dysfunction. And hyperhemoglobinemia could serve as a potential sign for the early identification of HMERF.

Identification of Genetic Variants Associated with Severe Myocardial Bridging through Whole-Exome Sequencing

Myocardial bridging (MB) is a congenital coronary artery anomaly and an important cause of angina. The genetic basis of MB is currently unknown. This study used a whole-exome sequencing technique and analyzed genotypic differences. Eight coronary angiography-confirmed cases of severe MB and eight age- and sex-matched control patients were investigated. In total, 139 rare variants that are potentially pathogenic for severe MB were identified in 132 genes. Genes with multiple rare variants or co-predicted by ClinVar and CADD/REVEL for severe MB were collected, from which heart-specific genes were selected under the guidance of tissue expression levels. Functional annotation indicated significant genetic associations with abnormal skeletal muscle mass, cardiomyopathies, and transmembrane ion channels. Candidate genes were reviewed regarding the functions and locations of each individual gene product. Among the gene candidates for severe MB, rare variants in DMD, SGCA, and TTN were determined to be the most crucial. The results suggest that altered anchoring proteins on the cell membrane and intracellular sarcomere unit of cardiomyocytes play a role in the development of the missed trajectory of coronary vessels. Additional studies are required to support the diagnostic application of cardiac sarcoglycan and dystroglycan complexes in patients with severe MB.

Changes of ubiquitylated proteins in atrial fibrillation associated with heart valve disease: proteomics in human left atrial appendage tissue

Background

Correlations between posttranslational modifications and atrial fibrillation (AF) have been demonstrated in recent studies. However, it is still unclear whether and how ubiquitylated proteins relate to AF in the left atrial appendage of patients with AF and valvular heart disease.

Methods

Through LC-MS/MS analyses, we performed a study on tissues from eighteen subjects (9 with sinus rhythm and 9 with AF) who underwent cardiac valvular surgery. Specifically, we explored the ubiquitination profiles of left atrial appendage samples.

Results

In summary, after the quantification ratios for the upregulated and downregulated ubiquitination cutoff values were set at >1.5 and <1:1.5, respectively, a total of 271 sites in 162 proteins exhibiting upregulated ubiquitination and 467 sites in 156 proteins exhibiting downregulated ubiquitination were identified. The ubiquitylated proteins in the AF samples were enriched in proteins associated with ribosomes, hypertrophic cardiomyopathy (HCM), glycolysis, and endocytosis.

Conclusions

Our findings can be used to clarify differences in the ubiquitination levels of ribosome-related and HCM-related proteins, especially titin (TTN) and myosin heavy chain 6 (MYH6), in patients with AF, and therefore, regulating ubiquitination may be a feasible strategy for AF.

A novel mutation in the TTN gene resulted in left ventricular noncompaction: a case report and literature review

BACKGROUND

Left ventricular noncompaction (LVNC) is a specific type of cardiomyopathy characterized by coarse trabeculae and interspersed trabecular crypts within the ventricles. Clinical presentation varies widely and may be nonsignificant or may present with progressive heart failure, malignant arrhythmias, and multiorgan embolism. The mode of inheritance is highly heterogeneous but is most commonly autosomal dominant. The TTN gene encodes titin, which is not only an elastic component of muscle contraction but also mediates multiple signalling pathways in striated muscle cells. In recent years, mutations in the TTN gene have been found to be associated with LVNC, but the exact pathogenesis is still not fully clarified.

CASE PRESENTATION

In this article, we report a case of an adult LVNC patient with a TTN gene variant, c.87857G > A (p. Trp29286*), that has not been reported previously. This 43-year-old adult male was hospitalized repeatedly for heart failure. Echocardiography showed reduced myocardial contractility, dilated left ventricle with many prominent trabeculae, and a loose texture of the left ventricular layer of myocardium with crypt-like changes. During the out-of-hospital follow-up, the patient had no significant signs or symptoms of discomfort.

CONCLUSION

This case report enriches the mutational spectrum of the TTN gene in LVNC and provides a basis for genetic counselling and treatment of this patient. Clinicians should improve their understanding of LVNC, focusing on exploring its pathogenesis and genetic characteristics to provide new directions for future diagnosis and treatment.

Circular Intronic RNA circTTN Inhibits Host Gene Transcription and Myogenesis by Recruiting PURB Proteins to form Heterotypic Complexes

Muscle cell growth plays an important role in skeletal muscle development. Circular RNAs (circRNAs) have been proven to be involved in the regulation of skeletal muscle growth and development. In this study, we explored the effect of circTTN on myoblast growth and its possible molecular mechanism. Using C2C12 cells as a functional model, the authenticity of circTTN was confirmed by RNase R digestion and Sanger sequencing. Previous functional studies have showed that the overexpression of circTTN inhibits myoblast proliferation and differentiation. Mechanistically, circTTN recruits the PURB protein on the Titin (TTN) promoter to inhibit the expression of the TTN gene. Moreover, PURB inhibits myoblast proliferation and differentiation, which is consistent with circTTN function. In summary, our results indicate that circTTN inhibits the transcription and myogenesis of the host gene TTN by recruiting PURB proteins to form heterotypic complexes. This work may act as a reference for further research on the role of circRNA in skeletal muscle growth and development.

Genetic landscape in Russian patients with familial left ventricular noncompaction

Background

Left ventricular noncompaction (LVNC) cardiomyopathy is a disorder that can be complicated by heart failure, arrhythmias, thromboembolism, and sudden cardiac death. The aim of this study is to clarify the genetic landscape of LVNC in a large cohort of well-phenotyped Russian patients with LVNC, including 48 families (n=214).

Methods

All index patients underwent clinical examination and genetic analysis, as well as family members who agreed to participate in the clinical study and/or in the genetic testing. The genetic testing included next generation sequencing and genetic classification according to ACMG guidelines.

Results

A total of 55 alleles of 54 pathogenic and likely pathogenic variants in 24 genes were identified, with the largest number in the MYH7 and TTN genes. A significant proportion of variants -8 of 54 (14.8%) -have not been described earlier in other populations and may be specific to LVNC patients in Russia. In LVNC patients, the presence of each subsequent variant is associated with increased odds of having more severe LVNC subtypes than isolated LVNC with preserved ejection fraction. The corresponding odds ratio is 2.77 (1.37 -7.37; p <0.001) per variant after adjustment for sex, age, and family.

Conclusion

Overall, the genetic analysis of LVNC patients, accompanied by cardiomyopathy-related family history analysis, resulted in a high diagnostic yield of 89.6%. These results suggest that genetic screening should be applied to the diagnosis and prognosis of LVNC patients.

Fetal akinesia deformation sequence syndrome associated with recessive TTN variants

Arthrogryposis multiplex congenita (AMC) [also known as multiple joints contracture or Fetal Akinesia Deformation Sequence (FADS)] is etiologically a heterogeneous condition with an estimated incidence of approximately 1 in 3000 live births and much higher incidence when prenatally diagnosed cases are included. The condition can be acquired or secondary to fetal exposures and can also be caused by a variety of single-gene disorders affecting the brain, spinal cord, peripheral nerves, neuromuscular junction, muscle, and a variety of disorders affecting the connective tissues (Niles et al., Prenatal Diagnosis, 2019; 39:720-731). The introduction of next-generation gene sequencing uncovered many genes and causative variants of AMC but also identified genes that cause both dominant and recessive inherited conditions with the variability of clinical manifestations depending on the genes and variants. Molecular diagnosis in these cases is not only important for prognostication but also for the determination of recurrence risk and for providing reproductive options including preimplantation and prenatal diagnosis. TTN, the largest known gene in the human genome, has been known to be associated with autosomal dominant dilated cardiomyopathy. However, homozygote and compound heterozygote pathogenic variants with recessive inheritance have rarely been reported. We report the effect of recessive variants located within the fetal IC and/or N2BA isoforms in association with severe FADS in three families. All parents were healthy obligate carriers and none of them had cardiac or skeletal muscle abnormalities. This report solidifies FADS as an alternative phenotypic presentation associated with homozygote/compound heterozygous pathogenic variants in the TTN.

