When discussing the deficiency of Factor VIII with a childs family the nurse explains that it causes which complication?

Primary sites of factor VIII (FVIII) production are thought to be the vascular endothelium in the liver and the reticuloendothelial system. Liver transplantation corrects FVIII deficiency in persons with hemophilia.

FVIII messenger RNA has been detected in the liver, spleen, and other tissues. [4] Studies of FVIII production in transfected cell lines have shown that following synthesis, FVIII moves to the lumen of the endoplasmic reticulum, where it is bound to several proteins that regulate secretion, particularly immunoglobulin binding protein, from which it has to dissociate in an energy-dependent process.

Cleavage of FVIII's signal peptide and the addition of oligosaccharides also occur in the endoplasmic reticulum. The chaperone proteins, calnexin and calreticulin, enhance both FVIII secretion and degradation.

A part of the factor FVIII protein in the endoplasmic reticulum is degraded within the cell. The other part enters the Golgi apparatus, where several changes occur to produce the heavy and light chains and to modify the carbohydrates. The addition of sulfates to tyrosine residues of the heavy and light chains is necessary for full procoagulant activity, with the sulfated region playing a role in thrombin interaction. This posttranslational sulfation of tyrosine residues impacts the procoagulant activity of factor VIII and its interaction with von Willebrand factor (vWF).

von Willebrand factor

FVIII circulates in plasma in a noncovalently bound complex with vWF, which plays significant roles in the function, production, stabilization, conformation, and immunogenicity of FVIII. [5] VWF has been termed FVIII-related antigen (FVIII-R); related terminology for FVIII is FVIII-coagulant (FVIII-C).

VWF appears to promote assembly of the heavy and light chains of FVIII and more efficient secretion of FVIII from the endoplasmic reticulum. It also directs FVIII into the Weibel-Palade bodies, which are the intracellular storage sites for vWF.

In plasma, vWF stabilizes FVIII and protects it from degradation. In the presence of normal vWF protein, the half-life of FVIII is approximately 12 hours, whereas in the absence of vWF, the half-life of FVIII-C is reduced to 2 hours. [6, 7, 8]

The role of the coagulation system is to produce a stable fibrin clot at sites of injury. The clotting mechanism has two pathways: intrinsic and extrinsic. See the image below.

The intrinsic system is initiated when factor XII is activated by contact with damaged endothelium. The activation of factor XII can also initiate the extrinsic pathway, fibrinolysis, kinin generation, and complement activation.

In conjunction with high-molecular-weight kininogen (HMWK), factor XIIa converts prekallikrein (PK) to kallikrein and activates factor XI. Activated factor XI, in turn, activates factor IX in a calcium-dependent reaction. Factor IXa can bind phospholipids. Then, factor X is activated on the phospholipid surface; activation of factor X involves a complex (tenase complex) of factor IXa, thrombin-activated FVIII, calcium ions, and phospholipid.

In the extrinsic system, the conversion of factor X to factor Xa involves tissue factor (TF), or thromboplastin; factor VII; and calcium ions. TF is released from the damaged cells and is thought to be a lipoprotein complex that acts as a cell surface receptor for factor VII, with its resultant activation. TF also adsorbs factor X to enhance the reaction between factor VIIa, factor X, and calcium ions. Factor IXa and factor XII fragments can also activate factor VII.

In the common pathway, factor Xa (generated through the intrinsic or extrinsic pathways) forms a prothrombinase complex with phospholipids, calcium ions, and thrombin-activated factor Va. The complex cleaves prothrombin into thrombin and prothrombin fragments 1 and 2.

Thrombin converts fibrinogen into fibrin and activates FVIII, factor V, and factor XIII. Fibrinopeptides A and B, the results of the cleavage of peptides A and B by thrombin, cause fibrin monomers to form and then polymerize into a meshwork of fibrin; the resultant clot is stabilized by factor XIIIa and the cross-linking of adjacent fibrin strands.

Because of the complex interactions of the intrinsic and extrinsic pathways (factor IXa activates factor VII), the existence of only one in vivo pathway with different mechanisms of activation has been suggested. See the image below.

FVIII and factor IX circulate in an inactive form. When activated, these 2 factors cooperate to cleave and activate factor X, a key enzyme that controls the conversion of fibrinogen to fibrin. Therefore, the lack of FVIII may significantly alter clot formation and, as a consequence, result in clinical bleeding.

The gene for FVIII (F8C) is located on the long arm of chromosome X, within the Xq28 region. The gene is unusually large, representing 186 kb of the X chromosome. It comprises 26 exons and 25 introns. Mature FVIII contains 2332 amino acids. See the image below.

Approximately 40% of cases of severe FVIII deficiency arise from a large inversion that disrupts the FVIII gene. Deletions, insertions, and point mutations account for the remaining 50-60% of the F8C defects that cause hemophilia A.

