Cuando la genética estaba oculta: miocardiopatía hipertrófica por variante MYBPC3 c. 1102A>T (p.Lys368*) refractaria a manejo médico: reporte de un caso / When genetics were hidden: hypertrophic cardiomyopathy due to MYBPC3 c. 1102A>T (p.Lys368*) variant refractory to medical management: case report / Quando a genética estava oculta: cardiomiopatia hipertrófica por variante MYBPC3 c. 1102A>T (p.Lys368*) refractária à manejo médico: reporte de um caso

La miocardiopatía hipertrófica es cada vez más diagnosticada. Es una condición genética que genera hipertrofia miocárdica, fibrosis, isquemia y apoptosis con obstrucción del tracto de salida del ventrículo izquierdo. Puede generar síncope, falla cardíaca y muerte súbita. El tratamiento es farmacológico y se requiere cirugía si hay refractariedad. Se presenta un caso de miocardiopatía hipertrófica asociada a variante genética patogénica en un paciente no respondedor a manejo médico óptimo. La importancia de este artículo radica en lo determinante que es la genética para el abordaje diagnóstico y el establecimiento del origen y pronóstico de esta enfermedad.

Hypertrophic cardiomyopathy is increasingly diagnosed. It is a genetic condition that leads to myocardial hypertrophy, fibrosis, ischemia, and apoptosis with obstruction of the left ventricular outflow tract. It can result in syncope, heart failure, and sudden death. Treatment is pharmacological, and surgery is required in cases of refractoriness. A case of hypertrophic cardiomyopathy associated with a pathogenic genetic variant is presented in a patient unresponsive to optimal medical management. The importance of this article lies in how crucial genetics is for the proper diagnostic approach and the establishment of the origin and prognosis of this disease.

A miocardiopatia hipertrófica está sendo diagnosticada cada vez mais. É uma condição genética que leva à hipertrofia miocárdica, fibrose, isquemia e apoptose com obstrução do trato de saída do ventrículo esquerdo. Pode resultar em síncope, insuficiência cardíaca e morte súbita. O tratamento é farmacológico e a cirurgia é necessária em casos de refratariedade. Apresenta-se um caso de miocardiopatia hipertrófica associada a uma variante genética patogênica em um paciente não responsivo ao manejo médico ótimo. A importância deste artigo reside na determinante genética para a abordagem diagnóstica adequada e para o estabelecimento da origem e prognóstico desta doença.

Myocardial Perfusion Defects in Hypertrophic Cardiomyopathy Mutation Carriers.

Background Impaired myocardial blood flow (MBF) in the absence of epicardial coronary disease is a feature of hypertrophic cardiomyopathy (HCM). Although most evident in hypertrophied or scarred segments, reduced MBF can occur in apparently normal segments. We hypothesized that impaired MBF and myocardial perfusion reserve, quantified using perfusion mapping cardiac magnetic resonance, might occur in the absence of overt left ventricular hypertrophy (LVH) and late gadolinium enhancement, in mutation carriers without LVH criteria for HCM (genotype-positive, left ventricular hypertrophy-negative). Methods and Results A single center, case-control study investigated MBF and myocardial perfusion reserve (the ratio of MBF at stress:rest), along with other pre-phenotypic features of HCM. Individuals with genotype-positive, left ventricular hypertrophy-negative (n=50) with likely pathogenic/pathogenic variants and no evidence of LVH, and matched controls (n=28) underwent cardiac magnetic resonance. Cardiac magnetic resonance identified LVH-fulfilling criteria for HCM in 5 patients who were excluded. Individuals with genotype-positive, left ventricular hypertrophy-negative had longer indexed anterior mitral valve leaflet length (12.52±2.1 versus 11.55±1.6 mm/m2, P=0.03), lower left ventricular end-systolic volume (21.0±6.9 versus 26.7±6.2 mm/m2, P≤0.005) and higher left ventricular ejection fraction (71.9±5.5 versus 65.8±4.4%, P≤0.005). Maximum wall thickness was not significantly different (9.03±1.95 versus 8.37±1.2 mm, P=0.075), and no subject had significant late gadolinium enhancement (minor right ventricle‒insertion point late gadolinium enhancement only). Perfusion mapping demonstrated visual perfusion defects in 9 (20%) carriers versus 0 controls (P=0.011). These were almost all septal or near right ventricle insertion points. Globally, myocardial perfusion reserve was lower in carriers (2.77±0.83 versus 3.24±0.63, P=0.009), with a subendocardial:subepicardial myocardial perfusion reserve gradient (2.55±0.75 versus 3.2±0.65, P=<0.005; 3.01±0.96 versus 3.47±0.75, P=0.026) but equivalent MBF (2.75±0.82 versus 2.65±0.69 mL/g per min, P=0.826). Conclusions Regional and global impaired myocardial perfusion can occur in HCM mutation carriers, in the absence of significant hypertrophy or scarring.