Rare copy number variation analysis identifies disease-related variants in atrioventricular septal defect patients

Atrioventricular septal defect (AVSD) is a deleterious subtype of congenital heart diseases (CHD) characterized by atrioventricular canal defect. The pathogenic genetic changes of AVSD remain elusive, particularly for copy number variation (CNV), a large segment variation of the genome, which is one of the major forms of genetic variants resulting in congenital heart diseases. In the present study, we recruited 150 AVSD cases and 100 healthy subjects as controls for whole exome sequencing (WES). We identified total 4255 rare CNVs using exon Hidden Markov model (XHMM) and screened rare CNVs by eliminating common CNVs based on controls and Database of Genomic Variants (DGV). Each patient contained at least 9 CNVs, and the CNV burden was prominently presented in chromosomes 19,22,21&16. Small CNVs (<500 kb) were frequently observed. By leveraging gene-based burden test, we further identified 20 candidate AVSD-risk genes. Among them, DYRK1A, OBSCN and TTN were presented in the core disease network of CHD and highly and dynamically expressed in the heart during the development, which indicated they possessed the high potency to be AVSD-susceptible genes. These findings not only provided a roadmap for finally unveiling the genetic cause of AVSD, but also provided more resources and proofs for clinical genetics.

Cardiomyopathy prevalence exceeds 30% in individuals with TTN variants and early atrial fibrillation

PURPOSE

TTN truncating variants (TTNtvs) represent the largest known genetic cause of dilated cardiomyopathies (DCMs), however their penetrance for DCM in general populations is low. More broadly, patients with cardiomyopathies (CMs) often exhibit other cardiac conditions, such as atrial fibrillation (Afib), which has also been linked to TTNtvs. This retrospective analysis aims to characterize the relationship between different cardiac conditions in those with TTNtvs and identify individuals with the highest risk of DCM.

METHODS

In this work we leverage longitudinal electronic health record and exome sequencing data from approximately 450,000 individuals in 2 health systems to statistically confirm and pinpoint the genetic footprint of TTNtv-related diagnoses aside from CM, such as Afib, and determine whether vetting additional significantly associated phenotypes better stratifies CM risk across those with TTNtvs. We focused on TTNtvs in exons with a percentage spliced in >90% (hiPSI TTNtvs), a representation of constitutive cardiac expression.

RESULTS

When controlling for CM and Afib, other cardiac conditions retained only nominal association with TTNtvs. A sliding window analysis of TTNtvs across the locus confirms that the association is specific to hiPSI exons for both CM and Afib, with no meaningful associations in percent spliced in ≤90% exons (loPSI TTNtvs). The combination of hiPSI TTNtv status and early Afib diagnosis (before age 60) found a subset of TTNtv individuals at high risk for CM. The prevalence of CM in this subset was 33%, a rate that was 3.5 fold higher than that in individuals with hiPSI TTNtvs (9% prevalence), 5-fold higher than that in individuals without TTNtvs with early Afib (6% prevalence), and 80-fold higher than that in the general population.

CONCLUSION

Our retrospective analyses revealed that those with hiPSI TTNtvs and early Afib (∼1/2900) have a high prevalence of CM (33%), far exceeding that in other individuals with TTNtvs and in those without TTNtvs with an early Afib diagnosis. These results show that combining phenotypic information along with genomic population screening can identify patients at higher risk for progressing to symptomatic heart failure.

Identification and validation of a TTN-associated immune prognostic model for skin cutaneous melanoma

TTN is the most commonly mutated gene in skin cutaneous melanoma (SKCM). Tumor mutational burden (TMB) can generate new antigens that regulate the recognition of T cells, which will significantly affect the prognosis of patients. The TTN gene has a long coding sequence and a high number of mutant sites, which allows SKCM patients to produce higher TMB and may influence the immune response. It has been found that the overall survival (OS) of SKCM patients with TTN mutation was significantly higher than that of wild-type patients. However, the effect of TTN mutation on the immune microenvironment of SKCM has not been fully investigated. Here, we systematically explored the relationship and potential mechanisms between TTN mutation status and the immune response. We first revealed that TTN mutated SKCM were significantly associated with four immune-related biological processes. Next, 115 immune genes differentially expressed between TTN mutation and wild-type SKCM patients were found to significantly affect the OS of SKCM patients. Then, we screened four immune-related genes (CXCL9, PSMB9, CD274, and FCGR2A) using LASSO regression analysis and constructed a TTN mutation-associated immune prognostic model (TM-IPM) to distinguish the SKCM patients with a high or low risk of poor prognosis, independent of multiple clinical characteristics. SKCM in the low-risk group highly expressed a large number of immune-related genes, and functional enrichment analysis of these genes showed that this group was involved in multiple immune processes and pathways. Furthermore, the nomogram constructed by TM-IPM with other clinicopathological parameters can provide a predictive tool for clinicians. Moreover, we found that CD8⁺ T cells were significantly enriched in the low-risk group. The expression level of immune checkpoints was higher in the low-risk group than in the high-risk group. Additionally, the response to chemotherapeutic agents was higher in the low-risk group than in the high-risk group, which may be related to the long survival in the low-risk group. Collectively, we constructed and validated a TM-IPM using four immune-related genes and analyzed the potential mechanisms of TM-IPM to predict patient prognosis and response to immunotherapy from an immunological perspective.

Enrichment of titin-truncating variants in exon 327 in dilated cardiomyopathy and its relevance to reduced nonsense-mediated mRNA decay efficiency

Titin truncating variants (TTNtvs) are the most common genetic cause of dilated cardiomyopathy (DCM). Among four regions of titin, A-band enrichment of DCM-causing TTNtvs is widely accepted but the underlying mechanism is still unknown. Meanwhile, few reports have identified exon 327 as a highly mutated A-band exon but the degree of exon 327 enrichment has not been quantitatively investigated. To find the real hotspot of DCM-causing TTNtvs, we aimed to reassess the degree of TTNtv enrichment in known titin regions and in exon 327, separately. In addition, we tried to explain exon 327 clustering in terms of nonsense-mediated mRNA decay (NMD) efficiency and a dominant negative mechanism recently proposed. Research papers focusing on TTNtvs found in patients with DCM were collected. A total of 612 patients with TTNtv-realated DCM were obtained from 10 studies. In the four regions of TTN and exon 327, the degree of TTNtvs enrichment was calculated in a way that the effect of distribution of highly expressed exons was normalized. As a result, exon 327 was the only region that showed significant enrichment for DCM-related TTNtv (p < .001). On the other hand, other A-band exons had almost the same number of TTNtv of random distribution. A review of RNAseq data revealed that the median allelic imbalance deviation of exon 327 TTNtvs was .04, indicating almost zero NMD. From these findings, we propose that the widely accepted A-band enrichment of DCM-related TTNtv is mostly attributable to exon 327 enrichment. In addition, based on the recently demonstrated dominant negative mechanism, the extremely low NMD efficiency seems to contribute to exon 327 enrichment.

Heterogeneous pattern of gene expression driven by TTN mutation is involved in the construction of a prognosis model of lung squamous cell carcinoma

Objective

To investigate the impact that TTN mutation had on the gene heterogeneity expression and prognosis in patients with lung adenocarcinoma.

Methods

In this study, the Cancer Genome Atlas (TCGA) dataset was used to analyze the TTN mutations in lung adenocarcinoma. Lung adenocarcinoma data was collected from the TCGA database, clinical information of patients was analyzed, and bioinformatics statistical methods were applied for mutation analysis and prognosis survival analysis. The results were verified using the GEO dataset.

Results

The incidence of TTN mutations in lung adenocarcinoma was found to be 73%, and it was related to the prognosis of lung adenocarcinoma. Ten genes were screened with significant contributions to prognosis. A prognosis model was constructed and verified by LASSO COX analysis in the TCGA and GEO datasets based on these ten beneficial factors. The independent prognostic factor H2BC9 for TTN mutation-driven gene heterogeneity expression was screened through multi-factor COX regression analysis.

Conclusion

Our data showed that the gene heterogeneity expression, which was driven by TTN mutations, prolonged the survival of lung adenocarcinoma patients and provided valuable clues for the prognosis of TTN gene mutations in lung adenocarcinoma.