Low FVIII levels may arise from defects outside the FVIII gene, as in type IIN von Willebrand disease, in which the molecular defect resides in the FVIII-binding domain of von Willebrand factor.

FVIII deficiency, dysfunctional FVIII, or FVIII inhibitors lead to the disruption of the normal intrinsic coagulation cascade, resulting in excessive hemorrhage in response to trauma and, in severe cases, spontaneous hemorrhage. Hemorrhage sites include joints (eg, knee, elbow); muscles; the central nervous system (CNS); and the gastrointestinal, genitourinary, pulmonary, and cardiovascular systems. Intracranial hemorrhage occurs most commonly in patients younger than 18 years and can be fatal.

Hemorrhage into joints

The hallmark of hemophilia is hemorrhage into joints. This bleeding is painful and leads to long-term inflammation and deterioration of the joint.

Human synovial cells synthesize high levels of tissue factor pathway inhibitor, resulting in a higher degree of factor Xa (FXa) inhibition, which predisposes hemophilic joints to bleed. This effect may also account for the dramatic response of activated factor VII (FVIIa) infusions in patients with acute hemarthroses and FVIII inhibitors.

Bleeding into a joint may lead to synovial inflammation, which predisposes the joint to further bleeds. A joint that has had repeated bleeds (by one definition, at least 4 bleeds within a 6-month period) is termed a target joint. Commonly, this occurs in knees though ankles and elbows are other commonly affected joints.

Repeated hemarthroses lead to progressive synovial hypertrophy, hemosiderin deposition, fibrosis, and damage to cartilage, with subchondral bone-cyst formation. This results in permanent deformities, misalignment, loss of mobility, and extremities of unequal lengths.

Approximately 30% of patients with severe hemophilia A develop alloantibody inhibitors that can bind FVIII. These inhibitors are typically immunoglobulin G (IgG), predominantly of the IgG4 subclass, that neutralize the coagulant effects of replacement therapy. However, the inhibitors do not fix complement and do not result in the end-organ damage observed with circulating immune complexes

Inhibitors occur at a young age (about 50% by age 10 years), principally in patients with less than 1% FVIII. Both genetic and environmental factors determine the frequency of inhibitor development. Specific molecular abnormalities (eg, gene deletions, stop codon mutations, frameshift mutations) are associated with a higher incidence of inhibitor development. In addition, inhibitors are more likely to develop in black children. Missense mutations are associated with a low risk of inhibitor development. [9]

The association of product used with the risk of inhibitor formation remains controversial. In a study of 574 patients with severe hemophilia A, 177 of whom developed inhibitors, the risks of inhibitor development were similar with recombinant and plasma-derived FVIII products. No association was found between the development of inhibitors and the von Willebrand factor content of products, switching from a plasma-derived to a recombinant product, or switching among brands of FVIII products. Unexpectedly, however, inhibitors developed more often with second-generation full-length recombinant products than with third-generation products. [10]

A study with 303 previously untreated or minimally treated children with hemophilia demonstrated a increased risk of inhibitor formation in patients who used recombinant products. [11] However, the European Medicines Agency (EMA) Pharmacovigilance Risk Assessment Committee (PRAC) concluded that "there is no clear and consistent evidence of a difference in the incidence of inhibitor development between the two classes of factor VIII medicines: those derived from plasma and those made by recombinant DNA technology." [12]

Due to conflicting data and challenging methodological limitations, choice of initial treatment in previously untreated or minimally treated patients should be done in a colaborative fashion between patients/caregivers and treatment teams wtih experience in these issues.

In the United States, levels of FVIII inhibitors are most often measured by the Bethesda method. In this method, 1 Bethesda unit (BU) equals the amount of antibody that destroys one half of the FVIII in an equal mixture of normal plasma and patient plasma in 2 hours at 37°C. Inhibitor levels are described as low titer or high titer, depending on whether they are less than or more than 5 BU, respectively; high-titer inhibitor levels are typically far higher than 5 BU.

The Nijmegen modification uses immunodepleted FVIII–deficient plasma instead of an imidazole saline buffer to ensure pH control to prevent non–antibody-mediated loss of FVIII-C activity during the prolonged 2-hour incubation period. [13] The Bethesda assay tends to underestimate the titer of VIII autoantibody because of its characteristics, in contrast to a hemophilic antibody. [14] The Oxford assay is another modification of the Bethesda inhibitor test.

Acquired hemophilia is the development of FVIII inhibitors (autoantibodies) in persons without a history of FVIII deficiency. This condition can be idiopathic (occurring usually in people >50 y).  It can be associated with underlying collagen vascular disease or the peripartum period, or it may represent a drug reaction (eg, to penicillin). High titers of FVIII autoantibodies may be associated with malignancies, particularly lymphoproliferative malignancies. [15]