Genetic determinants of clinical phenotype in hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disease that affects approximately one in 500 people. HCM is a recognized genetic disorder most often caused by mutations involving myosin-binding protein C (MYBPC3) and β-myosin heavy chain (MYH7) which are responsible for approximately three-quarters of the identified mutations.

METHODS

As a part of the international multidisciplinary SILICOFCM project ( www.silicofcm.eu ) the present study evaluated the association between underlying genetic mutations and clinical phenotype in patients with HCM. Only patients with confirmed single pathogenic mutations in either MYBPC3 or MYH7 genes were included in the study and divided into two groups accordingly. The MYBPC3 group was comprised of 48 patients (76%), while the MYH7 group included 15 patients (24%). Each patient underwent clinical examination and echocardiography.

RESULTS

The most prevalent symptom in patients with MYBPC3 was dyspnea (44%), whereas in patients with MYH7 it was palpitations (33%). The MYBPC3 group had a significantly higher number of patients with a positive family history of HCM (46% vs. 7%; p = 0.014). There was a numerically higher prevalence of atrial fibrillation in the MYH7 group (60% vs. 35%, p = 0.085). Laboratory analyses revealed normal levels of creatinine (85.5 ± 18.3 vs. 81.3 ± 16.4 µmol/l; p = 0.487) and blood urea nitrogen (10.2 ± 15.6 vs. 6.9 ± 3.9 mmol/l; p = 0.472) which were similar in both groups. The systolic anterior motion presence was significantly more frequent in patients carrying MYH7 mutation (33% vs. 10%; p = 0.025), as well as mitral leaflet abnormalities (40% vs. 19%; p = 0.039). Calcifications of mitral annulus were registered only in MYH7 patients (20% vs. 0%; p = 0.001). The difference in diastolic function, i.e. E/e' ratio between the two groups was also noted (MYBPC3 8.8 ± 3.3, MYH7 13.9 ± 6.9, p = 0.079).

CONCLUSIONS

Major findings of the present study corroborate the notion that MYH7 gene mutation patients are presented with more pronounced disease severity than those with MYBPC3.

[Management of hypertrophic cardiomyopathy - the most common inherited heart disease]

Hypertrophic cardiomyopathy is the most common cardiogenetic disease affecting 1/500-1/1 000 individuals. Dyspnea is common but chest pain, dizziness or fainting may also cause considerable limitation for the patient. The diagnosis can be suspected from ECG. Echocardiography confirms hypertrophy of at least 15 mm, usually in the septum. If the obstruction of the outflow tract is severe, myectomy or alcohol ablation can relieve symptoms. Genetic evaluation of family members is advisable. To reduce symptoms, betablockers are used; verapamil or disopyramide are alternatives. Atrial fibrillation is often prevalent and requires special attention concerning anticoagulation and rhythm or rate control. An end-stage heart failure warrants advanced treatment options such as cardiac resynchronization therapy, ventricular assist devices or heart transplant. Sudden cardiac death is unpredictable and evaluation of risk markers is important to identify potential candidates for an implantable defibrillator.

[Profiles of genotypes of familial hypertrophic cardiomyopathy according to data of clinical studies]

With the aim of studying clinical profiles of hereditary cases of hypertrophic cardiomyopathy (HCMP) we examined 64 patients with HCMP of both sexes (mean age 43.8+/-11.7 years). Genealogy of 40 patients (62.5%) revealed no cases of the disease among first degree relatives. They were defined as sporadic forms of HCMP. Genealogical screening revealed 22 patients (37.5%) with familial forms of HCMP. In 8 cases study of genealogy of probands detected 16 more patients. Results of assessment of familial history, ECG and echocardiographic investigations reflected degree of thickening of interventricular septum, asymmetric character of distribution of hypertrophy in the myocardium, and cases of sudden deaths in first degree relatives as possible hereditary signs in familial HCMP determining variations of clinical phenotype of the disease through interrelated disturbances of contractile and electrical myocardial functions.

MYBPC3 polymorphism is a modifier for expression of cardiac hypertrophy in patients with hypertrophic cardiomyopathy

Clinical phenotype of hypertrophic cardiomyopathy exhibits significant inter- and intra-familial heterogeneities. To test if MYBPC3 polymorphism could modify the expression of cardiac hypertrophy, 226 patients with hypertrophic cardiomyopathy and 226 age- and sex-matched controls were recruited according to the diagnostic criteria of WHO. Genotyping was completed by using PCR, restrictive enzyme digestion, and sequencing. Three polymorphisms of MYBPC3 were studied, only the GG genotype at 18443 in exon 30 associated with thicker left ventricular wall (25.2+/-5.9 mm) in patient group, not the AA and AG genotypes (19.0+/-5.0mm, P<0.001). After multiple regression analysis for adjustment of age and sex, the association remained. No difference was found in the genotype distribution between control and patients. Our results point out that GG genotype of MYBPC3 might be a genetic risk factor for the expression of cardiac hypertrophic phenotype in the patients with hypertrophic cardiomyopathy.