Whole-Exome Sequencing Identifies Genetic Variants for Severe Adolescent Idiopathic Scoliosis in a Taiwanese Population

Adolescent idiopathic scoliosis (AIS) is a three-dimensional spinal curvature deformity that appears in the adolescent period. In this study, we performed whole-exome sequencing on 11 unrelated Taiwanese patients with a Cobb's angle greater than 40 degrees. Our results identified more than 200 potential pathogenic rare variants, however, most of which were carried only by one individual. By in silico pathogenicity annotation studies, we found that TTN, CLCN1, and SOX8 were the most important genes, as multiple pathogenic variants were within these genes. Furthermore, biological functional annotation indicated critical roles of these AIS candidate genes in the skeletal muscle. Importantly, a pathogenic variant on SOX8 was shared by over 35% of the patients. These results highlighted TTN, CLCN1, and SOX8 as the most likely susceptibility genes for severe AIS.

TTN as a candidate gene for distal arthrogryposis type 10 pathogenesis

Background

Arthrogryposis is a medical term used to describe congenital contractures which often affect multiple limbs. Distal arthrogryposis (DA) is one of the major categories of arthrogryposis that primarily affects the distal parts of the body, i.e., the hands and the legs. Although ten different types and several subtypes of DAs have been described, the genes associated with each of these DAs are yet to be characterized. Distal arthrogryposis type 10 (DA10) is a rare genetic disease, which is distinguished from the other arthrogryposis types by plantar flexion contractures resulting in toe-walking during infancy as well as variability in contractures of the hip, hamstring, elbow, wrist and finger joints with no ocular or neurological abnormalities. Symptoms of DA10 indicate impairment specifically in the musculoskeletal system. DA10 is still poorly studied.

Aim

The objective of this study was to identify the candidate gene for DA10 by scrutinizing the protein-protein interaction (PPI) networks using in silico tools.

Results

Among the genes that reside within the previously reported genomic coordinates (human chromosome assembly 38 or GRCh38 coordinates 2:179,700,000–188,500,000) of the causative agent of DA10, only TTN (the gene that codes for the protein Titin or TTN) follows the expression pattern similar to the other known DA associated genes and its expression is predominant in the skeletal and heart muscles. Titin also participates in biological pathways and processes relevant to arthrogryposes. TTN-related known skeletal muscle disorders follow the autosomal-dominant pattern of inheritance, which is a common characteristic of distal arthrogryposes as well.

Conclusion

Based on the findings of the analyses and their correlation with previous reports, TTN appears to be the candidate gene for DA10. Our attempt to discover a potential candidate gene may eventually lead to an understanding of disease mechanism and possible treatment strategies, as well as demonstrate the suitability of PPI in the search for candidate genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-022-00405-5.

Exploring the Potential of Symmetric Exon Deletion to Treat Non-Ischemic Dilated Cardiomyopathy by Removing Frameshift Mutations in TTN

Non-ischemic dilated cardiomyopathy (DCM) is one of the most frequent pathologies requiring cardiac transplants. Even though the etiology of this disease is complex, frameshift mutations in the giant sarcomeric protein Titin could explain up to 25% of the familial and 18% of the sporadic cases of DCM. Many studies have shown the potential of genome editing using CRISPR/Cas9 to correct truncating mutations in sarcomeric proteins and have established the grounds for myoediting. However, these therapies are still in an immature state, with only few studies showing an efficient treatment of cardiac diseases. This publication hypothesizes that the Titin (TTN)-specific gene structure allows the application of myoediting approaches in a broad range of locations to reframe TTNtvvariants and to treat DCM patients. Additionally, to pave the way for the generation of efficient myoediting approaches for DCM, we screened and selected promising target locations in TTN. We conceptually explored the deletion of symmetric exons as a therapeutic approach to restore TTN’s reading frame in cases of frameshift mutations. We identified a set of 94 potential candidate exons of TTN that we consider particularly suitable for this therapeutic deletion. With this study, we aim to contribute to the development of new therapies to efficiently treat titinopathies and other diseases caused by mutations in genes encoding proteins with modular structures, e.g., Obscurin.

The Trier Treatment Navigator (TTN) in action: Clinical case study on data-informed psychological therapy

BACKGROUND

Although psychotherapy has shown to be effective for most patients, about one-third of patients do not benefit or deteriorate during treatment. Technical progress has allowed the integration of routine outcome monitoring (ROM) into treatment, helping therapists detect patients at risk for a nonresponse or poor outcome early on. Psychological therapy can be enhanced by providing therapists with individual treatment recommendations for these at-risk patients. One example of such a comprehensive feedback system is the Trier Treatment Navigator (TTN).

OBJECTIVE/METHOD

This clinical case study aims to illustrate the implementation of the TTN in a cognitive behavioral therapy (CBT) outpatient clinic in the treatment of a 30-year-old patient called Ms. Daun, who has a recurrent depressive disorder. Based on this case, the benefits of applying information from ROM in psychotherapy, important context factors, and possible implementation issues are discussed.

RESULTS/CONCLUSION

We conclude by encouraging practitioners to integrate ROM into their clinical thinking and daily practice.

Reading Frame Repair of TTN Truncation Variants Restores Titin Quantity and Functions

BACKGROUND

Titin truncation variants (TTNtvs) are the most common inheritable risk factor for dilated cardiomyopathy (DCM), a disease with high morbidity and mortality. The pathogenicity of TTNtvs has been associated with structural localization as A-band variants overlapping myosin heavy chain-binding domains are more pathogenic than I-band variants by incompletely understood mechanisms. Demonstrating why A-band variants are highly pathogenic for DCM could reveal new insights into DCM pathogenesis, titin (TTN) functions, and therapeutic targets.

METHODS

We constructed human cardiomyocyte models harboring DCM-associated TTNtvs within A-band and I-band structural domains using induced pluripotent stem cell and CRISPR technologies. We characterized normal TTN isoforms and variant-specific truncation peptides by their expression levels and cardiomyocyte localization using TTN protein gel electrophoresis and immunofluorescence, respectively. Using CRISPR to ablate A-band variant-specific truncation peptides through introduction of a proximal I-band TTNtv, we studied genetic mechanisms in single cardiomyocyte and 3-dimensional, biomimetic cardiac microtissue functional assays. Last, we engineered a full-length TTN protein reporter assay and used next-generation sequencing assays to develop a CRISPR therapeutic for somatic cell genome editing TTNtvs.

RESULTS

An A-band TTNtv dose-dependently impaired cardiac microtissue twitch force, reduced full-length TTN levels, and produced abundant TTN truncation peptides. TTN truncation peptides integrated into nascent myofibril-like structures and impaired myofibrillogenesis. CRISPR ablation of TTN truncation peptides using a proximal I-band TTNtv partially restored cardiac microtissue twitch force deficits. Cardiomyocyte genome editing using SpCas9 and a TTNtv-specific guide RNA restored the TTN protein reading frame, which increased full-length TTN protein levels, reduced TTN truncation peptides, and increased sarcomere function in cardiac microtissue assays.

CONCLUSIONS

An A-band TTNtv diminished sarcomere function greater than an I-band TTNtv in proportion to estimated DCM pathogenicity. Although both TTNtvs resulted in full-length TTN haploinsufficiency, only the A-band TTNtv produced TTN truncation peptides that impaired myofibrillogenesis and sarcomere function. CRISPR-mediated reading frame repair of the A-band TTNtv restored functional deficits, and could be adapted as a one-and-done genome editing strategy to target ≈30% of DCM-associated TTNtvs.

Mutations in the TTN Gene are a Prognostic Factor for Patients with Lung Squamous Cell Carcinomas

Purpose

To analyze the relationship between titin (TTN) mutation gene and tumor mutational burden (TMB) and the with prognosis of lung squamous cell carcinomas (LUSC), and to explore the feasibility of TTN as a potential prognostic marker of for LUSC.

Methods

We analyzed the somatic mutation landscape of LUSC samples using datasets obtained from The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) databases. Sequence data were divided into wild and mutant groups, and differences in TMB values between the groups compared using a Mann–Whitney U-test. The Kaplan Meier method was used to analyze the correlation between TTN mutation and LUSC prognosis, whereas CIBERSORT algorithm was used to calculate the degree of relative enrichment degree of among tumor-infiltrating lymphocytes in LUSC.

