Stellan Mörner

Atlas of the clinical genetics of human dilated cardiomyopathy

AIM Numerous genes are known to cause dilated cardiomyopathy (DCM). However, until now technological limitations have hindered elucidation of the contribution of all clinically relevant disease genes to DCM phenotypes in larger cohorts. We now utilized next-generation sequencing to overcome these limitations and screened all DCM disease genes in a large cohort. METHODS AND RESULTS In this multi-centre, multi-national study, we have enrolled 639 patients with sporadic or familial DCM. To all samples, we applied a standardized protocol for ultra-high coverage next-generation sequencing of 84 genes, leading to 99.1% coverage of the target region with at least 50-fold and a mean read depth of 2415. In this well characterized cohort, we find the highest number of known cardiomyopathy mutations in plakophilin-2, myosin-binding protein C-3, and desmoplakin. When we include yet unknown but predicted disease variants, we find titin, plakophilin-2, myosin-binding protein-C 3, desmoplakin, ryanodine receptor 2, desmocollin-2, desmoglein-2, and SCN5A variants among the most commonly mutated genes. The overlap between DCM, hypertrophic cardiomyopathy (HCM), and channelopathy causing mutations is considerably high. Of note, we find that >38% of patients have compound or combined mutations and 12.8% have three or even more mutations. When comparing patients recruited in the eight participating European countries we find remarkably little differences in mutation frequencies and affected genes. CONCLUSION This is to our knowledge, the first study that comprehensively investigated the genetics of DCM in a large-scale cohort and across a broad gene panel of the known DCM genes. Our results underline the high analytical quality and feasibility of Next-Generation Sequencing in clinical genetic diagnostics and provide a sound database of the genetic causes of DCM.

Regional and Global Right Ventricular Function in Healthy Individuals Aged 20–90 Years: A Pulsed Doppler Tissue Imaging Study Umeå General Population Heart Study

The aim of the present study was to describe regional and global right ventricular (RV) function in a wide age range of healthy subjects of both sexes. We studied 255 (125 females) healthy individuals randomly selected from the Umeå General Population Register, age 58 ± 19 (range 22–89) years. RV function was studied using myocardial tissue Doppler imaging of the RV free wall. Isovolumic contraction (IVCv), systolic (Sv), early (Ev), and late (Av) diastolic velocities were measured. Furthermore, isovolumic periods and ejection time intervals were also measured. Conventional Doppler was used to study RV global filling properties. While systolic myocardial velocities were conserved over age, there was a decrease in myocardial E/A ratio with increasing age (r =−0.67, P < 0.001, for base) taken from the RV free wall. A similar age relation was found in RV global filling velocities with a reduced tricuspid E/A ratio (r =−0.57, P < 0.001). Furthermore, a significant correlation was found between global and regional E/A ratios at the basal (r = 0.58, P ≤ 0.001) and mid‐segmental levels (r = 0.46, P ≤ 0.001). Systolic myocardial velocities behaved independent of age whereas regional as well as global E/A ratio were age‐related. No relationship was found between regional isovolumic time intervals and age. Knowledge of these age‐dependent relationships is fundamental when evaluating RV function in patients.

Identification of the genotypes causing hypertrophic cardiomyopathy in northern Sweden

Hypertrophic cardiomyopathy (HCM) is a heterogenous disease, with variable genotypic and phenotypic expressions, often caused by mutations in sarcomeric protein genes. The aim of this study was to identify the genotypes and associated phenotypes related to HCM in northern Sweden. In 46 unrelated individuals with familial or sporadic HCM, mutation analysis of eight sarcomeric protein genes was performed; the cardiac beta-myosin heavy chain, cardiac myosin-binding protein C, cardiac troponin T, alpha-tropomyosin, cardiac essential and regulatory myosin light chains, cardiac troponin I and cardiac alpha-actin. A total of 11 mutations, of which six were novel ones, were found in 13 individuals. Seven mutations were located in the myosin-binding protein C gene, two in the beta-myosin heavy chain gene and one in the regulatory myosin light chain and troponin I genes, respectively. This is the first Swedish study, where a population with HCM has been genotyped. Mutations in the cardiac myosin-binding protein C gene were the most common ones found in northern Sweden, whereas mutations in the beta-myosin heavy chain gene were less frequent than previously described. There are differences in the phenotypes mediated by these genes characterised by a more late-onset disease for the myosin-binding protein C gene mutations. This should be taken into consideration, when evaluating clinical findings in the diagnosis of the disease, especially in young adults in families with HCM, where penetrance can be expected to be incomplete in the presence of a myosin-binding protein C gene mutation.