Uncommon cause of a common disease

Myocardial infarction is a common life-threatening condition. Multiple agents can be used to treat acute coronary syndrome (ACS). These therapeutic agents pose potential life-threatening complications when used outside the realm of the acute coronary syndrome. Hypertrophic cardiomyopathy (HCM) is a common inherited cardiac disorder, occurring in 1 in 500 individuals, which may mimic ACS. The hypertrophy most typically involves the septum in patients with HCM. As many as 25% of Japanese patients with HCM have predominately apical involvement. Apical hypertrophic cardiomyopathy (AHC) occurs in only 1 to 2% of the non-Japanese population. Despite its low incidence, physicians caring for patients with chest pain need to consider AHC in their differential diagnosis. We present the case of a patient with chest pain and electrocardiographic changes suggestive of ACS who was later found to have AHC.

Familial cardiomyopathies: significant causes of heart failure

Familial dilated cardiomyopathies (FDCMs) account for about one third of idiopathic dilated cardiomyopathies, yet clinicians under-appreciate their prevalence. Among the inherited cardiomyopathies, FDCMs account for the greatest burden of heart failure and its associated morbidities. This paper summarizes significant molecular-genetic data, and discusses clinical manifestations of the major inherited cardiomyopathies, and the importance of clinical and genetic screening. Suggestions are provided as to how to proceed with screening. The purpose of this paper is to update clinicians about this rapidly growing scientific field, and to encourage application of current evidence to their practices.

[Heart rate variability in patients with hypertrophic cardiomyopathy and in their close relatives]

The results of HRV analysis in patients with hypertrophic cardiomyopathy (HCM) are conflicting. We evaluated short-term HRV in patients with familiar HRV and in their close relatives. 31 families of patients with HCM were examined. There were 43 patients with HCM confirmed by 2D-echo (HCM-group, 23 f, 20 m, aged 46 +/- 14 ys), and 157 family members (REL-group, 75 f, 82 m, aged 29 +/- 17 ys). The control group consisted of 180 healthy subjects (80 f, 100 m, aged 33 +/- 12 ys). In each subject 512 consecutive sinus beats were recorded in supine position during spontaneous breathing using computer-assisted amplifier (A/D 12 bit, 1 kHz). Mean RR interval (RRI, ms), its standard deviation (SDRR, ms) and spectral measures (FFT, Blackman-Harris window): PSD of high frequency (HF) and low frequency (LF) [ms2/Hz], as well as respiratory rate (BPM) were measured. Patients with HCM had significantly shorter RRI (867 +/- 121) as compared to the controls (919 +/- 138, p < 0.05). The RRI was also shorter in the relatives (851 +/- 150, p < 0.01). In HCM and REL groups the respiratory rate was faster (16.7 +/- 3.0 and 17.1 +/- 3.4, respectively), as compared to the controls (14.5 +/- 2.9, both p < 0.01). The HRV measures were reduced in the HCM-group (SDRR 31.4 +/- 10.6, lnHF 7.71 +/- 0.65, lnLF 8.22 +/- 0.65 and LF/HF 1.07 +/- 0.10), as compared to the controls (SDRR 64.8 +/- 23.9, lnHF 8.79 +/- 0.61, lnLF 8.87 +/- 0.65, all p < 0.001 and LF/HF 1.01 +/- 0.07, p < 0.01). In the REL-group SDRR and lnHF were significantly reduced (SDRR 52.4 +/- 24.1, lnHF 8.48 +/- 0.78, p < 0.001), while the remaining parameters were comparable. The HRV reduction was more expressed in HCM-patients and family-members < 30 years of age. A significantly reduced age-, sex- and RRI-adjusted SDNN was observed in 54% pts in HCM-group and in 42% subjects in members-group. Reduced heart rate variability is frequently seen not only in patients with diagnosed HCM, but also in a substantial number of their kindred.

Modifier genes for hypertrophic cardiomyopathy

During the past decade, more than 100 mutations in 11 causal gene coding for sarcomeric proteins, the gamma subunit of AMP-activated protein kinase and triplet-repeat syndromes and in mitochondrial DNA, have been identified in patients with hypertrophic cardiomyopathy (HCM). Genotype-phenotype correlation studies show significant variability in the phenotype expression of HCM among affected individuals with identical causal mutations. Overall, causal mutations account for a fraction of the variability of phenotypes and genetic background, referred to as the modifier genes, play a significant role. The final phenotype is the result of interactions between the causal genes, genetic background (modifier genes), and probably the environmental factors. The individual modifier genes for HCM remain largely unknown, and a large-scale genome-wide approach and candidate gene analysis are needed. Current studies are limited to simple polymorphism association studies, which explore the association of functional single nucleotide polymorphisms in genes implicated in cardiac growth with the severity of the clinical phenotypes, primarily cardiac hypertrophy. Several potential modifier genes including genes encoding the components of the renin-angiotensin-aldosterone system have emerged. The most commonly implicated is an insertion/deletion polymorphism in the angiotensin-1 converting enzyme 1 gene, which is associated with the risk of sudden cardiac death and the severity of hypertrophy. Therapeutic interventions aimed at targeting the modifier genes have shown salutary effects in animal models of HCM. It has now recognized that modifier genes affect the expression of cardiac phenotype. Identification of the modifier genes will complement the results of studies of causative genes and could enhance genetic based diagnosis, risk stratification, and implementation of preventive and therapeutic measures in patients with HCM.