Results

Analysis of both datasets revealed high mutations in the TTN gene, with mutants exhibiting a significantly higher TMB value relative to the wild-type (P < 0.001). Prognosis of the TTN mutant group in LUSC was significantly better than that of wild-type (P = 0.009). Kaplan Meier curves showed that TTN mutation may be an independent prognostic factor in LUSC patients (HR: 0.64, 95% CI 0.48–0.85, P = 0.001), while GSEA analysis revealed that TTN mutation plays a potential role in the development of LUSC. Finally, analysis of LUSC immune microenvironment revealed that TTN mutation was significantly associated with enrichment of macrophages M1 (p < 0.05).

Conclusion

TTN mutation is associated with TMB, and is positively correlated with prognosis of LUSC. Therefore, this mutation may serve as a potential prognostic indicator of LUSC.

Gene Mutations Related to Glucocorticoid Resistance in Pediatric Acute Lymphoblastic Leukemia

OBJECTIVE

To investigate the correlation between gene mutations and glucocorticoid resistance in pediatric acute lymphoblastic leukemia (ALL).

METHODS

A total of 71 children with ALL admitted to our center between September 2019 and September 2021 were enrolled. DNA obtained from bone marrow or peripheral blood samples at initial diagnosis was used for genetic testing via whole exome sequencing. Meanwhile, patient clinical information was collected. Subsequently, the correlations of gene mutations with clinical features and glucocorticoid resistance were analyzed.

RESULTS

Of the 71 children enrolled, 61 (85.9%) had B-cell ALL (B-ALL) and 10 (14.1%) had T-cell ALL (T-ALL). The five genes with the highest mutation frequency in B-ALL were TTN (24.4%), FLT3 (14.6%), TP53 (14.6%), MUC16 (9.8%), and EPPK1 (9.8%). In contrast, those with the highest frequency in T-ALL were NOTCH1 (54.5%), FBXW7 (27.3%), TTN (27.3%), MUC16 (27.3%), and PHF6 (18.2%). Upon statistical analysis, TTN and NOTCH1 mutations were found to be associated with prednisone resistance. Further, TTN and MUC16 mutations were associated with a lower age at diagnosis, and NOTCH1 mutations were associated with T-ALL in female patients. Leukocyte counts and LDH levels did not differ based on the presence of any common gene mutation, and no association between these gene mutations and overall survival was observed.

CONCLUSIONS

Our study is the first to demonstrate the association between TTN mutation and glucocorticoid resistance in ALL. Our findings could guide strategies for overcoming drug resistance and aid in the development of drug targets.

Clinical, pathological, and molecular genetic analysis of 7 Chinese patients with hereditary myopathy with early respiratory failure

Hereditary myopathy with early respiratory failure (HMERF) is a subtype of myofibrillar myopathy. Mutations located on exon 344 of the titin-A band, the 119th fibronectin-3 domain (FN₃ 119), are responsible for HMERF. In this article, we retrospectively analyzed the clinical features, findings of muscle imaging, muscle pathology, immunohistochemistry, and ultrastructural characteristics of seven patients diagnosed with HMERF at a single center in China. Muscle MRI showed the involvement of semitendinosus in four patients. The common pathological features were variability in fiber diameter, increased internal nuclei, endomysial fibrosis, and cytoplasmic bodies. On immunohistochemical examination, the cytoplasmic bodies stained positive for calpain-3, p53, and programmed death-ligand 1. Electron microscopy showed cytoplasmic bodies, distorted sarcomere architecture, glycogen pool, and subsarcolemmal accumulation of mitochondria and lysosomes. We retrospectively reviewed four reported HMERF patients in China. Among the 11 patients, the median age at onset was 34 years (range 14-54). Allelic frequency of mutation c.95195C > T was 36.36%. This study characterizes the phenotype and genotype spectrum of HMERF in China.

Shared Genetic Etiology of Primary Dilated Cardiomyopathy and Ischemic Dilated Cardiomyopathy

Background: Mutations in genes encoding sarcomere and cytoskeletal proteins are major causes of primary dilated cardiomyopathy (DCM). Likewise, ischemic myocardial injury is a major cause of secondary cardiac remodeling, which, in a subset, is severe and resembles DCM. The latter is referred to as ischemic dilated cardiomyopathy (IDCM). We postulated the presence of pathogenic and likely pathogenic variants (PVs and LPVs, respectively) in genes known to cause primary DCM might predispose the heart to severe cardiac dilatation and dysfunction post myocardial ischemic injury, i.e., IDCM. Methods: We performed whole-exome sequencing in 1,041 patients with primary DCM, 215 patients with IDCM, and 414 healthy controls. Indices of cardiac size and function were similar between those with primary and ischemic DCM. PVs and LPVs, including the truncating variants in 36 genes known to cause primary DCM were identified and compared among the three groups. Results: Pathogenic variants and LPVs were detected in 266 individuals, comprised of 215/1,041 (20.7%) patients with DCM, 27/215 (12.6%) patients with IDCM, and 24/414 (5.8%) control individuals. PVs and LPVs in the TTN gene were the most common and detected in 130/1,041 (12.5%) of patients with DCM, 15/215 (7.0%) of cases with IDCM, and 10/414 (2.4%) control individuals. Of 135 TTNtv, 118 involved exons that were >90% spliced in. These variants were found in 120/1,041 (11.5%) of DCM patients, 6/215 (2.8%) of IDCM cases, and only in 1/414 (0.2%) of the control population (p < 0.001 among the three groups). Conclusions: Pathogenic variants and LPVs in genes known to cause primary DCM are enriched in patients with IDCM, suggesting that such variants function as susceptibility alleles for cardiac dilatation and dysfunction in post myocardial ischemic injury. Thus, IDCM shares a partial genetic etiology with the primary DCM.

Whole-exome sequencing identified compound heterozygous variants in the TTN gene causing Salih myopathy with dilated cardiomyopathy in an Iranian family

BACKGROUND

Salih myopathy, characterised by both congenital myopathy and fatal dilated cardiomyopathy, is an inherited muscle disorder that affects skeletal and cardiac muscles. TTN has been identified as the main cause of this myopathy, the enormous size of this gene poses a formidable challenge to molecular genetic diagnostics.

METHOD

In the present study, whole-exome sequencing, cardiac MRI, and metabolic parameter assessment were performed to investigate the genetic causes of Salih myopathy in a consanguineous Iranian family who presented with titinopathy involving both skeletal and heart muscles in an autosomal recessive inheritance pattern.

RESULTS

Two missense variants of TTN gene (NM_001267550.2), namely c.61280A>C (p. Gln20427Pro) and c.54970G>A (p. Gly18324Ser), were detected and segregations were confirmed by polymerase chain reaction-based Sanger sequencing.

CONCLUSIONS

The compound heterozygous variants, c.61280A>C, (p. Gln20427Pro) and c.54970G>A, (p. Gly18324Ser) in the TTN gene appear to be the cause of Salih myopathy and dilated cardiomyopathy in the family presented. Whole-exome sequencing is an effective molecular diagnostic tool to identify the causative genetic variants of large genes such as TTN.

Effect of TTN Mutations on Immune Microenvironment and Efficacy of Immunotherapy in Lung Adenocarcinoma Patients

Immune checkpoint inhibitors (ICIs) effectively treat lung adenocarcinoma (LUAD) with fewer side effects. However, for LUAD patients, the lack of predictive markers for ICIs makes their clinical benefits less than ideal. Despite reports suggesting that a TTN (titin) mutation plays an important role in immunotherapy of solid tumors and gastric cancer, the relationship between the TTN mutation and LUAD immunotherapy has not been determined. We collected a LUAD cohort with whole-exome sequencing (WES) and immunotherapy prognosis. The ICI cohort was used to explore the relationship between TTN mutation status and prognosis. Then, the Cancer Genome Atlas (TCGA)-LUAD and Chen-LUAD cohorts were downloaded from the cbioportal website. We also used CIBERSORT, gene-set enrichment analysis (GSEA), and single-sample GSEA (ssGSEA) to evaluate the proportion of immune cells and the degree of pathway activation in LUAD patients, respectively. DDR signaling pathways obtained from the Molecular Signatures Database (MSigDB), tumor mutation burden (TMB), and NAL were used to evaluate the immunogenicity of LUAD patients. In the ICI cohort, TTN-mutant (TTN-MT) had significantly longer overall survival (OS) than TTN-wildtype (TTN-WT) (P = 0.009). Univariate and multivariate COX models showed that TTN mutation status can independently predict immunotherapy prognosis. Notably, the results of tumor immune microenvironment (TIME) analysis showed that TTN-MT patients had inflammatory TIME, which showed enriched activated immune cells and higher immune scores. Immunogenicity analysis showed higher immunogenicity in TTN-MT patients, which indicated high levels of gene mutations in TMB, NAL, and DDR pathways. GSEA and ssGSEA results showed that TTN-MT was substantially enriched in chemokine secretion, inflammatory factor secretion, and antigen presentation. Some pathways related to immunosuppression and immune depletion were significantly downregulated. TTN-MT is associated with significantly prolonged OS in LUAD patients. Additionally, TTN-MT is related to high immunogenicity and inflammatory TIME, suggesting that TTN-MT may be a potential predictive marker for patients with LUAD to accept ICIs.