Therapeutic potential of AAV9-S15D-RLC gene delivery in humanized MYL2 mouse model of HCM.

Familial hypertrophic cardiomyopathy (HCM) is an autosomal dominant disorder characterized by ventricular hypertrophy, myofibrillar disarray, and fibrosis, and is primarily caused by mutations in sarcomeric genes. With no definitive cure for HCM, there is an urgent need for the development of novel preventive and reparative therapies. This study is focused on aspartic acid-to-valine (D166V) mutation in the myosin regulatory light chain, RLC (MYL2 gene), associated with a malignant form of HCM. Since myosin RLC phosphorylation is critical for normal cardiac function, we aimed to exploit this post-translational modification via phosphomimetic-RLC gene therapy. We hypothesized that mimicking/modulating cardiac RLC phosphorylation in non-phosphorylatable D166V myocardium would improve heart function of HCM-D166V mice. Adeno-associated virus, serotype-9 (AAV9) was used to deliver phosphomimetic human RLC variant with serine-to-aspartic acid substitution at Ser15-RLC phosphorylation site (S15D-RLC) into the hearts of humanized HCM-D166V mice. Improvement of heart function was monitored by echocardiography, invasive hemodynamics (PV-loops) and muscle contractile mechanics. A significant increase in cardiac output and stroke work and a decrease in relaxation constant, Tau, shown to be prolonged in HCM mice, were observed in AAV- vs. PBS-injected HCM mice. Strain analysis showed enhanced myocardial longitudinal shortening in AAV-treated vs. control mice. In addition, increased maximal contractile force was observed in skinned papillary muscles from AAV-injected HCM hearts. Our data suggest that myosin RLC phosphorylation may have important translational implications for the treatment of RLC mutations-induced HCM and possibly play a role in other disease settings accompanied by depressed Ser15-RLC phosphorylation. KEY MESSAGES: HCM-D166V mice show decreased RLC phosphorylation and decompensated function. AAV9-S15D-RLC gene therapy in HCM-D166V mice, but not in WT-RLC, results in improved heart performance. Global longitudinal strain analysis shows enhanced contractility in AAV vs controls. Increased systolic and diastolic function is paralleled by higher contractile force. Phosphomimic S15D-RLC has a therapeutic potential for HCM.

Novel α-Actin Gene Mutation p.(Ala21Val) Causing Familial Hypertrophic Cardiomyopathy, Myocardial Noncompaction, and Transmural Crypts. Clinical-Pathologic Correlation.

