Prevention of spontaneous bleeding in dogs with haemophilia A and haemophilia B.

Dogs with haemophilia A or haemophilia B exhibit spontaneous bleeding comparable with the spontaneous bleeding phenotype that occurs in humans with severe haemophilia. The phenotypic and genotypic characteristics of haemophilic dogs have been well-described, and such dogs are suitable for testing prophylactic protein replacement therapy and gene transfer strategies. In dogs with haemophilia, long-term effects on spontaneous bleeding frequency (measured over years) can be used as an efficacy endpoint in such studies. Although complete correction of coagulopathy has not been achieved, published data show that prophylactic factor replacement therapy and gene transfer can markedly reduce the frequency of spontaneous bleeding in haemophilic dogs. Further studies are currently ongoing.

Novel factor VIII variants with a modified furin cleavage site improve the efficacy of gene therapy for hemophilia A.

Essentials Factor (F) VIII is an inefficiently expressed protein. Furin deletion FVIII variants were purified and characterized using in vitro and in vivo assays. These minimally modified novel FVIII variants have enhanced function. These variants provide a strategy for increasing FVIII expression in hemophilia A gene therapy. SUMMARY: Background The major challenge for developing gene-based therapies for hemophilia A is that human factor VIII (hFVIII) has intrinsic properties that result in inefficient biosynthesis. During intracellular processing, hFVIII is predominantly cleaved at a paired basic amino acid cleaving enzyme (PACE) or furin cleavage site to yield a heterodimer that is the major form of secreted protein. Previous studies with B-domain-deleted (BDD) canine FVIII and hFVIII-R1645H, both differing from hFVIII by a single amino acid at this site, suggested that these proteins are secreted mainly in a single polypeptide chain (SC) form and exhibit enhanced function. Objective We hypothesized that deletion(s) of the furin site modulates FVIII biology and may enhance its function. Methods A series of recombinant hFVIII-furin deletion variants were introduced into hFVIII-BDD [Δ1645, 1645-46(Δ2), 1645-47(Δ3), 1645-48(Δ4), or Δ1648] and characterized. Results In vitro, recombinant purified Δ3 and Δ4 were primarily SC and, interestingly, had 2-fold higher procoagulant activity compared with FVIII-BDD. In vivo, the variants also have improved hemostatic function. After adeno-associated viral (AAV) vector delivery, the expression of these variants is 2-4-fold higher than hFVIII-BDD. Protein challenges of each variant in mice tolerant to hFVIII-BDD showed no anti-FVIII immune response. Conclusions These data suggest that the furin deletion hFVIII variants are superior to hFVIII-BDD without increased immunogenicity. In the setting of gene-based therapeutics, these novel variants provide a unique strategy to increase FVIII expression, thus lowering the vector dose, a critical factor for hemophilia A gene therapy.

Gene therapy for immune tolerance induction in hemophilia with inhibitors.

The development of inhibitors, i.e. neutralizing alloantibodies against factor (F) VIII or FIX, is the most significant complication of protein replacement therapy for patients with hemophilia, and is associated with both increased mortality and substantial physical, psychosocial and financial morbidity. Current management, including bypassing agents to treat and prevent bleeding, and immune tolerance induction for inhibitor eradication, is suboptimal for many patients. Fortunately, there are several emerging gene therapy approaches aimed at addressing these unmet clinical needs of patients with hemophilia and inhibitors. Herein, we review the mounting evidence from preclinical hemophilia models that the continuous uninterrupted expression of FVIII or FIX delivered as gene therapy can bias the immune system towards tolerance induction, and even promote the eradication of pre-existing inhibitors. We also discuss several gene transfer approaches that directly target immune cells in order to promote immune tolerance. These preclinical findings also shed light on the immunologic mechanisms that underlie tolerance induction.

Factor V Leiden improves in vivo hemostasis in murine hemophilia models.

The role of factor V Leiden (FVL) as a modifier of the severe hemophilia phenotype is still unclear. We used mice with hemophilia A or B crossed with FVL to elucidate in vivo parameters of hemostasis. Real-time thrombus formation in the microcirculation was monitored by deposition of labeled platelets upon laser-induced endothelial injury using widefield microscopy in living animals. No thrombi formed in hemophilic A or B mice following vascular injuries. However, hemophilic mice, either heterozygous or homozygous for FVL, formed clots at all injured sites. Injection of purified activated FV into hemophilic A or B mice could mimic the in vivo effect of FVL. In contrast to these responses to a laser injury in a microvascular bed, FVL did not provide sustained hemostasis following damage of large vessels in a ferric chloride carotid artery injury model, despite of the improvement of clotting times and high circulating thrombin levels. Together these data provide evidence that FVL has the ability to improve the hemophilia A or B phenotype, but this effect is principally evident at the microcirculation level following a particular vascular injury. Our observations may partly explain the heterogeneous clinical evidence of the beneficial role of FVL in hemophilia.

