Congenital hypofibrinogenemia

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Congenital hypofibrinogenemia
Specialty Hematology

Congenital hypofibrinogenemia is a rare disorder in which one of the three genes responsible for producing fibrinogen, a critical blood clotting factor, is unable to make a functional fibrinogen glycoprotein because of an inherited mutation. In consequence, liver cells, the normal site of fibrinogen production, make small amounts of this critical coagulation protein, blood levels of fibrinogen are low, and individuals with the disorder may develop a coagulopathy, i.e. a diathesis or propensity to experience episodes of abnormal bleeding. However, individuals with congenital hypofibrinogenemia may also have episodes of abnormal blood clot formation, i.e. thrombosis. This seemingly paradoxical propensity to develop thrombosis in a disorder causing a decrease in a critical protein for blood clotting may be due to the function of fibrin (the split product of fibrinogen that is the basis for forming blood clots) to promote the lysis or disintegration of blood clots. Lower levels of fibrin may reduce the lysis of early fibrin strand depositions and thereby allow these depositions to develop into clots. [1]

Contents

Congenital hypofibrinogenemia must be distinguished from: a) congenital afibrinogenemia, a rare disorder in which blood fibrinogen levels are either exceedingly low or undetectable due to mutations in both fibrinogen genes; b) congenital hypodysfibrinogenemia, a rare disorder in which one or more genetic mutations cause low levels of blood fibrinogen, at least some of which is dysfunctional and thereby contributes to excessive bleeding; and c) acquired hypofibrinogenemia, a non-hereditary disorder in which blood fibrinogen levels are low because of e.g. severe liver disease or because of excessive fibrinogen consumption resulting from, e.g. disseminated intravascular coagulation. [1] [2]

Certain gene mutations causing congenital hypofibrinogenemia disrupt the ability of liver cells to secrete fibrinogen. In these instances, the un-mutated gene maintains blood fibrinogen at reduce levels but the mutated gene produces a fibrinogen that accumulates in liver cells sometimes to such extents that it becomes toxic. In the latter cases, liver disease may ensue in a syndrome termed fibrinogen storage disease. [3]

Signs and symptoms

Individuals with congenital hypofibringenemia often lack any symptoms are detected by routine lab testing of fibrinogen or when tested for it because close relatives have symptomatic hypofibrinogenemia. Indeed, studies indicate that, among family members with the identical congenital hypofibrinogenemia mutation, some never exhibit symptoms and those that are symptomatic develop symptoms only as adults. [1]

No liver disease

Individuals with this disorder are usually less symptomatic than patients with other fibrinogen disorders because their fibrinogen levels are generally sufficient to prevent spontaneous bleeding. Those with particularly low blood fibrinogen levels (<0.5 gram/liter) may develop serious bleeding spontaneously and many with the disorder do so following trauma or surgery. Depending on their fibrinogen levels, women with the disorder may also bleed excessively during delivery and the postpartum period; in rare cases, they may have an increased risk of suffering miscarriages. [1] [4] [5] Individuals with the disorder also experience thrombotic events which may include blockage of large arteries in relatively young patients who have high levels of cardiovascular risk factors. The thrombi which form in these individuals are unstable, tend to embolize, and may therefore lead to thromboembolic events such as pulmonary embolism. Both bleeding and thrombotic events can occur at separate times or even concurrently in the same individual with the disorder. [1]

Fibrinogen storage disease

All individuals with mutations causing fibrinogen storage disease have low blood fibrinogen levels but usually lack severe bleeding episodes, thrombotic episodes or liver disease. Individuals that do have fibrinogen storage disease often come to attention either because they have close relatives with the disease, are found to be hypofibrinogenemic during routing testing, or exhibit clinical (e.g. jaundice) or laboratory (e.g. elevated blood levels of liver enzymes) evidence of liver disease. Unlike other forms of congenital hypofibrinogenemia, a relatively high percentage of individuals with fibrinogen storage disease have been diagnosed in children of very young age. [3] [6] [7]

