Pathogenic troponin T mutants with opposing effects on myofilament Ca2+ sensitivity attenuate cardiomyopathy phenotypes in mice.

Mutations in cardiac troponin T (TnT) associated with hypertrophic cardiomyopathy generally lead to an increase in the Ca2+ sensitivity of contraction and susceptibility to arrhythmias. In contrast, TnT mutations linked to dilated cardiomyopathy decrease the Ca2+ sensitivity of contraction. Here we tested the hypothesis that two TnT disease mutations with opposite effects on myofilament Ca2+ sensitivity can attenuate each other's phenotype. We crossed transgenic mice expressing the HCM TnT-I79N mutation (I79N) with a DCM knock-in mouse model carrying the heterozygous TnT-R141W mutation (HET). The results of the Ca2+ sensitivity in skinned cardiac muscle preparations ranked from highest to lowest were as follow: I79N > I79N/HET > NTg > HET. Echocardiographic measurements revealed an improvement in hemodynamic parameters in I79N/HET compared to I79N and normalization of left ventricular dimensions and volumes compared to both I79N and HET. Ex vivo testing showed that the I79N/HET mouse hearts had reduced arrhythmia susceptibility compared to I79N mice. These results suggest that two disease mutations in TnT that have opposite effects on the myofilament Ca2+ sensitivity can paradoxically ameliorate each other's disease phenotype. Normalizing myofilament Ca2+ sensitivity may be a promising new treatment approach for a variety of diseases.

S100A12 as a marker of worse cardiac output and mortality in pulmonary hypertension.

BACKGROUND AND OBJECTIVE: Molecular biomarkers are needed to refine prognostication and phenotyping of pulmonary hypertension (PH) patients. S100A12 is an emerging biomarker of various inflammatory diseases. This study aims to determine the prognostic value of S100A12 in PH. METHODS: Exploratory microarray analysis performed on peripheral blood mononuclear cells (PBMC) collected from idiopathic pulmonary fibrosis (IPF) patients suggested an association between S100A12 and both PH and mortality. So the current study was designed to evaluate for an association between S100A12 in peripheral blood collected from two well-phenotyped PH cohorts in two other centres to derive and validate an association between S100A12 protein serum concentrations and mortality. RESULTS: The majority of the patients in the discovery and validation cohorts were either World Health Organization (WHO) group 1 (pulmonary arterial hypertension (PAH)) or 3 (lung disease-associated) PH. In the discovery PH cohort, S100A12 was significantly increased in patients with PH (n = 51) compared to controls (n = 22) (29.8 vs 15.7 ng/mL, P < 0.001) and negatively correlated with cardiac output (r = -0.58, P < 0.001) in PH patients. When S100A12 data were pooled from both cohorts, PAH and non-PAH PH patients had higher S100A12 compared to healthy external controls (32.6, 30.9, 15.7 ng/mL; P < 0.001). S100A12 was associated with an increased risk in overall mortality in PH patients in both the discovery (n = 51; P = 0.008) and validation (n = 40; P < 0.001) cohorts. CONCLUSION: S100A12 levels are increased in PH patients and are associated with increased mortality.

Rare variants in genes encoding MuRF1 and MuRF2 are modifiers of hypertrophic cardiomyopathy.

Modifier genes contribute to the diverse clinical manifestations of hypertrophic cardiomyopathy (HCM), but are still largely unknown. Muscle ring finger (MuRF) proteins are a class of muscle-specific ubiquitin E3-ligases that appear to modulate cardiac mass and function by regulating the ubiquitin-proteasome system. In this study we screened all the three members of the MuRF family, MuRF1, MuRF2 and MuRF3, in 594 unrelated HCM patients and 307 healthy controls by targeted resequencing. Identified rare variants were confirmed by capillary Sanger sequencing. The prevalence of rare variants in both MuRF1 and MuRF2 in HCM patients was higher than that in control subjects (MuRF1 13/594 (2.2%) vs. 1/307 (0.3%), p = 0.04; MuRF2 22/594 (3.7%) vs. 2/307 (0.7%); p = 0.007). Patients with rare variants in MuRF1 or MuRF2 were younger (p = 0.04) and had greater maximum left ventricular wall thickness (p = 0.006) than those without such variants. Mutations in genes encoding sarcomere proteins were present in 19 (55.9%) of the 34 HCM patients with rare variants in MuRF1 and MuRF2. These data strongly supported that rare variants in MuRF1 and MuRF2 are associated with higher penetrance and more severe clinical manifestations of HCM. The findings suggest that dysregulation of the ubiquitin-proteasome system contributes to the pathogenesis of HCM.

