Hanna J. Tadros

COX14 encodes a transmembrane protein essential for cytochrome c oxidase (COX) complex assembly. A homozygous missense variant in COX14 was reported in three siblings from a single consanguineous family with severe, fatal infantile mitochondrial complex IV deficiency nuclear type 10 (MC4DN10; MIM# 619053). No additional cases have been identified since, and the ClinGen Mitochondrial Disease Gene Curation Expert Panel classified the COX14 –MC4DN10 gene–disease association as having limited evidence. We report a 9‐year‐old male with biallelic COX14 variants (c.82delT, p.Tyr28Thrfs*83, and c.3G>A, p.Met1?) representing the second unrelated family with MC4DN10. In contrast to the fatal neonatal course previously described, this individual demonstrates an attenuated encephalomyopathic phenotype with prolonged survival. Initial presentation at 6 months included hypotonia, feeding difficulties, and developmental delay. Previously unreported features included growth hormone deficiency, ascending aortic dilation, and distinct neuroradiological findings. At age 8 years, he developed neurological regression and ataxia with brain MRI findings consistent with Leigh syndrome. Muscle biopsy confirmed reduced COX enzymatic activity (33% of mean). Identification of a second unrelated family with biallelic COX14 variants and biochemically confirmed complex IV deficiency strengthens the gene–disease association for MC4DN10. This individual presents an attenuated encephalomyopathic phenotype with novel endocrine and cardiovascular manifestations, underscoring the importance of genomic evaluation in suspected mitochondrial disorders even in the absence of classic biochemical markers such as lactic acidosis.

TOP3A ‐related mitochondrial disease is a rare autosomal recessive primary mitochondrial cytopathy caused by loss‐of‐function of the mitochondrial‐specific isoform of topoisomerase 3α, leading to multiple mitochondrial DNA deletions and mitochondrial DNA depletion. This condition has been associated with two different phenotypes. Very young patients present with severe growth faltering and early mortality, that is consistent with a Bloom syndrome‐like disorder. Adult‐onset chronic progressive external ophthalmoplegia, myopathy, and sensory ataxia, with rare hypertrophic cardiomyopathy (a MIRAS‐like phenotype), reflects a mitochondrial disorder. In this article, we expand the phenotype spectrum of TOP3A ‐related mitochondrial disease with a mitochondrial childhood onset form and present four previously unreported patients, including the outcomes of heart transplantation for three patients. Histopathological, electron microscopical, biochemical, and molecular characterization of muscle and heart tissue indicated mitochondrial dysfunction with combined complex deficiency associated with a mitochondrial DNA maintenance disorder primarily expressed in the heart. Heart transplantation was successful in patients with TOP3A ‐related mitochondrial disease that presented with cardiomyopathy in childhood, although there is slowly progressive neurological disease. In childhood, TOP3A ‐related disease presents with a combination of developmental delays, sensorineural hearing loss, cardiomyopathy with rhythm abnormalities, stroke‐like episodes, and Leigh‐like phenotype, and, in some, epilepsy. These mitochondrial phenotypes are different from the infantile Bloom‐like syndrome and the adult‐onset form.

Individuals with hypoplastic left heart syndrome (HLHS) have an underdeveloped left ventricle and require surgery to reconfigure blood flow for survival. Here we profiled the HLHS right-ventricular microenvironment by single-nucleus RNA sequencing and spatial transcriptomics at birth (before heart failure), after surgery with heart failure and after ventricular assist device (VAD) unloading (reduced hypoxia and volume overload). We show that HLHS cardiomyocytes, both within the heart and when derived from induced pluripotent stem cells, are intrinsically senescent. The HLHS myocardium contained a senescent microvascular niche with endothelial cells, pericytes and YAP-high fibroblasts, consistent with hypoxic and mechanical stress. This senescent niche is similar to adult myocardial infarction but not pediatric dilated cardiomyopathy with heart failure, pointing to a prominent role of hypoxia in senescence. The microvascular senescent niche was improved by VAD, providing insight into the potential to reverse cardiac cell states that lead to heart failure.

Animal models are an essential part of preclinical research, serving to protect patients through safety and efficacy studies before human trials begin. Prior to the passage of the Food and Drug Administration (FDA) Modernization Act 2.0 in 2022, animal studies were generally required by regulators in preclinical safety evaluations. This Act amended the Federal Food, Drug, and Cosmetic Act to clarify that while animal testing had been the default standard, it is no longer a mandatory requirement for regulatory filings involving drugs and biological products¹. Additionally, the Act explicitly specifies in vitro, in silico, and in chemico testing as alternatives to assess pre-clinical safety and efficacy. The FDA and others refer to these alternative platforms as New Approach Methodologies (NAMs) with an emphasis on the 3Rs of replacing, reducing and refining the use of animal testing². This shift opens new pathways for developing and evaluating precision therapies in cardiovascular disease particularly if human-derived, genetically accurate models can outperform animal studies in predictive power and translatability.