Pathophysiology

Fibrinogen is made and secreted into the blood by liver hepatocytes. The final secreted protein is composed of two trimers each of which is composed of three polypeptide chains, (also termed α) encoded by the FGA gene, (also termed β) encoded by the FGB gene, and γ encoded by the FGG gene. All three genes are located on the long or "p" arm of human chromosome 4 (at positions 4q31.3, 4q31.3, and 4q32.1, respectively). [8] [9] The genes are ordered FGB, FGA, and FGG and are transcribed into messenger RNA in tight synchrony. [6] The messenger RNAs associate with the endoplasmic reticulum, translated into polypeptides, and enter the endoplasmic reticulum where they assembled together. The assembled protein is passes to the Golgi apparatus where it is glycosylated, hydroxylated, sulfated, and phosphorylated to form the mature fibrinogen glycoprotein that is secreted into the blood. Congenital hypofibrinogenemia results from inherited mutations in one of the three fibrinogen chains that results in the disruption of fibrinogen synthesis, assembly, stability, processing through the endoplasmic reticulum-Golgi apparatus pathway, and/or secretion into the blood. [3] [6] [10]

There are >25 fibrinogen mutations that have been associated with hypofibrinogenemia. The following Table lists examples of those mutations which cause hypofibrinogenemia that is not associated with liver injury. The Table gives: a) each mutated protein's trivial name; b) the gene mutated (i.e. FGA, FGB, or FGG), its mutation site (i.e. numbered nucleotide in the gene beginning with the initial nucleotide base at the (start codon) of genomic DNA (as indicated by the "g." notation), and name of the nucleotides (i.e. C, T, A, G) at these sites before>after the mutation; and c) the name of the altered fibrinogen peptide (Aα, Bβ, or λ), the numbered position(s) of the amino acid changed by the mutation in the circulating peptide of the mutated fibrinogen, and the identity of the amino acids before-after the mutation using standard three letter abbreviations. [3] In the Table, fs indicates a mutation that causes a Translational frameshift and consequently a premature stop codon (designated by "X") mutation and translation of a shortened fibrinogen chain, del is a deletion, and ins is an insertion.[ citation needed ]

Trivial nameGene: mutationPolypeptide chain: mutationTrivial nameGene: mutationPolypeptide chain: mutation
fibrinogen Grand LyonFGA: g.5011_5012delCinsTTGGAATTTT (del followed by ins)Aα: Thr560PhefsX99 (fs followed by X)fibrinogen HamiltonFGB: g.7044G>TBβ: Asp316Tyr
fibrinogen Mount EdenFGB: g.8035G>ABβ: Trp440Xfibrinogen DorfenFGG: g.75218C>Tγ: Ala289Val
fibrinogen Saint Germain IIFGAG: g.7686A>Gγ: Asn345Serfibrinogen MuncieFGG: g.9402C>Tγ: Thr371Ile

As of 2016, there have been six mutations discovered to be associated with the accumulation of the mutated fibrinogen in the endoplasmic reticulum and consequential development of liver injury that may lead to liver cirrhosis, i.e. fibrinogen storage disease. Other fibrinogen mutations have also led to their accumulation in the endoplasmic reticulum but have not been associated with liver injury perhaps because these fibrinogens are less toxic to the liver than those that cause liver injury. The following Table lists these 6 mutations. Note that all of these 6 mutations occur in the FGG gene, that all the mutations are missense mutations except for the deletion mutation of fibrinogen Anger, and that the Table reports the gene mutation site as found in cloned (as notated by "c.") rather than genomic DNA. Fibrinogen Aguadilla is the most common mutation known to cause fibrinogen storage disease. [1] [3] [7] The abbreviations in this Table are defined in the previous Table.

