The spectrum of factor XI deficiency in Italy

Hereditary coagulation factor XI deficiency: a rare or neglected disease? Results from a retrospective, single-centre cohort in northern Italy

To examine real-life clinical data regarding hereditary factor XI (FXI) deficiency from a secondary care centre. Retrospective review of clinical records for every FXI:C 0.7 IU/ml or less reported from 2012 to 2020. Seventy-nine patients were included. Six (7.6%) had a severe deficiency (FXI:C <0.2 IU/ml). Only 55 (69.6%) patients were referred to the Haemostasis Centre. Among them, six (15%) were subsequently not identified at increased haemorrhagic risk before a surgical/obstetrical procedure. Thirty-three (41.8%) experienced at least one bleeding event, minor (25 patients) and/or major (16 patients). Minor bleedings were predominantly spontaneous and more frequent in women, major events were mainly provoked. No correlation was found between FXI:C and risk of bleeding ( P  = 0.9153). Lower FXI:C, but not a positive bleeding history, was related with higher likelihood of being referred to the Haemostasis Centre ( P  = 0.0333). Hereditary FXI deficiency prevalence is likely underestimated, real-life clinical practices outside reference centres could be suboptimal.

Molecular basis of rare congenital bleeding disorders

Rare bleeding disorders (RBDs), including factor (F) I, FII, FV, FVII, combined FV and FVIII (CF5F8), FXI, FXIII and vitamin-K dependent coagulation factors (VKCF) deficiencies, are a heterogeneous group of hemorrhagic disorder with a variable bleeding tendency. RBDs are due to mutation in underlying coagulation factors genes, except for CF5F8 and VKCF deficiencies. FVII deficiency is the most common RBD with >330 variants in the F7 gene, while only 63 variants have been identified in the F2 gene. Most detected variants in the affected genes are missense (>50% of all RBDs), while large deletions are the rarest, having been reported in FVII, FX, FXI and FXIII deficiencies. Most were located in the catalytic and activated domains of FXI, FX, FXIII and prothrombin deficiencies. Understanding the proper molecular basis of RBDs not only can help achieve a timely and cost-effective diagnosis, but also can help to phenotype properties of the disorders.

Factor XI deficiency: About 20 cases and literature review

INTRODUCTION

Factor XI deficiency is a rare coagulation disorder with variable bleeding manifestations.

AIM

To evaluate the correlation between the degree of factorXI deficiency and the clinical expression of the disease.

METHODS

Retrospective study, spanning 10 years from January 1, 2010 to December 31, 2019, concerning patients followed at the Hemophilia Center at Aziza Othmana Hospital in Tunis. The data were collected from the medical records. The determination of PT, APTT, fibrinogen level and coagulation factors are performed by coagulometric technique on STA® compact / ACL TOP®. FactorXI deficiency was confirmed on two different samples. Statistical analysis of the clinical-biological correlation was performed using the chi-square test. The significance level was 0.05.

RESULTS

Twenty patients were collected. The mean age of discovery was 25 years with a sex ratio (M/F) =0.33. The circumstances of discovery were incidental in 14 patients. A family history of bleeding was reported in 30% of cases. Eight patients underwent surgery, six of whom had a simple postoperative course. The APTT was prolonged and isolated in 75% of cases. The hemostasis test was normal in 5 cases. The average FactorXI level was 24%. The tendency to bleed did not seem to be correlated with FactorXI levels.

CONCLUSION

Prospective multicenter studies including molecular study would be necessary to better elucidate this rare disorder.

Factor XI gene variants in factor XI-deficient patients of Southern Italy: identification of a novel mutation and genotype-phenotype relationship

Congenital Factor XI (FXI) deficiency shows a high variability in clinical phenotype. To date, many allele variants have been shown to cause this bleeding disorder. However, the genotype–phenotype relationship is difficult to establish. This report provides insights into this bleeding disorder. Sixteen unrelated Italian index cases with congenital FXI deficiency and their relatives were investigated. After the identification of the deficiency, we obtained DNA from each subject and analyzed the FXI gene using direct sequencing. We identified 5 and 11 individuals with severe and moderate deficiency of FXI activity, respectively. Most patients (8/16) carried mutations in the Apple 2 domain and 4 patients showed c.403G>T (p.Glu135*; type II mutation). Four novel compound heterozygosities were identified. Bleeding symptoms were present in two severely deficient subjects carrying the combinations c.901T>C (p.Phe301Leu)/c.1556G>A (p.Trp519*) and c.943G>A (p.Glu315)/c.1556G>A (p.Trp519*), respectively. Bleeding episodes were also observed in the presence of a moderate deficiency in two individuals heterozygous for c.449C>T (p.Thr150Met) and c.1253G>T (p.Gly418Val), respectively. One novel mutation, c.1682C>A (p.Ala561Asp), was identified as potentially deleterious in an asymptomatic individual. We confirm an unclear prediction of phenotype from mutational data. The FXI levels should be coupled with FXI analysis for a more comprehensive prediction of the bleeding phenotype in FXI deficiency.

