Michelle Michels

Cardiac Myosin-Binding Protein C Mutations and Hypertrophic Cardiomyopathy: Haploinsufficiency, Deranged Phosphorylation, and Cardiomyocyte Dysfunction

Background— Mutations in the MYBPC3 gene, encoding cardiac myosin-binding protein C (cMyBP-C), are a frequent cause of familial hypertrophic cardiomyopathy. In the present study, we investigated whether protein composition and function of the sarcomere are altered in a homogeneous familial hypertrophic cardiomyopathy patient group with frameshift mutations in MYBPC3 (MYBPC3mut). Methods and Results— Comparisons were made between cardiac samples from MYBPC3 mutant carriers (c.2373dupG, n=7; c.2864_2865delCT, n=4) and nonfailing donors (n=13). Western blots with the use of antibodies directed against cMyBP-C did not reveal truncated cMyBP-C in MYBPC3mut. Protein expression of cMyBP-C was significantly reduced in MYBPC3mut by 33±5%. Cardiac MyBP-C phosphorylation in MYBPC3mut samples was similar to the values in donor samples, whereas the phosphorylation status of cardiac troponin I was reduced by 84±5%, indicating divergent phosphorylation of the 2 main contractile target proteins of the &bgr;-adrenergic pathway. Force measurements in mechanically isolated Triton-permeabilized cardiomyocytes demonstrated a decrease in maximal force per cross-sectional area of the myocytes in MYBPC3mut (20.2±2.7 kN/m2) compared with donor (34.5±1.1 kN/m2). Moreover, Ca2+ sensitivity was higher in MYBPC3mut (pCa50=5.62±0.04) than in donor (pCa50=5.54±0.02), consistent with reduced cardiac troponin I phosphorylation. Treatment with exogenous protein kinase A, to mimic &bgr;-adrenergic stimulation, did not correct reduced maximal force but abolished the initial difference in Ca2+ sensitivity between MYBPC3mut (pCa50=5.46±0.03) and donor (pCa50=5.48±0.02). Conclusions— Frameshift MYBPC3 mutations cause haploinsufficiency, deranged phosphorylation of contractile proteins, and reduced maximal force-generating capacity of cardiomyocytes. The enhanced Ca2+ sensitivity in MYBPC3mut is due to hypophosphorylation of troponin I secondary to mutation-induced dysfunction.

The Importance of Genetic Counseling, DNA Diagnostics, and Cardiologic Family Screening in Left Ventricular Noncompaction Cardiomyopathy

Background—Left ventricular (LV) noncompaction (LVNC) is a distinct cardiomyopathy featuring a thickened bilayered LV wall consisting of a thick endocardial layer with prominent intertrabecular recesses with a thin, compact epicardial layer. Similar to hypertrophic and dilated cardiomyopathy, LVNC is genetically heterogeneous and was recently associated with mutations in sarcomere genes. To contribute to the genetic classification for LVNC, a systematic cardiological family study was performed in a cohort of 58 consecutively diagnosed and molecularly screened patients with isolated LVNC (49 adults and 9 children). Methods and Results—Combined molecular testing and cardiological family screening revealed that 67% of LVNC is genetic. Cardiological screening with electrocardiography and echocardiography of 194 relatives from 50 unrelated LVNC probands revealed familial cardiomyopathy in 32 families (64%), including LVNC, hypertrophic cardiomyopathy, and dilated cardiomyopathy. Sixty-three percent of the relatives newly diagnosed with cardiomyopathy were asymptomatic. Of 17 asymptomatic relatives with a mutation, 9 had noncompaction cardiomyopathy. In 8 carriers, nonpenetrance was observed. This may explain that 44% (14 of 32) of familial disease remained undetected by ascertainment of family history before cardiological family screening. The molecular screening of 17 genes identified mutations in 11 genes in 41% (23 of 56) tested probands, 35% (17 of 48) adults and 6 of 8 children. In 18 families, single mutations were transmitted in an autosomal dominant mode. Two adults and 2 children were compound or double heterozygous for 2 different mutations. One adult proband had 3 mutations. In 50% (16 of 32) of familial LVNC, the genetic defect remained inconclusive. Conclusion—LVNC is predominantly a genetic cardiomyopathy with variable presentation ranging from asymptomatic to severe. Accordingly, the diagnosis of LVNC requires genetic counseling, DNA diagnostics, and cardiological family screening.