Centronuclear myopathy due to a de novo nonsense variant and a maternally inherited splice-site variant in TTN: A case report

Next-generation sequencing has resulted in an explosion of rare de novo TTN variants. The clinical interpretation of these de novo variants in patients with recessive titinopathy is very difficult. Here, we provided a useful way to identify compound heterozygous mutations with a de novo one.

The Combined Human Genotype of Truncating TTN and RBM20 Mutations Is Associated with Severe and Early Onset of Dilated Cardiomyopathy

A major cause of heart failure is cardiomyopathies, with dilated cardiomyopathy (DCM) as the most common form. Over 40 genes are linked to DCM, among them TTN and RBM20. Next Generation Sequencing in clinical DCM cohorts revealed truncating variants in TTN (TTNtv), accounting for up to 25% of familial DCM cases. Mutations in the cardiac splicing factor RNA binding motif protein 20 (RBM20) are also known to be associated with severe cardiomyopathies. TTN is one of the major RBM20 splicing targets. Most of the pathogenic RBM20 mutations are localized in the highly conserved arginine serine rich domain (RS), leading to a cytoplasmic mislocalization of mutant RBM20. Here, we present a patient with an early onset DCM carrying a combination of (likely) pathogenic TTN and RBM20 mutations. We show that the splicing of RBM20 target genes is affected in the mutation carrier. Furthermore, we reveal RBM20 haploinsufficiency presumably caused by the frameshift mutation in RBM20.

Novel compound heterozygous TTN variants as a cause of severe neonatal congenital contracture syndrome without cardiac involvement diagnosed with rapid trio exome sequencing

This report focuses on a case of severe congenital myopathy with arthrogryposis without cardiac involvement due to compound heterozygous variants in the TTN gene. The proband presented with severe axial hypotonia, arthrogryposis and severe respiratory insufficiency with ventilator dependence. Electromyogram was abnormal with absent motor responses but preserved sensory nerve responses. Rapid gene-agnostic trio exome sequencing detected novel compound heterozygous variants in the TTN gene. One variant is a truncating frameshift located in the meta-transcript only exon 195. The other variant is a nonsense variant in exon 327 which affects all recognised post-natal transcripts apart from one. This case presents with a severe phenotype and adds to the expanding known variants associated with autosomal recessive titinopathy. It also demonstrates the utility of rapid trio exome sequencing when used early in the clinical course.

Genetic analysis using targeted next-generation sequencing of sporadic Chinese patients with idiopathic dilated cardiomyopathy

Background

Inherited dilated cardiomyopathy (DCM) contributes to approximately 25% of idiopathic DCM cases, and the proportion is even higher in familial DCM patients. Most studies have focused on familial DCM, whereas the genetic profile of sporadic DCM in Chinese patients remains unknown.

Methods

Between June 2018 and September 2019, 24 patients diagnosed with idiopathic DCM without a family history were included in the present study. All patients underwent genetic screening for 80 DCM-related genes using targeted next-generation sequencing.

Results

By in silico analysis, 10 of 99 detected variants were considered pathogenic or likely-pathogenic, including seven TTN truncating variants (TTNtv), one in-frame deletion in TNNT2, one missense mutation in RBM20, and one frameshift deletion variant in FLNC. Of these variants, eight are reported for the first time.

Conclusions

Using targeted next-generation sequencing, potential genetic causes of idiopathic DCM were identified. Sarcomere mutations remained the most common genetic cause of inherited DCM in this cohort of sporadic Chinese DCM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02832-3.

Clinical Significance of Variants in the TTN Gene in a Large Cohort of Patients With Sporadic Dilated Cardiomyopathy

Background: Mutations in the TTN gene are the most common causes of dilated cardiomyopathy (DCM). The clinical significance of TTN gene variants remains inadequately understood.

Methods: Whole-exome sequencing and phenotypic characterisation were performed, and patients were followed up for a median of 44 months.

Results: We analyzed the association of the TTN variants with the clinical outcomes in a prospective study of 1,041 patients with sporadic DCM. TTN truncating variants (tTTN) were detected in 120 (11.5%) patients as compared with 2.4/10,000 East Asian populations in the Genome Aggregation Database (GnomAD; p < 0.0001). Pathogenic TTN missense variants were also enriched in DCM as compared with the GnomAD populations (27.6 vs. 5.9%, p < 0.0001). DCM patients with tTTN had a lower left ventricular ejection fraction (28.89 ± 8.72 vs. 31.81 ± 9.97, p = 0.002) and a lower frequency of the left bundle branch block (3.3 vs. 11.3%, p = 0.011) than those without or with mutations in other known causal genes (OCG). However, tTTN were not associated with the composite primary endpoint of cardiac death and heart transplantation during the follow-up period [adjusted hazard ratio (HR): 0.912; 95% confidence interval: 0.464–1.793; p = 0.790]. There was also no sex-dependent effect. Concomitant tTTN and pathogenic variants in OCG were present in only eight DCM patients and did not affect the outcome.

Conclusion: The phenotype of DCM caused by tTTN, major causes of sporadic DCM, is not distinctly different from those caused by other causal genes for DCM.

TTN/OBSCN 'Double-Hit' predicts favourable prognosis, 'immune-hot' subtype and potentially better immunotherapeutic efficacy in colorectal cancer

Colorectal cancer (CRC) remains a leading cause of cancer-related deaths worldwide. Although treatment strategies for solid tumours have been revolutionized by immunotherapy, only a small subset of CRC patients benefit. Using two-independent cohorts, we found the common frequently mutated genes TTN and OBSCN had the significant correlation with higher tumour mutation burden (TMB) and favourable overall survival. TTN and OBSCN also displayed significant commutation phenomenon. Therefore, based on the status of TTN and OBSCN, we stratified patients into 'Double-WT' phenotype, 'Single-Hit' phenotype and 'Double-Hit' phenotype. Importantly, the 'Double-Hit' phenotype had favourable prognosis, low malignant events propensity, and highest TMB, immune cells infiltration abundance, POLE mutation rate, microsatellite instability ratio, as well as immune checkpoints expression compared with the other two phenotypes. These results indicated that the 'Double-Hit' phenotype suggested 'immune-hot' tumours and potentially better immunotherapeutic efficacy. Bioinformatic algorithm assessment of immunotherapy responses also confirmed this conclusion, and the 'Double-Hit' phenotype was found to be a better predictor of immunotherapy than PD-L1, PD-1, CTLA-4, TMB and microsatellite status. This study revealed CRC patients with TTN/OBSCN 'Double-Hit' was significantly associated favourable prognosis, 'immune-hot' subtype and potentially better immunotherapeutic efficacy.

Clinical Considerations for a Family with Dilated Cardiomyopathy, Sudden Cardiac Death, and a Novel TTN Frameshift Mutation

Dilated cardiomyopathy (DCM) is the leading indication for heart transplantation. TTN gene truncating mutations account for about 25% of familial DCM cases and for 18% of sporadic DCM cases. The clinical relevance of specific variants in TTN has been difficult to determine because of the sheer size of the protein for which TTN encodes, as well as existing extensive genetic variation. Clinicians should communicate novel clinically-relevant variants and genotype–phenotype associations, so that animal studies evaluating the molecular mechanisms are always conducted with a focus on clinical significance. In the present study, we report for the first time the novel truncating heterozygous variant NM_001256850.1:c.72777_72783del (p.Phe24259Leufs*51) in the TTN gene and its association with DCM in a family with sudden death. This variant occurs in the A-band region of the sarcomere, in a known mutational hotspot of the gene. Truncating titin variants that occur in this region are the most common cause of DCM and have been rarely reported in asymptomatic individuals, differently from other pathogenic TTN gene variants. Further studies are warranted to better understand this particular clinically-relevant variant.

