Behnaz Pezeshkpoor

Fidanacogene elaparvovec is an adeno-associated virus (AAV)-based gene therapy that enables endogenous factor IX (FIX) expression in hemophilia B, potentially eliminating the need for prophylactic FIX replacement. Post-treatment monitoring focuses on FIX durability, hepatic safety, and immune-mediated loss of expression. A 40-year-old man with severe hemophilia B received a single intravenous dose of fidanacogene elaparvovec in the phase 3 BENEGENE-2 trial (NCT03861273). FIX activity was assessed by one-stage and chromogenic assays. Liver enzymes, clinical parameters, and adverse events were monitored. Prednisolone was initiated for liver enzyme elevation and later switched to budesonide in response to declining FIX levels. Follow-up continued for 4 years. FIX activity peaked at week 6 (~30 IU/dL) and remained stable until week 16. Moderate ALT elevation (peak ~70 U/L) responded to prednisolone. Between weeks 22–28, FIX levels declined without ALT elevation. Budesonide (9 mg/day) was started at week 25 for 3 months and gradually tapered, stabilizing FIX activity at 10-20 IU/dL. This level has been maintained for 4 years without bleeding episodes or FIX replacement. Fidanacogene elaparvovec provided sustained, clinically meaningful FIX expression. Budesonide may offer an effective hepatocyte-targeted alternative to systemic corticosteroids while supporting long-term transgene expression.

Venous thromboembolism (VTE) is multifactorial, and established hereditary risk factors explain only part of heritable risk. The protein C (PC) pathway is central to anticoagulant control, and common variants in thrombomodulin and endothelial PC receptor genes (THBD, PROCR) have been proposed as modulators. In 73 participants, we used standardized in vivo coagulation activation with recombinant activated factor VII (15 μg/kg) and measured thrombin markers and activated PC (APC) over 8 hours. Endothelial colony-forming cell–based ex vivo experiments were performed in 43 participants. In vivo, the ratio of APC area under the curve (AUC) to thrombin-antithrombin complex (TAT) AUC, which reflects the endogenous anticoagulant response relative to thrombin generation, provided the best model fit (adjusted R2 = 0.345). The APC response was lower in individuals with previous VTE (median, 0.13 vs 0.26) and PROCR 655A>G carriers (0.11 vs 0.26), but higher in factor V Leiden (FVL) carriers (0.32 vs 0.14) and THBD 1418C>T carriers (0.38 vs 0.13). The THBD 1418C>T effect was driven by reduced TAT AUC (30.6 vs 82.7 pmol × h/L), whereas the PROCR 655A>G effect reflected a lower APC AUC (8.6 vs 10.7 pmol × h/L). Ex vivo, the APC AUC/thrombin AUC ratio was lower with previous VTE and PROCR 655A>G, higher with FVL, and not associated with THBD 1418C>T. No in vivo or ex vivo association was observed for PROCR 4678C>G. This study provides in vivo evidence that common THBD and PROCR variants modulate PC pathway function, establishing the APC response as a sensitive end point for subtle genetic effects beyond FVL.

Mild bleeding disorders (MBDs) comprise a heterogeneous group of inherited conditions characterized by clinically relevant bleeding symptoms despite largely normal or inconclusive results in routine hemostatic testing. These disorders account for a substantial proportion of referrals to specialized hemostasis clinics and include von Willebrand disease (VWD), inherited platelet function disorders, and mild coagulation factor deficiencies. Despite systematic diagnostic algorithms, many patients with MBDs remain without a definitive diagnosis and are classified as having bleeding disorder of unknown cause (BDUC), complicating clinical management and counseling. Conventional diagnostic approaches rely on structured bleeding assessment tools, detailed family history, and stepwise laboratory testing. Biological variability, assay limitations, and phenotypic overlap often result in inconclusive findings. Recent advances in genetic analysis have begun to transform this diagnostic landscape. Targeted next-generation sequencing panels, whole-exome sequencing (WES), and whole-genome sequencing (WGS) enable identification of pathogenic variants across numerous hemostasis-related genes. In MBDs, genetic testing is valuable for refining diagnoses in qualitative VWD, confirming inherited platelet disorders, and identifying rare mild coagulopathies. In contrast, its diagnostic yield in type 1 and low von Willebrand factor (VWF) is modest, reflecting complex genetic architecture, modifier effects, and incomplete penetrance. In BDUC, genetic testing has revealed monogenic causes in some patients and multifactorial contributions in others. Genetic testing should therefore be regarded as a complementary tool rather than a replacing conventional diagnostics. Integrated with clinical and laboratory findings and supported by expert variant interpretation, it can reduce diagnostic uncertainty and improve disease classification in patients with MBDs.

