Pediatric thrombosis (PT) represents a rare condition that can manifest from neonatal life to adolescence, encompassing life-threatening complications. Its pathogenesis is attributed to immature hemostasis in conjunction with environmental and genetic factors, predominantly including those resulting in increased levels of plasminogen activator inhibitor 1 (PAI-1), the principal inhibitor of fibrinolysis, which is subject to upstream regulation by angiotensin-converting enzyme (ACE). Although the implication of microRNAs (miRNAs), epigenetic modulators of gene expression, has been demonstrated in adult thrombosis, evidence is lacking in the pediatric setting. Here, we investigated the involvement of two miRNA regulators of PAI-1 (SERPINE1 gene) in PT, in relation to clinical and genetic parameters that induce PAI-1 fluctuations. Following bioinformatic target-prediction, miRNA expression was assessed by quantitative real-time PCR in serum-samples of 19 pediatric patients with thrombosis (1–18 months post-incident), and 19 healthy controls. Patients were genotyped for the SERPINE1-4G/5G and ACE-I/D polymorphisms by PCR-based assays. Genotypic and thrombosis-related clinical data were analyzed in relation to miRNA-expression. Two miRNAs (miR-145-5p, miR-34a-5p) were identified to target SERPINE1 mRNA, with miR-34a additionally targeting the mRNA of ACE. The expression of miR-34a was significantly decreased in patients compared to controls (p = 0.029), while no difference was observed in miR-145 expression. Within patients, miR-34a expression demonstrated a peak 1–3 months post-thrombosis and was diminished upon treatment completion (p = 0.031), followed by a slight long-term increase. MiR-34a levels differed significantly by thrombosis site (p = 0.019), while a significant synergistic interaction between site and onset type (provoked/unprovoked) was detected (p = 0.016). Finally, an epistatic modification was observed in cerebral cases, since double homozygosity (4G/4G + D/D) led to a miR-34 decrease, with D/D carriership reversing the 4G/4G-induced upregulation of miR-34a (p = 0.006). Our findings suggest that in pediatric thrombosis, downregulation of miR-34a is indicative of impaired fibrinolytic capacity, attributed to deficient regulation of the inhibitory ACE/PAI-1 axis.

Background: Pediatric thrombosis (PT) represents a rare condition that can manifest from neonatal life to adolescence, encompassing life-threatening complications. Its pathogenesis is attributed to immature hemostasis in conjunction with environmental and genetic factors, predominantly including those resulting in increased levels of plasminogen activator inhibitor 1 (PAI-1), the principal inhibitor of fibrinolysis, subject to upstream regulation by ACE (angiotensin-converting enzyme). Although the implication of microRNAs (miRNAs), epigenetic modulators of gene-expression, is demonstrated in adult-thrombosis, evidence is lacking in the pediatric setting. Here, we investigated the involvement of two miRNA-regulators of PAI-1 in PT, in relation to clinical and genetic parameters that induce PAI-1 fluctuations. Methods: Following bioinformatic target-prediction, miRNA expression was assessed by quantitative real-time PCR, in serum-samples of 19 pediatric patients with thrombosis (1-18 months post-incident), and 19 controls. Patients were genotyped for the PAI-1-4G/5G and ACE-I/D polymorphisms by PCR-based assays. Genotypic and thrombosis-related clinical data were analyzed in relation to miRNA-expression. Results: Two miRNAs (miR-145-5p, miR-34a-5p) were identified to target PAI-1 mRNA, with miR-34a additionally targeting ACE mRNA. The expression of miR-34a was significantly decreased in patients compared to controls (p=0.029), while no difference was observed for miR-145. Within patients, miR-34a demonstrated a peak 1-3 months post-thrombosis and was diminished upon treatment-completion (p=0.031), followed by a slight long-term increase. MiR-34a expression differed significantly by thrombosis site (p=0.019), while a significant synergistic interaction between site and onset-type (provoked/unprovoked) was detected (p=0.016). Finally, an epistatic modification was observed in cerebral cases, since double homozygosity (4G/4G+D/D) led to miR-34a diminishing, with DD carriership reversing the 4G4G-induced upregulation of miR-34a (p=0.006). Conclusions: Our findings suggest that in pediatric thrombosis, downregulation of miR-34a is indicative of impaired fibrinolytic capacity, attributed to deficient regulation of the inhibitory ACE/PAI-1 axis.

Introduction Limited studies have reported data on the real-world clinical use of extended half-life (EHL) IX products in children and adolescents with haemophilia B, also referred to as people with haemophilia B (PWHB). Aim To examine the real-life experience with EHL factor IX products in PWHB regarding the clinical experience with standard half-life products (SHL). Methods A retrospective review of medical records of PWHB who have been prescribed EHL IX factor concentrates was conducted. Results Fourteen male PWHB were enrolled in the study, all with severe bleeding phenotypes being on prophylaxis (1–6 years old: n = 3, 7–12 years old: n = 5 and 13–18 years old: n = 6). Four of them were previously untreated patients; nine out of fourteen children (64%) had severe, four had moderate, and one child had mild haemophilia B. Median length of follow-up was 45 months (range 16–84 months). Children who transitioned from SHL prophylaxis to EHL prophylaxis experienced changes in their treatment outcomes. The median dosing interval increased from 3.5 days to 7 days, mean trough levels rose from 4.3% to 15.3% among children with severe haemophilia B, and the mean annual bleeding rate (ABR) decreased from 1.8 to 1 (p = 0.3, Wilcoxon test). Significant differences were found in EHL vs. SHL use regarding (a) the factor IX consumption for prophylaxis and bleeds (p = 0.046, t-test), with the EHL consumption (45.6 IU/kg/week) being significantly lower than the SHL consumption (70.3 IU/kg/week), and (b) the factor IX consumption only for prophylaxis (p = 0.022, t-test), with the EHL consumption (37.0 IU/kg/week) being significantly lower than the SHL consumption (66.0 IU/kg/week). There was no inhibitor development. Conclusion This study demonstrates the successful use of EHL prophylaxis in PWHB.