Severe congenital factor XIII deficiency caused by novel W187X and G273V mutations in theF13Agene; diagnosis and classification according to the ISTH/SSC guidelines

Novel Insights into Heterozygous Factor XIII Deficiency

The prevalence and clinical significance of heterozygous factor XIII (FXIII) deficiency has long been debated, with controversial reports emerging since 1988. In the absence of large epidemiologic studies, but based on a few studies, a prevalence of 1 per 1,000 to 5,000 is estimated. In southeastern Iran, a hotspot area for the disorder, a study of more than 3,500 individuals found an incidence of 3.5%. Between 1988 and 2023, a total of 308 individuals were found with heterozygous FXIII deficiency, of which molecular, laboratory, and clinical presentations were available for 207 individuals. A total of 49 variants were found in the F13A gene, most of which were missense (61.2%), followed by nonsense (12.2%) and small deletions (12.2%), most occurring in the catalytic domain (52.1%) of the FXIII-A protein and most frequently in exon 4 (17%) of the F13A gene. This pattern is relatively similar to homozygous (severe) FXIII deficiency. In general, heterozygous FXIII deficiency is an asymptomatic condition without spontaneous bleeding tendency, but it can lead to hemorrhagic complications in hemostatic challenges such as trauma, surgery, childbirth, and pregnancy. Postoperative bleeding, postpartum hemorrhage, and miscarriage are the most common clinical manifestations, while impaired wound healing has been rarely reported. Although some of these clinical manifestations can also be observed in the general population, they are more common in heterozygous FXIII deficiency. While studies of heterozygous FXIII deficiency conducted over the past 35 years have shed light on some of the ambiguities of this condition, further studies on a large number of heterozygotes are needed to answer the major questions related to heterozygous FXIII deficiency.

Genetic landscape in coagulation factor XIII associated defects – Advances in coagulation and beyond

Coagulation factor XIII (FXIII) acts as a fine fulcrum in blood plasma that maintains the balance between bleeding and thrombosis by covalently crosslinking the pre-formed fibrin clot into an insoluble one that is resistant to premature fibrinolysis. In plasma, FXIII circulates as a pro-transglutaminase complex composed of the dimeric catalytic FXIII-A encoded by the F13A1 gene and dimeric carrier/regulatory FXIII-B subunits encoded by the F13B gene. Growing evidence accumulated over decades of exhaustive research shows that not only does FXIII play major roles in both pathological extremes of hemostasis i.e. bleeding and thrombosis, but that it is, in fact, a pleiotropic protein with physiological roles beyond coagulation. However, the current FXIII genetic-epidemiological literature is overwhelmingly derived from the bleeding pathology associated with its deficiency. In this article we review the current clinical, functional, and molecular understanding of this fascinating multifaceted protein, especially putting into the same perspective its genetic landscape.

Plasma proteomics associated with autoimmune coagulation factor deficiencies reveals the link between inflammation and autoantibody development

Autoimmune coagulation factor deficiency (AiCFD) is characterized by sudden excessive bleeding due to autoantibodies against coagulation factors. This occurs primarily in elderly patients with no family history or previous clotting issues. However, the detailed mechanisms underlying autoantibody development are not well understood. Here, we evaluated the plasma proteome in patients with AiCFD and compared it with that of 22 healthy controls and 17 patients with non-autoimmune acquired factor XIII deficiency (acF13D). We identified eighteen proteins whose plasma levels were higher in AiCFD than in either healthy controls or patients with acF13D. Most of these proteins were found to be acute-phase reactants or immunoglobulins. Patients with acF13D had lower levels of nine of these proteins and higher levels of the remaining nine compared to healthy controls. However, in all cases, these protein levels were much higher in patients with AiCFD than in those with acF13D. These results suggest that an inflammatory response independent of the acute inflammation caused by bleeding can occur, which may lead to the development of AiCFD. Therefore, we believe that severe and/or chronic inflammation, probably due to an underlying disease or aging, is the most important factor in autoantibody development.

Rapid immunochromatographic test for detection of anti-factor XIII A subunit antibodies can diagnose 90 % of cases with autoimmune haemorrhaphilia XIII/13

Autoimmune haemorrhaphilia XIII/13 (AH13) is an acquired lifethreatening bleeding disorder due to anti-factor XIII (FXIII) autoantibodies (auto-Abs). AH13 patients may die of haemorrhage without correct diagnosis and proper treatment because of lack of awareness and the absence of rapid easy-to-use tests specific for this disease. Currently, the definitive diagnosis is established by cumbersome and time-consuming laboratory tests such as dot-blot assays and enzymelinked immunosorbent assays (ELISA), and therefore these tests are generally not carried out. To save AH13 patients’ lives, there is an urgent necessity for developing a rapid test for FXIII auto-Abs. We first generated and characterised mouse monoclonal antibodies (mAb) against human FXIII A subunit (FXIII-A), and then developed a rapid immunochromatographic test (ICT) for detection of anti-FXIII-A auto- Abs using one mAb with a dissociation constant of 9.3 × 10-11 M. The auto-Ab-FXIII-A complex was captured by the mAb on a nitrocellulose membrane and visualised by Au-conjugated anti-human IgG Ab. Mixing with healthy control plasma improved the detection of auto-Abs in patients having extremely low levels of FXIII-A. The specificity and sensitivity of the ICT were 87% and 94%, respectively. We also detected auto-Abs against activated FXIII (FXIIIa) in three patients by pre-converting FXIII to FXIIIa by thrombin treatment. ICT values were significantly inversely correlated with FXIII activity levels, indicating an association between the quantity of anti-FXIII autoantibodies and AH13. This reliable rapid ICT assay can be applied to a point-of-care test to detect anti-FXIII-A auto-Abs, and will contribute to early diagnosis and treatment of AH13.

Blood coagulation factor XIII and factor XIII deficiency

Factor XIII (FXIII) is a multifunctional pro-γ-transglutaminase that, in addition to its well-known role in hemostasis, has a crucial role in angiogenesis, maintenance of pregnancy, wound healing, bone metabolism, and even cardio protection. FXIII deficiency (FXIIID) is a rare bleeding disorder (RBD) with an estimated incidence of one per two million that is accompanied by life-threatening bleeding such as umbilical cord bleeding, recurrent spontaneous miscarriage, and intracranial hemorrhage (ICH). Today, the disease is successfully managed by FXIII concentrate and recombinant FXIII for prophylaxis, management of minor and major bleeding, treatment of ICH, and successful delivery in women with recurrent pregnancy loss. Molecular analysis of patients with FXIIID revealed a wide spectrum of mutations, most frequently missense mutations in the FXIII-A subunit, with a few recurrent mutations observed worldwide. In vitro expression studies revealed that most of the missense mutations cause intracellular instability of the FXIII protein and, subsequently, FXIIID.