Background Despite major advances in platelet function testing and molecular genetic diagnostics, the evaluation of inherited thrombocytopenia and thrombocytopathy remains challenging. Overlapping clinical phenotypes, variants of uncertain significance (VUS), and structural variants detectable only by complementary copy-number variant (CNV) analysis or array comparative genomic hybridization (CGH) frequently impede diagnostic classification. Methods We report seven pediatric patients from five unrelated families, structured into two diagnostic parts. Part 1 addresses inherited platelet disorders evaluated using a standardized diagnostic algorithm including complete blood count, light transmission aggregometry (LTA), flow cytometry (FC)-based platelet phenotyping, and targeted next-generation sequencing (NGS) including CNV analysis. Part 2 focuses on disorders involving the von Willebrand factor (VWF) axis, assessed by the VWF antigen (VWF:Ag), VWF collagen binding activity (VWF:CBA), VWF multimer analysis, ADAMTS13 activity and antigen, LTA, and molecular genetic testing. Results Three diagnostically relevant constellations were identified. In Part 1, one patient with a classical Hermansky–Pudlak syndrome phenotype required CNV analysis to detect compound heterozygous pathogenic variants. Two siblings fulfilled diagnostic criteria for Glanzmann thrombasthenia based on LTA, FC, and genetic testing. A third patient showed a Glanzmann-like phenotype in LTA and FC but carried a homozygous VUS in ITGA2B combined with a heterozygous ANKRD26 nonsense mutation. In Part 2, three additional patients demonstrated rare VWF-mediated mechanisms of thrombocytopenia due to ADAMTS13 deficiency or von Willebrand disease type 2B. Conclusions This case series highlights the diagnostic complexity of pediatric platelet disorders and emphasizes the importance of a multimodal approach integrating functional platelet assays, NGS including CNV analysis, and careful clinical correlation.

Thrombin generation assays (TGA) provide a dynamic and integrative assessment of thrombin generation in clotting plasma ex vivo. The method is characterized by triggering coagulation, typically via the extrinsic pathway, and continuously measuring thrombin activity using a fluorogenic peptide substrate to derive key parameters such as peak thrombin and the endogenous thrombin potential. Several assay platforms are currently available, with the original Calibrated Automated Thrombogram (CAT) still being widely used in clinical and research settings, not least due to its flexibility and ability to analyze both platelet-poor as well as platelet-rich plasma. Thrombin generation assays have the potential to support the evaluation and monitoring of treatment of bleeding disorders, including hemophilia A and B and other inherited or acquired coagulation factor deficiencies. They may contribute to risk stratification in thrombotic disorders, and support the assessment of anticoagulant therapies. However, besides ongoing developments and optimization of trigger reagents, inter-assay variability and susceptibility to pre- and analytical variables challenge assay standardization and inter-laboratory comparability. Continued refinement, harmonization, and prospective clinical validation will be essential to unlock the full diagnostic potential of TGA.

Efanesoctocog alfa (efa) is a recombinant coagulation factor VIII (FVIII) concentrate, engineered for improved extended half-life in hemophilia A treatment. Its design results in discrepancies in FVIII diagnostic tests, as has so far been demonstrated using spiked sample material (efa added to FVIII-deficient plasma). The aim of the present study was to evaluate FVIII assay discrepancies in post-infusion samples obtained from patients treated with efa. This retrospective analysis included 43 male patients on efa prophylaxis (26 on once weekly and 17 on twice weekly treatment scheme) summoned for determination of incremental recoveries. FVIII activity was measured at trough (3.5 or 7 days post-infusion) and peak levels (30 minutes post-infusion) using three diagnostic tests: two one-stage clotting assays (OSCAs) based on Actin FSL (AFSL) or Actin FS (AFS), and a chromogenic substrate assay (FVIII CSA). Incremental recoveries as determined by the recommended AFSL-based OSCA were found to be comparable between patient groups. At peak levels (64 to 214 IU/dL), comparable overestimation (1.9-fold) of plasma efa activity relative to Actin FSL-based OSCA was observed for both, the AFS-based OSCA and the FVIII CSA. In contrast, at trough levels (5 to 64 IU/dL), rate of overestimation relative to the AFSL-based OSCA results was found to be lower for the FVIII CSA (1.3-fold) when compared with the AFS-based OSCA (1.9-fold). Further analysis demonstrated different behavior of spiked and post-infusion samples within the FVIII CSA. Future studies will reveal underlying mechanisms and assess if drug-specific calibration will sufficiently correct for this phenomenon.