High mobility group box 1 contributes to the pathogenesis of experimental pulmonary hypertension via activation of Toll-like receptor 4.

Survival rates for patients with pulmonary hypertension (PH) remain low, and our understanding of the mechanisms involved are incomplete. Here we show in a mouse model of chronic hypoxia (CH)-induced PH that the nuclear protein and damage-associate molecular pattern molecule (DAMP) high mobility group box 1 (HMGB1) contributes to PH via a Toll-like receptor 4 (TLR4)-dependent mechanism. We demonstrate extranuclear HMGB1 in pulmonary vascular lesions and increased serum HMGB1 in patients with idiopathic pulmonary arterial hypertension. The increase in circulating HMGB1 correlated with mean pulmonary artery pressure. In mice, we similarly detected the translocation and release of HMGB1 after exposure to CH. HMGB1-neutralizing antibody attenuated the development of CH-induced PH, as assessed by measurement of right ventricular systolic pressure, right ventricular hypertrophy, pulmonary vascular remodeling and endothelial activation and inflammation. Genetic deletion of the pattern recognition receptor TLR4, but not the receptor for advanced glycation end products, likewise attenuated CH-induced PH. Finally, daily treatment of mice with recombinant human HMGB1 exacerbated CH-induced PH in wild-type (WT) but not Tlr4(-/-) mice. These data demonstrate that HMGB1-mediated activation of TLR4 promotes experimental PH and identify HMGB1 and/or TLR4 as potential therapeutic targets for the treatment of PH.

Validation of an Integrated Genetic-Epigenetic Test for the Assessment of Coronary Heart Disease.

BACKGROUND: Coronary heart disease (CHD) is the leading cause of death in the world. Unfortunately, many of the key diagnostic tools for CHD are insensitive, invasive, and costly; require significant specialized infrastructure investments; and do not provide information to guide postdiagnosis therapy. In prior work using data from the Framingham Heart Study, we provided in silico evidence that integrated genetic-epigenetic tools may provide a new avenue for assessing CHD. METHODS AND RESULTS: In this communication, we use an improved machine learning approach and data from 2 additional cohorts, totaling 449 cases and 2067 controls, to develop a better model for ascertaining symptomatic CHD. Using the DNA from the 2 new cohorts, we translate and validate the in silico findings into an artificial intelligence-guided, clinically implementable method that uses input from 6 methylation-sensitive digital polymerase chain reaction and 10 genotyping assays. Using this method, the overall average area under the curve, sensitivity, and specificity in the 3 test cohorts is 82%, 79%, and 76%, respectively. Analysis of targeted cytosine-phospho-guanine loci shows that they map to key risk pathways involved in atherosclerosis that suggest specific therapeutic approaches. CONCLUSIONS: We conclude that this scalable integrated genetic-epigenetic approach is useful for the diagnosis of symptomatic CHD, performs favorably as compared with many existing methods, and may provide personalized insight to CHD therapy. Furthermore, given the dynamic nature of DNA methylation and the ease of methylation-sensitive digital polymerase chain reaction methodologies, these findings may pave a pathway for precision epigenetic approaches for monitoring CHD treatment response.

Functional effects of the TMEM43 Ser358Leu mutation in the pathogenesis of arrhythmogenic right ventricular cardiomyopathy.