Long-Term Outcome of Alcohol Septal Ablation in Patients with Obstructive Hypertrophic Cardiomyopathy: A Word of Caution

Background—The impact of alcohol septal ablation (ASA)-induced scar is not known. This study sought to examine the long-term outcome of ASA among patients with obstructive hypertrophic cardiomyopathy. Methods and Results—Ninety-one consecutive patients (aged 54±15 years) with obstructive hypertrophic cardiomyopathy underwent ASA. Primary study end point was a composite of cardiac death and aborted sudden cardiac death including appropriate cardioverter-defibrillator discharges for fast ventricular tachycardia/ventricular fibrillation. Secondary end points were noncardiac death and other nonfatal complications. Outcomes of ASA patients were compared with 40 patients with hypertrophic cardiomyopathy who underwent septal myectomy. During 5.4±2.5 years, primary and/or secondary end points were seen in 35 (38%) ASA patients of whom 19 (21%) patients met the primary end point. The 1-, 5-, and 8-year survival-free from the primary end point was 96%, 86%, and 67%, respectively in ASA patients versus 100%, 96%, and 96%, respectively in myectomy patients during 6.6±2.7 years (log-rank, P=0.01). ASA patients had a ≈5-fold increase in the estimated annual primary end point rate (4.4% versus 0.9%) compared with myectomy patients. In a multivariable model including a propensity score, ASA was an independent predictor of the primary end point (unadjusted hazard ratio, 5.2; 95% CI, 1.2 to 22.1; P=0.02 and propensity score-adjusted hazard ratio, 6.1; 95% CI, 1.4 to 27.1; P=0.02). Conclusions—This study shows that ASA has potentially unwanted long-term effects. This poses special precaution, given the fact that ASA is practiced worldwide at increasing rate. We recommend myectomy as the preferred intervention in patients with obstructive hypertrophic cardiomyopathy.

Perturbed Length-Dependent Activation in Human Hypertrophic Cardiomyopathy With Missense Sarcomeric Gene Mutations

Rationale: High-myofilament Ca2+ sensitivity has been proposed as a trigger of disease pathogenesis in familial hypertrophic cardiomyopathy (HCM) on the basis of in vitro and transgenic mice studies. However, myofilament Ca2+ sensitivity depends on protein phosphorylation and muscle length, and at present, data in humans are scarce. Objective: To investigate whether high myofilament Ca2+ sensitivity and perturbed length-dependent activation are characteristics for human HCM with mutations in thick and thin filament proteins. Methods and Results: Cardiac samples from patients with HCM harboring mutations in genes encoding thick (MYH7, MYBPC3) and thin (TNNT2, TNNI3, TPM1) filament proteins were compared with sarcomere mutation-negative HCM and nonfailing donors. Cardiomyocyte force measurements showed higher myofilament Ca2+ sensitivity in all HCM samples and low phosphorylation of protein kinase A (PKA) targets compared with donors. After exogenous PKA treatment, myofilament Ca2+ sensitivity was similar (MYBPC3mut, TPM1mut, sarcomere mutation-negative HCM), higher (MYH7mut, TNNT2mut), or even significantly lower (TNNI3mut) compared with donors. Length-dependent activation was significantly smaller in all HCM than in donor samples. PKA treatment increased phosphorylation of PKA-targets in HCM myocardium and normalized length-dependent activation to donor values in sarcomere mutation-negative HCM and HCM with truncating MYBPC3 mutations but not in HCM with missense mutations. Replacement of mutant by wild-type troponin in TNNT2mut and TNNI3mut corrected length-dependent activation to donor values. Conclusions: High-myofilament Ca2+ sensitivity is a common characteristic of human HCM and partly reflects hypophosphorylation of PKA targets compared with donors. Length-dependent sarcomere activation is perturbed by missense mutations, possibly via posttranslational modifications other than PKA hypophosphorylation or altered protein–protein interactions, and represents a common pathomechanism in HCM.