Prevalence of the prothrombin gene variant 20210 G --> A among patients with myocardial infarction.

OBJECTIVE: The aim of this study was to determine the prevalence of the prothrombin variant allele 20210A among survivors of myocardial infarction. BACKGROUND: The prothrombin gene variant has been identified as a novel genetic risk factor for venous thrombosis. However, the risk of developing arterial thrombosis as a result of the presence of this mutated allele is unknown. METHODS: The G-->A transition at position 20210 of the 3'-untranslated region was determined in 220 survivors of myocardial infarction and in 295 individuals from the general population. RESULTS: The prevalence of heterozygotes for the prothrombin mutated allele was 3% among patients with myocardial infarction and 0.7% in the general population (P = 0.03). No age-related difference in the prevalence of the mutated allele was observed. However, for individuals over 45 years old the prevalence among females was higher than among males (5% vs. 0%). CONCLUSION: These data suggest that being heterozygote for the allele variant 20210A of the prothrombin gene could be a genetic risk factor for developing myocardial infarction.

Factor V Leiden is not common in children with portal vein thrombosis.

Portal vein thrombosis (PVT) is a rare condition affecting both children and adults, and occurs in association with a wide variety of clinical situations. On the other hand, the development of PVT in patients under these situations indicates that other contributing factors could be involved. Recently a missense mutation in the factor V gene (1691G-->A), known as factor V Leiden, has been identified and results in abnormal factor V product, resistant to proteolytic inactivation by activated protein C and thus predisposes to thrombosis. This study was carried out to verify if children with PVT have an increase in frequency of factor V Leiden. Allele-specific restriction analysis and single strand conformational polymorphism (SSCP) were used to test for factor V Leiden in 20 children with PVT and 64 normal children. None of the PVT children were heterozygous or homozygous for the factor V Leiden, and one control child was heterozygous. This study demonstrates that factor V Leiden is not common in children with PVT, and is not a prerequisite for this thrombotic event.

Prevalence of the prothrombin gene variant (nt20210A) in venous thrombosis and arterial disease.

The prothrombin gene variant resulting form a G-->A transition at position 20210 has been described as a common genetic risk factor for venous thrombosis. However, the risk for developing arterial disease is unknown. In this investigation, we studied 116 patients with venous thrombosis and 71 with arterial disease, all of whom were compared with 295 controls. Additionally, we also investigated the distribution of the prothrombin alleles among African descendents and Amazonian Indians from Brazil. The prevalence of 0.7% for 20210A allele in the control group increased to 4.3% (P = 0.021) among patients with venous thrombosis. There was also a high prevalence of the mutated allele in a selected arterial disease group (5.7%) without hyperlipoproteinemia, hypertension, and diabetes mellitus when compared to the controls (P = 0.013). Heterozygotes for the allele 20210A were common among individuals of African descent (2%) and rare among Indians. These data support the hypothesis that the prothrombin variant is a risk factor for venous thrombosis and suggest that it may also be a risk factor for arterial disease.

The mutation Ala677-->Val in the methylene tetrahydrofolate reductase gene: a risk factor for arterial disease and venous thrombosis.

Mild hyperhomocysteinemia has been identified as a risk factor for arterial disease and for venous thrombosis. Individuals homozygous for the thermolabile variant of the methylene tetrahydrofolate reductase gene (MTHFR) which results from a common mutation Ala677-->Val and is found in 5-15% of the general population, have significantly elevated plasma homocysteine levels and may account for one of the genetic risk factors in vascular disease. We have analyzed the prevalence of MTHFR-T homozygotes in patients with arterial disease or venous thrombosis. We studied 191 patients with arterial disease and 127 individuals with venous thrombosis and compared with 296 unmatched controls. The results showed that there was a high prevalence of homozygotes for the mutated MTHFR-T allele among a group of patients with arterial disease (19%) in the absence of hyperlipoproteinemia, hypertension, and diabetes mellitus when compared to controls (4%), odds ratio of 5.52 (95% C.I., 2.27 to 13.51). The prevalence of homozygotes among patients with venous thrombosis was 11%, odds ratio of 2l93 (95% C.I., 1.23 to 7.01). The risk of venous thrombosis remained high, odds ratio of 2.63, even after we excluded 27 patients with hereditary thrombophilia (e.g. factor V Leiden, dysfibrinogenemia, deficiency of protein C, protein S, antithrombin III, or factor XII) from the 127 overall cases with venous thrombosis. These data support the hypothesis that being a homozygote for the MTHFR-T is a risk factor for the development of arterial disease and also for venous thrombosis.