Inhibition of Histone Deacetylases 4 and 5 Reduces Titin Proteolysis and Prevents Reduction of TTN Gene Expression in Atrophied Rat Soleus Muscle after Seven-Day Hindlimb Unloading

The effect of HDACs 4 and 5 on the level of atrophy, calpain-1 and titin content, and TTN gene expression in rat soleus after 7-day gravitational unloading (hindlimb suspension model) was studied. The development of atrophic changes induced by gravitational unloading in rat soleus was accompanied by an increase in the calpain-1 content, an increase in titin proteolysis, and a decrease in the mRNA content of the protein. Inhibition of HDACs 4 and 5 did not eliminate the development of unloading-induced atrophy but significantly prevented proteolysis of titin and the decrease in the TTN gene expression.

Whole-exome sequencing in patients with protein aggregate myopathies reveals causative mutations associated with novel atypical phenotypes

Background

Myofibrillar myopathies (MFM) are a subgroup of protein aggregate myopathies (PAM) characterized by a common histological picture of myofibrillar dissolution, Z-disk disintegration, and accumulation of degradation products into inclusions. Mutations in genes encoding components of the Z-disk or Z-disk-associated proteins occur in some patients whereas in most of the cases, the causative gene defect is still unknown. We aimed to search for pathogenic mutations in genes not previously associated with MFM phenotype.

Methods

We performed whole-exome sequencing in four patients from three unrelated families who were diagnosed with PAM without aberrations in causative genes for MFM.

Results

In the first patient and her affected daughter, we identified a heterozygous p.(Arg89Cys) missense mutation in LMNA gene which has not been linked with PAM pathology before. In the second patient, a heterozygous p.(Asn4807Phe) mutation in RYR1 not previously described in PAM represents a novel, candidate gene with a possible causative role in the disease. Finally, in the third patient and his symptomatic daughter, we found a previously reported heterozygous p.(Cys30071Arg) mutation in TTN gene that was clinically associated with cardiac involvement.

Conclusions

Our study identifies a new genetic background in PAM pathology and expands the clinical phenotype of known pathogenic mutations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10072-020-04876-7.

Novel heterozygous truncating titin variants affecting the A-band are associated with cardiomyopathy and myopathy/muscular dystrophy

BACKGROUND

Variants in TTN are frequently identified in the genetic evaluation of skeletal myopathy or cardiomyopathy. However, due to the high frequency of TTN variants in the general population, incomplete penetrance, and limited understanding of the spectrum of disease, interpretation of TTN variants is often difficult for laboratories and clinicians. Currently, cardiomyopathy is associated with heterozygous A-band TTN variants, whereas skeletal myopathy is largely associated with homozygous or compound heterozygous TTN variants. Recent reports show pathogenic variants in TTN may result in a broader phenotypic spectrum than previously recognized.

METHODS

Here we report the results of a multisite study that characterized the phenotypes of probands with variants in TTN. We investigated TTN genotype-phenotype correlations in probands with skeletal myopathy and/or cardiomyopathy. Probands with TTN truncating variants (TTNtv) or pathogenic missense variants were ascertained from two academic medical centers. Variants were identified via clinical genetic testing and reviewed according to the American College of Medical Genetics criteria. Clinical and family history data were documented via retrospective chart review. Family studies were performed for probands with atypical phenotypes.

RESULTS

Forty-nine probands were identified with TTNtv or pathogenic missense variants. Probands were classified by clinical presentation: cardiac (n = 30), skeletal muscle (n = 12), or both (cardioskeletal, n = 7). Within the cardioskeletal group, 5/7 probands had heterozygous TTNtv predicted to affect the distal (3') end of the A-band. All cardioskeletal probands had onset of proximal-predominant muscle weakness before diagnosis of cardiovascular disease, five pedigrees support dominant transmission.

CONCLUSION

Although heterozygous TTNtv in the A-band is known to cause dilated cardiomyopathy, we present evidence that these variants may in some cases cause a novel, dominant skeletal myopathy with a limb-girdle pattern of weakness. These findings emphasize the importance of multidisciplinary care for patients with A-band TTNtv who may be at risk for multisystem disease.

Sequential Whole Exome Sequencing Reveals Somatic Mutations Associated with Platinum Response in NSCLC

Purpose

Resistance is one of the main limitations of successful platinum treatment in non-small-cell lung cancer (NSCLC) patients. In this study, we aimed to identify somatic mutations associated with platinum response.

Patients and Methods

A total of 57 patients who received platinum-based chemotherapy only and 13 patients who received neoadjuvant chemotherapy (NAC) were enrolled. Somatic mutations were obtained from targeted and whole exome sequencing (WES).

Results

Somatic mutations in a total of 225 genes were observed. Nonsynonymous variants in EGFR, TTN, TP53 and KRAS, and copy number variations (SCNVs) in chromosome 8q24.3 and 22q11.21 were identified to be associated with platinum response. Based on these mutations, the mutational signature associated with the failure of DNA double-strand break and calcium signaling pathways were identified to be associated with platinum response. Besides, we observed a decrease in tumor mutational burden after chemotherapy. We also evaluated the mutation spectrum consistency between cell-free DNA (cfDNA) and tissue DNA. Somatic mutations detected in cfDNA were consistent with that in tDNA, which indicated that plasma might be used for somatic mutation detection.

Conclusion

These results support that somatic mutations can affect platinum drug response and provide potential clinical biomarkers for NSCLC treatment.

[Selective muscular atrophy in a family with hereditary myopathy with early respiratory failure]

Hereditary myopathy with early respiratory failure (HMERF) with heterozygous mutations in the titin gene (TTN) is characterized by respiratory failure developing from the early phase of limb weakness or gait disturbance. Here, we describe a characteristic distribution of muscle involvement in three members of a HMERF family with a TTN mutation. Despite the differences in severity exhibited among the father, daughter and son, the systemic imaging studies showed a similar pattern among these individuals. The semitendinosus and fibularis longus muscles were selectively affected, as described previously. In addition, we found marked atrophy in the sternocleidomastoid and psoas major muscles, regardless of the disease severity. The atrophy in selective trunk muscles observed in routine CT scans can be useful for the differential diagnosis of hereditary myopathies with heart and respiratory failure.

Fetal Pulmonary Artery Acceleration/Ejection Ratio for Transient Tachypnea of the Newborn in Uncomplicated Term Small for Gestational Age Fetuses

OBJECTIVE

Transient tachypnea of the newborn (TTN) is the leading cause of neonatal morbidity in preterm deliveries and has been reported in term small-for-gestational-age (SGA) fetuses; therefore, determination of fetal lung maturity before delivery is extremely important. Our present study aimed to evaluate the ratio of fetal pulmonary artery acceleration time to ejection time (At/Et) in uncomplicated term SGA fetuses and whether this ratio changes with TTN.

STUDY DESIGN

One hundred seventy-five pregnant women with uncomplicated pregnancies who delivered after 37 gestational weeks were included in this cross-sectional study. Participants were divided by birth weight percentiles into SGA (n = 86) and healthy control groups (n = 89). All participants underwent ultrasound examination to determine fetal pulmonary artery At/Et. After delivery, the neonates were grouped according to diagnosis of TTN (i.e., TTN-positive SGA group [n = 14], TTN-negative SGA group [n = 72], and TTN-negative control group [n = 86]), and the fetal pulmonary artery At/Et was compared between the two.

RESULTS

Maternal demographic characterizes were similar between groups. At/Et was 0.309 ± 0.181 in the SGA group and 0.348 ± 0.213 in the control group and was significantly lower in the SGA group. At/Et was 0.290 ± 0.007 in the TTN-positive SGA group, 0.313 ± 0.017 in the TTN-negative SGA group, and 0.351 ± 0.186 in the TTN-negative control group, a significant difference. Additionally fetal pulmonary artery At/Et was found to be inverse correlated with TTN. (-0,464 P = 0.000). The cut-off value of 0.298 provided optimal specificity of 93.0 % and sensitivity of 81.0 % for subsequent diagnosis of TTN in term SGA newborns in the neonatal period.

