Genetic Background of Inherited Factor XIII-A Subunit Deficiency: Review of the Literature and Description of Two New Cases

We read with great interest the paper by Dorgalaleh et al,[1] in this journal, who described inherited factor XIII (FXIII) deficiency and the molecular analysis of this disorder in the Iranian population. Inherited FXIII deficiency is a rare bleeding disorder affecting approximately one person per 1 to 3 million.[2] In areas with an advanced incidence of consanguineous marriages, the prevalence may be higher. The previous authors reported estimated prevalence in the Iranian population as 12-fold higher.[1] An autosomal recessive inheritance pattern is typical; thus, homozygous, or compound heterozygous patients are affected. Heterozygous patients usually do not manifest with bleeding episodes. However, there are reports on heterozygous carriers of FXIII deficiency with prolonged or massive bleeding in stressful situations like minor trauma, pregnancy, or surgery.[3]

For the two new cases we can describe, belonging to a single Slovak family (2 siblings and their parents), inherited FXIII deficiency was investigated as follows.

The 13-month-old girl was first examined at the Department of Hematology and Transfusion Medicine for delayed, prolonged, and recurrent tongue bleeding after trauma caused by a plastic bottle. The tongue wound was sutured and antifibrinolytics were used. In addition, one unit of red blood cells and fresh frozen plasma (FFP) were administered because of posthemorrhagic severe anemia. The family history of bleeding disorders was negative; the child was healthy until the age of 1 year; however, patient bleeding history dated back from her infancy (day 7 after delivery), when she bled significantly from the umbilical stump ([Fig. 1]). To stop the bleeding from umbilical stump one unit of FFP was administered. The coagulation screen (prothrombin time [PT], activated partial thromboplastin time [aPTT], thrombin time [TT], fibrinogen level) and bleeding time were normal. Therefore, clot solubility test with 5 M urea was performed. The clot rapidly dissolved within 2 hours. The chromogenic assay confirmed a severe FXIII deficiency (FXIII activity < 1%). The antigen levels of FXIII-A subunit measured by enzyme-linked immunosorbent assay (ELISA) were markedly decreased (FXIII-A₂B₂ complex < 0.1%, FXIII-A₂ subunit < 0.1%, FXIII-B₂ subunit 66.0%) ([Table 1]). The results of the examinations confirmed a severe deficiency of the FXIII-A subunit. The presence of an FXIII inhibitor was excluded by mixing studies. As mentioned above, at the age of 13 months, the girl had tongue bleeding after plastic bottle injury; in age of 22 months, FFP (10 mL/kg) was administered after head trauma with superficial excision, and in age of 24 months, a plasma-derived FXIII (pdFXIII) concentrate (40 IU/kg) was applied due to the head injury after slipping and falling on the pavement.

Fig. 1 Bleeding episodes.

Table 1 Summary of coagulation examination findings in both cases and their parents

	Girl with FXIII deficiency	Boy with FXIII deficiency	Mother	Father
PT (%) [70.0–115.0][a]	103.1	93	109.0	91.0
PT (INR) [0.80–1.24][a]	1.0	1.04	0.95	1.06
aPTT (s) [27.0–40.0][a]	26.2	21.5	33.9	20.7
aPTT-ratio [0.90–1.30][a]	0.91	0.74	1.16	0.71
Thrombin time (s) [13.0–18.0][a]	14.8	18.7	17.1	14.8
Fibrinogen (g/L) [1.60–4.0][a]	2.37	1.58	2.45	2.93
Clot solubility [< 24 h][a]	2	1	> 48	> 48
FXIII-activity [60–150%][a]	< 1%	< 1%	78.4%	73%
FXIII-A2B2 antigen	< 0.1%	< 0.1%	–	–
FXIII-A2 antigen [75.2–154.8%][a]	< 0.1%	< 0.1%	–	–
FXIII-B2 antigen [75.2–154.8%][a]	66.0%	80.1%	–	–
FV Leiden	Heterozygous	Wild-type	Heterozygous	Wild-type
p.Gly210Arg	Heterozygous	Heterozygous	Wild-type	Heterozygous
p.Tyr482Asnfs*13	Heterozygous	Heterozygous	Heterozygous	Wild-type

Abbreviations: aPTT, activated partial thromboplastin time; FXIII, factor XIII; INR, international normalized ratio; PT, prothrombin time.

^a Normal range.