Inherited thrombophilia as a risk factor for the development of ischemic stroke in young adults.

INTRODUCTION: Several recent studies have analyzed a possible effect of thrombophilia risk factors such as factor V Leiden, the prothrombin variant (allele 20210 A), and homozygosity for thermolabile methylenetetrahydrofolate reductase (MTHFR-T) on the development of ischemic stroke (IS). In the present study, we determined the role of these prothrombotic polymorphisms in the early onset of arterial IS or cerebral venous thrombosis (CVT) in a group of young Brazilian adults of Caucasian and African descent. MATERIALS AND METHODS: We conducted a cross-sectional study of 167 survivors of IS (153 patients with arterial IS and 14 cases of CVT; 66 men: 101 women; 124 of Caucasian and 43 of African origin; median age: 32.6 years; range: 15 to 45 years) and compared the prevalence of inherited thrombophilia risk factors with a control group of 225 sex and age matched individuals of the same ethnic background. To determine the interaction with atherogenic risk factors, the following diagnoses were considered: hypertension, hyperlipoproteinemia, diabetes mellitus, smoking status and use of oral contraceptives. RESULTS: In the arterial IS group, no significant variation was found between patients and controls of Caucasian origin regarding the prevalence of factor V Leiden (P = 0.92), the prothrombin variant (P = 0.13) or homozygosity for MTHFR-T (P = 0.61). Among Brazilians of African descent, 10.3% were homozygous for MTHFR-T, which was significantly elevated, odds ratio of 5.9 (95% CI: 0.88 to 49.15). In the CVT group, two Caucasian patients (20%) were heterozygous for the prothrombin variant, odds ratio of 9.7 (95% CI: 0.95 to 89.71) and one patient was carrier of factor V Leiden (P = 0.49). No prothrombotic polymorphism was identified in patients with CVT of African descent. All women in the CVT group were in use of oral contraceptives or in the post-partum state. DISCUSSION: Inherited thrombophilia risk factors were not found to increase the risk of arterial IS among young patients of Caucasian descent. However, a potential role of homozygosity for MTHFR-T was observed in a small group of patients of African origin. The analysis of patients with CVT revealed an increased risk due to the prothrombin gene variant or oral contraceptive use. Further studies including all incoming patients with IS are necessary to evaluate the impact of inherited thrombophilia risk factors on early mortality.

Geographic distribution of the 20210 G to A prothrombin variant.

A variant in prothrombin (clotting factor II), a G to A transition at nucleotide position 20210, has recently been shown to be associated with the prothrombin plasma levels and the risk of both venous and arterial thrombosis. The purpose of this study was to investigate the prevalence of carriership of this mutation in various populations. We combined data from 11 centres in nine countries, where tests for this mutation had been performed in groups representing the general population. We calculated an overall prevalence estimate, by a precision-weighted method, and, since the distribution of the prevalences did not appear homogeneous, by an unweighted average of the prevalences. We examined differences in the prevalences by geographical location and ethnic background as a possible explanation for the heterogeneity. Among a total of 5527 individuals who had been tested, 111 heterozygous carriers of the 20210A mutation were found. The prevalence estimates varied from 0.7 to 4.0 between the centres. The overall prevalence estimate was 2.0 percent (CI95 1.4-2.6%). The variation around the summary estimate appeared more than was expected by chance alone, and this heterogeneity could be explained by geographic differences. In southern Europe, the prevalence was 3.0 percent (CI95 2.3 to 3.7%), nearly twice as high as the prevalence in northern Europe (1.7%, CI95 1.3 to 2.2%). The prothrombin variant appeared very rare in individuals from Asian and African descent. The 20210A prothrombin variant is a common abnormality, with a prevalence of carriership between one and four percent. It is more common in southern than in northern Europe. Since this distribution within Europe is very different to that of another prothrombotic mutation (factor V Leiden or factor V R506Q), founder effects are the most likely explanation for the geographical distribution of both mutations.

Prevalence of the mutation C677 --> T in the methylene tetrahydrofolate reductase gene among distinct ethnic groups in Brazil.

