Genetic Studies of Hypertrophic Cardiomyopathy in Singaporeans Identify Variants in TNNI3 and TNNT2 That Are Common in Chinese Patients

BACKGROUND

To assess the genetic architecture of hypertrophic cardiomyopathy (HCM) in patients of predominantly Chinese ancestry.

METHODS

We sequenced HCM disease genes in Singaporean patients (n=224) and Singaporean controls (n=3634), compared findings with additional populations and White HCM cohorts (n=6179), and performed in vitro functional studies.

RESULTS

Singaporean HCM patients had significantly fewer confidently interpreted HCM disease variants (pathogenic/likely pathogenic: 18%, P<0.0001) but an excess of variants of uncertain significance (24%, P<0.0001), as compared to Whites (pathogenic/likely pathogenic: 31%, excess of variants of uncertain significance: 7%). Two missense variants in thin filament encoding genes were commonly seen in Singaporean HCM (TNNI3:p.R79C, disease allele frequency [AF]=0.018; TNNT2:p.R286H, disease AF=0.022) and are enriched in Singaporean HCM when compared with Asian controls (TNNI3:p.R79C, Singaporean controls AF=0.0055, P=0.0057, genome aggregation database-East Asian AF=0.0062, P=0.0086; TNNT2:p.R286H, Singaporean controls AF=0.0017, P<0.0001, genome aggregation database-East Asian AF=0.0009, P<0.0001). Both these variants have conflicting annotations in ClinVar and are of low penetrance (TNNI3:p.R79C, 0.7%; TNNT2:p.R286H, 2.7%) but are predicted to be deleterious by computational tools. In population controls, TNNI3:p.R79C carriers had significantly thicker left ventricular walls compared with noncarriers while its etiological fraction is limited (0.70 [95% CI, 0.35-0.86]) and thus TNNI3:p.R79C is considered variant of uncertain significance. Mutant TNNT2:p.R286H iPSC-CMs (induced pluripotent stem cells derived cardiomyocytes) show hypercontractility, increased metabolic requirements, and cellular hypertrophy and the etiological fraction (0.93 [95% CI, 0.83-0.97]) support the likely pathogenicity of TNNT2:p.R286H.

CONCLUSIONS

As compared with Whites, Chinese HCM patients commonly have low penetrance risk alleles in TNNT2 or TNNI3 but exhibit few clinically actionable HCM variants overall. This highlights the need for greater study of HCM genetics in non-White populations.

Myosin Sequestration Regulates Sarcomere Function, Cardiomyocyte Energetics, and Metabolism, Informing the Pathogenesis of Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is caused by pathogenic variants in sarcomere protein genes that evoke hypercontractility, poor relaxation, and increased energy consumption by the heart and increased patient risks for arrhythmias and heart failure. Recent studies show that pathogenic missense variants in myosin, the molecular motor of the sarcomere, are clustered in residues that participate in dynamic conformational states of sarcomere proteins. We hypothesized that these conformations are essential to adapt contractile output for energy conservation and that pathophysiology of HCM results from destabilization of these conformations.

METHODS

We assayed myosin ATP binding to define the proportion of myosins in the super relaxed state (SRX) conformation or the disordered relaxed state (DRX) conformation in healthy rodent and human hearts, at baseline and in response to reduced hemodynamic demands of hibernation or pathogenic HCM variants. To determine the relationships between myosin conformations, sarcomere function, and cell biology, we assessed contractility, relaxation, and cardiomyocyte morphology and metabolism, with and without an allosteric modulator of myosin ATPase activity. We then tested whether the positions of myosin variants of unknown clinical significance that were identified in patients with HCM, predicted functional consequences and associations with heart failure and arrhythmias.

RESULTS

Myosins undergo physiological shifts between the SRX conformation that maximizes energy conservation and the DRX conformation that enables cross-bridge formation with greater ATP consumption. Systemic hemodynamic requirements, pharmacological modulators of myosin, and pathogenic myosin missense mutations influenced the proportions of these conformations. Hibernation increased the proportion of myosins in the SRX conformation, whereas pathogenic variants destabilized these and increased the proportion of myosins in the DRX conformation, which enhanced cardiomyocyte contractility, but impaired relaxation and evoked hypertrophic remodeling with increased energetic stress. Using structural locations to stratify variants of unknown clinical significance, we showed that the variants that destabilized myosin conformations were associated with higher rates of heart failure and arrhythmias in patients with HCM.

CONCLUSIONS

Myosin conformations establish work-energy equipoise that is essential for life-long cellular homeostasis and heart function. Destabilization of myosin energy-conserving states promotes contractile abnormalities, morphological and metabolic remodeling, and adverse clinical outcomes in patients with HCM. Therapeutic restabilization corrects cellular contractile and metabolic phenotypes and may limit these adverse clinical outcomes in patients with HCM.