BACKGROUND: Mutations of α-actin gene (ACTC1) have been phenotypically related to various cardiac anomalies, including hypertrophic cardiomyopathy and dilated cardiomyopathy and left ventricular (LV) myocardial noncompaction. A novel ACTC mutation is reported as cosegregating for familial hypertrophic cardiomyopathy and LV myocardial noncompaction with transmural crypts. METHODS AND RESULTS: In an Italian family of 7 subjects, 4 aged 10 (II-1), 14 (II-2), 43 (I-4) and 46 years (I-5), presenting abnormal ECG changes, dyspnea and palpitation (II-2, I-4, and I-5), and recurrent cerebral ischemic attack (I-5), underwent 2-dimensional echo, cardiac magnetic resonance, Holter monitoring, and next-generation sequencing gene analysis. Patients II-2 and I-5 with ventricular tachycardia underwent a cardiac invasive study, including coronary with LV angiography and endomyocardial biopsy. In all the affected members, ECG showed right bundle branch block and left anterior hemiblock with age-related prolongation of QRS duration. Two-dimensional echo and cardiac magnetic resonance documented LV myocardial noncompaction in all and in I-4, I-5, and II-2 a progressive LV hypertrophy up to 22-mm maximal wall thickness. Coronary arteries were normal. LV angiography showed transmural crypts progressing to spongeous myocardial transformation with LV dilatation and dysfunction in the oldest subject. At histology and electron microscopy detachment of myocardiocytes were associated with cell and myofibrillar disarray and degradation of intercalated discs causing disanchorage of myofilaments to cell membrane. Next-generation sequencing showed in affected members an unreported p.(Ala21Val) mutation of ACTC. CONCLUSIONS: Novel p.(Ala21Val) mutation of ACTC1 causes myofibrillar and intercalated disc alteration leading to familial hypertrophic cardiomyopathy and LV myocardial noncompaction with transmural crypts.

ß-Myosin heavy chain variant Val606Met causes very mild hypertrophic cardiomyopathy in mice, but exacerbates HCM phenotypes in mice carrying other HCM mutations.

RATIONALE: Approximately 40% of hypertrophic cardiomyopathy (HCM) is caused by heterozygous missense mutations in ß-cardiac myosin heavy chain (ß-MHC). Associating disease phenotype with mutation is confounded by extensive background genetic and lifestyle/environmental differences between subjects even from the same family. OBJECTIVE: To characterize disease caused by ß-cardiac myosin heavy chain Val606Met substitution (VM) that has been identified in several HCM families with wide variation of clinical outcomes, in mice. METHODS AND RESULTS: Unlike 2 mouse lines bearing the malignant myosin mutations Arg453Cys (RC/+) or Arg719Trp (RW/+), VM/+ mice with an identical inbred genetic background lacked hallmarks of HCM such as left ventricular hypertrophy, disarray of myofibers, and interstitial fibrosis. Even homozygous VM/VM mice were indistinguishable from wild-type animals, whereas RC/RC- and RW/RW-mutant mice died within 9 days after birth. However, hypertrophic effects of the VM mutation were observed both in mice treated with cyclosporine, a known stimulator of the HCM response, and compound VM/RC heterozygous mice, which developed a severe HCM phenotype. In contrast to all heterozygous mutants, both systolic and diastolic function of VM/RC hearts was severely impaired already before the onset of cardiac remodeling. CONCLUSIONS: The VM mutation per se causes mild HCM-related phenotypes; however, in combination with other HCM activators it exacerbates the HCM phenotype. Double-mutant mice are suitable for assessing the severity of benign mutations.

Myocardial KRAS(G12D) expression does not cause cardiomyopathy in mice.