Vascular disease is a serious public health problem in the industrialized world, and is a frequent cause of death among the adult population of Brazil. Mild hyperhomocysteinemia has been identified as a risk factor for arterial disease, venous thrombosis, and neural tube defects. Individuals homozygous for the thermolabile variant of methylenetetrahydrofolate reductase (MTHFR-T) are found in 5-15% of the general population and have significantly elevated plasma homocysteine levels which represent one of the genetic risk factors for vascular diseases. We have analyzed the prevalence of individuals homozygous for the MTHFR-T in 327 subjects representing the three distinct ethnic groups in Brazil. The prevalence of homozygotes for the mutated allele MTHFR-T was high among persons of Caucasian descent (10%) and considerably lower among Black (1.45%) and Indians persons populations (1.2%). These data suggest that screening for the MTHFR-T allele should help in identifying individuals with a high risk of vascular disease among populations with a heterogeneous background.

Antithrombin deficiency in Brazilian patients with venous thrombosis: molecular characterization of a single splice site mutation, an insertion and a de novo point mutation.

The prevalence of antithrombin (AT) deficiency in 342 unselected Brazilian patients with venous thrombosis was 1.16%, which increased to 3% when only patients under the age of 50 or with a familial history of thrombosis were considered. In two patients, a clinical (contraceptive use) or genetic risk factor (factor V Leiden and C677T in the methylene tetrahydrofolate reductase gene [MTHFR]) was identified and corroborated the hypothesis that an interaction of factors accounted for the appearance of thrombosis. However, no risk factor other than AT deficiency was identified in one patient with an important clinical and family history of spontaneous thrombosis. Three mutations were identified in these patients: a G-->A transition in intron 5 at position +1 (5'-->3'), three base insertions corresponding to arginine at position 5383 in exon 3A, and a G-->A transition at 13328, corresponding to an Ala404Thr de novo mutation. The polymorphisms in the genes coding for coagulation factors XII and XIII and fibrinogen normally associated with an increased risk for venous thrombosis were not related to thrombosis in these patients. This is the first study in South America to assess the prevalence of AT deficiency and to report the molecular characterization of the mutations involved.

The impact of the search for thrombophilia risk factors among antiphospholipid syndrome patients with thrombosis.

Thrombosis is a major clinical feature of the antiphospholipid syndrome. Interactions between genetic and acquired factors could contribute to thrombosis development. In this study, we evaluated 40 patients with antiphospholipid syndrome and thrombosis, 31 primary and nine secondary to systemic lupus erythemathosus, to estimate the carrier rates of factor V Leiden, 20210A --> G prothrombin variant and 677C --> T in the MTHFR gene. Protein C, protein S and antithrombin were measured in 30 patients, with a median of 100.66 +/- 23.86, 93.57 +/- 36.44 and 98.8 +/- 5.67%, respectively. None of the patients were deficient on these natural anticoagulants. No significant variation was found between the patient group and the controls, regarding the prevalence of homozygotes for the mutated 677T allele (2.5 versus 5.4%), or heterozygotes for factor V Leiden (0 versus 0.7%). Despite the fact that these mutations are relatively common in Brazilian thrombophilic patients, its low prevalence in this cohort of patients suggest that these genetic alterations are not risk factors for thrombosis in antiphospholipid syndrome. The prevalence of the mutated allele 20210A of the prothrombin gene was higher in patients when compared with controls (5 versus 0.7%; P = 0.01), suggesting that prothrombin variant could increase the risk of thrombosis in patients with antiphospholipid syndrome.

Glutathione peroxidase, reduced glutathione, superoxide dismutase and catalase in red cells of patients with hairy cell leukemia.

Red cell antioxidant enzymes have been recently studied in malignant lymphomas and the results are controversial. Hairy cell leukemia is a rare chronic lymphoproliferative disorder originating probably in a pluripotent stem cell. In the present study, glutathione peroxidase (Gpx), reduced glutathione (GSH), superoxide dismutase (SOD), and catalase were measured in a homogeneous group of patients with untreated hairy cell leukemia and normal controls. Glutathione peroxidase, catalase and SOD activities were significantly lower in patients than in normals. GSH was not significantly different in patients compared to controls. There was no correlation between Gpx, GSH, SOD, and catalase and hemoglobin; reticulocytes, leukocytes, hairy cells, platelets number or splenomegaly. Taken together these data suggest a decreased activity of red cell antioxidant enzymes in hairy cell leukemia and support a pluripotent stem cell defect of these abnormalities.

