Genetic markers in hypertensive hypertrophic cardiomyopathy

Suman Omana Soman; G Vijayaraghavan; Ramesh Natarajan; CC Karta; Radhakrishnan R Nair; Heera R Pillai

doi:10.4103/ACCJ.ACCJ_9_19

ORIGINAL ARTICLE

Year : 2019 | Volume : 1 | Issue : 1 | Page : 20-23

Genetic markers in hypertensive hypertrophic cardiomyopathy

Suman Omana Soman¹, G Vijayaraghavan², Ramesh Natarajan², CC Karta³, Radhakrishnan R Nair⁴, Heera R Pillai⁴
¹ Department of Cardiology, Badr Al Samaa Hospital, Muscat, Oman and Former PhD Fellow in the Department of Cardiology, Kerala Institute of Medical Sciences, Trivandrum, Kerala, India
² Department of Cardiology, Kerala Institute of Medical Sciences, Trivandrum, Kerala, India
³ Society for Continuing Medical Education and Research (SOCOMER), Kerala Institute of Medical Sciences, Trivandrum, Kerala, India
⁴ LMDD Rajiv Gandhi Centre for Biotechnology, Trivandrum, Kerala, India

Date of Submission	07-Nov-2019
Date of Decision	09-Nov-2019
Date of Acceptance	11-Nov-2019
Date of Web Publication	13-Dec-2019

Correspondence Address:
Dr. Suman Omana Soman
Badr Al Samaa Group of Hospitals, Muscat
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ACCJ.ACCJ_9_19

Abstract

Background: The concept of hypertrophic cardiomyopathy came from observations on patients with systemic hypertension (HTN) where few patients developed inappropriate hypertrophy and even outflow tract obstruction. Over a period of time, research workers found that it is hereditary disorder and has no relationship with systemic HTN. However, many workers have observed that some patients with HTN have massive left ventricular hypertrophy disproportionate to the severity or duration of HTN. Materials and Methods: By using echocardiography, we identified inappropriate left ventricular hypertrophy in long-standing hypertensive patients. Markers of genetic abnormality were tested in those patients to find whether they differ from the usual hypertensive population. Results: We identified 29 hypertensive patients with severe concentric left ventricular hypertrophy (wall thickness, ≥1.6 cm). All patients were considered to have essential HTN. From these patients, we collected blood samples for detailed genetic study. Twenty-nine adult patients with age between 20 and 50 years of either sex with HTN on medications for 5 years or more were selected. Genotyping was done by sequencing. Genetic mutations were detected in 3 (11%) of 27 patients. myosin-binding protein of chromosome were detected in two patients, and mycophenolic acid xanthine hypoxanthine of igg was detected in one patient. Conclusion: In our study, we found that these genes are involved in hypertensive hypertrophic cardiomyopathy also. This suggests that patients with inappropriate left ventricular hypertrophy have a genetic involvement and all the family members should be screened.

Keywords: Genetics, hypertension, hypertrophy

How to cite this article:
Soman SO, Vijayaraghavan G, Natarajan R, Karta C C, Nair RR, Pillai HR. Genetic markers in hypertensive hypertrophic cardiomyopathy. Ann Clin Cardiol 2019;1:20-3

How to cite this URL:
Soman SO, Vijayaraghavan G, Natarajan R, Karta C C, Nair RR, Pillai HR. Genetic markers in hypertensive hypertrophic cardiomyopathy. Ann Clin Cardiol [serial online] 2019 [cited 2023 Mar 26];1:20-3. Available from: http://www.onlineacc.org/text.asp?2019/1/1/20/273006

Introduction

Hypertrophic cardiomyopathy (HCM) is the most common familial heart disease demonstrated over the past 20 years with vast genetic heterogeneity. It is inherited as an autosomal dominant trait and is attributed to mutations in one of a number of genes that encode for one of the sarcomere proteins.^[1] Whenever a mutation is identified through genetic testing, family-specific genetic testing can be used to identify relatives at-risk for the disease.^[2] First report from United Kingdom on HCM was by Sir Russell Brock. All patients had long-standing systemic hypertension (HTN) and Brock inferred that the HCM was the result of long-standing hypertensive hypertrophy.^[3] Patients had inappropriate hypertrophy with mild-to-moderate systemic HTN often characterized by severe concentric left ventricular hypertrophy, small cavity dimensions, and high ejection fraction. This entity is similar to what Eric Topol described in 1985 as hypertensive HCM.^[4] The concept of hypertrophic cardiomyopathy came from observations on patients with systemic HTN where few patients developed inappropriate hypertrophy and even outflow tract obstruction. Over a period of time, research workers found that it is hereditary disorder and has no relationship with systemic HTN. However, many workers have observed that some patients with HTN have massive left ventricular hypertrophy disproportionate to the severity or duration of HTN.