Contractile Dysfunction Irrespective of the Mutant Protein in Human Hypertrophic Cardiomyopathy With Normal Systolic Function

Background— Hypertrophic cardiomyopathy (HCM), typically characterized by asymmetrical left ventricular hypertrophy, frequently is caused by mutations in sarcomeric proteins. We studied if changes in sarcomeric properties in HCM depend on the underlying protein mutation. Methods and Results— Comparisons were made between cardiac samples from patients carrying a MYBPC3 mutation (MYBPC3mut; n=17), mutation negative HCM patients without an identified sarcomere mutation (HCMmn; n=11), and nonfailing donors (n=12). All patients had normal systolic function, but impaired diastolic function. Protein expression of myosin binding protein C (cMyBP-C) was significantly lower in MYBPC3mut by 33±5%, and similar in HCMmn compared with donor. cMyBP-C phosphorylation in MYBPC3mut was similar to donor, whereas it was significantly lower in HCMmn. Troponin I phosphorylation was lower in both patient groups compared with donor. Force measurements in single permeabilized cardiomyocytes demonstrated comparable sarcomeric dysfunction in both patient groups characterized by lower maximal force generating capacity in MYBPC3mut and HCMmn, compared with donor (26.4±2.9, 28.0±3.7, and 37.2±2.3 kN/m2, respectively), and higher myofilament Ca2+-sensitivity (EC50=2.5±0.2, 2.4±0.2, and 3.0±0.2 &mgr;mol/L, respectively). The sarcomere length-dependent increase in Ca2+-sensitivity was significantly smaller in both patient groups compared with donor (&Dgr;EC50: 0.46±0.04, 0.37±0.05, and 0.75±0.07 &mgr;mol/L, respectively). Protein kinase A treatment restored myofilament Ca2+-sensitivity and length-dependent activation in both patient groups to donor values. Conclusions— Changes in sarcomere function reflect the clinical HCM phenotype rather than the specific MYBPC3 mutation. Hypocontractile sarcomeres are a common deficit in human HCM with normal systolic left ventricular function and may contribute to HCM disease progression.

Long-Term Outcome of Alcohol Septal Ablation in Patients With Obstructive Hypertrophic CardiomyopathyClinical Perspective

Background—The impact of alcohol septal ablation (ASA)-induced scar is not known. This study sought to examine the long-term outcome of ASA among patients with obstructive hypertrophic cardiomyopathy. Methods and Results—Ninety-one consecutive patients (aged 54±15 years) with obstructive hypertrophic cardiomyopathy underwent ASA. Primary study end point was a composite of cardiac death and aborted sudden cardiac death including appropriate cardioverter-defibrillator discharges for fast ventricular tachycardia/ventricular fibrillation. Secondary end points were noncardiac death and other nonfatal complications. Outcomes of ASA patients were compared with 40 patients with hypertrophic cardiomyopathy who underwent septal myectomy. During 5.4±2.5 years, primary and/or secondary end points were seen in 35 (38%) ASA patients of whom 19 (21%) patients met the primary end point. The 1-, 5-, and 8-year survival-free from the primary end point was 96%, 86%, and 67%, respectively in ASA patients versus 100%, 96%, and 96%, respectively in myectomy patients during 6.6±2.7 years (log-rank, P=0.01). ASA patients had a ≈5-fold increase in the estimated annual primary end point rate (4.4% versus 0.9%) compared with myectomy patients. In a multivariable model including a propensity score, ASA was an independent predictor of the primary end point (unadjusted hazard ratio, 5.2; 95% CI, 1.2 to 22.1; P=0.02 and propensity score-adjusted hazard ratio, 6.1; 95% CI, 1.4 to 27.1; P=0.02). Conclusions—This study shows that ASA has potentially unwanted long-term effects. This poses special precaution, given the fact that ASA is practiced worldwide at increasing rate. We recommend myectomy as the preferred intervention in patients with obstructive hypertrophic cardiomyopathy.