Minimal doses of hydroxyurea for sickle cell disease.

The use of hydroxyurea (HU) can improve the clinical course of sickle cell disease. However, several features of HU treatment remain unclear, including the predictability of drug response and determination of adequate doses, considering positive responses and minimal side effects. In order to identify adequate doses of HU for treatment of sickle cell disease, 10 patients, 8 with sickle cell anemia and 2 with S beta thalassemia (8SS, 2S beta), were studied for a period of 6 to 19 months in an open label dose escalation trial (10 to 20 mg kg-1 day-1). Hemoglobin (Hb), fetal hemoglobin (Hb F) and mean corpuscular volume (MCV) values and reticulocyte, neutrophil and platelet counts were performed every two weeks during the increase of the HU dose and every 4 weeks when the maximum HU dose was established. Reduction in the number of vasoocclusive episodes was also considered in order to evaluate the efficiency of the treatment. The final Hb and Hb F concentrations, and MCV values were significantly higher than the initial values, while the final reticulocyte and neutrophil counts were significantly lower. There was an improvement in the concentration of Hb (range: 0.7-2.0 g/dl) at 15 mg HU kg-1 day-1, but this concentration did not increase significantly when the HU dose was raised to 20 mg kg-1 day-1. The concentration of Hb F increased significantly (range: 1.0-18.1%) when 15 mg HU was used, and continued to increase when the dose was raised to 20 mg kg-1 day-1. The final MCV values increased 11-28 fl (femtoliters). However, reticulocyte (range: 51-205 x 10(9)/l) and neutrophil counts (range: 9.5-1.3 x 10(9)/l) obtained at this dose were significantly lower than those obtained with 15 mg kg-1 day-1. All patients reported a decrease in frequency or severity of vasoocclusive episodes. These results suggest that a hydroxyurea dose of 15 mg kg-1 day-1 seems to be adequate for treatment of sickle cell disease in view of the minimal side effects observed and the improvement in laboratory and clinical parameters.

Detection of somatic mutations of the PIG-A gene in Brazilian patients with paroxysmal nocturnal hemoglobinuria.

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal syndrome characterized by intravascular hemolysis mediated by complement, thrombotic events and alterations in hematopoiesis. Basically, the molecular events which underlie the complexity of the syndrome consist of the absence of the glycosylphosphatidylinositol (GPI) anchor as a consequence of somatic mutations in the PIG-A gene, located on the X chromosome. The GPI group is responsible for the attachment of many proteins to the cytoplasmic membrane. Two of them, CD55 and CD59, have a major role in the inhibition of the action of complement on the cellular membrane of blood cells. The absence of GPI biosynthesis can lead to PNH. Since mutations in the PIG-A gene are always present in patients with PNH, the aim of this study was to characterize the mutations in the PIG-A gene in Brazilian patients. The analysis of the PIG-A gene was performed using DNA samples derived from bone marrow and peripheral blood. Conformation-sensitive gel electrophoresis was used for screening the mutation and sequencing methods were used to identify the mutations. Molecular analysis permitted the identification of three point mutations in three patients: one G-->A transition in the 5' portion of the second intron, one T-->A substitution in the second base of codon 430 (Leu430-->stop), and one deletion DeltaA in the third base of codon 63. This study represents the first description of mutations in the PIG-A gene in a Brazilian population.

Studies on the components of the contact phase system in patients with acute nonlymphoblastic leukemia.

The objective of the present study was to evaluate factors of the plasma kallikrein system in patients with acute nonlymphoblastic leukemia (ANLL), and compare the results to a normal control group. A prospective study was performed in the Tertiary Health Care Institution, Hemocentro, Campinas State University, Campinas, São Paulo, Brazil. Thirty-five patients, diagnosed as ANLL between 1988 and 1991, were considered for participation. Eleven patients were not eligible, according to the exclusion criteria: infection/septicemia, previous treatment or blood transfusion. The study was performed with 24 ANLL patients, average age 34 years (16-69 years), 14 men and 10 women. Nineteen healthy volunteers, workers from the Hematology Center, average age 32 years (21-59 years), 11 men and 8 women, were the control group. Plasmatic prekallikrein, C1-inhibitor, alpha 2-macroglobulin, activated partial thromboplastin time, prothrombin time, factor XII, factor XI, factor V and prealbumin were measured. Plasmatic prekallikrein (p = 0.02) and prealbumin (p = 0.03) were significantly decreased, and prothrombin time increased (p = 0.003) in the patient group when compared to the control. Significant correlation (r = 0.49, critical value = 0.43, p < 0.05) between prekallikrein and prealbumin, and between prothrombin time and factor V (r = 0.54, critical value = 0.44, p < 0.05) was demonstrated in the patient group. No correlation was found between parameters analysed and circulant blast count or leukemia subgroups. Statistical analysis was performed by the Wilcoxon test. Correlation between the parameters was also verified. These results suggest activation of the contact system or impaired liver synthesis in patients with ANLL, and could contribute to disease complications.