AIMS: Germ-line mutations in genes encoding components of the RAS/mitogen-activated protein kinase (MAPK) pathway cause developmental disorders called RASopathies. Hypertrophic cardiomyopathy (HCM) is the most common myocardial pathology and a leading cause of death in RASopathy patients. KRAS mutations are found in Noonan and cardio-facio-cutaneous syndromes. KRAS mutations, unlike mutations of RAF1 and HRAS, are rarely associated with HCM. This has been attributed to the fact that germ-line KRAS mutations cause only a moderate up-regulation of the MAPK pathway. Highly bioactive KRAS mutations have been hypothesized to cause severe cardiomyopathy incompatible with life. The aim of this study was to define the impact of KRAS(G12D) expression in the heart. METHODS AND RESULTS: To generate mice with endogenous cardiomyocyte-specific KRAS(G12D) expression (cKRAS(G12D) mice), we bred mice with a Cre-inducible allele expressing KRAS(G12D) from its endogenous promoter (Kras2(LSL)) to mice expressing Cre under control of the cardiomyocyte-specific α-myosin heavy chain promoter (αMHC-Cre). cKRAS(G12D) mice showed high levels of myocardial ERK and AKT signalling. However, surprisingly, cKRAS(G12D) mice were born in Mendelian ratios, appeared healthy, and had normal function, size, and histology of the heart. CONCLUSION: Mice with cardiomyocyte-specific KRAS(G12D) expression do not develop heart pathology. These results challenge the view that the level of MAPK activation correlates with the severity of HCM in RASopathies and suggests that MAPK-independent strategies may be of interest in the development of new treatments for these syndromes.

Long-term rescue of a familial hypertrophic cardiomyopathy caused by a mutation in the thin filament protein, tropomyosin, via modulation of a calcium cycling protein.

We have recently shown that a temporary increase in sarcoplasmic reticulum (SR) cycling via adenovirus-mediated overexpression of sarcoplasmic reticulum ATPase (SERCA2) transiently improves relaxation and delays hypertrophic remodeling in a familial hypertrophic cardiomyopathy (FHC) caused by a mutation in the thin filament protein, tropomyosin (i.e., α-TmE180G or Tm180). In this study, we sought to permanently alter calcium fluxes via phospholamban (PLN) gene deletion in Tm180 mice in order to sustain long-term improvements in cardiac function and adverse cardiac remodeling/hypertrophy. While similar work has been done in FHCs resulting from mutations in thick myofilament proteins, no one has studied these effects in an FHC resulting from a thin filament protein mutation. Tm180 transgenic (TG) mice were crossbred with PLN knockout (KO) mice and four groups were studied in parallel: 1) non-TG (NTG), 2) Tm180, 3) PLNKO/NTG and 4) PLNKO/Tm180. Tm180 mice exhibit increased heart weight/body weight and hypertrophic gene markers compared to NTG mice, but levels in PLNKO/Tm180 mice were similar to NTG. Tm180 mice also displayed altered function as assessed via in situ pressure-volume analysis and echocardiography at 3-6 months and one year; however, altered function in Tm180 mice was rescued back to NTG levels in PLNKO/Tm180 mice. Collagen deposition, as assessed by Picrosirius Red staining, was increased in Tm180 mice but was similar in NTG and in PLNKO/Tm180 mice. Extracellular signal-regulated kinase (ERK1/2) phosphorylation increased in Tm180 mice while levels in PLNKO/Tm180 mice were similar to NTGs. The present study shows that by modulating SR calcium cycling, we were able to rescue many of the deleterious aspects of FHC caused by a mutation in the thin filament protein, Tm.

The left and right ventricle of a patient with a R723G mutation of the beta-myosin heavy chain and severe hypertrophic cardiomyopathy show no differences in the expression of myosin mRNA.