BACKGROUND: The Ser358Leu mutation in TMEM43, encoding an inner nuclear membrane protein, has been implicated in arrhythmogenic right ventricular cardiomyopathy (ARVC). The pathogenetic mechanisms of this mutation are poorly understood. METHODS: To determine the frequency of TMEM43 mutations as a cause of ARVC, we screened 11 ARVC families for mutations in TMEM43 and five desmosomal genes previously implicated in the disease. Functional studies were performed in COS-7 cells transfected with wildtype, mutant, and 1:2 wildtype:mutant TMEM43 to determine the effect of the Ser358Leu mutation on the stability and cellular localization of TMEM43 and other nuclear envelope and desmosomal proteins, assessed by solubility assays and immunofluorescence imaging. mRNA expression was assessed of genes potentially affected by dysfunction of the nuclear lamina. RESULTS: Three novel mutations in previously documented desmosomal genes, but no mutations in TMEM43, were identified. COS-7 cells transfected with mutant TMEM43 exhibited no change in desmosomal stability. Stability and nuclear membrane localization of mutant TMEM43 and of lamin B and emerin were normal. Mutant TMEM43 did not alter the expression of genes located on chromosome 13, previously implicated in nuclear envelope protein mutations leading to skeletal muscular dystrophies. CONCLUSIONS: Mutant TMEM43 exhibits normal cellular localization and does not disrupt integrity and localization of other nuclear envelope and desmosomal proteins. The pathogenetic role of TMEM43 mutations in ARVC remains uncertain.

Genetic resiliency associated with dominant lethal TPM1 mutation causing atrial septal defect with high heritability.

Analysis of large-scale human genomic data has yielded unexplained mutations known to cause severe disease in healthy individuals. Here, we report the unexpected recovery of a rare dominant lethal mutation in TPM1, a sarcomeric actin-binding protein, in eight individuals with large atrial septal defect (ASD) in a five-generation pedigree. Mice with Tpm1 mutation exhibit early embryonic lethality with disrupted myofibril assembly and no heartbeat. However, patient-induced pluripotent-stem-cell-derived cardiomyocytes show normal beating with mild myofilament defect, indicating disease suppression. A variant in TLN2, another myofilament actin-binding protein, is identified as a candidate suppressor. Mouse CRISPR knock-in (KI) of both the TLN2 and TPM1 variants rescues heart beating, with near-term fetuses exhibiting large ASD. Thus, the role of TPM1 in ASD pathogenesis unfolds with suppression of its embryonic lethality by protective TLN2 variant. These findings provide evidence that genetic resiliency can arise with genetic suppression of a deleterious mutation.

Activation of cardiac hypertrophic signaling pathways in a transgenic mouse with the human PRKAG2 Thr400Asn mutation.

Human mutations in PRKAG2, the gene encoding the gamma2 subunit of AMP activated protein kinase (AMPK), cause a glycogen storage cardiomyopathy. In a transgenic mouse with cardiac specific expression of the Thr400Asn mutation in PRKAG2 (TG(T400N)), we previously reported initial cardiac hypertrophy (ages 2-8 weeks) followed by dilation and failure (ages 12-20 weeks). We sought to elucidate the molecular mechanisms of cardiac hypertrophy. TG(T400N) mice showed significantly increased cardiac mass/body mass ratios up to approximately 3-fold beginning at age 2 weeks. Cardiac expression of ANP and BNP were approximately 2- and approximately 5-fold higher, respectively, in TG(T400N) relative to wildtype (WT) mice at age 2 weeks. NF-kappaB activity and nuclear translocation of the p50 subunit were increased approximately 2- to 3-fold in TG(T400N) hearts relative to WT during the hypertrophic phase. Phosphorylated Akt and p70S6K were elevated approximately 2-fold as early as age 2 weeks. To ascertain whether these changes in TG(T400N) mice were a consequence of increased AMPK activity, we crossbred TG(T400N) with TG(alpha2DN) mice, which express a dominant negative, kinase dead mutant of the AMPK alpha2 catalytic subunit and have low myocardial AMPK activity. Genetic reversal of AMPK overactivity led to a reduction in hypertrophy, nuclear translocation of NF-kappaB, phosphorylated Akt, and p70S6K. We conclude that inappropriate activation of AMPK secondary to the T400N PRKAG2 mutation is associated with the early activation of NF-kappaB and Akt signaling pathway, which mediates cardiac hypertrophy.