Trivial nameGene: mutationPolypeptide chain: mutationTrivial nameGene: mutationPolypeptide chain: mutation
fibrinogen BresciaFGG: c.928G>Cγ: Gly284Argfibrinogen AguadillaFGG: c.1201C>Tγ: Arg375Trp (commonest mutation in fibrinogen storage disease)
fibrinogen AngerFGG: c.1115_1129 (del of GAGTTTATTACCAAG)γ: G436_350 (del of intervening amino acids)fibrinogen AI DuPontFGG: c.1018A>Cγ: AlaThr314Pro
fibrinogen PisaFGAG: c.1024G>Aγ: Asp316Asnfibrinogen BeogradFGG: c.1174G>Aγ: Gly366Ser

Diagnosis

The diagnosis of hypofibrinogenemia is indicated in individuals who have low levels (<1.5 gram/liter) of plasma fibrinogen as determined by both immunological (e.g. immunoelectrophoresis and (i.e. able to be clotted) methods. The ratio of immunological to functional fibrinogen masses should be ~1.0 as assayed with partial thromboplastin time, activated partial thromboplastin time, thrombin time, and reptilase time tests. [8] These tests are used to distinguish hypofibrinogenemia from hypodysfibrinogenemia, a typically more severe disorder in which plasma fibrinogen levels are low and this fibrinogen includes at least in part dysfunctional fibrinogen. Immunological/functional fibrinogen ratios for the plasma of individuals with hypodysfibrinogenemia for all the cited tests are usually <0.7. Where available, further analyses are recommended; these include analyses of the fibrinogen genes and protein chains for mutations and specialized studies of individuals in vitro induced blood clots for stability and susceptibility to lyses. [11]

The diagnosis of fibrin storage disease requires liver biopsy and the finding of immunologically detectable fibrinogen inclusion bodies in hepatocytes. [3]

Treatment

No symptoms

Recommended treatment of asymptomatic congenital hypofibrinogenemia depends in part on the expectations of developing bleeding and/or thrombotic complications as indicated by the personal history of the affected individual and family members. Where possible, determination of the exact mutation causing the disorder and the propensity of this mutation type to develop these complications may be helpful. [11] Individuals with fibrinogen levels >1.0 gram/liter typically do not develop bleeding or thrombosis episodes. Individuals with fibrinogen levels of 0.5-1.0 grams/liter require fibrinogen supplementation preferably with a plasma-derived fibrinogen concentrate to maintain fibrinogen levels of >1 gram/liter prior to major surgery. Individuals with fibrinogen levels of <0.5 gram/liter require fibrinogen supplementation to maintain fibrinogen levels of a) >1 to 2 gram/liter at the end of pregnancy and during the postpartum period; b) > 1 gram/liter prior to major surgery; c) > 0.5 to 1 gram/liter during the first two trimesters of pregnancy; and d) >0.5 gram/liter prior to minor surgery. Tranexamic acid may be used in place of fibrinogen supplementation as prophylactic treatment prior to minor surgery and to treat minor bleeding episodes. [11]

Symptoms

Individuals with hypofibrinogenemia who have a history of excessive bleeding should be treated at a center specialized in treating hemophilia and avoid all medications that interfere with normal platelet function. During bleeding episodes, treatment with fibrinogen concentrates or, if unavailable infusion of fresh frozen plasma and/or cryoprecipitate (a fibrinogen-rich plasma fraction) to maintain fibrinogen activity levels >1 gram/liter. [11]

Individuals with hypofibrinogenemia who experience episodic thrombosis should also be treated at a center specialized in treating hemophilia. Standard recommendations for these individuals are that they use antithrombotic agents and be instructed on antithrombotic behavioral methods in high risk situations (e.g. long car rides and air flights). Acute venous thrombosis episodes should be treated with low molecular weight heparin for a time that depends on personal and family history of thrombosis events. Prophylactic treatment prior to minor surgery should avoid fibrinogen supplementation and use anticoagulation measures; prior to major surgery, fibrinogen supplementation should be used only if serious bleeding occurs; otherwise, prophylactic anticoagulation measures are recommended. [11]

Fibrin storage disease

There are too few cases of fibrinogen storage disease to establish optimal treatments for the liver diseases. Management of the disorder has been based on general recommendations for patients with liver disease, particularly Alpha 1 antitrypsin deficiency-associated liver disease. In the latter disease, autophagy, the pathway that cells use to dispose of dysfunctional or excessively stored components including proteins, has been targeted using autophagy-enhancing drugs, e.g. carbamazepine, vitamin E, and ursodeoxycholic acid. These drugs have been tested in individual patients with fibrin storage disease with some success in reducing evidence of liver injure, i.e. reduction in blood liver enzyme levels. These and other autophagy-enhancing drugs are suggested to be further studied in fibrinogen storage disease. [3]

Related Research Articles

<span class="mw-page-title-main">Thrombus</span> Blood clot

A thrombus, colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of cross-linked fibrin protein. The substance making up a thrombus is sometimes called cruor. A thrombus is a healthy response to injury intended to stop and prevent further bleeding, but can be harmful in thrombosis, when a clot obstructs blood flow through healthy blood vessels in the circulatory system.