Furthermore, at the age of 30 months, a brother to our patient was delivered by her mother. Due to the high risk of giving birth to a child with FXIII deficiency, the newborn was thoroughly clinically examined; there was no skin and mucosal bleeding and no intracranial hemorrhage. The laboratory results of the screening coagulation tests were within normal limits for patient age; nevertheless, the clot solubility test was extremely shortened (1 hour). The chromogenic assay revealed a reduced FXIII activity (< 0.1%) and confirmed FXIII deficiency. The levels of FXIII-A and FXIII-B subunits (FXIII-A₂B₂ complex < 0.1%, FXIII-A₂ subunit < 0.1%, FXIII-B₂ subunit 80.1%) were quantitatively determined by ELISA ([Table 1]). The results of the examinations confirmed a severe deficiency of the FXIII-A subunit. Due to the severity of the deficit, the boy was hospitalized for observation. In personal history of the patient at 7 days of age, umbilical cord hemorrhage started, which stopped completely after administration of FFP (10 mL/kg) ([Fig. 1]). Later, the patient had hematoma formation in the lower limbs after minimal walking trauma; at 18 months of age, the hemarthroses of the metatarsophalangeal joint of the toe in the right lower limb developed which was presented with pain, swelling, and reduced joint mobility. This was verified by ultrasound examination and treated with a pdFXIII concentrate (40 IU/kg). After administration, the patient's clinical condition was immediately improved. At the age of 19 months, due to a nose injury without fracture but with a nasal root hematoma and major epistaxis developed, pdFXIII concentrate was also administered with excellent effect.

All bleeding episodes of both siblings are summarized in [Fig. 1].

In general, delayed bleeding from the umbilical cord stump occurs in 80 to 90% of newborns with severe FXIII deficiency and is considered a diagnostic feature of the disorder.[4] Intracranial bleeding is more frequent in FXIII deficiency than in other inherited coagulation disorders, with incidence as high as 30%. Brain bleeds may occur with or without trauma, and often at an early age. They are the main cause of death for patients with severe FXIII deficiency that do not receive regular prophylactic replacement therapy. Ecchymoses, superficial bruising (60%), gingival bleeding, epistaxis, gastrointestinal bleeding, hematuria, menorrhagia, soft tissue hematomas, muscle bleeding, and prolonged bleeding with trauma are common, and recurrent soft tissue bleeding may lead to formation of hemorrhagic cysts (pseudotumors). Hemarthroses are less frequent than in FVIII or FIX deficiency.[4] Bleeding that is delayed 12 to 36 hours postinjury is characteristic for FXIII deficiency, although hemorrhage can be immediate in some cases. Bleeding at the time of invasive procedures may be minimal, but delayed hemorrhage often occurs.[5] Delayed wound healing has been observed in up to 17% of deficient patients, possibly related to a defect in angiogenesis, cell growth, and smooth muscle cell migration.[2] Recurrent spontaneous abortions occur with most pregnancies in untreated FXIII-deficient women, possibly due to abnormal formation of the cytotrophoblastic shell and poor attachment of the placenta to the uterus; bleeding associated with delivery is also observed. These problems are recognized complications in patients with factor levels less than 5% of normal, while in pregnant women the FXIII level needs to be higher than 10% to reliably prevent pregnancy loss.[6] Universally, FXIII-deficient patients have variable bleeding tendency, from mild to severe. Bleeding severity depends on the level of FXIII activity in the plasma; however, there is not an exact match between bleeding symptoms and factor level (and certainly less robust than in hemophilia A and B). Furthermore, the laboratory tests used to measure FXIII levels are not very exact at low levels (< 10% activity). To avoid the overestimation of FXIII activity the subtraction of a plasma blank, in which FXIII is inhibited by 1 mM iodoacetamide, is recommended. A reagent for plasma blank measurement is included in the TECHNOCHROM kit.[7] Patients with very low levels (< 1–5%) may experience severe spontaneous, even life-threatening bleeding. Others with congenital FXIII deficiency (but ≥ 30%) may have no symptoms at all or only bleeding during trauma, surgical procedure, or problems with pregnancy.[6] The diagnosis of FXIII deficiency should be based on laboratory tests. The usual screening tests for coagulopathies (PT, aPTT, and TT) do not show prolongation in cases of FXIII deficiency. Therefore, if clinical symptoms indicate a bleeding diathesis, full evaluation of the clotting system should include a test that detects FXIII deficiency according to the International Society of Thrombosis and Haemostasis algorithm for proper diagnosis and classification of FXIII deficiency.[4] Treatment of patients with congenital FXIII deficiency consists of replacement therapy by plasma-derived purified and pasteurized concentrate of FXIII (pdFXIII) or recombinant FXIII concentrate. In patients with severe FXIII deficiency and those with a history of intracranial hemorrhage, there is an indication for prophylactic administration of FXIII concentrate. Prophylaxis is highly efficient because of the long half-life of FXIII from 10 to 14 days. When prophylactic treatment is available, the prognosis is very good due to good response to treatment, although there is life-long risk of bleeding.[8] The initial dose of FXIII concentrate is 40 IU/kg body weight and routine prophylaxis dosing should be guided by the most recent trough FXIII activity level, with dosing every 28 days (4 weeks) to maintain a trough FXIII activity level of approximately 5 to 20%. To prevent miscarriage there is needed to maintain FXIII levels > 10% in early gestation, and > 30% to prevent significant bleeds at the time of delivery. Although FXIII concentrate is preferred for prophylaxis or treatment of acute bleeding, if it is not available, FFP or cryoprecipitate can be used.[9]