BACKGROUND: Hypertrophic cardiomyopathy (HCM) is a relatively rare but debilitating diagnosis in the pediatric population, and patients with end-stage HCM require heart transplantation. Here, we have examined the transcriptome in ventricular tissue from this patient group to identify cell states and underlying cellular processes unique to pediatric HCM. METHODS: We performed single-nucleus RNA sequencing (snRNA-seq) on explanted hearts at transplant in 3 pediatric patients with end-stage HCM and compared findings to pediatric control and adult HCM. RESULTS: We identified distinct underlying cellular processes in cardiomyocytes, fibroblasts, endothelial cells, and myeloid cells compared with controls. Pediatric HCM was enriched in cardiomyocytes exhibiting stressed myocardium gene signatures and underlying pathways associated with cardiac hypertrophy; cardiac fibroblasts exhibited activation signatures and compared with adult patients, exhibited heightened downstream processes associated with fibrosis and a unique, myofibroblast-like cluster with increased metabolic stress and antiapoptotic properties. We noted depletion of tissue-resident macrophages and increased vascular remodeling in endothelial cells in pediatric HCM. CONCLUSIONS: Our analysis provides the first snRNA-seq analysis focused on end-stage pediatric HCM. Fibroblast-mediated cellular processes were the most prominent in pediatric HCM, which had more downstream processes associated with fibrosis than did adult HCM.

Hypertrophic cardiomyopathy (HCM) is a relatively rare but debilitating diagnosis in the pediatric population and patients with end-stage HCM require heart transplantation. In this study, we performed single-nucleus RNA sequencing on pediatric HCM and control myocardium. We identified distinct underling cellular processes in pediatric, end-stage HCM in cardiomyocytes, fibroblasts, endothelial cells, and myeloid cells, compared to controls. Pediatric HCM was enriched in cardiomyocytes exhibiting “stressed” myocardium gene signatures and underlying pathways associated with cardiac hypertrophy. Cardiac fibroblasts exhibited clear activation signatures and heightened downstream processes associated with fibrosis, more so than adult counterparts. There was notable depletion of tissue-resident macrophages, and increased vascular remodeling in endothelial cells. Our analysis provides the first single nuclei analysis focused on end-stage pediatric HCM.

BACKGROUND: With genetic testing advancements, the burden of incidentally identified cardiac disease-associated gene variants is rising. These variants may carry a risk of sudden cardiac death, highlighting the need for accurate diagnostic interpretation. We sought to identify pathogenic hotspots in sudden cardiac death-associated genes using amino acid-level signal-to-noise (S:N) analysis and develop a web-based precision medicine tool, DiscoVari , to improve variant evaluation. METHODS: The minor allele frequency of putatively pathogenic variants was derived from cohort-based cardiomyopathy and channelopathy studies in the literature. We normalized disease-associated minor allele frequencies to rare variants in an ostensibly healthy population (Genome Aggregation Database) to calculate amino acid-level S:N. Amino acids with S:N above the gene-specific threshold were defined as hotspots. DiscoVari was built using JavaScript ES6 and using open-source JavaScript library ReactJS, web development framework Next.js, and JavaScript runtime NodeJS. We validated the ability of DiscoVari to identify pathogenic variants using variants from ClinVar and individuals clinically evaluated at the Duke University Hospitals with cardiac genetic testing. RESULTS: We developed DiscoVari as an internet-based tool for S:N-based variant hotspots. Upon validation, a higher proportion of ClinVar likely pathogenic/pathogenic variants localized to DiscoVari hotspots (43.1%) than likely benign/benign variants (17.8%; P< 0.0001). Further, 75.3% of ClinVar variants reclassified to likely pathogenic/pathogenic were in hotspots, compared with 41.3% of those reclassified as variants of uncertain significance ( P< 0.0001) and 23.4% of those reclassified as likely benign/benign ( P P< 0.01). CONCLUSIONS: DiscoVari reliably identifies disease-susceptible amino acid residues to evaluate variants by searching amino acid-specific S:N ratios.

Objective We explore shared decision making (DM) in guardians of children with heart disease by assessing the desired weight of influence on DM and factors that may alter the relative weight of parent or medical team influence. Methods Guardians of patients 1 week in the paediatric cardiac intensive care unit (PCICU) were recruited. Twelve vignettes were designed including technical (antibiotic selection, intubation, peripherally inserted central catheter placement, ventricular assist device placement, heart transplant, organ rejection, heart rhythm abnormalities and resuscitation effort) and non-technical vignettes (cessation of life-sustaining therapies, depression treatment, obesity and palliative care referral). Participants responded to questions on DM characteristics and one question querying preference for relative weight of parent or medical team influence on DM. Results Of 209 participants approached, 183 were included. Most responded with equal desire of medical team and parental influence on DM in all vignettes (range 41.0%–66.7%). Technical scenarios formed one cluster based on DM characteristics, compared with non-technical scenarios. Factors that increase the relative weight of parental influence on DM include desired input and involvement in big-picture goals (OR 0.274, CI [0.217 to 0.346]; OR 0.794, CI [0.640 to 0.986]). Factors that increase the relative weight of medical team influence on DM include perception of medical expertise needed (OR 1.949 [1.630 to 2.330]), urgency (OR 1.373 [1.138 to 1.658]), benefit (OR 1.415 [1.172 to 1.710]), number of PCICU admissions (OR 1.134 [1.024 to 1.256]) and private insurance (OR 1.921 [1.144 to 3.226]). Conclusion Although factors may alter the weight of influence on DM, most parents desire equal parental and medical team influence on DM.