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Background: We have developed a new clinical research approach for the quantification of cellular proliferation in human infants to address unanswered questions about tissue renewal and regeneration. The approach consists of oral 15N-thymidine administration to label cells in S-phase, followed by Multi-isotope Imaging Mass Spectrometry for detection of the incorporated label in cell nuclei. To establish the approach, we performed an observational study to examine uptake and elimination of 15N-thymidine. We compared at-home label administration with in-hospital administration in infants with tetralogy of Fallot, a form of congenital heart disease, and infants with heart failure. Methods: We examined urine samples from 18 infants who received 15N-thymidine (50 mg/kg body weight) by mouth for five consecutive days. We used Isotope Ratio Mass Spectrometry to determine enrichment of 15N relative to 14N (%) in urine. Results/findings: 15N-thymidine dose administration produced periodic rises of 15N enrichment in urine. Infants with tetralogy of Fallot had a 3.2-fold increase and infants with heart failure had a 4.3-fold increase in mean peak 15N enrichment over baseline. The mean 15N enrichment was not statistically different between the two patient populations (p = 0.103). The time to peak 15N enrichment in tetralogy of Fallot infants was 6.3 ± 1 hr and in infants with heart failure 7.5 ± 2 hr (mean ± SEM). The duration of significant 15N enrichment after a dose was 18.5 ± 1.7 hr in tetralogy of Fallot and in heart failure 18.2 ± 1.8 hr (mean ± SEM). The time to peak enrichment and duration of enrichment were also not statistically different (p = 0.617 and p = 0.887). Conclusions: The presented results support two conclusions of significance for future applications: (1) Demonstration that 15N-thymidine label administration at home is equivalent to in-hospital administration. (2) Two different types of heart disease show no differences in 15N-thymidine absorption and elimination. This enables the comparative analysis of cellular proliferation between different types of heart disease. [ABSTRACT FROM AUTHOR]

Background: Fontan associated liver disease (FALD) potentially impacts Fontan patients undergoing heart transplant. This multi‐center study sought to identify pre‐transplant risk factors and characterize any post‐transplant liver recovery in those patients undergoing heart‐alone transplant. Methods: Review of Fontan patients at 12 pediatric institutions who underwent heart transplant between 2001‐2019. Radiologists reviewed pre and post‐transplant liver imaging for fibrosis. Laboratory, pathology and endoscopy studies were reviewed. Results: 156 patients underwent transplant due to decreased ventricular function (49%), protein losing enteropathy (31%) or plastic bronchitis (10%); median age at transplant was 13.6 years (interquartile range IQR 7.8, 17.2) with a median of 9.3 years (IQR 3.2, 13.4) between the Fontan operation and transplant. Few patients had pre‐transplant endoscopy (18%), and liver biopsy (19%). There were 31 deaths (20%). The median time from transplant to death was 0.5 years (95% Confidence Interval CI 0.0, 3.6). The five‐year survival was 73% (95% CI 64%, 83%). Deaths were related to cardiac causes in 68% (21/31) and infection in 6 (19%). A pre‐transplant elevation in bilirubin was a predictor of death. Higher platelet levels were protective. Immediate post‐transplant elevations in creatinine, AST, ALT, and INR were predictive of death. Advanced liver fibrosis identified on ultrasound, computed tomography, or magnetic resonance imaging was not predictive of death. Liver imaging suggested some improvement in liver congestion post‐transplant. Conclusions: Elevated bilirubin, but not fibrosis on liver imaging, was associated with post‐heart transplant mortality in Fontan patients in this multicenter retrospective study. Additionally, heart transplant may alter the progression of FALD. [ABSTRACT FROM AUTHOR]