CONCLUSION

The risk for TTN increases in uncomplicated term SGA fetuses. The fetal pulmonary artery At/Et appears to be a noninvasive useful method by which to predict TTN in these fetuses.

Cardiomyopathy due to PRDM16 mutation: First description of a fetal presentation, with possible modifier genes

PRDM16 (positive regulatory domain 16) is localized in the critical region for cardiomyopathy in patients with deletions of chromosome 1p36, as defined by Gajecka et al., American Journal of Medical Genetics, 2010, 152A, 3074-3083, and encodes a zinc finger transcription factor. We present the first fetal case of left ventricular non-compaction (LVNC) with a PRDM16 variant. The third-trimester obstetric ultrasound revealed a hydropic fetus with hydramnios and expanded hypokinetic heart. After termination of pregnancy, foetopathology showed a eutrophic fetus with isolated cardiomegaly. Endocardial fibroelastosis was associated with non-compaction of the myocardium of the left ventricle. Exome sequencing (ES) identified a de novo unreported p.(Gln353*) heterozygous nonsense variant in PRDM16. ES also identified two rare variants of unknown significance, according to the American College of Medical Genetics and Genomics guidelines, in the titin gene (TTN): a de novo missense p.(Lys14773Asn) variant and a c.33043+5A>G variant inherited from the mother. Along with the PRDM16 de novo probably pathogenic variant, TTN VOUS variants could possibly contribute to the severity and early onset of the cardiac phenotype. Because of the genetic heterogeneity of cardiomyopathies, large panels or even ES could be considered as the main approaches for the molecular diagnosis, particularly in fetal presentations, where multiple hits seem to be common.

Cylindrical spirals in two families: Clinical and genetic investigations

Cylindrical spirals are a rare ultrastructural finding on muscle biopsy, with fewer than 20 reported cases since its first description in 1979. These structures are sometimes observed with tubular aggregates and are thought to comprise longitudinal sarcoplasmic reticulum. While mutations in genes encoding key components of Ca²⁺ handling (ORAI1 and STIM1) underlie tubular aggregate myopathy, no causative genes have been associated with cylindrical spirals. Here we describe two families with cylindrical spirals on muscle biopsy with a suspected genetic cause. In one family we identified a known truncating variant in EBF3, previously associated with a neurodevelopmental disorder. The affected individuals in this family present with clinical features overlapping with those described for EBF3 disease. An isolated proband in the second family harbours bi-allelic truncating variants in TTN and her clinical course and other features on biopsy are highly concordant for titinopathy. From experimental studies, EBF3 is known to be involved in Ca²⁺ regulation in muscle, thus EBF3 dysregulation may represent a novel mechanism of impaired Ca²⁺ handling leading to cylindrical spirals. Additional cases of EBF3 disease or titinopathy with cylindrical spirals need to be identified to support the involvement of these genes in the pathogenesis of cylindrical spirals.

Homozygous missense variant in the TTN gene causing autosomal recessive limb-girdle muscular dystrophy type 10

Background

Limb-girdle muscular dystrophies (LGMDs) are large group of heterogeneous genetic diseases, having a hallmark feature of muscle weakness. Pathogenic mutations in the gene encoding the giant skeletal muscle protein titin (TTN) are associated with several muscle disorders, including cardiomyopathy, recessive congenital myopathies and limb-girdle muscular dystrophy (LGMD) type10. The phenotypic spectrum of titinopathies is expanding, as next generation sequencing (NGS) technology makes screening of this large gene possible.

Aim

This study aimed to identify the pathogenic variant in a consanguineous Pakistani family with autosomal recessive LGMD type 10.

Methods

DNA from peripheral blood samples were obtained, whole exome sequencing (WES) was performed and several molecular and bioinformatics analysis were conducted to identify the pathogenic variant. TTN coding and near coding regions were further amplified using PCR and sequenced via Sanger sequencing.

Results

Whole exome sequencing analysis revealed a novel homozygous missense variant (c.98807G > A; p.Arg32936His) in the TTN gene in the index patients. No heterozygous individuals in the family presented LGMD features. The variant p.Arg32936His leads to a substitution of the arginine amino acid at position 32,936 into histidine possibly causing LGMD type 10.

Conclusion

We identified a homozygous missense variant in TTN, which likely explains LGMD type 10 in this family in line with similar previously reported data. Our study concludes that WES is a successful molecular diagnostic tool to identify pathogenic variants in large genes such as TTN in highly inbred population.

A novel TTN deletion in a family with skeletal myopathy, facial weakness, and dilated cardiomyopathy

BACKGROUND

Pathogenic variants in TTN (OMIM 188840), encoding the largest human protein, are known to cause dilated cardiomyopathy and several forms of skeletal myopathy. The clinical interpretation of TTN variants is challenging, however, due to the frequency of missense changes, variable testing and reporting practices in commercial laboratories, and incomplete understanding of the spectrum of TTN-related disease.

METHODS

We report a heterozygous TTN deletion segregating in a family with an unusual skeletal myopathy phenotype associated with facial weakness, gait abnormality, and dilated cardiomyopathy.

RESULTS

A novel 16.430 kb heterozygous deletion spanning part of the A- and M-bands of TTN was identified in the proband and his symptomatic son, as well as in an additional son whose symptoms were identified on clinical evaluation. The deletion was found to be de novo in the proband.

CONCLUSION

Pathogenic variants in TTN may be an unrecognized cause of skeletal myopathy phenotypes, particularly when accompanied by dilated cardiomyopathy.

Novel missense variant in TTN cosegregating with familial atrioventricular block

BACKGROUND

Cardiovascular diseases are the most common cause of death globally. In which atrioventricular block (AVB) is a common disorder with genetic causes, but the responsible genes have not been fully identified yet. To determine the underlying causative genes involved in cardiac AVB, here we report a three-generation Chinese family with severe autosomal dominant cardiac AVB that has been ruled out as being caused by known genes mutations.

METHODS

Whole-exome sequencing was performed in five affected family members across three generations, and co-segregation analysis was validated on other members of this family.

RESULTS

Whole-exome sequencing and subsequent co-segregation validation identified a novel germline heterozygous point missense mutation, c.49287C > A (p.N16429K), in the titin (TTN, NM_001267550.2) gene in all 5 affected family members but not in the unaffected family members, neither in the large population according to the Genome Aggregation Database (https://gnomad.broadinstitute.org/). The point mutation is predicted to be functionally deleterious by in-silico software tools. Our finding was further supported by the conservative analysis across species.

CONCLUSION

Based on this study, TTN was identified as a potential novel candidate gene for autosomal dominant AVB; this study expands the mutational spectrum of TTN gene and is the first to implicate TTN mutations as AVB disease causing in a Chinese pedigree.

Two novel mutations in TTN of a patient with congenital myopathy: A case report

Background

Early‐onset myopathies show a wide spectrum of phenotypes and are composed of various types of inherited neuromuscular diseases, making it difficult to diagnose. TTN mutation‐related myopathy is a known cause of early‐onset myopathy. Since a next‐generation sequencing (NGS) has enabled sequencing of the vast amount of DNA, TTN, which is the longest coding sequence of any human gene, mutations can now be revealed. We report a 10‐year‐old female with severe congenital muscular weakness and delayed motor development since birth.

Methods

Next‐generation sequencing as well as electromyography and muscle biopsy were performed.

Results

To date, she is incapable of walking alone. Her younger sister had similar but more severe symptoms with respiratory failure. In electromyography, short‐duration, small‐amplitude motor unit action potential, and early recruitment patterns were observed in the involved proximal muscles, suggesting myopathy. Muscle histopathology showed a specific atrophy of increased fiber size variability, frequent nuclear internalization, as well as degeneration and regeneration of fibers with type I fiber predominance, consistent with the findings of a previous report about congenital titinopathy. A NGS study revealed two different possible pathogenic variants in TTN: (a) canonical splicing mutation in the intron 105 (c. 29963‐1G>C) and (b) frameshift and truncating mutation in the exon 339 (c.92812dup/p.Arg30938LysfsTer15). All variants were confirmed by conventional Sanger sequencing.

Conclusion

We propose that unbiased genomic sequencing can be helpful in screening patients with early‐onset myopathy.