BACKGROUND: In familial hypertrophic cardiomyopathy (FHC), asymmetric left ventricular (LV) hypertrophy has been considered to be the predominant phenotypic expression, whereas right ventricular (RV) involvement is still ambiguous. In most cases, the right ventricle remains unaffected until secondary pulmonary hypertension develops. Several FHC-causing mutations of genes encoding sarcomere-related proteins have been identified which are transmitted in an autosomal-dominant manner. METHODS: We report the case of a 61 year old member of a Catalan family with a Arg723Gly missense mutation of the ß-myosin heavy chain (ß-MHC), that is associated with a malignant phenotype characterized by sudden cardiac death and heart failure. Because of progressive systolic LV dysfunction, the patient received a heart transplant in 2003. RESULTS: Molecular analysis of the myocardial tissue of the explanted heart, taken from the left and right ventricle, showed a similar deviation of the ratio of mutant vs wild type mRNA of the ß-MHC of 71.8 ± 5% and 68.5 ± 3%, respectively. This finding was confirmed for LV biopsies of this patient on protein level, showing a similar proportion of mutated ß-myosin. But since the patient is heterozygous for the ß-MHC mutation and the mutation is located in a coding region, the relative increase of the expression of the mutant allele is unexpected. It has been demonstrated before by our group for several ß-MHC mutations that the relative abundance of mutated mRNA/protein correlates with the clinical severity of the disease. But since the right ventricle shows no (or only minor) manifestation in terms of hypertrophy or dysfunction, the level of mRNA and protein expression is not the only factor responsible for the development of the phenotype of FHC. CONCLUSIONS: Several mechanisms through which cardiac stresses may incite maladaptive cardiac remodeling primarily of the left ventricle that result in myocardial hypertrophy and heart failure are proposed. One of those triggers could be the enhanced work load of the left ventricle, especially if a LV outflow tract gradient is present, in contrast to the lesser demands to the right ventricle which is adapted to the low pressure system of the pulmonary circulation. Further studies are needed to confirm the results of this case, as well as functional studies involving both ventricles.

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.

Diastolic dysfunction in familial hypertrophic cardiomyopathy transgenic model mice.

AIMS: Several mutations in the ventricular myosin regulatory light chain (RLC) were identified to cause familial hypertrophic cardiomyopathy (FHC). Based on our previous cellular findings showing delayed calcium transients in electrically stimulated intact papillary muscle fibres from transgenic Tg-R58Q and Tg-N47K mice and, in addition, prolonged force transients in Tg-R58Q fibres, we hypothesized that the malignant FHC phenotype associated with the R58Q mutation is most likely related to diastolic dysfunction. METHODS AND RESULTS: Cardiac morphology and in vivo haemodynamics by echocardiography as well as cardiac function in isolated perfused working hearts were assessed in transgenic (Tg) mutant mice. The ATPase-pCa relationship was determined in myofibrils isolated from Tg mouse hearts. In addition, the effect of both mutations on RLC phosphorylation was examined in rapidly frozen ventricular samples from Tg mice. Significantly, decreased cardiac function was observed in isolated perfused working hearts from both Tg-R58Q and Tg-N47K mice. However, echocardiographic examination showed significant alterations in diastolic transmitral velocities and deceleration time only in Tg-R58Q myocardium. Likewise, changes in Ca(2+) sensitivity, cooperativity, and an elevated level of ATPase activity at low [Ca(2+)] were only observed in myofibrils from Tg-R58Q mice. In addition, the R58Q mutation and not the N47K led to reduced RLC phosphorylation in Tg ventricles. CONCLUSION: Our results suggest that the N47K and R58Q mutations may act through similar mechanisms, leading to compensatory hypertrophy of the functionally compromised myocardium, but the malignant R58Q phenotype is most likely associated with more severe alterations in cardiac performance manifested as impaired relaxation and global diastolic dysfunction. At the molecular level, we suggest that by reducing the phosphorylation of RLC, the R58Q mutation decreases the kinetics of myosin cross-bridges, leading to an increased myofilament calcium sensitivity and to overall changes in intracellular Ca(2+) homeostasis.

The binary endocardial appearance is a poor discriminator of Anderson-Fabry disease from familial hypertrophic cardiomyopathy.