Outcome and Complications after Implantable Cardioverter Defibrillator Therapy in Hypertrophic Cardiomyopathy: Systematic Review and Meta-Analysis

Background—Previous observational studies demonstrated that patients with hypertrophic cardiomyopathy at risk for sudden cardiac death (SCD) may benefit from implantable cardioverter defibrillator (ICD) therapy. A complete overview of outcome and complications after ICD therapy is currently not available. This study pools data from published studies on outcome and complications after ICD therapy in patients with hypertrophic cardiomyopathy. Methods and Results—A PubMed database search returned 27 studies on 16 cohorts reporting outcome and complications after ICD therapy in patients with hypertrophic cardiomyopathy. In case of >1 publications on a particular cohort, the publication with the largest number of patients was included in the meta-analysis. ICD interventions, complications, and mortality rates were extracted, pooled, and analyzed. There were 2190 patients (mean age, 42 years; 38% women), most of whom (83%) received an ICD for primary prevention of SCD. Risk factors for SCD were left ventricular wall thickness ≥30 mm (20%), family history of SCD (43%), nonsustained ventricular tachycardia (46%), syncope (41%), and abnormal blood pressure response (25%). During the 3.7-year follow-up, the annualized cardiac mortality rate was 0.6%, the noncardiac mortality rate was 0.4%, and the appropriate ICD intervention rate was 3.3%. The annualized inappropriate ICD intervention rate was 4.8% and the annualized ICD-related complication rate was 3.4%. Conclusions—This meta-analysis demonstrates a low cardiac and noncardiac mortality rate after ICD therapy in patients with hypertrophic cardiomyopathy. Appropriate ICD intervention occurred at a rate of 3.3%/year, thereby, most probably, preventing SCD. Inappropriate ICD intervention and complications are not uncommon.

Disease penetrance and risk stratification for sudden cardiac death in asymptomatic hypertrophic cardiomyopathy mutation carriers

AIMS To investigate the outcome of cardiac evaluation and the risk stratification for sudden cardiac death (SCD) in asymptomatic hypertrophic cardiomyopathy (HCM) mutation carriers. METHODS AND RESULTS Seventy-six HCM mutation carriers from 32 families identified by predictive DNA testing underwent cardiac evaluation including history, examination, electrocardiography, Doppler echocardiography, exercise testing, and 24 h Holter monitoring. The published diagnostic criteria for HCM in adult members of affected families were used to diagnose HCM. Thirty-three (43%) men and 43 (57%) women with a mean age of 42 years (range 16-79) were examined; in 31 (41%) HCM was diagnosed. Disease penetrance was age related and men were more often affected than women (P = 0.04). Myosin Binding Protein C (MYBPC3) mutation carriers were affected at higher age than Myosin Heavy Chain (MYH7) mutation carriers (P = 0.01). Risk factors for SCD were present in affected and unaffected carriers. CONCLUSION Hypertrophic cardiomyopathy was diagnosed in 41% of carriers. Disease penetrance was age dependent, warranting repeated cardiologic evaluation. The MYBPC3 mutation carriers were affected at higher age than MYH7 mutation carriers. Risk factors for SCD were present in carriers with and without HCM. Follow-up studies are necessary to evaluate the effectiveness of risk stratification for SCD in this population.

Diastolic abnormalities as the first feature of hypertrophic cardiomyopathy in Dutch myosin-binding protein C founder mutations.