[Hypertrophic cardiomyopathy: a genetically-carried heart disease]

Hypertrophic cardiomyopathy (HCM) is a cardiac muscle disease with characteristic (mostly asymmetrically distributed) hypertrophy of a non-dilated left ventricle in the absence of another cardiac or systemic disease that can cause left ventricle hypertrophy. The prevalence of HCM in the general population is estimated to be 1 in 500 persons. It is an inheritable disease of the heart with a heterogeneous expression and a great diversity of morphological, functional and clinical features. The genes involved code for components of a large protein complex ('the sarcomere'), which ensures the contraction of the cardiac muscle. Electrocardiography, echocardiography and cardiac MRI play a role in the diagnosis. Medicinal treatment can improve the diastolic filling and the ventricle function. In addition to this there are surgical and non-surgical possibilities for myocardial reduction. For patients with life-threatening arrhythmias and for the primary prevention of sudden death for high-risk patients, an internally implantable cardioverter-defibrillator is indicated. The early detection of patients with a predisposition for HCM is only possible by means of genotyping.

Mutations of the light meromyosin domain of the beta-myosin heavy chain rod in hypertrophic cardiomyopathy

Familial hypertrophic cardiomyopathy (HCM) is caused by mutations in 9 sarcomeric protein genes. The most commonly affected is beta-myosin heavy chain (MYH7), where missense mutations cluster in the head and neck regions and directly affect motor function. Comparable mutations have not been described in the light meromyosin (LMM) region of the myosin rod, nor would these be expected to directly affect motor function. We studied 82 probands with HCM in whom no mutations had been found in MYH7 exons encoding the head and neck regions of myosin nor in the other frequently implicated disease genes. Primers were designed to amplify exons 24 to 40 of MYH7. These amplimers were subjected to temperature modulated heteroduplex analysis by denaturing high-performance liquid chromatography. An Ala1379Thr missense mutation in exon 30 segregated with disease in three families and was not present in 200 normal chromosomes. The mutation occurred on two haplotypes, indicating that it was not a polymorphism linked with another disease-causing mutation. The position of this residue within the LMM region of myosin suggests that it may be important for thick filament assembly or for accessory protein binding. A further missense mutation in exon 37, Ser1776Gly, segregated with disease in a single family and was absent from 400 population-matched control chromosomes. Because the Ser1776 residue occupies a core position in the myosin rod at which the substitution of glycine is extremely energetically unfavorable, it is likely to disrupt the coiled-coil structure. We conclude that mutation of the LMM can cause HCM and that such mutations may act through novel mechanisms of disease pathogenesis involving myosin filament assembly or interaction with thick filament binding proteins.

Genotype-phenotype assessment in autosomal recessive arrhythmogenic right ventricular cardiomyopathy (Naxos disease) caused by a deletion in plakoglobin

OBJECTIVES

The purpose of this study was to examine the genotype-phenotype relation with respect to penetrance, age and severity of expression, disease progression and prognosis in a recessively inherited arrhythmogenic right ventricular cardiomyopathy (ARVC).

BACKGROUND

Naxos disease is a recessively inherited ARVC caused by a mutation in the gene encoding plakoglobin (cell adhesion protein) in which the cardiac phenotype is associated with palmoplantar keratoderma and woolly hair.

METHODS

Twelve families with Naxos disease underwent cardiac and molecular genetic investigation. Serial cardiac assessment with annual resting 12-lead and 24-h ambulatory electrocardiogram (ECG) and two-dimensional echocardiography was performed during 1 to 16 years, median 7 +/- 6 years in all 78 surviving members.

RESULTS

Twenty-eight surviving members were homozygous and 40 were heterozygous for the mutation. All adults who were homozygous (n = 26) fulfilled the diagnostic criteria for ARVC, the youngest by the age of 13 years. In eight who were heterozygous, minor ECG or echocardiographic abnormalities were observed. Of the 26 subjects who were affected homozygotes, 92% showed ECG abnormalities, 92% ventricular arrhythmias, 100% right ventricular structural alterations and 27% left ventricular involvement. During follow-up (10 +/- 6 years), 16 (62%) developed structural progression, 12 (46%) arrhythmic events and 7 (27%) heart failure. The annual disease-related and sudden death mortality was 3% and 2.3%, respectively.

CONCLUSIONS

Autosomal recessive ARVC caused by a mutation in plakoglobin was 100% penetrant by adolescence. Affected subjects who were homozygous experienced progressive disease with adverse prognosis. A minority of subjects who were heterozygous showed minor ECG/echocardiographic changes, but clinically significant disease did not develop.