Midterm outcomes of off-pump and on-pump coronary artery revascularization in renal transplant recipients.

OBJECTIVES: Renal transplant recipients have high mortality from cardiac causes and are frequently in need of coronary interventions. Surgical coronary revascularization is associated with significant morbidity and mortality in this patient population. This study was undertaken to evaluate outcomes of on-pump versus off-pump revascularization in renal transplant recipients. METHODS: We retrospectively reviewed 43 renal transplant recipients who underwent surgical coronary revascularization with functioning allografts. Revascularization was performed on-pump [coronary artery bypass grafting (CABG)] in 21 patients and off-pump [off-pump coronary artery bypass (OPCAB)] in 22 patients. RESULTS: Preoperative characteristics did not differ between the two groups except for age and incidence of prior sternotomy. Total operative time and transfusion requirements were similar. The on-pump group received a higher number of bypass grafts (p = 0.03). Overall 30-day, one-year, five-year, and eight-year survival was 90%, 76%, 61%, and 32% for CABG group, and 95%, 86%, 62%, and 48% for OPCAB group (p = 0.53). The postoperative peak creatinine was higher in the CABG patients than in OPCAB patients (p = 0.04). At discharge, there was no difference in mean creatinine between the two groups. The rate of return to permanent dialysis after revascularization was similar (28% for CABG and 22% for OPCAB, p = 0.73). There was no difference in dialysis-free survival up to eight-years postrevascularization (p = 0.63). CONCLUSIONS: Despite higher mortality risk, surgical coronary revascularization can be performed safely in renal transplant recipients. OPCAB resulted in no improvement in patient survival or renal allograft function compared to on-pump revascularization.

Exploring experiences of hypertrophic cardiomyopathy diagnosis, treatment, and impacts on quality of life among middle-aged and older adults: An interview study.

BACKGROUND: Limited studies exist that describe diagnosis, treatment, and management experiences of patients with hypertrophic cardiomyopathy (HCM). This study's purpose is to characterize patient experiences related to symptom onset, diagnosis, symptom management, support from healthcare professionals, and impacts on daily living. METHODS: Semi-structured interviews were conducted using open-ended questions and question probes were conducted with adults aged ≥18 years diagnosed with HCM ≥1 year prior. Interview recordings were transcribed verbatim and inductive and deductive thematic analyses were performed. RESULTS: A total of 32 interviews were conducted. The majority of participants were female (53.1%), aged ≥45 years (90.6%), white (96.9%), and non-Hispanic (96.9%). Participants with longer time to HCM diagnosis described having atypical HCM symptoms, denial of their own symptoms, and experiences of misdiagnoses. For HCM information and support, participants utilized personal healthcare professionals as well as non-medical resources. Participants described experiences of anxiety, denial, and upset feelings about their diagnosis, but also gratitude, acceptance, and increased mindfulness toward healthy habits. Individuals reported making changes in daily activities because of reduced physical capacity and making changes in lifestyle choices because of desire to be close to HCM specialists. Over time, participants also described becoming less fearful through utilization of available resources and treatment options. CONCLUSIONS: The diverse but often challenging experiences of individuals with HCM suggest that increasing availability and utilization of HCM patient resources may be effective at reducing the unfavorable physical and psychological impacts of HCM. Common reports of misdiagnoses resulting in delayed HCM diagnosis also indicate a need for HCM-related educational opportunities for healthcare professionals.

COVID-19: Understanding Inter-Individual Variability and Implications for Precision Medicine.