OBJECTIVES To test the hypothesis that carriers of Dutch founder mutations in cardiac myosin-binding protein C (MYBPC3), without left ventricular hypertrophy (LVH) or electrocardiographic abnormalities, have diastolic dysfunction on tissue Doppler imaging (TDI), which can be used for the screening of family members in the hypertrophic cardiomyopathy (HCM) population. BACKGROUND TDI is a more sensitive technique for the assessment of left ventricular contraction and relaxation abnormalities than is conventional echocardiography. METHODS Echocardiographic studies including TDI were performed in genotyped hypertrophic cardiomyopathy patients (genotype-positive, G+/LVH+; n = 27), mutation carriers without LVH (G+/LVH-; n = 27), and healthy controls (n = 55). The identified mutations in MYBPC3 in the G+/LVH+ subjects were c.2864_2865delCT (12 subjects), c.2373dupG (n = 8), and p. Arg943X (n = 7). In the G+/LVH- subjects, the following mutations were identified: c.2864_2865delCT (n = 11), c.2373dupG (n = 8), and p. Arg943X (n = 8). RESULTS Mean TDI-derived systolic and early and late diastolic mitral annular velocities were significantly lower in the G+/LVH+ subjects compared with the other groups. However, there was no difference between controls and G+/LVH- subjects. Mean TDI-derived late mitral annular diastolic velocities were significantly higher in the G+/LVH- subjects compared with controls and G+/LVH+ subjects. Using a cut-off value of mean +/- 2 SD, an abnormal late mitral annular diastolic velocity was found in 14 (51%) of G+/LVH- patients. There was no difference among the 3 different mutations. CONCLUSIONS In contrast to earlier reports, mean mitral annular systolic velocity and early mitral annular diastolic velocity velocities were not reduced in G+/LVH- subjects, and TDI velocities were not sufficiently sensitive for determination of the affected status of an individual subject. Our findings, however, support the theory that diastolic dysfunction is a primary component of pre-clinical HCM.

Long-Term Outcomes After Medical and Invasive Treatment in Patients With Hypertrophic Cardiomyopathy

OBJECTIVES The aim of this study was to determine the long-term outcomes (all-cause mortality and sudden cardiac death [SCD]) after medical therapy, alcohol septal ablation (ASA), and myectomy in patients with hypertrophic cardiomyopathy (HCM). BACKGROUND Therapy-resistant obstructive HCM can be treated both surgically and percutaneously. But there is no consensus on the long-term effects of ASA, especially on SCD. METHODS This study included 1,047 consecutive patients with HCM (mean age 52 ± 16 years, 61% men) from 3 tertiary referral centers. A total of 690 patients (66%) had left ventricular outflow tract gradients ≥ 30 mm Hg, of whom 124 (12%) were treated medically, 316 (30%) underwent ASA, and 250 (24%) underwent myectomy. Primary endpoints were all-cause mortality and SCD. Kaplan-Meier graphs and Cox regression models were used for statistical analyses. RESULTS The mean follow-up period was 7.6 ± 5.3 years. Ten-year survival was similar in medically treated patients (84%), ASA patients (82%), myectomy patients (85%), and patients with nonobstructive HCM (85%) (log-rank p = 0.50). The annual rate of SCD was low after invasive therapy: 1.0%/year in the ASA group and 0.8%/year in the myectomy group. Multivariate analysis demonstrated that the risk for SCD was lower after myectomy compared with the ASA group (hazard ratio: 2.1; 95% confidence interval: 1.0 to 4.4; p = 0.04) and the medical group (hazard ratio: 2.3; 95% confidence interval: 1.0 to 5.2; p = 0.04). CONCLUSIONS Patients with obstructive HCM who are treated at referral centers for HCM care have good survival and low SCD risk, similar to that of patients with nonobstructive HCM. The SCD risk of patients after myectomy was lower than after ASA or in the medical group.