Novel missense variant in TTN cosegregating with familial atrioventricular block

Walking with giants: The challenges of variant impact assessment in the giant sarcomeric protein titin

Titin, the so-called "third filament" of the sarcomere, represents a difficult challenge for the determination of damaging genetic variants. A single titin molecule extends across half the length of a sarcomere in striated muscle, fulfilling a variety of vital structural and signaling roles, and has been linked to an equally varied range of myopathies, resulting in a significant burden on individuals and healthcare systems alike. While the consequences of truncating variants of titin are well-documented, the ramifications of the missense variants prevalent in the general population are less so. We here present a compendium of titin missense variants-those that result in a single amino-acid substitution in coding regions-reported to be pathogenic and discuss these in light of the nature of titin and the variant position within the sarcomere and their domain, the structural, pathological, and biophysical characteristics that define them, and the methods used for characterization. Finally, we discuss the current knowledge and integration of the multiple fields that have contributed to our understanding of titin-related pathology and offer suggestions as to how these concurrent methodologies may aid the further development in our understanding of titin and hopefully extend to other, less well-studied giant proteins. This article is categorized under: Cardiovascular Diseases > Genetics/Genomics/Epigenetics Congenital Diseases > Genetics/Genomics/Epigenetics Congenital Diseases > Molecular and Cellular Physiology.

[Recent studies on dilated cardiomyopathy caused by TTN mutations in children]

The mutations of TTN gene that encodes titin are the most common mutation type among the genetic causes of dilated cardiomyopathy (DCM). This article reviews the worldwide studies on potential molecular pathogenesis (transcription, post-translational modification, etc.), clinical phenotypes, and gene therapies of pediatric DCM caused by TTN mutations, with the hope of providing a reference for the precision treatment of pediatric DCM caused by TTN mutations.

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.

Identification of a novel splicing mutation and genotype-phenotype correlations in rare PLS3-related childhood-onset osteoporosis

Background

X-linked early-onset osteoporosis, caused by mutations in plastin3 (PLS3), is an extremely rare disease characterized by low bone mineral density (BMD) and recurrent osteoporotic fractures. There is limited information on genetic and phenotypic spectrum, as well as genotype–phenotype correlations of the disease. Moreover, whether decreased PLS3 levels were also involved in osteoporosis among subjects without PLS3 pathogenic mutations remains unknown.

Methods

Whole-exome sequencing and bidirectional Sanger sequencing were performed for screening and validation of pathogenic mutations. Serum biochemical parameters and clinical information of the subjects were retrospectively collected. ELISA and online datasets were utilized to investigate the association between PLS3 expression and BMD.

Results

We identified a novel splicing mutation (c.892-2A > G) which led to the skipping of exon 9 in a family with X-linked early-onset osteoporosis. Scoliosis represents a potential new phenotype in the patients harboring PLS3 mutations, which may be corrected by brace treatment. Genotype–phenotype analysis reveals that there was no significant difference in BMD z-scores between different types of reported mutations including this study (p = 0.5). There is a marginally significant negative correlation between age and BMD z-score (p = 0.059, r = − 0.30). The conditions of osteoporosis in all patients were improved after bisphosphonates therapy, with mean BMD z-score increased from − 2.9 to − 0.57 (p < 0.0001). Serum PLS3 levels in adolescents and adults without PLS3 pathogenic mutations but representing osteoporosis were also evaluated, while no association was found between bone mineral density and PLS3 levels (p > 0.05).

Conclusions

Our findings expanded the mutation and phenotype spectrum of the rare disease and highlights the importance of early diagnosis and early treatment with bisphosphonates. More reports of cases with PLS3 mutation and function studies of the gene are warranted to understand genotype–phenotype correlations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02380-z.

Familial risk of atrioventricular block in first-degree relatives

Objective

Rare cases of genetically inherited atrioventricular block (AVB) have been reported; however, the heredity of AVB remains unknown. We aimed to assess the heredity of AVB.

Design, setting and participants

Using data from the Danish Civil Registration Registry, we established a nationwide cohort of individuals with parental links. Data were merged with information from the Danish Pacemaker and Implantable Cardioverter Defibrillator Registry, containing information on all pacemaker implantations performed in Denmark during the study period, to identify patients who received a first-time pacemaker because of AVB.

Results

A total of 4 648 204 individuals had parental links and a total of 26 880 consecutive patients received a first-time pacemaker due to AVB. Overall, the adjusted rate ratio (RR) of pacemaker implantation due to AVB was 2.1 (95% CI 1.8 to 2.5) if a father, mother or sibling had AVB compared with the risk in the general population. The adjusted RR was 2.2 (1.7–2.9) for offspring of mothers with AVB, 1.9 (1.5–2.4) for offspring of fathers with AVB and 3.5 (2.3–5.4) for siblings to a patient with AVB. The risk increased inversely proportionally with the age of the index case at the time of pacemaker implantation. The corresponding adjusted RRs were 15.8 (4.8–52.3) and 10.0 (3.3–30.4) if a mother or father, respectively, had a pacemaker implantation before 50 years.

Conclusion and relevance

First-degree relatives to a patient with AVB carry an increased risk of AVB with the risk being strongly inversely associated with the age of the index case at pacemaker implantation. These findings indicate a genetic component in the development of AVB in families with an early-onset disease.

Matrix metalloproteinase 1 1 G/2 G gene polymorphism is associated with acquired atrioventricular block via linking a higher serum protein level

Limited studies are available regarding the pathophysiological mechanism of acquired atrioventricular block (AVB). Matrix metalloproteinases (MMPs) and angiotensin-converting enzyme (ACE) have been implicated in the pathogenesis of arrhythmia. However, the relationship between these molecules and acquired AVB is still unclear. One hundred and two patients with documented acquired AVB and 100 controls were studied. Gene polymorphisms of the MMP1 and ACE encoding genes were screened by the gene sequencing method or polymerase chain reaction-fragment length polymorphism assay, followed by an association study. The frequencies of the MMP1 −1607 2G2G genotype and MMP1 −1607 2 G allele were significantly higher in the AVB group than that in the controls (OR = 1.933, P = 0.027 and OR = 1.684, P = 0.012, respectively). Consistently, the level of serum MMP1 was significantly greater in acquired AVB patients than that in controls (6568.9 ± 5748.6 pg/ml vs. 4730.5 ± 3377.1 pg/ml, P = 0.019). In addition, the MMP1 2G2G genotype showed a higher MMP-1 serum level than the other genotypes (1G1G/1G2G) (7048.1 ± 5683.0 pg/ml vs. 5072.4 ± 4267.6 pg/ml, P = 0.042). MMP1 1 G/2 G gene polymorphism may contribute to determining the disease susceptibility of acquired AVB by linking the MMP serum protein level.