Materials and Methods

By using echocardiography, we identified inappropriate left ventricular hypertrophy in long-standing hypertensive patients. Markers of genetic abnormality were tested in those patients to find whether they differ from the usual hypertensive population.

During 18 months from September 1, 2011, 9000 patients underwent echocardiography in our laboratory; the mean age was 53.1 ± 11.2 years. Only patients within the age of 50 were selected. We identified 29 hypertensive patients [Table 1] with severe concentric left ventricular hypertrophy (wall thickness, ≥1.6 cm). All patients were considered to have essential HTN. The patients underwent a detailed echocardiographic study to confirm that they belong to a separate group of patients rather than the conventional hypertensive heart disease. From these patients, we collected blood samples for a detailed genetic study. A volume of 5–10 ml blood was collected from the study participants. Twenty-nine adult patients with age between 20 and 50 years of either sex with HTN on medications for 5 years or more were selected. Patients with systemic diseases, heart failure, renal failure, and pregnancy were excluded from our study.

Table 1: The characteristics of our patients

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DNA extraction

DNA was isolated by standard protocols by employing DNA extraction kit (Qiagen DNA purification kit, Germany). DNA was checked in 0.7% Agarose gel electrophoresis to confirm integrity. Subsequently, the purity of DNA was assessed spectrophotometrically.

Evaluation of mutation status

Allelic-specific oligonucleotide primers were obtained for MYH16, TPT13, TPT 24 (1000 pmol) (Sigma). Oligonucleotide sequences employed in the study are given in [Table 2]. Primers were prepared in working concentration of 10 pmol, and amplification of each DNA sample was performed according to the manufacturer's protocol (EMERALD 2X PCR mix, Takara bio). Polymerase chain reaction (PCR) amplification was carried out using the Biorad C 1000 ™ Thermal cycler. The amplified PCR products were checked on a 2% agarose gel and genotyping was subsequently done by sequencing.

Table 2: Oligonucleotide sequences

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Determination of insertion-deletion polymorphism in angiotensin-converting enzyme gene

PCR was used to determine the Ins/Del polymorphism in intron 16 of angiotensin-converting enzyme (ACE) gene. The oligonucleotide sequences used were forward primer: 5'-GCC CTG CAG GTG TCT GCA GCATGT-3' and reverse primer: 5'-GGA TGG CTC TCC CCG CCT TGT CTC-3' (10 pmol) (Sigma).^[5] The PCR product obtained after amplification was checked in 2% agarose gel electrophoresis. The ACE I/D polymorphism consists of the presence (Insertion) or absence (Deletion) of 287 bp-Alu repeats in intron16 resulting in three genotypes: Insertion homozygous (Ins/Ins), Insertion-deletion (Ins-Del) heterozygous, and deletion homozygous (Del/Del). Therefore, after electrophoresis, each DNA sample revealed one of the three possible patterns: a 597-bp band (Ins-Ins Genotype), a 319 bp (Del/Del Genotype) or both 597 bp and 319 bp bands (Ins/Del genotype).

Collection of echocardiographic data

Cross-sectional echocardiograms were obtained for all patients in the three standard views – parasternal long-axis views, apical two- and four-chamber views, and subxiphoid views. Wall thickness and cavity dimensions in end-systole and end-diastole (simultaneous with the start of the QRS complex of the electrocardiogram) were measured on the parasternal, long-axis view at the level of the chordae tendineae. Ejection fraction was estimated from the borders of systolic and diastolic still images in the parasternal short-axis and long-axis echocardiograms, according to a formula based on Simpson's rule.