Abstract 438: Familial Cardiomyopathy Mutations Affect Mechanosensing at the Molecular and Cellular Levels

Familial cardiomyopathies are the leading cause of sudden cardiac death in young people, affecting more than 1 in 500 people. Two common forms, hypertrophic (HCM) and dilated (DCM) cardiomyopathies, are characterized by remodeling of the heart tissue, frequently accompanied by fibrosis and myocyte disarray. These diseases are primarily caused by mutations in sarcomeric proteins that regulate the contraction of the heart; however, it is not clear how these point mutations at the molecular level lead to the disease phenotype seen in patients. To better understand this process, we have examined the molecular and cellular consequences of two mutations in troponin T, R92Q and ΔK210, that cause HCM and DCM, respectively. Using recombinant proteins and a battery of in vitro biochemical and biophysical techniques, we find that R92Q increases activation of the thin filament by stabilizing myosin force generating states while ΔK210 reduces the ability of myosin to access these states at submaximal calcium levels. To study these mutations at the single cell level, we used CRISPR/Cas9 to generate human stem cell derived cardiomyocytes bearing these mutations. We examined the structural and contractile properties of single cells on engineered hydrogels that mimic either healthy or diseased hearts. Consistent with our molecular studies, we find that R92Q causes increased force production and power output. Interestingly, the ΔK210 mutation does not affect cellular force or power output on substrates that mimic the stiffness of the healthy heart, but it causes disordering of the sarcomeres on stiff substrates. This suggests a mechanism for ΔK210 where fibrosis leads to progressive loss of contractile function via mechanosensitive structural remodeling. Taken together, these results (1) demonstrate that alterations in force production and mechanosensing contribute to the disease pathogenesis in familial cardiomyopathies and (2) illuminate the differential mechanisms that lead to either HCM or DCM.

An international programme in nursing and midwifery: building capacity for the new millennium

AIM

The global economy is changing rapidly and frequently affects the ability of the health sector to respond to a variety of needs. Nurses and midwives are reaching across national boundaries to strengthen their ability to improve the health of populations. This article describes an innovative programme of collaboration among different nations to strengthen the capacity of nurses and midwives.

BACKGROUND

Over the course of 4 years, nurses and midwives from several countries in East Central Europe, Central America, and the Caribbean came together in the United States and in Europe to learn about opportunities for growth and collaboration to improve professional development, leadership capacity, educational and curricular development, and knowledge about international health.

CONCLUSION

Programme participants reported increased capacity to perform their professional roles as a result of their having participated in this programme. More capacity building activities are needed to further enable nursing professionals to meet the demands for health care around the world.

An organizational climate intervention associated with increased handwashing and decreased nosocomial infections

Handwashing practices are persistently suboptimal among healthcare professionals and are also stubbornly resistant to change. The purpose of this quasi-experimental intervention trial was to assess the impact of an intervention to change organizational culture on frequency of staff handwashing (as measured by counting devices inserted into soap dispensers on four critical care units) and nosocomial infections associated with methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). All staff in one of two hospitals in the mid-Atlantic region received an intervention with multiple components designed to change organizational culture; the second hospital served as a comparison. Over a period of 8 months, 860,567 soap dispensings were recorded, with significant improvements in the study hospital after 6 months of follow-up. Rates of MRSA were not significantly different between the two hospitals, but rates of VRE were significantly reduced in the intervention hospital during implementation.

Graduate Home Health Education: A Survey of Home Health Educators and Agency Personnel

To determine if there is a body of essential content that should be common to master's-level home care programs, a purposive sample of 200 nurses involved in home health or community health nursing was selected. The respondents (N = 118), including faculty and educational administrators (N = 61) and supervisors and administrators of home health agencies (N = 57), were asked their perceptions of the knowledge needed and their priorities for curriculum content for master's-prepared home care specialists in both clinical and administrative roles. There was agreement in most content areas, but significant differences were found between faculty and agency personnel in their priorities for community health concepts, and in their evaluation of nursing theory and epidemiology as essential content in both roles. We believe these results have important implications for nurse educators. As schools prepare students for leadership roles in today's home care environment, it is critical that pertinent content be well integrated into the curriculum.

Impact of Medicare payment policy on home health resources utilization

In this study, the association between Medicare regulations and the provision of public home health care is examined. Medicare clients were compared with non-Medicare groups of those 65 years of age or over and those under 65. Results suggested that both age- and payer-related factors contribute to utilization of services. Older patients showed greater need for chronic illness care relative to younger patients; however, Medicare patients used fewer resources and had poorer outcomes relative to older non-Medicare patients.

Nonreimbursed home health care: beyond the bills

The unprecedented growth in the home care industry over the past decade has produced a highly competitive environment for care delivery. To survive, most agencies are implementing strategies to maximize reimbursable care. This focus, while likely to improve an agency's financial situation, is fraught with potential problems. Reimbursed care represents only a small portion of the care that is required and delivered. Still, aside from anecdotes, little reporting has been done to document such additional service, much less to consider the consequences of reducing or deleting it. We selected a sample of 350 public health home care episodes throughout Virginia, and reviewed billing records to determine the number of billed home visits attached to them. We then reviewed home health records for the matching episodes and recorded all visits and other care-related activities (e.g., telephone calls, conferences, laboratory trips). Total home visits increased, with an average of 1.5 unbilled home visits per episode. In addition, 10 additional care-related activities take place per patient, none of which is billed. These findings represent one of the first attempts to quantify the amounts and types of nonbilled care delivered by nurses. This care consumes significant nursing resources and, as a result, may be destined to be reduced or totally eliminated.

Nursing activities and reimbursement in clinical case management

If governmental agencies, third-party payers, and employers expect to obtain the benefits of clinical case management, then the indirect activities required for clinical case management and documented by this study must be considered in calculating home health care reimbursement rates.

Out of the Ivory Tower: the value of collaborative research

Collaboration is an underutilized strategy for combining the strengths and perspective of home health care professionals in service and academic settings. This paper explores the importance of collaborative research strategies, focusing on the role of the unique talents, resources, and perspectives offered by each health professional to the research process. Finally, personal, professional and organizational barriers to collaboration are examined in order to alert would-be researcher collaborators to obstacles they are likely to encounter. When both the strengths of and obstacles to collaborative research are anticipated, collaboration can encourage research that is relevant to the needs and experiences of both home health service providers and academicians.