Christine L Chiu

Compound and double mutations in patients with hypertrophic cardiomyopathy: implications for genetic testing and counselling

Objective: To report the frequency of single and multiple gene mutations in an Australian cohort of patients with hypertrophic cardiomyopathy (HCM). Methods: Genetic screening of seven HCM genes (β-MHC, MyBP-C, cTnT, cTnI, ACTC, MYL2, and MYL3) was undertaken in 80 unrelated probands. Screening was by denaturing high performance liquid chromatography and direct DNA sequencing. Clinical data were collected on all patients and on genotyped family members. Results: 26 mutations were identified in 23 families (29%). Nineteen probands (24%) had single mutations (11 β-MHC, 4 MyBP-C, 3 cTnI, 1 cTnT). Multiple gene mutations were identified in four probands (5%): one had a double mutation and the others had compound mutations. Six of 14 affected individuals from multiple mutation families (43%) experienced a sudden cardiac death event, compared with 10 of 55 affected members (18%) from single mutation families (p = 0.05). There was an increase in septal wall thickness in patients with compound mutations (mean (SD): 30.7 (3.1) v 24.4 (7.4) mm; p<0.05). Conclusions: Multiple gene mutations occurring in HCM families may result in a more severe clinical phenotype because of a “double dose” effect. This highlights the importance of screening the entire panel of HCM genes even after a single mutation has been identified.

DNA Mutation Detection Using Denaturing High‐Performance Liquid Chromatography (DHPLC)

DHPLC is an efficient method for candidate gene scanning with a high level of automation. Single‐base substitutions and insertions or deletions of up to 1.5 kb in PCR amplified DNA fragments can be detected. The method exploits the differential retention of homoduplex and heteroduplex DNA species under conditions of partial thermal denaturation. DHPLC provides a useful platform for high‐throughput mutation detection and SNP discovery.

Mutations in Alpha-Actinin-2 Cause Hypertrophic Cardiomyopathy: A Genome-Wide Analysis

OBJECTIVES This study describes a genome-wide linkage analysis of a large family with clinically heterogeneous hypertrophic cardiomyopathy (HCM). BACKGROUND Familial HCM is a disorder characterized by genetic heterogeneity. In as many as 50% of HCM cases, the genetic cause remains unknown, suggesting that other genes may be involved. METHODS Clinical evaluation, including clinical history, physical examination, electrocardiography, and 2-dimensional echocardiography, was performed, and blood was collected from family members (n = 23) for deoxyribonucleic acid analysis. The family was genotyped with markers from the 10-cM AB PRISM Human Linkage mapping set (Applied Biosystems, Foster City, California), and 2-point linkage analysis was performed. RESULTS Affected family members showed marked clinical diversity, ranging from asymptomatic individuals to those with syncope, heart failure, and premature sudden death. The disease locus for this family was mapped to chromosome 1q42.2-q43, near the marker D1S2850 (logarithm of odds ratio = 2.82, theta = 0). A missense mutation, Ala119Thr, in the alpha-actinin-2 (ACTN2) gene was identified that segregated with disease in the family. An additional 297 HCM probands were screened for mutations in the ACTN2 gene using high-resolution melt analysis. Three causative ACTN2 mutations, Thr495Met, Glu583Ala, and Glu628Gly, were identified in an additional 4 families (total 1.7%) with HCM. CONCLUSIONS This is the first genome-wide linkage analysis that shows mutations in ACTN2 cause HCM. Mutations in genes encoding Z-disk proteins account for a small but significant proportion of genotyped HCM families.

Genetic basis of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) was the first cardiovascular disorder in which a genetic basis was identified. The disease is characterized by a marked thickening of the left ventricle and is the most common structural cause of sudden cardiac death in those aged under 35 years. HCM is primarily a disease of the sarcomere with over 250 mutations identified currently within 13 sarcomere-related genes. At present, genetic screening is available for the genes shown to cause HCM most frequently, with a mutation pick-up rate of up to 60%. Current research is focused on the identification of additional causative genes and elucidation into signaling mechanisms involved in HCM pathogenesis, as well as investigation of modifying factors that can alter the clinical phenotype in HCM. The unifying goal of these studies is to improve our understanding of disease pathogenesis in HCM, thereby facilitating the process of new diagnostic and therapeutic approaches in patients, ultimately leading to disease prevention and possible curative treatment.