M-mode echocardiograms were recorded in all patients [Figure 1]. The following features were measured: peak normalized rate of reduction of dimension during systole (expressed/s); peak rate of increase of dimension during diastole (cm/s); length of early diastolic filling period (ms) and interval between minimum cavity dimension and the start of mitral valve opening (ms). The size of the left atrium (cm) was also measured.

Figure 1: M mode of echocardiogram shows left ventricular hypertrophy

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Results

All 29 patients had systemic HTN, which had been present for more than 5 years and age group of <50 years. HTN is defined as systolic blood pressure (BP) ≥140 mmHg and diastolic BP ≥90 mmHg^[⁶^] (ESC-2013). In our patients, systolic BP was 160 mmHg (±20) and diastolic BP was 90 mmHg (±10). There was a male predominance of 27 (93.1%) and 2 (6.9%) females. 7 (24.1%) patients were in the age group of 30–39 and 22 (75.9%) were between 40 and 50. 3 (10.4%) patients were diabetic, 13 (44.8%) patients had associated dyslipidemia, 4 (13.7%) patients had family history of coronary artery disease, and 4 (13.7%) had family history of HTN. 6.9% (2) had HCM.

Left ventricular hypertrophy according to the Sokolow-Lyon index was present in 13 (48.15%) patients and 14 (51.85%) patients without left ventricular hypertrophy.^[7] About 3.75% has right bundle branch block (RBBB) and the rest are in normal sinus rhythm.

In our patients, the left atrial size was 4 cm (±0.5), the left ventricular internal diameter in systole was 3.3 cm (±1.2), and left ventricular internal diameter in diastole was 4.5 cm (±1), ejection fraction was 75 (±10).

Genotyping was done by sequencing. Genetic mutations were detected in 3 (11%) patients out of 27. Myosin-binding protein (MBP) of chromosome was detected in two patients, and mycophenolic acid xanthine hypoxanthine of igg was detected in one patient.

Discussion

In literature, it is evident that HCM has a strong genetic association. The genetic involvement in HCM was first discovered by Dr. Seidman's group in 1990, after that, there were several hundred genes were identified by the other scientists.^[8] Concentric left ventricular hypertrophy, but mainly asymmetric hypertrophy of the left ventricle, is the common diagnostic feature. The inter-ventricular septum is the main site of involvement in HCM. Many patients may show mild hypertrophy initially, and they may develop severe hypertrophy later in life.^[9]

Long-term HTN can cause left ventricular hypertrophy in elderly patients.^[10] However, many young hypertensive patients also had inappropriate hypertrophy. Hence, in our study, we included all patients below the age of 50 years, and in the analysis, we found that some of these patients with left ventricular hypertrophy had a genetic association. Tarazi and Levy said that the severity of the left ventricular hypertrophy cannot be related to the duration of HTN, but maybe due to predisposed myocardial sensitivity.^[11] Devereux et al. described that only minority of patients develops hypertrophy is associated with chronic HTN.^[12] Maron and Epstein and Wigle et al., described the history of systemic HTN as exclusion for diagnosing idiopathic HCM, but there are many exceptions.^[13],[14]

Data from the Framingham study stated that patients with systemic HTN have a six-fold increase in the likelihood of heart failure; they found that 75% of these patients were hypertensive.^{[5],[15],[16]}

Many, probably the majority of these patients have left ventricular hypertrophy leads to ventricular dilatation and reduced ejection fraction. About 50%–60% of patients with a high index of clinical suspicion for HCM will have a mutation identified in at least 1 of 9 sarcomeric genes. Approximately 45% of these mutations occur in the β myosin heavy chain gene on chromosome 14 q11.2–3, while approximately 35% involve the cardiac myosin-binding protein C (MyBP-C) gene. Mutations in cardiac MyBP-C account for about 20% of familial HCM.^{[9],[17],[18],[19],[20],[21]} In our study, we found that these genes are involved in hypertensive hypertrophic cardiomyopathy also.

Conclusion

Genetic studies have not been done in patients with hypertensive hypertrophic cardiomyopathy in India. It is not proven that there is any genetic involvement in these groups of patients. We did genotyping by sequencing and PCR of intron 16 of ACE gene, not all the variants. We could find genetic abnormality in 10.4% (n = 3) of patients. This suggests that patients with inappropriate left ventricular hypertrophy have a genetic involvement and all the family members should be screened.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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