Coronavirus disease 2019 (COVID-19) is characterized by heterogeneity in susceptibility to the disease and severity of illness. Understanding inter-individual variation has important implications for not only allocation of resources but also targeting patients for escalation of care, inclusion in clinical trials, and individualized medical therapy including vaccination. In addition to geographic location and social vulnerability, there are clear biological differences such as age, sex, race, presence of comorbidities, underlying genetic variation, and differential immune response that contribute to variability in disease manifestation. These differences may have implications for precision medicine. Specific examples include the observation that androgens regulate the expression of the enzyme transmembrane protease, serine 2 which facilitates severe acute respiratory syndrome coronavirus 2 viral entry into the cell; therefore, androgen deprivation therapy is being explored as a treatment option in males infected with COVID-19. An immunophenotyping study of COVID-19 patients has shown that a subset develop T cytopenia which has prompted a clinical trial that is testing the efficacy of interleukin-7 in these patients. Predicting which COVID-19 patients will develop progressive disease that will require hospitalization has important implications for clinical trials that target outpatients. Enrollment of patients at low risk for progression of disease and hospitalization would likely not result in such therapy demonstrating efficacy. There are efforts to use artificial intelligence to integrate digital data from smartwatch applications or digital monitoring systems and biological data to enable identification of the high risk COVID-19 patient. The ultimate goal of precision medicine using such modern technology is to recognize individual differences to improve health for all.

SGLT1, a novel cardiac glucose transporter, mediates increased glucose uptake in PRKAG2 cardiomyopathy.

Human mutations in the gene PRKAG2 encoding the gamma2 subunit of AMP-activated protein kinase (AMPK) cause a glycogen storage cardiomyopathy. Transgenic mice (TG(T400N)) with the human T400N mutation exhibit inappropriate activation of AMPK and consequent glycogen storage in the heart. Although increased glucose uptake and activation of glycogen synthesis have been documented in PRKAG2 cardiomyopathy, the mechanism of increased glucose uptake has been uncertain. Wildtype (WT), TG(T400N), and TG(alpha2DN) (carrying a dominant negative, kinase dead alpha2 catalytic subunit of AMPK) mice were studied at ages 2-8 weeks. Cardiac mRNA expression of sodium-dependent glucose transporter 1 (SGLT1), but not facilitated-diffusion glucose transporter 1 (GLUT1) or GLUT4, was increased approximately 5- to 7-fold in TG(T400N) mice relative to WT. SGLT1 protein was similarly increased at the cardiac myocyte sarcolemma in TG(T400N) mice. Phlorizin, a specific SGLT1 inhibitor, attenuated cardiac glucose uptake in TG(T400N) mice by approximately 40%, but not in WT mice. Chronic phlorizin treatment reduced cardiac glycogen content by approximately 25% in TG(T400N) mice. AICAR, an AMPK activator, increased cardiac SGLT1 mRNA expression approximately 3-fold in WT mice. Relative to TG(T400N) mice, double transgenic (TG(T400N)/TG(alpha2DN)) mice had decreased ( approximately 50%) cardiac glucose uptake and decreased (approximately 70%) cardiac SGLT1 expression. TG(T400N) hearts had increased binding activity of the transcription factors HNF-1 and Sp1 to the promoter of the gene encoding SGLT1. Our data suggest that upregulation of cardiac SGLT1 is responsible for increased cardiac glucose uptake in the TG(T400N) mouse. Increased AMPK activity leads to upregulation of SGLT1, which in turn mediates increased cardiac glucose uptake.

Transcriptional coactivator PGC-1 alpha controls the energy state and contractile function of cardiac muscle.

Skeletal and cardiac muscle depend on high turnover of ATP made by mitochondria in order to contract efficiently. The transcriptional coactivator PGC-1alpha has been shown to function as a major regulator of mitochondrial biogenesis and respiration in both skeletal and cardiac muscle, but this has been based only on gain-of-function studies. Using genetic knockout mice, we show here that, while PGC-1alpha KO mice appear to retain normal mitochondrial volume in both muscle beds, expression of genes of oxidative phosphorylation is markedly blunted. Hearts from these mice have reduced mitochondrial enzymatic activities and decreased levels of ATP. Importantly, isolated hearts lacking PGC-1alpha have a diminished ability to increase work output in response to chemical or electrical stimulation. As mice lacking PGC-1alpha age, cardiac dysfunction becomes evident in vivo. These data indicate that PGC-1alpha is vital for the heart to meet increased demands for ATP and work in response to physiological stimuli.

Alterations of phospholamban function can exhibit cardiotoxic effects independent of excessive sarcoplasmic reticulum Ca2+-ATPase inhibition.