Evidence for FHL1 as a novel disease gene for isolated hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is characterized by asymmetric left ventricular hypertrophy, diastolic dysfunction and myocardial disarray. HCM is caused by mutations in sarcomeric genes, but in >40% of patients, the mutation is not yet identified. We hypothesized that FHL1, encoding four-and-a-half-LIM domains 1, could be another disease gene since it has been shown to cause distinct myopathies, sometimes associated with cardiomyopathy. We evaluated 121 HCM patients, devoid of a mutation in known disease genes. We identified three novel variants in FHL1 (c.134delA/K45Sfs, c.459C>A/C153X and c.827G>C/C276S). Whereas the c.459C>A variant was associated with muscle weakness in some patients, the c.134delA and c.827G>C variants were associated with isolated HCM. Gene transfer of the latter variants in C2C12 myoblasts and cardiac myocytes revealed reduced levels of FHL1 mutant proteins, which could be rescued by proteasome inhibition. Contractility measurements after adeno-associated virus transduction in rat-engineered heart tissue (EHT) showed: (i) higher and lower forces of contraction with K45Sfs and C276S, respectively, and (ii) prolonged contraction and relaxation with both mutants. All mutants except one activated the fetal hypertrophic gene program in EHT. In conclusion, this study provides evidence for FHL1 to be a novel gene for isolated HCM. These data, together with previous findings of proteasome impairment in HCM, suggest that FHL1 mutant proteins may act as poison peptides, leading to hypertrophy, diastolic dysfunction and/or altered contractility, all features of HCM.

Do troponin and B‐natriuretic peptide detect cardiomyopathy in transthyretin amyloidosis?

Objectives.  Cardiomyopathy is a well known complication in familial amyloidotic polyneuropathy (FAP). Troponin T and B‐natriuretic peptide (BNP) have been shown to be excellent markers for heart complications in AL‐amyloidosis. The aim of the study was to investigate troponin T, troponin I and BNP as markers for myocardial damage and failure in FAP.

Assessment of regional rotation patterns improves the understanding of the systolic and diastolic left ventricular function: an echocardiographic speckle-tracking study in healthy individuals

UNLABELLED Aim To elucidate the complexity of left ventricular motion throughout the cardiac cycle, we studied regional rotation in detail. METHODS AND RESULTS Regional rotation in six subdivisions of the circumference at three levels was studied by using speckle-tracking echocardiography in 40 healthy subjects. At the basal level the inferoseptal segments rotated significantly more clockwise during systole than the opposing anterolateral segments. At the papillary level the inferoseptal segments differed significantly from the anterolateral segments, where the inferoseptal segments rotated clockwise and the anterolateral segments rotated counter-clockwise. The apical level showed significant difference in regional rotation only at aortic valve opening. In early systole, untwist before the main systolic twist was seen at the basal and apical levels; however, the duration of the basal untwist was much longer than that of the apical. The diastolic phases of rotation at the basal and apical levels matched the different filling phases. CONCLUSION Large regional differences in rotation are present at the basal and papillary levels in healthy subjects. The diastolic untwist matches the phases of both the E-wave and A-wave and seems to be related with intraventricular pressure differences, indicating that untwist plays an important role in the filling of the ventricle.

Amyloid heart disease mimicking hypertrophic cardiomyopathy

Objective.  To investigate the importance of transthyretin (TTR) gene mutations in explaining the phenotypic expression in patients diagnosed with hypertrophic cardiomyopathy (HCM) in northern Sweden.