[Detection of hemophilia A gene carriers in a Brazilian population]. / Detecção de portadoras de gene da hemofilia A em uma população brasileira.

The identification of carriers for the hemophilia A gene was carried out in 20 families of hemophilia A patients. The detection of the carriers was performed on the basis of the study of restriction length fragment polymorphism (RLFPs) for the enzymes BclI and HindIII. The procedures for the determination of RLFPs included the amplification of fragment of the factor VIII gene by the polymerase chain reaction (PCR) followed by digestion with the appropriate enzyme. We studied 84 relatives of the patients with hemophilia A and was possible to detect carriers in 76% of the families. The results presented here indicate that is possible to identify carriers for hemophilia A in most of the families of patients from the Brazilian population employing a limited number of RFLPs.

Apoptotic effects of platelet factor VIII on megakaryopoiesis: implications for a modified human FVIII for platelet-based gene therapy.

BACKGROUND: Ectopically expressed B-domainless factor VIII in megakaryocytes is stored in α-granules, is effective in a number of murine hemostatic models, and is protected from circulating inhibitors. However, this platelet (p) FVIII has different temporal-spatial availability from plasma FVIII, with limited efficacy in other murine hemostatic models. OBJECTIVES AND METHODS: We sought to improve pFVIII hemostatic efficacy by expressing canine (c) FVIII, which has higher stability and activity than human (h) FVIII in FVIII(null) mice. RESULTS AND CONCLUSIONS: We found that pcFVIII was more effective than phFVIII at restoring hemostasis, but peak pcFVIII antigen levels were lower and were associated with greater megakaryocyte apoptosis than phFVIII. These new insights suggest that pFVIII gene therapy strategies should focus on enhancing activity rather than levels. We previously showed that modification of the PACE/furin cleavage site in hFVIII resulted in secretion of hFVIII primarily as a single-chain molecule with increased biological activity. In megakaryocytes, this variant was expressed at the same level as phFVIII with a lentiviral bone marrow transplant approach to reconstitute FVIII(null) mice, but was more effective, resulting in near-normal hemostasis in the cremaster laser injury model. These studies may have implications for pFVIII gene therapy in hemophilia A.

An engineered U1 small nuclear RNA rescues splicing defective coagulation F7 gene expression in mice.

BACKGROUND: The ability of the spliceosomal small nuclear RNA U1 (U1snRNA) to rescue pre-mRNA splicing impaired by mutations makes it an attractive therapeutic molecule. Coagulation factor deficiencies due to splicing mutations are relatively frequent and could therefore benefit from this strategy. However, the effects of U1snRNAs in vivo remain unknown. OBJECTIVES: To assess the rescue of the F7 c.859+5G>A splicing mutation (FVII+5A), causing severe human factor VII (hFVII) deficiency, by the modified U1snRNA+5a (U1+5a) in a murine model. METHODS: Mice expressing the human F7 c.859+5G>A mutant were generated following liver-directed expression by plasmid or recombinant adeno-associated viral (AAV) vector administration. The rescue of the splice-site defective pre-mRNA by U1+5a was monitored in liver and plasma through hFVII-specific assays. RESULTS: Injection of plasmids encoding the U1+5a rescued plasma hFVII levels, which increased from undetectable to ~8.5% of those obtained with the wild-type hFVII plasmid control. To assess long-term effects, mice were injected with low and high doses of two AAV vectors encoding the FVII+5A splice site mutant as template to be corrected by U1+5a. This strategy resulted in hFVII plasma levels of 3.9 ± 0.8 or 23.3 ± 5.1 ng mL⁻¹ in a dose-dependent manner, corresponding in patients to circulating FVII levels of ~1-4.5% of normal. Moreover, in both experimental models, we also detected correctly spliced hFVII transcripts and hFVII-positive cells in liver cells. CONCLUSIONS: Here we provide the first in vivo proof of-principle of the rescue of the expression of a splicing-defective F7 mutant by U1snRNAs, thus highlighting their therapeutic potential in coagulation disorders.