Factor XI (FXI) deficiency is an autosomal bleeding disorder characterized by low FXI levels, resulting in bleeding after trauma or surgery. Genetic variants affecting FXI structure and function often result in bleeding diatheses.This study aimed to estimate the variant detection rate (VDR), and assess its correlation with FXI activity (FXI:C) in a large cohort of FXI-deficient patients.Genetic defects in the F11 gene were analyzed in 316 index patients (IPs) using Sanger or next-generation sequencing. Multiplex ligation-dependent probe amplification or copy number variation analysis was used to detect duplications and deletions.Genetic defects were identified in 249 IPs (VDR of 79%). A strong negative correlation (Pearson coefficient: −0.891) was found between FXI:C levels and VDRs: higher FXI:C levels corresponded to a lower likelihood of detecting genetic alterations, with a significant decline in VDR beyond 60 IU/dL. A total of 286 genetic variants were identified in F11 gene: 56% missense, 24% nonsense, 11% small deletions/insertions, and 6% splice-site variants. Large deletions were rare (3%). A total of 48 novel variants were detected. Ashkenazi Jewish founder variants were the most frequent (14.3%). Variants p.Gln134Ter, p.Ile215_Asp216del, and p.Glu315Lys (27% of cases) were recurrent. In four cases, large deletions extended beyond the F11 gene and included the neighboring KLKB1 gene, encoding prekallikrein.This study demonstrated a significant negative correlation between FXI:C levels and VDRs, underscoring the importance of genetic testing. Findings included combined deficiencies in FXI and prekallikrein due to large deletions affecting both F11 and KLKB genes.

Emicizumab is a bispecific monoclonal antibody that mimics the cofactor function of activated factor VIII (FVIIIa). It is approved for routine prophylaxis in patients with severe or moderate congenital hemophilia A (HA), both with and without FVIII inhibitors, and is increasingly used as a first-line treatment in acquired HA (AHA). Owing to its predictable pharmacokinetic profile, emicizumab monitoring is generally limited to cases with suspected reduced efficacy, such as due to poor adherence or the development of anti-drug antibodies (ADAs). However, emicizumab interferes with standard clotting assays, particularly by shortening activated partial thromboplastin times (APTT). To address this, modified FVIII one-stage clotting assays (mOSA), which use higher sample pre-dilution and emicizumab-specific calibration, are commonly employed to estimate plasma levels, although other assay formats like emicizumab-calibrated chromogenic substrate assays based on human factors or liquid chromatography tandem mass spectrometry are also available. Additionally, global assays such as in vitro thrombin generation testing are being explored to better reflect clinical hemostatic efficacy. This review summarizes current knowledge on assay interferences caused by emicizumab, challenges in functional measurement of plasma levels, and strategies to ensure reliable laboratory assessment. We also discuss the relevance and methods for ADA detection and provide an overview of current and emerging strategies for thrombin generation measurement as a global indicator of treatment effectiveness.

Inherited platelet disorders (IPDs) are rare bleeding disorders characterized by impaired platelet function and/or reduced blood platelet count. Their diagnosis typically relies on complex laboratory methods, including flow cytometry, aggregometry, and molecular genetic analysis. In recent years, immunofluorescence microscopy has been established as an alternative diagnostic method for IPDs. Background/Objectives: This study aims to validate a quantitative approach enhancing reproducibility through automated image analysis for diagnosing IPDs using immunofluorescence microscopy, with Bernard–Soulier Syndrome (BSS) and Glanzmann thrombasthenia (GT) as model IPDs. Methods: Native blood smears from patients with suspected BSS or GT were stained using a standardized immunofluorescence protocol targeting platelet surface glycoproteins, granules, and cytoskeletal components. The slides were analyzed using an automated fluorescence microscope, and a rule-based subpopulation analysis was implemented to quantify fluorescence signals. The results were compared to those of a healthy control group, as well as data from flow cytometry and molecular genetic testing. Results: The automated analysis successfully differentiated BSS and GT patients from healthy controls based on distinct fluorescence signal patterns. In BSS samples, CD42b (GPIbα) expression was absent or severely reduced, while GT samples showed a deficiency of CD41/CD61 (GPIIb/IIIa). The platelet size distribution confirmed macrothrombocytopenia in BSS patients. Flow cytometry and molecular genetic testing corroborated these findings, supporting the diagnostic reliability of the automated immunofluorescence microscopy approach. Conclusions: This proof-of-principle study demonstrates that automated quantitative immunofluorescence microscopy is a viable alternative for diagnosing IPDs, offering a standardized, objective, and efficient method, particularly in settings where flow cytometry is not feasible.