High incidence of FXI deficiency in a Spanish town caused by 11 different mutations and the first duplication of F11: Results from the Yecla study

INTRODUCTION

Factor XI (FXI) deficiency is a rare disorder with molecular heterogeneity in Caucasians but relatively frequent and molecularly homogeneous in certain populations.

AIM

To characterize FXI deficiency in a Spanish town of 60 000 inhabitants.

METHODS

A total of 324 764 APTT tests were screened during 20 years. FXI was evaluated by FXI:C and by Western blot. Genetic analysis of F11 was performed by sequencing, multiplex ligation-dependent probe amplification and genotyping.

RESULTS

Our study identified 46 unrelated cases and 170 relatives with FXI deficiency carrying 12 different genetic defects. p.Cys56Arg, described as founder mutation in the French-Basque population, was identified in 109 subjects from 24 unrelated families. This mutation was also identified in 2% of the general population. p.Cys416Tyr, c.1693G>A and p.Pro538Leu were identified in 7, 6 and 2 unrelated families, respectively. NGS analysis of the whole F11 gene revealed a common haplotype for each of the four recurrent mutations, suggesting a founder effect. The analysis of plasma FXI of four p.Pro538Leu homozygous carriers revealed that this variant was not activated by FXIIa. We identified four mutations previously described in other Caucasian subjects with FXI deficiency (p.Lys536Asn; p.Thr322Ile, p.Arg268Cys and c.325G>A) and four new gene defects: p.(Cys599Tyr) potentially causing a functional deficiency, p.(Ile426Thr), p.(Ile592Thr) and the first worldwide duplication of 1653 bp involving exons 8 and 9. Bleeding was rare and mild.

CONCLUSIONS

Our population-cohort study supplies new evidences that FXI deficiency in Caucasians is more common than previously thought and confirmed the wide underlying genetic heterogeneity, caused by both recurrent and sporadic mutations.

Clinical manifestations and mutation spectrum of 57 subjects with congenital factor XI deficiency in China

Congenital factor XI (FXI) deficiency is a rare bleeding disorder with unpredictable bleeding tendency. Few studies in a large cohort have been reported regarding associations between FXI activity (FXI:C) or genotypes and bleeding symptoms currently. This study characterized clinical manifestations and mutation spectrum of 57 subjects with FXI deficiency in China. Clinical data were collected and mutations were identified by direct sequencing and determined by mRNA analysis. The result revealed bleeding symptoms were only found in 12 patients (12/57, 21.1%) with severely reduced FXI:C, and prolonged bleeding post injury/surgery as well as easy bruising were the commonest bleeding manifestations presented in respective 5 cases (5/12, 41.7%). A total number of 37 mutations were identified including 19 missense mutations, 9 nonsense mutations, 6 splice site mutations and 3 small deletions. Among them, 4 missense mutations, 5 splice mutations, 3 small deletions and a nonsense mutation were newly detected. W228*, G400V, Q263* and c.1136-4delGTTG with a total frequency of 48.3% were the most four common mutations in Chinese patients. RT-PCR analysis was carried out and confirmed that both c.596-8T>A and c.1136-4delGTTG were pathogenic due to frameshift resulting in respective truncated proteins. Our findings suggested clinical manifestations had little to do with FXI:C or genotypes, which required further study. This study, the largest investigation of FXI deficiency in China revealed that the F11 mutation spectrum of Chinese population was distinct from those of other populations earlier established.

Immune tolerance induction to factor IX through B cell gene transfer: TLR9 signaling delineates between tolerogenic and immunogenic B cells

A subset of patients with severe hemophilia B, the X-linked bleeding disorder resulting from absence of coagulation factor IX (FIX), develop pathogenic antibody responses during replacement therapy. These inhibitors block standard therapy and are often associated with anaphylactic reactions to FIX. Established clinical immune tolerance induction protocols often fail for FIX inhibitors. In a murine model of this immune complication, retrovirally transduced primary B cells expressing FIX antigen fused with immunoglobulin-G heavy chain prevented antibody formation to FIX and was also highly effective in desensitizing animals with preexisting response. In contrast, transplant of B cells that received the identical expression cassette via nucleofection of plasmid vector substantially heightened antibody formation against FIX, a response that could be blocked by toll-like receptor 9 (TLR9) inhibition. While innate responses to TLR4 activation or to retrovirus were minimal in B cells, plasmid DNA activated TLR9, resulting in CpG-dependent NF-κB activation/IL-6 expression and adaptor protein 3 dependent, CpG-independent induction of IFN-I. Neither response was seen in TLR9-deficient B cells. Therefore, TLR9 signaling in B cells, in particular in response to plasmid vector, is highly immunogenic and has to be avoided in design of tolerance protocols.