<span class="mw-page-title-main">Coagulation</span> Process of formation of blood clots

Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism of coagulation involves activation, adhesion and aggregation of platelets, as well as deposition and maturation of fibrin.

<span class="mw-page-title-main">Disseminated intravascular coagulation</span> Medical condition

Disseminated intravascular coagulation (DIC) is a condition in which blood clots form throughout the body, blocking small blood vessels. Symptoms may include chest pain, shortness of breath, leg pain, problems speaking, or problems moving parts of the body. As clotting factors and platelets are used up, bleeding may occur. This may include blood in the urine, blood in the stool, or bleeding into the skin. Complications may include organ failure.

Factor V Leiden is a variant of human factor V, which causes an increase in blood clotting (hypercoagulability). Due to this mutation, protein C, an anticoagulant protein that normally inhibits the pro-clotting activity of factor V, is not able to bind normally to factor V, leading to a hypercoagulable state, i.e., an increased tendency for the patient to form abnormal and potentially harmful blood clots. Factor V Leiden is the most common hereditary hypercoagulability disorder amongst ethnic Europeans. It is named after the Dutch city of Leiden, where it was first identified in 1994 by Rogier Maria Bertina under the direction of Pieter Hendrick Reitsma. Despite the increased risk of venous thromboembolisms, people with one copy of this gene have not been found to have shorter lives than the general population.

<span class="mw-page-title-main">Fibrinogen</span> Soluble protein complex in blood plasma and involved in clot formation

Fibrinogen is a glycoprotein complex, produced in the liver, that circulates in the blood of all vertebrates. During tissue and vascular injury, it is converted enzymatically by thrombin to fibrin and then to a fibrin-based blood clot. Fibrin clots function primarily to occlude blood vessels to stop bleeding. Fibrin also binds and reduces the activity of thrombin. This activity, sometimes referred to as antithrombin I, limits clotting. Fibrin also mediates blood platelet and endothelial cell spreading, tissue fibroblast proliferation, capillary tube formation, and angiogenesis and thereby promotes revascularization and wound healing.

<span class="mw-page-title-main">Thrombin</span> Enzyme involved in blood coagulation in humans

Thrombin is a serine protease, an enzyme that, in humans, is encoded by the F2 gene. Prothrombin is proteolytically cleaved to form thrombin in the clotting process. Thrombin in turn acts as a serine protease that converts soluble fibrinogen into insoluble strands of fibrin, as well as catalyzing many other coagulation-related reactions.

Fibrinolysis is a process that prevents blood clots from growing and becoming problematic. Primary fibrinolysis is a normal body process, while secondary fibrinolysis is the breakdown of clots due to a medicine, a medical disorder, or some other cause.

<span class="mw-page-title-main">Thrombophilia</span> Abnormality of blood coagulation

Thrombophilia is an abnormality of blood coagulation that increases the risk of thrombosis. Such abnormalities can be identified in 50% of people who have an episode of thrombosis that was not provoked by other causes. A significant proportion of the population has a detectable thrombophilic abnormality, but most of these develop thrombosis only in the presence of an additional risk factor.

Congenital afibrinogenemia is a rare, genetically inherited blood fibrinogen disorder in which the blood does not clot normally due to the lack of fibrinogen, a blood protein necessary for coagulation. This disorder is autosomal recessive, meaning that two unaffected parents can have a child with the disorder. The lack of fibrinogen expresses itself with excessive and, at times, uncontrollable bleeding.