BACKGROUND: Low activity of the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2a) resulting from strong inhibition by phospholamban (PLN) can depress cardiac contractility and lead to dilated cardiomyopathy and heart failure. Here, we investigated whether PLN exhibits cardiotoxic effects via mechanisms other than chronic inhibition of SERCA2a by studying a PLN mutant, PLN(R9C), that triggers cardiac failure in humans and mice. METHODS AND RESULTS: Because PLN(R9C) inhibits SERCA2a mainly by preventing deactivation of wild-type PLN, SERCA2a activity could be increased stepwise by generating mice that carry a PLN(R9C) transgene and 2, 1, or 0 endogenous PLN alleles (PLN(+/+)+TgPLN(R9C), PLN(+/-)+TgPLN(R9C), and PLN(-/-)+TgPLN(R9C), respectively). PLN(-/-) +TgPLN(R9C) hearts demonstrated accelerated sarcoplasmic reticulum Ca(2+) uptake rates and improved hemodynamics compared with PLN(+/+)+TgPLN(R9C) mice but still responded poorly to beta-adrenergic stimulation because PLN(R9C) impairs protein kinase A-mediated phosphorylation of both wild-type and mutant PLN. PLN(+/+)+TgPLN(R9C) mice died of heart failure at 21+/-6 weeks, whereas heterozygous PLN(+/-)+TgPLN(R9C) mice survived to 48+/-11 weeks, PLN(-/-)+TgPLN(R9C) mice to 66+/-19 weeks, and wild-type mice to 94+/-27 weeks (P<0.001). Although Ca(2+) reuptake kinetics in young PLN(-/-)+TgPLN(R9C) mice exceeded those measured in wild-type control animals, this parameter alone was not sufficient to prevent the eventual development of dilated cardiomyopathy. CONCLUSIONS: The data demonstrate an association between the dose-dependent inhibition of SERCA2a activity by PLN(wt) and the time of onset of heart failure and show that a weak inhibitor of SERCA2a, PLN(R9C), which is diminished in its ability to modify the level of SERCA2a activity, leads to heart failure despite fast sarcoplasmic reticulum Ca(2+) reuptake.

Genomewide RNA expression profiling in lung identifies distinct signatures in idiopathic pulmonary arterial hypertension and secondary pulmonary hypertension.

Idiopathic pulmonary arterial hypertension (PAH) is a life-threatening condition characterized by pulmonary arteriolar remodeling. This investigation aimed to identify genes involved specifically in the pathogenesis of PAH and not other forms of pulmonary hypertension (PH). Using genomewide microarray analysis, we generated the largest data set to date of RNA expression profiles from lung tissue specimens from 1) 18 PAH subjects and 2) 8 subjects with PH secondary to idiopathic pulmonary fibrosis (IPF) and 3) 13 normal subjects. A molecular signature of 4,734 genes discriminated among these three cohorts. We identified significant novel biological changes that were likely to contribute to the pathogenesis of PAH, including regulation of actin-based motility, protein ubiquitination, and cAMP, transforming growth factor-beta, MAPK, estrogen receptor, nitric oxide, and PDGF signaling. Bone morphogenic protein receptor type II expression was downregulated, even in subjects without a mutation in this gene. Women with PAH had higher expression levels of estrogen receptor 1 than normal women. Real-time quantitative PCR confirmed differential expression of the following genes in PAH relative to both normal controls and PH secondary to IPF: a disintegrin-like and metalloprotease with thrombospondin type 1 motif 9, cell adhesion molecule with homology to L1CAM, cytochrome b(558) and beta-polypeptide, coagulation factor II receptor-like 3, A-myb myeloblastosis viral oncogene homolog 1, nuclear receptor coactivator 2, purinergic receptor P2Y, platelet factor 4, phospholamban, and tropomodulin 3. This study shows that PAH and PH secondary to IPF are characterized by distinct gene expression signatures, implying distinct pathophysiological mechanisms.

Diversity, Equity, and Inclusiveness in Medicine and Cardiology: Next Steps for JAHA.