Due to the presence of FXIII deficiency in both children, the determination of the FXIII level in both parents and genetic examination were necessary. The mother did not have any significant bleeding symptoms or spontaneous abortions. The father also did not have history of spontaneous bleeding. The results of laboratory tests in both parents confirmed normal FXIII level (blood clot solubility test > 48 hours, FXIII activity was normal) ([Table 1]). Genetic examination of all four family members had shown the presence of two mutations in F13-A1 subunit gene; the mother expresses a 4 base pair (bp) deletion (p.Tyr482Asnfs*13) in exon 11 in heterozygous form ([Fig. 2A]) and the father expresses a missense mutation p.Gly210Arg in heterozygous form which is located in the catalytic core, in exon 5, F13-A1 subunit gene ([Fig. 2B]). The first potentially causal mutation, originated from the mother, is 4 bp deletion in exon 11 of F13-A1 ([Fig. 2A]). According to online available mutation tester (http://www.mutationtaster.org/), this frameshift mutation, p.Tyr482Asnfs*13, leads to a premature termination of protein synthesis 13 amino acids behind the deletion, at amino acid position 495. The only report in the literature of this deletion is from Ivaškevičius et al.[10] Here, messenger ribonucleic acid studies or Western blotting methods may confirm presence of a truncated protein as a result of the premature termination; however, pathogenicity of this deletion is very likely. The second identified missense mutation, originated from the father, was p.Gly210Arg ([Fig. 2B]). Protein modeling of the Gly210Arg presented by Vysokovsky et al[11] predicted that mutant protein Arg210 significantly disrupts the folding of the catalytic core domain leading to misfolding and an instability of the protein. Mutational spectrum of FXIII-A deficiency is heterogeneous. From more than 150 unique F13-A1 mutations the most common are missense variations which comprise about a half of all identified mutations. Deletions and insertions are very frequent as well (missense ∼50%, deletion/insertions ∼24%, splice site ∼14%, and nonsense mutations ∼12%). Homozygous mutations are typical but also compound heterozygosity is common.[12] High degree of heterogeneity in disease-causing mechanisms has been described in inherited FXIII deficiency. Mutations are transmitted throughout the F13-A1 gene, the majority between exons 3 and 14. Thus, mutations affect different areas of the protein and lead to wide range of clinical manifestations in FXIII deficiency patients. These mutations may cause instability of heterotetramer and then lead to quantitative defects or disrupt functional activity of the protein by impairment of its catalytical activity, binding to fibrinogen or activation by thrombin or calcium ions.[13]

Fig. 2 (A) Sequence analysis identifying a heterozygous 4-bp deletion (-/TTAC) at position 1443–1446 in F13-A1 subunit. (B) Sequence analysis identifying a heterozygous C→T substitution at nucleotide 631 (arrow) in F13-A1 subunit.

Our children inherited both these mutations from their parents. So, the combination represents a unique genotype and the clinical phenotype is similar to the homozygous form of FXIII deficiency. Due to a proven FXIII deficiency (FXIII-A subunit) and bleeding phenotype, both siblings are now on prophylactic treatment with pdFXIII concentrate. Due to autosomal recessive inheritance manner of inherited FXIII deficiency, heterozygous parents are without bleeding complications. In the siblings, we propose an accumulative effect of both p.Gly210Arg and p.Tyr482Asnfs*13 variants in the catalytic core of F13-A1. Our proposal is supported by extremely low levels of FXIII-A₂ antigen while FXIII-B₂ antigen is normal. No neutralizing inhibitor was present in either of siblings.

Publikationsverlauf

Artikel online veröffentlicht:
10. Juni 2021

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