The impact of hemophilia in affected women and girls is insufficiently recognized, resulting in suboptimal evaluation of bleeding symptoms, delay in diagnosis, and missed management opportunities. The aim of this collaborative International Society on Thrombosis and Haemostasis (ISTH) Scientific Subcommittee on Pediatric and Neonatal Thrombosis and Haemostasis, Factor (F)VIII, FIX, and Rare Coagulation Disorders, and Women's Health Issues in Thrombosis and Haemostasis project is to provide guidance recommendations regarding screening and diagnosis of hemophilia carriers (HC)/women and girls with hemophilia (WGwH) in addition to the previously published revised nomenclature by the Scientific Subcommittee of the ISTH. We provide several guidance recommendations regarding the nomenclature, utilization of the ISTH-Bleeding Assessment Tool as a tool to quantify bleeding phenotype, FVIII/FIX assays for testing, assay discrepancy, genetic testing, and testing during pregnancy and postpartum, to help guide hemophilia providers to streamline the screening and diagnosis of HC/WGwH in a uniform manner. We hope that once the screening and diagnosis of HC/WGwH become a uniform standard practice globally, this will pave the way for global harmonization of terminologies and improved management, bringing gender equity in hemophilia care a step forward.

The advent of nonreplacement therapies, such as emicizumab, has contributed to a marked reduction of the observed incidence of factor (F)VIII inhibitors in patients with severe hemophilia A. However, it should be clarified whether this decline reflects delayed FVIII exposure or a true reduction in immunogenicity. Thus, understanding the mechanisms driving anti-FVIII inhibitor formation, particularly during early exposure in previously untreated patients, remains a key objective in hemophilia care and is a still unmet need. Ten years ago, the Survey of Inhibitors in Plasma-Product Exposed Toddlers (SIPPET) trial marked a turning point by providing the first randomized evidence that plasma-derived FVIII products containing von Willebrand factor are associated with a lower inhibitor incidence than recombinant FVIII. These findings influenced international guidelines, prompted changes in clinical practice, and highlighted the importance of the choice of the product type during the early, immunologically vulnerable period of exposure to FVIII. Post-SIPPET studies expanded this evidence base, offering deeper insights into the immunogenicity of FVIII products and offering mechanistic insights into the influence on inhibitor development of gene mutations, nonneutralizing antibodies, immunoglobulin G subclass responses, epitope specificity, and epigenetic modulation. The legacy of SIPPET is not only in its immediate clinical impact but also in its catalyzing role for a broader, multidisciplinary effort to understand inhibitor occurrence in severe hemophilia A.

Severe hemophilia A is a bleeding condition caused by a deficiency in clotting factor VIII (FVIII ≤1 IU/dL) that results in spontaneous and excessive posttraumatic bleeding. The current standard of care is prophylaxis with exogenous FVIII or bispecific antibodies that mimic FVIII function. Valoctocogene roxaparvovec is a gene therapy approved for adults with severe hemophilia A that enables endogenous FVIII production to protect against bleeding. As a newer treatment modality, workflows for gene therapy administration and postinfusion care are still unfamiliar to many health care professionals and may be perceived as implementation barriers. We are 10 hemophilia gene therapy providers across the United States, Italy, and Germany sharing our experiences of administering valoctocogene roxaparvovec in clinical practice to >25 patients with severe hemophilia A. In this study, we provide our insights into patient preparation, establishment of treatment centers and multidisciplinary teams, postinfusion management, and patient follow-up to facilitate open communication and collaboration among the treatment community.

The identification of biomarkers of chronic Graft-versus-Host Disease (cGvHD) remains an unmet clinical need. Elevated von Willebrand factor (VWF) and factor VIII (FVIII) reflect inflammation and endothelial activation and might be interesting candidates for biomarkers of cGvHD. This prospective study evaluated 83 cGvHD patients and 39 allogeneic hematopoietic stem cell transplants recipients without cGvHD. VWF antigen (VWF:Ag), VWF activity (VWF:Ac), and FVIII activity were significantly elevated in cGvHD patients (p < 0.001), with the highest levels observed in active disease. Higher VWF:Ag and VWF:Ac were associated with liver and oral cGvHD. In multivariate analysis, lower albumin was the strongest predictor of both higher VWF:Ag (R[2] = 0.576) and higher VWF:Ac (R[2] = 0.540), followed by older age, higher LDH, and number of affected organs. For higher FVIII, systemic immunosuppressive therapy emerged as the main predictor (R[2] = 0.247). Longitudinal analysis showed declining levels of these factors with cGvHD remission and persistent elevation in active disease. ROC analysis demonstrated diagnostic potential for early cGvHD of VWF:Ag >246.3% (AUC = 0.733) and VWF:Ac >271.4% (AUC = 0.728). These results show the potential of VWF and FVIII as novel biomarkers for diagnosis and disease activity in cGvHD. Additional validation in independent cohorts is warranted.

NKAP (NF-kappa-B-activating protein) is a ubiquitously expressed nuclear protein involved in multiple biological processes. Males with missense NKAP mutations have been reported to present with marfanoid features and behavioral and musculoskeletal abnormalities. We have previously reported that a disruptive NKAP mutation resulted in extremely skewed X chromosome inactivation (XCI), leading to phenotypic manifestation of hemophilia A (HA) in a HA carrier. In this study, with the aim of exploring the phenotypic manifestations of deleterious NKAP mutations in males, as well as their involvement in the mechanism of XCI regulation in females, we generated NKAP mutant mice using CRISPR/Cas9 technology. Gait analysis studies conducted in male mice hemizygous for mutant NKAP by the CatWalk XT system revealed significant alterations in gait parameters, consistent with hypotonia reported in human mutant NKAP patients. By breeding mutant NKAP mice with HA mice, we generated a double heterozygous mutant NKAP/HA mouse model, i.e., female mice carrying mutant NKAP with a WT F8 copy on one X chromosome, and WT NKAP with a mutant F8 copy on the other X chromosome. XCI pattern analysis using methylation-sensitive restriction enzymes demonstrated that mutant NKAP/HA females exhibited significant XCI skewing of the X chromosome bearing the mutant NKAP copy. Furthermore, these females exhibited significantly reduced F8 mRNA levels and FVIII (factor VIII) antigen levels, as demonstrated by quantitative RT-PCR and ELISA, respectively. Murine embryonic fibroblasts (MEFs) derived from a hemizygous mutant NKAP embryo exhibited markedly reduced proliferation rate and increased senescence compared to WT NKAP MEFs, suggesting that XCI skewing induced by mutant NKAP results from secondary selection against cells with an active X chromosome bearing the mutant NKAP copy.