We, the Editors of the Journal of the American Heart Association, sincerely regret the publication of the article "Diversity, Inclusion, and Equity: Evolution of Race and Ethnicity Considerations for the Cardiology Workforce in the United States of America From 1969 to 2019".1 We are aware that the publication of this flawed and biased article has caused a great deal of unnecessary pain and anguish to a number of parties, and reflects extremely poorly on us. We fully support the retraction of this article.

Reversibility of PRKAG2 glycogen-storage cardiomyopathy and electrophysiological manifestations.

BACKGROUND: PRKAG2 mutations cause glycogen-storage cardiomyopathy, ventricular preexcitation, and conduction system degeneration. A genetic approach that utilizes a binary inducible transgenic system was used to investigate the disease mechanism and to assess preventability and reversibility of disease features in a mouse model of glycogen-storage cardiomyopathy. METHODS AND RESULTS: Transgenic (Tg) mice expressing a human N488I PRKAG2 cDNA under control of the tetracycline-repressible alpha-myosin heavy chain promoter underwent echocardiography, ECG, and in vivo electrophysiology studies. Transgene suppression by tetracycline administration caused a reduction in cardiac glycogen content and was initiated either prenatally (Tg(OFF(E-8 weeks))) or at different time points during life (Tg(OFF(4-16 weeks)), Tg(OFF(8-20 weeks)), and Tg(OFF(>20 weeks))). One group never received tetracycline, expressing transgene throughout life (Tg(ON)). Tg(ON) mice developed cardiac hypertrophy followed by dilatation, ventricular preexcitation involving multiple accessory pathways, and conduction system disease, including sinus and atrioventricular node dysfunction. CONCLUSIONS: Using an externally modifiable transgenic system, cardiomyopathy, cardiac dysfunction, and electrophysiological disorders were demonstrated to be reversible processes in PRKAG2 disease. Transgene suppression during early postnatal development prevented the development of accessory electrical pathways but not cardiomyopathy or conduction system degeneration. Taken together, these data provide insight into mechanisms of cardiac PRKAG2 disease and suggest that glycogen-storage cardiomyopathy can be modulated by lowering glycogen content in the heart.

Patient with a PRKAG2 mutation who developed Immunoglobulin A nephropathy: a case report.

BACKGROUND: PRKAG2 syndrome (PS) is a rare, early-onset autosomal dominant inherited disease caused by mutations in PRKAG2, the gene encoding the regulatory γ2 subunit of adenosine monophosphate-activated protein kinase. PRKAG2 syndrome is associated with many cardiac manifestations, including pre-excitation, arrhythmias, left ventricular hypertrophy, and chronotropic incompetence frequently leading to early pacemaker placement. A meta-analysis of genome-wide association data in subjects with chronic kidney disease (CKD) identified a susceptibility locus in an intron of PRKAG2, which has been replicated in other studies. However, CKD has not been reported in patients with PS or mutations in PRKAG2. CASE SUMMARY: We report a case of a woman diagnosed at age 27 with PS when she presented with atrial fibrillation and pre-excitation on electrocardiogram. By age 35, she had developed mild renal insufficiency and a biopsy demonstrated IgA nephropathy (IGAN). DISCUSSION: This is the first reported case of IGAN in a patient with PS. We discuss both PS and IGAN and the potential mechanisms by which they could be related.

Family Relationships Associated With Communication and Testing for Inherited Cardiac Conditions.

The purpose of this study was to identify characteristics of family relationships associated with communication of genetic risk and testing behaviors among at-risk relatives in families with an inherited cardiac condition. Data were collected from 53 patients and parents of children with an inherited cardiac condition through interviews, pedigrees, and surveys. Associations were examined among family relationship characteristics and whether at-risk relatives were informed about their risk and tested for disease. Of 1,178 at-risk relatives, 52.5% were informed about their risk and 52.1% of those informed were tested. Emotional closeness, relationship quality, and communication frequency had significant bivariate associations with genetic risk communication. Communication frequency was associated with genetic risk communication and testing in multivariate models. This study provides new insight into the extent of genetic risk communication and testing in families with inherited cardiac conditions. Family relationships, especially communication frequency, are critical factors in family communication of genetic risk.