Sex hormone receptor gene variation associated with phenotype in male hypertrophic cardiomyopathy patients

Hypertrophic cardiomyopathy (HCM) is a clinically heterogeneous disease, which suggests that a number of factors exist which modify disease outcome. Gender may be one such factor as more males present with the disease compared with females. The aim of the present study was to determine if an association exists between genetic variation in sex hormone receptors and the development of left ventricular hypertrophy in HCM. The study population included 200 unrelated individuals from an Australian HCM cohort. Clinical evaluation was performed. Genetic analysis of the androgen receptor (AR), estrogen receptor 1 (ESR1), estrogen receptor 2 (ESR2), and aromatase (CYP19A1) genes, was carried out in all patients. Fewer (CAG)n repeats within the AR gene were significantly associated with higher maximal left ventricular wall thickness (LVWT) in males (P=0.008), adjusting for age. Male carriers of the A allele at SNP rs6915267, located in the promoter region of ESR1, had an 11% decrease in mean LVWT compared to male GG homozygotes (P=0.047). We report for the first time that variation at the AR gene is associated with left ventricular hypertrophy in males with HCM. Understanding the impact of sex hormones on phenotype will be helpful in the risk stratification and clinical management of HCM patients.

Association between parity and breastfeeding with maternal high blood pressure

OBJECTIVE The objective of this study was to determine how parity and breastfeeding were associated with maternal high blood pressure, and how age modifies this association. STUDY DESIGN Baseline data for 74,785 women were sourced from the 45 and Up Study, Australia. These women were 45 years of age or older, had an intact uterus, and had not been diagnosed with high blood pressure before pregnancy. Odds ratios (ORs) and 99% confidence intervals (CIs) for the association between giving birth, breastfeeding, lifetime breastfeeding duration, and average breastfeeding per child with high blood pressure were estimated using logistic regression. RESULTS The combination of parity and breastfeeding was associated with lower odds of having high blood pressure (adjusted OR, 0.89; 99% CI, 0.82-0.97; P < .001), compared with nulliparous women, whereas there was no significant difference between mothers who did not breastfeed and nulliparous women (adjusted OR, 1.06; 99% CI, 0.95-1.18; P = .20). Women who breastfed for longer than 6 months in their lifetime, or greater than 3 months per child, on average, had significantly lower odds of having high blood pressure when compared with parous women who never breastfed. The odds were lower with longer breastfeeding durations and were no longer significant in the majority of women over the age of 64 years. CONCLUSION Women should be encouraged to breastfeed for as long as possible and a womans breastfeeding history should be taken into account when assessing her likelihood of high blood pressure in later life.

Changes in Retinal Microvascular Caliber Precede the Clinical Onset of Preeclampsia

Preeclampsia is a leading cause of maternal morbidity and mortality. The degree of maternal cardiovascular dysfunction that precedes the onset of preeclampsia is largely unknown. This prospective cohort study aimed to characterize differences in vivo in retinal microvascular caliber and blood pressure throughout pregnancy in relation to preeclampsia development. Women were recruited from Royal Prince Alfred Hospital, Sydney, Australia, of which 92 women were included in the study. Retinal images and blood pressures were collected at 13, 19, 29, and 38 weeks of gestation. Retinal vessels were analyzed as the central retinal arteriolar equivalent corrected for mean arterial blood pressure and the central retinal venular equivalent corrected for mean arterial blood pressure, using generalized linear models adjusted for age and body mass index. The preeclampsia group were significantly older (P=0.002) and had a significantly higher mean body mass index (P=0.005). The central retinal arteriolar equivalent corrected for mean arterial blood pressure was significantly reduced at 13 (P=0.03), 19 (P=0.007), and 38 (P=0.03) weeks of gestation in the preeclampsia group. The central retinal venular equivalent corrected for mean arterial blood pressure was also significantly lower at 13 (P=0.04) and 19 (P=0.001) weeks of gestation in the women who progressed to preeclampsia. This study directly documents increased peripheral resistance in vivo, observed as the combination of constricted retinal arterioles or venules and elevated blood pressure, in women who later developed preeclampsia. This difference preceded the clinical signs of preeclampsia.