A novel mutation in TTN gene in a Saudi patient with bilateral facial weakness and scapular winging

Titin (TTN) is a large gene with 363 exons that encodes a large abundant protein (longest known polypeptide in nature) that is expressed in cardiac and skeletal muscles. TTN has an important role in the sarcomere organization, assembly of muscles, transmission of the force at the Z-line, passive myocyte stiffness, and resting tension maintenance in the I-band region. Mutation in extreme C terminus of TTN, situated at the end of M-band of the TTN in chromosome 2q31, results in tibial muscular dystrophy (TMD), also called Udd Distal Myopathy, which is an autosomal dominant distal myopathy. In this article, we report a novel mutation in TTN gene in a Saudi patient with bilateral facial weakness and scapular winging. This report adds to the literature a heterozygous missense variant c.85652C>G, p.(Pro28551Arg) in TTN gene, which may be related to genes that cause the disease, but more case validation is needed. The novel mutation described in the present study widened the genetic spectrum of TTN-associated diseases, which may benefit studies addressing this disease in the future.

Recessive mutations in proximal I-band of TTN gene cause severe congenital multi-minicore disease without cardiac involvement

Titin, encoded by the gene TTN, is one of the main sarcomere components. It is involved in not only maintaining the structure of cardiac and skeletal muscles, but also in their development, extensibility, elasticity, and signaling events. Congenital titinopathy increasingly appears an important and common form of axial predominant congenital myopathy. The pathophysiological role of TTN in congenital titinopathy and pediatric heart diseases is yet to be explored. Here, we delineate the phenotype of two female siblings who developed severe congenital multi-minicore disease without cardiac involvement. Genetic investigation by whole exome sequencing demonstrated compound heterozygous TTN mutations (c.15496+1G>A, p.5166_5258del; c.18597_18598insC, p.Thr6200Hisfs*15), corresponding to the Ig domain of the proximal I-band. Aberrant splicing causing exon skipping was verified by in vitro minigene analysis. Our results suggest that TTN mutations affecting the Ig domain of the proximal I-band may be a cause of severe congenital defect in skeletal muscles without severe cardiac involvement, thereby providing evidence for the hypothesis that congenital titinopathy patients carrying biallelic N2BA only mutations are at lower cardiac risk than those with other combinations of mutations. Meanwhile, this study confirm the hypothesis on recessive truncating variants of TTN experimentally and thus support earlier reported genotype-phenotype correlations.

An Extended Targeted Copy Number Variation Detection Array Including 187 Genes for the Diagnostics of Neuromuscular Disorders

BACKGROUND

Our previous array, the Comparative Genomic Hybridisation design (CGH-array) for nemaline myopathy (NM), named the NM-CGH array, revealed pathogenic copy number variation (CNV) in the genes for nebulin (NEB) and tropomyosin 3 (TPM3), as well as recurrent CNVs in the segmental duplication (SD), i.e. triplicate, region of NEB (TRI, exons 82-89, 90-97, 98-105). In the light of this knowledge, we have designed and validated an extended CGH array, which includes a selection of 187 genes known to cause neuromuscular disorders (NMDs).

OBJECTIVE

Our aim was to develop a reliable method for CNV detection in genes related to neuromuscular disorders for routine mutation detection and analysis, as a much-needed complement to sequencing methods.

METHODS

We have developed a novel custom-made 4×180 k CGH array for the diagnostics of NMDs. It includes the same tiled ultra-high density coverage of the 12 known or putative NM genes as our 8×60 k NM-CGH-array but also comprises a selection of 175 additional genes associated with NMDs, including titin (TTN), at a high to very high coverage. The genes were divided into three coverage groups according to known and potential pathogenicity in neuromuscular disorders.

RESULTS

The array detected known and putative CNVs in all three gene coverage groups, including the repetitive regions of NEB and TTN.

CONCLUSIONS

The targeted neuromuscular disorder 4×180 k array-CGH (NMD-CGH-array v1.0) design allows CNV detection for a broader spectrum of neuromuscular disorders at a high resolution.

Air pollution exposure during pregnancy: maternal asthma and neonatal respiratory outcomes

PURPOSE

Maternal asthma increases adverse neonatal respiratory outcomes, and pollution may further increase risk. Air quality in relation to neonatal respiratory health has not been studied.

METHODS

Transient tachypnea of the newborn (TTN), asphyxia, and respiratory distress syndrome (RDS) were identified using medical records among 223,375 singletons from the Consortium on Safe Labor (2002-2008). Community Multiscale Air Quality models estimated pollutant exposures. Multipollutant Poisson regression models calculated adjusted relative risks of outcomes for interquartile range increases in average exposure. Maternal asthma and preterm delivery were evaluated as effect modifiers.

RESULTS

TTN risk increased after particulate matter (PM) less than or equal to 10-micron exposure during preconception and trimester one (9-10%), and whole-pregnancy exposure to PM less than or equal to 2.5 microns (PM2.5; 17%) and carbon monoxide (CO; 10%). Asphyxia risk increased after exposure to PM2.5 in trimester one (48%) and whole pregnancy (84%), CO in trimester two and whole pregnancy (28-32%), and consistently for ozone (34%-73%). RDS risk was associated with increased concentrations of nitrogen oxides (33%-42%) and ozone (9%-21%) during all pregnancy windows. Inverse associations were observed with several pollutants, particularly sulfur dioxide. No interaction with maternal asthma was observed. Restriction to term births yielded similar results.

CONCLUSIONS

Several pollutants appear to increase neonatal respiratory outcome risks.

Molecular analysis of inherited cardiomyopathy using next generation semiconductor sequencing technologies

Background

Cardiomyopathies are the most common clinical and genetic heterogeneity cardiac diseases, and genetic contribution in particular plays a major role in patients with primary cardiomyopathies. The aim of this study is to investigate cases of inherited cardiomyopathy (IC) for potential disease-causing mutations in 64 genes reported to be associated with IC.

Methods

A total of 110 independent cases or families diagnosed with various primary cardiomyopathies, including hypertrophic cardiomyopathy, dilated cardiomyopathy, restrictive cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, left ventricular non-compaction, and undefined cardiomyopathy, were collected after informed consent. A custom designed panel, including 64 genes, was screened using next generation sequencing on the Ion Torrent PGM platform. The best candidate disease-causing variants were verified by Sanger sequencing.

Results

A total of 78 variants in 73 patients were identified. After excluding the variants predicted to be benign and VUS, 26 pathogenic or likely pathogenic variants were verified in 26 probands (23.6%), including a homozygous variant in the SLC25A4 gene. Of these variants, 15 have been reported in the Human Gene Mutation Database or ClinVar database, while 11 are novel. The majority of variants were observed in the MYH7 (8/26) and MYBPC3 (6/26) gene. Titin (TTN) truncating mutations account for 13% in our dilated cardiomyopathy cases (3/23).

Conclusions

This study provides an overview of the genetic aberrations in this cohort of Chinese IC patients and demonstrates the power of next generation sequencing in IC. Genetic results can provide precise clinical diagnosis and guidance regarding medical care for some individuals.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1605-5) contains supplementary material, which is available to authorized users.

Increasing Role of Titin Mutations in Neuromuscular Disorders

The TTN gene with 363 coding exons encodes titin, a giant muscle protein spanning from the Z-disk to the M-band within the sarcomere. Mutations in the TTN gene have been associated with different genetic disorders, including hypertrophic and dilated cardiomyopathy and several skeletal muscle diseases.

Before the introduction of next generation sequencing (NGS) methods, the molecular analysis of TTN has been laborious, expensive and not widely used, resulting in a limited number of mutations identified. Recent studies however, based on the use of NGS strategies, give evidence of an increasing number of rare and unique TTN variants. The interpretation of these rare variants of uncertain significance (VOUS) represents a challenge for clinicians and researchers.

The main aim of this review is to describe the wide spectrum of muscle diseases caused by TTN mutations so far determined, summarizing the molecular findings as well as the clinical data, and to highlight the importance of joint efforts to respond to the challenges arising from the use of NGS. An international collaboration through a clinical and research consortium and the development of a single accessible database listing variants in the TTN gene, identified by high throughput approaches, may be the key to a better assessment of titinopathies and to systematic genotype– phenotype correlation studies.