Background: Acute kidney disease (AKD) is defined as impaired kidney function present for <90 days with or without an acute kidney injury (AKI) event. Adults with AKD have an increased risk for progression to chronic kidney disease (CKD) and mortality. There are no data on the epidemiology of AKD in children after transplant. The aim of this study was to evaluate the incidence and risk factors for AKI, AKD, and CKD in children after transplantation. Methods: This is a retrospective cohort study of all children undergoing non‐kidney solid organ transplant between 2011 and 2019 at UPMC Children's Hospital of Pittsburgh. AKI and AKD were defined using the Kidney Disease Improving Global Outcomes criteria. Patients with a new estimated glomerular filtration rate <60 ml/min/1.73m2 persisting for >3 months met criteria for new CKD. Variables associated with AKI, AKD, and CKD were analyzed. Results: Among 338 patients, 37.9% met criteria for severe AKI, 13% for AKD, and 8% for a new diagnosis of CKD. Stage 3 AKI was independently associated with AKD (OR: 5.35; 95% CI: 2.23–12.86). Severe AKI was not associated with new‐onset CKD, whereas AKD was associated with new‐onset CKD (OR: 29.74; CI: 11.22–78.82). Conclusion: AKD may be superior to AKI in predicting risk of CKD in children after non‐kidney solid organ transplantation. [ABSTRACT FROM AUTHOR]

Nemaline Myopathy (NM) is a disorder of skeletal muscles caused by mutations in sarcomere proteins and characterized by accumulation of microscopic rod or thread‐like structures (nemaline bodies) in skeletal muscles. Patients diagnosed with both NM and infantile cardiomyopathy are very rare. A male infant presented, within the first few hours of life, with severe dilated cardiomyopathy, biventricular dysfunction and left ventricular noncompaction. A muscle biopsy on the 8th day of life from the right sternocleidomastoid muscle identified nemaline rods. Whole exome sequencing identified a c.1288 delT (homozygous pathogenic variant) in the CAP2 gene (NM_006366), yielding a CAP2 protein (NP_006357.1) with a p.C430fs. Both parents were heterozygous for the same variant but have no history of heart or muscle disease. Analysis of patient derived fibroblasts and cardiomyocytes derived from induced pluripotent stem cells confirmed the p.C430fs mutation (pathogenic variant), which appears to cause loss of both CAP2 protein and mRNA. The CAP2 gene encodes cyclase associated protein 2, an actin monomer binding and filament depolymerizing protein and CAP2 knockout mice develop severe dilated cardiomyopathy and muscle weakness. The patient underwent a heart transplant at 1 year of age. Heart tissue explanted at that time also showed nemaline rods and additionally disintegration of the myofibrillar structure. Other extra cardiac concerns include mild hypotonia, atrophic and widened scarring. This is the first description of a patient presenting with nemaline myopathy associated with a pathogenic variant of CAP2. [ABSTRACT FROM AUTHOR]

Background: Endomyocardial biopsy (EMB) is costly and discomforting yet remains a key component of surveillance after pediatric heart transplantation (HT). Donor‐derived cell‐free DNA (dd‐cfDNA) has been histologically validated with high negative predictive value, offering an alternative to surveillance EMB (sEMB). Methods: We implemented an alternative surveillance protocol using commercially available dd‐cfDNA assays in place of sEMB after pediatric HT. Recipients ≧7 months post‐HT with reassuring clinical assessment were referred for dd‐cfDNA. When not elevated above the manufacturers' threshold, sEMB was deferred. Subsequent clinical status and results of follow‐up EMB were analyzed. Results: Over 17 months, 58 recipients [34% female, median age at HT 3.1 years (IQR 0.6–10.6)] had dd‐cfDNA assessed per protocol. Median age was 14.8 years (8.4–18.3) and time from HT 6.0 years (2.2–11.2). Forty‐seven (81%) had non‐elevated dd‐cfDNA and 11 (19%) were elevated. During a median of 8.7 months (4.2–15), all are alive without allograft loss/new dysfunction. Among those with non‐elevated dd‐cfDNA, 24 (51%) had subsequent sEMB at 12.1 months (6.9–12.9) with 23 showing no acute rejection (AR): grade 0R/pAMR0 (n = 16); 1R(1A)/pAMR0 (n = 7). One had AR (grade 2R(3A)/pAMR0) on follow‐up sEMB after decreased immunosuppression following a diagnosis of PTLD. All 11 with elevated dd‐cfDNA had reflex EMB at 19 days (12–32) with AR in 4: grade 1R(1B‐2)/pAMR0 (n = 3); 1R(1B)/pAMR2 (n = 1). Conclusions: dd‐cfDNA assessment in place of selected, per‐protocol EMB decreased surveillance EMB by 81% in our pediatric HT recipient cohort with no short‐term adverse outcomes. Individual center approach to surveillance EMB will influence the utility of these findings. [ABSTRACT FROM AUTHOR]