Menopausal Hormone Therapy Is Associated with Having High Blood Pressure in Postmenopausal Women: Observational Cohort Study

Background The relationship between menopausal hormone therapy (MHT) and cardiovascular risk remains controversial, with a number of studies advocating the use of MHT in reducing risk of cardiovascular diseases, while others have shown it to increase risk. The aim of this study was to determine the association between menopausal hormone therapy and high blood pressure. Methods and Findings A total of 43,405 postmenopausal women were included in the study. Baseline data for these women were sourced from the 45 and Up Study, Australia, a large scale study of healthy ageing. These women reported being postmenopausal, having an intact uterus, and had not been diagnosed with high blood pressure prior to menopause. Odds ratios for the association between MHT use and having high blood pressure were estimated using logistic regression, stratified by age (<56 years, 56–61 years, 62–70 years and over 71 years) and adjusted for demographic and lifestyle factors. MHT use was associated with higher odds of having high blood pressure: past menopausal hormone therapy use: <56 years (adjusted odds ratio 1.59, 99% confidence interval 1.15 to 2.20); 56–61 years (1.58, 1.31 to 1.90); 62–70 years (1.26, 1.10 to 1.44). Increased duration of hormone use was associated with higher odds of having high blood pressure, with the effect of hormone therapy use diminishing with increasing age. Conclusions Menopausal hormone therapy use is associated with significantly higher odds of having high blood pressure, and the odds increase with increased duration of use. High blood pressure should be conveyed as a health risk for people considering MHT use.

Genetic discoveries in hypertension: steps on the road to therapeutic translation

Genes and environmental factors contribute to an individuals risk of hypertension. Recent advances in DNA sequencing technology have enabled the discovery of new causative genes in inherited forms of hypertension, identifying novel pathways for blood pressure control. Meta-analyses of genome-wide association studies have also identified regions of the genome that are significantly associated with blood pressure control, and these regions may be involved in an individuals response to antihypertensive medication. This article reviews the latest gene discoveries in inherited forms of hypertension, recent meta-analyses of genome-wide association studies, genetic determinants of antihypertensive therapy response, and development of genetic risk scores.

Temporal Changes in Retinal Microvascular Caliber and Blood Pressure During Pregnancy

The microvasculature plays an important role in regulating cardiovascular changes in pregnancy, but changes in microvasculature have been difficult to document in vivo. This study objectively quantifies changes in the maternal retinal arteriolar and venular caliber over the course of healthy pregnancy. Healthy pregnant women (n=53) were recruited from Royal Prince Alfred Hospital, Sydney, Australia. Retinal images and mean arterial blood pressures (MAP) were collected at 13, 19, 29, and 38 weeks of gestation and at 6-month postpartum. Retinal vessels were analyzed and summarized as the central retinal arteriolar equivalent and central retinal venular equivalent. Central retinal arteriolar equivalent and central retinal venular equivalent were corrected for MAP. Paired t tests were performed comparing consecutive time points, with a significance level of P<0.01. There was a decrease in MAP between 13- and 19-week gestation (P=0.001) followed by a return to baseline from 19 weeks to delivery. This was correlated by an increase in vessel caliber between 13- and 19-week gestation (central retinal arteriolar equivalent: P<0.001, central retinal venular equivalent: P=0.007) and a return to baseline from 19 weeks to delivery. There were no differences in the central retinal arteriolar equivalent or central retinal venular equivalent (both uncorrected and corrected for MAP) between nulliparous and parous women. The pattern of dilatation and constriction in the microvasculature mirrored the changes in MAP throughout pregnancy, reflecting changes in peripheral resistance. This study provides insights into physiological changes in the microvasculature throughout a healthy pregnancy. These results can be used as a baseline with which to compare the changes observed in pathological conditions of pregnancy.