Growth factor stimulation of cardiomyocytes induces changes in the transcriptional contents of secreted exosomes

Exosomes are nano-sized extracellular vesicles, released from various cells, which can stimulate or repress responses in targets cells. We recently reported that cultured cardiomyocytes are able to release exosomes and that they, in turn, are involved in facilitating events in target cells by alteration of gene expression. We investigated whether external stimuli of the cardiomyocyte might influence the transcriptional content of the released exosomes. Exosomes were isolated from media collected from cultured cardiomyocytes (HL-1) with or without growth factor treatment (TGF-β2 and PDGF-BB), with a series of differential centrifugations, including preparative ultracentrifugation and separation with a sucrose gradient. The exosomes were characterized with dynamic light scattering (DLS), electron microscopy (EM) and Western blot and analyzed with Illumina whole genome microarray gene expression. The exosomes were rounded in shape and had an average size of 50–90 nm in diameter with no difference between treatment groups. Analysis of the mRNA content in repeated experiments conclusively revealed 505 transcripts in the control group, 562 in the TGF-β2-treated group and 300 in the PDGF-BB-treated group. Common transcripts (217) were found in all 3 groups. We show that the mode of stimulation of parental cells affects the characteristics of exosomes released. Hence, there is a difference in mRNA content between exosomes derived from cultured cardiomyocytes stimulated, or not stimulated, with growth factors. We also conclude that all exosomes contain a basic package consisting of ribosomal transcripts and mRNAs coding for proteins with functions within the energy supply system.

Profound cardiac conduction delay predicts mortality in myotonic dystrophy type 1

Abstract.  Mörner S, Lindqvist P, Mellberg C, Olofsson B‐O, Backman C, Henein M, Lundblad D, Forsberg H (Umeå University Hospital, Umeå; Umeå University, Umeå; Sunderby Hospital, Luleå; Sweden). Profound cardiac conduction delay predicts mortality in myotonic dystrophy type 1. J Intern Med 2010; 268:59–65.

Ventricular dysfunction in type 1 myotonic dystrophy: electrical, mechanical, or both?

BACKGROUND Myotonic dystrophy type 1 (DM1) is a systemic disease which affects the heart and may be a cause of sudden death. Conduction disturbances are the major cardiac abnormalities seen in this condition. We sought to assess electrical and mechanical cardiac functions to identify abnormalities that might explain sudden cardiac death in DM1. METHODS Thirty six patients with DM1 and 16 controls were studied using echocardiography including myocardial Doppler. ECG recordings were also obtained. RESULTS Left ventricular (LV) dimensions were maintained but systolic function was reduced (p<0.001), including stroke volume (p<0.05). LV segmental myocardial isovolumic contraction time was prolonged (p<0.001) and correlated with PR interval (p<0.001). Isovolumic relaxation time was prolonged (p<0.05) and filling time was reduced (p<0.001). LV cavity was significantly asynchronous demonstrated by prolonged total isovolumic time (t-IVT) (p<0.001), high Tei index (p<0.001) and low ejection index (p<0.001). Right ventricular (RV) strain was reduced (p<0.001) as were its systolic and diastolic velocities (p<0.05 for both). 22/36 patients had prolonged LV t-IVT>12.3 s/min (upper 95% normal CI), 13 of whom had PR≥200 ms, 11 had QRS duration>120 ms (5 had combined abnormality) and the remaining 5 had neither. Over the 3 years follow up 10 patients had events, 6 of them cardiac. t-IVT was prolonged in 5/6 patients, PR interval in 4 and QRS duration in one. CONCLUSIONS In DM1 patients, LV conventional measurements are modestly impaired but cardiac time relations suggest marked asynchronous cavity function. Although our findings were primarily explained on the basis of long PR interval or broad QRS duration a minority presented an evidence for myocardial cause of asynchrony rather than electrical. Early identification of such abnormalities may guide towards a need for additional electrical resynchronization therapy which may improve survival in a way similar to what has been shown in heart failure trials.