OBJECTIVES: We compared the frequency of a binary endocardial appearance in patients with hypertrophic cardiomyopathy (HCM) and Anderson-Fabry disease (AFD). BACKGROUND: A recent study suggested that a binary endocardial appearance is a highly sensitive and specific discriminator of AFD from other causes of hypertrophic cardiomyopathy (HCM). METHODS: Fourteen patients with AFD (55.4 +/- 9.9 years, 9 men) and 14 patients with HCM (57.2 +/- 10.9 years, 9 men) were randomly selected from a dedicated patient database. Two-dimensional echo images were blindly reviewed by 2 experienced echocardiographers. RESULTS: Maximum left ventricular (LV) wall thickness, LV end-systolic dimension, fractional shortening, and left atrial size were similar in the 2 patient groups. The LV end-diastolic dimension was smaller in patients with HCM (p = 0.04). A binary sign was present in 8 of 28 patients (29%). The sensitivity and specificity of the binary sign as a discriminator of AFD from HCM were 35% and 79%, respectively. A binary sign was present in only 1 patient with LV wall thickness <15 mm. CONCLUSIONS: The binary endocardial appearance lacks sufficient sensitivity and specificity to be used as an echocardiographic screening tool.

Mitral valve abnormalities in hypertrophic cardiomyopathy: echocardiographic features and surgical outcomes.

BACKGROUND: Functional and intrinsic mitral valve (MV) abnormalities are common in hypertrophic cardiomyopathy (HCM); however, morphologic characteristics constituting indications for surgical intervention are incompletely defined. This study was conducted to define the echocardiographic features of MV pathology in patients with HCM and relate these to repairability of the MV, MV procedures performed, durability of repair, and survival. METHODS: From 1986 to 2003, 851 patients with HCM underwent operation, and 115 had a concomitant MV procedure. Detailed analysis of their 784 transthoracic and transesophageal echocardiograms, performed intraoperatively and postoperatively, was conducted. Outcomes were assessed by cross-sectional follow-up. RESULTS: Sixty-seven patients (58%) underwent MV repair, and 48 (42%) had MV replacement. The mean left ventricular outflow tract peak gradient was 70 +/- 50 mm Hg. Systolic anterior motion was present in 95%. Valve abnormalities were degenerative in 36 (31%), myxomatous in 23 (20%), papillary muscle in 23 (20%), restrictive chordal in 22 (19%), restrictive leaflet in 80 (70%), and long leaflet in 64 (56%). Patients undergoing MV repair had higher prevalence of long leaflets and degenerative MV pathology. The anterior mitral leaflet was 3.0 +/- 0.49 cm in the repair group vs 2.5 +/- 0.40 cm in the replacement group (p = 0.0001). MV replacement patients were older, more symptomatic, and had more renal dysfunction and lower hematocrits. By 3 years, 91% of patients with a repair were free of reoperation. CONCLUSIONS: Intrinsic MV pathology is frequently observed in HCM patients with symptomatic obstruction who undergo myectomy. Echocardiography can identify MV features predictive of successful valve repair. Repair, although durable, is feasible in only about half of patients.

The use of Tissue Doppler Imaging for the assessment of changes in myocardial structure and function in inherited cardiomyopathies.

Although there is still a long way to go, our understanding of the genetic basis of cardiomyopathies--dilated or hypertrophic--has significantly improved over the past decade. This new and intriguing era of cardiogenetics has already answered some important questions concerning the pathophysiology of these disorders, but it has also raised some new questions: how do we define "presymptomatic" mutation carriers? Should we treat them? Do we have any diagnostic tools to identify the presymptomatic subjects in those families where the underlying mutation has not been identified yet? To address at least part of these questions, there is a clear need for screening techniques in the early stage of the disease which have to be sensitive and non-invasive. In recent years Tissue Doppler Imaging (TDI) has emerged as a well suited technique for these purposes and several interesting papers on this issue have been published. This paper reviews the findings from TDI in several forms of inherited cardiomyopathy. Although the implementation of this technique in everyday clinical practice still requires some refinement, the results from these studies are encouraging and TDI is likely to be complementary to other established screening tools such as ECG and conventional echocardiography.