<span class="mw-page-title-main">Hypoprothrombinemia</span> Medical condition

Hypoprothrombinemia is a rare blood disorder in which a deficiency in immunoreactive prothrombin, produced in the liver, results in an impaired blood clotting reaction, leading to an increased physiological risk for spontaneous bleeding. This condition can be observed in the gastrointestinal system, cranial vault, and superficial integumentary system, affecting both the male and female population. Prothrombin is a critical protein that is involved in the process of hemostasis, as well as illustrating procoagulant activities. This condition is characterized as an autosomal recessive inheritance congenital coagulation disorder affecting 1 per 2,000,000 of the population, worldwide, but is also attributed as acquired.

<span class="mw-page-title-main">Factor X deficiency</span> Medical condition

Factor X deficiency is a bleeding disorder characterized by a lack in the production of factor X (FX), an enzyme protein that causes blood to clot in the coagulation cascade. Produced in the liver FX when activated cleaves prothrombin to generate thrombin in the intrinsic pathway of coagulation. This process is vitamin K dependent and enhanced by activated factor V.

<span class="mw-page-title-main">Factor VII deficiency</span> Medical condition

Factor VII deficiency is a bleeding disorder characterized by a lack in the production of Factor VII (FVII) (proconvertin), a protein that causes blood to clot in the coagulation cascade. After a trauma factor VII initiates the process of coagulation in conjunction with tissue factor in the extrinsic pathway.

Factor XIII deficiency occurs exceedingly rarely, causing a severe bleeding tendency. The incidence is one in a million to one in five million people, with higher incidence in areas with consanguineous marriage such as Iran that has the highest global incidence of the disorder. Most are due to mutations in the A subunit gene. This mutation is inherited in an autosomal recessive fashion.

The dysfibrinogenemias consist of three types of fibrinogen disorders in which a critical blood clotting factor, fibrinogen, circulates at normal levels but is dysfunctional. Congenital dysfibrinogenemia is an inherited disorder in which one of the parental genes produces an abnormal fibrinogen. This fibrinogen interferes with normal blood clotting and/or lysis of blood clots. The condition therefore may cause pathological bleeding and/or thrombosis. Acquired dysfibrinogenemia is a non-hereditary disorder in which fibrinogen is dysfunctional due to the presence of liver disease, autoimmune disease, a plasma cell dyscrasias, or certain cancers. It is associated primarily with pathological bleeding. Hereditary fibrinogen Aα-Chain amyloidosis is a sub-category of congenital dysfibrinogenemia in which the dysfunctional fibrinogen does not cause bleeding or thrombosis but rather gradually accumulates in, and disrupts the function of, the kidney.

<span class="mw-page-title-main">Fibrinogen gamma chain</span> Protein-coding gene in the species Homo sapiens

Fibrinogen gamma chain, also known as fibrinogen gamma gene (FGG), is a human gene found on chromosome 4.

<span class="mw-page-title-main">Quebec platelet disorder</span> Medical condition

Quebec platelet disorder (QPD) is a rare autosomal dominant bleeding disorder first described in a family from the province of Quebec in Canada. The disorder is characterized by large amounts of the fibrinolytic enzyme urokinase-type plasminogen activator (uPA) in platelets. This causes accelerated fibrinolysis (blood clot breakdown) which can result in bleeding.

Cryofibrinogenemia refers to a condition classified as a fibrinogen disorder in which a person's blood plasma is allowed to cool substantially, causing the (reversible) precipitation of a complex containing fibrinogen, fibrin, fibronectin, and, occasionally, small amounts of fibrin split products, albumin, immunoglobulins and other plasma proteins.

<span class="mw-page-title-main">Factor I deficiency</span> Medical condition

Factor I deficiency, also known as fibrinogen deficiency, is a rare inherited bleeding disorder related to fibrinogen function in the blood coagulation cascade. It is typically subclassified into four distinct fibrinogen disorders: afibrinogenemia, hypofibrinogenemia, dysfibrinogenemia, and hypodysfibrinogenemia.

Hypodysfibrinogenemia, also termed congenital hypodysfibrinogenemia, is a rare hereditary fibrinogen disorder cause by mutations in one or more of the genes that encode a factor critical for blood clotting, fibrinogen. These mutations result in the production and circulation at reduced levels of fibrinogen at least some of which is dysfunctional. Hypodysfibrinogenemia exhibits reduced penetrance, i.e. only some family members with the mutated gene develop symptoms.

References

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