Dysfibrinogenemia

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Dysfibrinogenemia
Other namesDysfibrinogenemia, familial[1]

The dysfibrinogenemias consist of three types of fibrinogen disorders in which a critical blood clotting factor,

plasma cell dyscrasias, or certain cancers. It is associated primarily with pathological bleeding.[5] 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.[6]

Congenital dysfibrinogenemia is the commonest of these three disorders. Some 100 different genetic

mutations occurring in more than 400 families have been found to cause it.[5][7] All of these mutations as well as those causing hereditary fibrinogen Aα-Chain amyloidosis exhibit partial penetrance, i.e. only some family members with one of these mutant genes develop dysfibrinogenemia-related symptoms.[8][6] While both of these congenital disorders as well as acquired dysfibrinogenemia are considered very rare, it is estimated that ~0.8% of individuals with venous thrombosis have either a congenital or acquired dysfibrinogenemia. Hence, the dysfibrinogenemia disorders may be highly under-diagnosed conditions due to isolated thrombotic events that are not appreciated as reflecting an underlying fibrinogen disorder.[3]

Congenital dysfibrinogenemia is distinguished from a similar inherited disorder, congenital hypodysfibrinogenemia. Both disorders involve the circulation of dysfunctional fibrinogen but in congenital hypodysfibrinogenemia plasma fibrinogen levels are low while in congenital dysfibrinogenemia they are normal. Furthermore, the two disorders involve different gene mutations and inheritance patterns as well as somewhat different symptoms.[3][9]

Fibrinogen

Main article: Fibrinogen

Fibrinogen is a

sialylation enzyme pathways thereby converting the heximer to a functional fibrinogen glycoprotein. The final circulating glycoprotein (notated as (AαBβγ)2, (αβγ)2, Aα2Bβ2γ2, or α2β2γ2) is arranged as a long flexible rod with nodules at both ends termed D domains and central nodule termed the E domain.[11][12]

The normal process of blood clot formation involves the coordinated operation of two separate pathways that feed into a final common pathway: 1)

B formed from this cleavage. In the final common pathway fibrin is cross-linked by activated clotting factor XIII (termed factor XIIIa) to form mature gel-like fibrin clots. Subsequent fibrinolysis pathways act to limit clot formation and dissolve clots no longer needed. Fibrinogen and its Aα fibrin chain have several functions in this process:[4][10][13][14]

Based on these fibrinogen functions, a fibrinogen mutation may act either to inhibit or promote blood clot formation and/or lysis to thereby produce in individuals a

diathesis to develop pathological bleeding, thrombosis, or both conditions.[4]

Congenital dysfibrinogenemia

Presentation

Many cases of congenital dysfibrinogenemia are asymptomatic. Since manifestations of the disorder generally occur in early adulthood or middle-age, younger individuals with a gene mutation causing it may not have had time to develop symptoms while previously asymptomatic individuals of advanced age with such a mutation are unlikely to develop symptoms. Bleeding episodes in most cases of this disorder are mild and commonly involve

cerebral hemorrhage. In one study of 37 individuals >50 years old afflicted with this disorder, 19% had a history of thrombosis. Thrombotic complications occur in both arteries and veins and include transient ischemic attack, ischemic stroke, myocardial infarction, retinal artery thrombosis, peripheral artery thrombosis, and deep vein thrombosis. In one series of 33 individuals with a history of thrombosis due to congenital dysfibrinogenemia, five developed chronic pulmonary hypertension due to ongoing pulmonary embolism probably stemming form deep vein thrombosis. About 26% of individuals with the disorder suffer both bleeding and thrombosis complications.[5][14]

Pathophysiology

Congenital dysfibrinogenemia is most often caused by a single

codon coded for the amino acid arginine at either the 35th position of FGA (termed Arg35; see fibrinogen Metz1 and fibrinogen Bicetre in the Table below) and or the 301st position of FGG (termed Arg301; see fibrinogen Baltimore IV in the Table below).[11]

The following Table lists examples of mutations causing congenital dysfibrinogenemias. It gives: a) the mutated protein's trivial name; b) the gene mutated (i.e. FGA, FGB, or FGG), its mutation site (i.e. numbered nucleotide in the

cloned gene), and the names of the nucleotides (i.e. C, T, A, G) at these sites before>after the mutation; c) the altered fibrinogen peptide (Aα, Bβ, or λ) and the amino acids (using standard abbreviations) found in the normal-mutated circulating fibrinogen; d) the cause of the mutated fibrinogen's misfunction(s); e) the clinical consequence(s) of the mutation; and f) comments. Unless noted as a deletion (del), frame shift (fs), or homozygous mutation, all mutations are heterozygous, missense mutations.[5][15]

Trivial name Gene: site of mutation Protein chain: site mutation Pathophysiology Clinical disorder Comment
fibrinogen Detroit FGA: c.114G>C/T Aα: Arg19Ser abnormal Polymerization bleeding relatively rare; first description of congenital dysfibrinogenmia[16]
fibrinogen Metz1 FGA: c.103C>T Aα: Arg35Cys delayed release of
fibrinopeptide A
 bleeding relatively common
fibrinogen Bicetrel FGA: c.104C>G Aα: Arg35His delayed release of
fibrinopeptide A
 bleeding relatively common
fibrinogen Perth FGA: c.1541delC Aα: Pro495Leufs thin clot, increased clot strength, impaired plasmin generation bleeding and thrombosis relatively rare
fibrinogen Naples FGB: c.292G>A Bβ: Ala68thr defective thrombin binding thrombosis relatively rare; homozygous
fibrinogen BaltimoreIV FGG: c.901C>T λ: Arg301Cys impaired fiber interactions thrombosis relatively common
fibrinogen Vlissingen FGG: c.1033_1038del λ: del Asn319-Asp320 impaired fiber interactions thrombosis relatively rare; nucleotides 1033-1038 and amino acids 319-320 deleted
fibrinogen BarccelonaIV FGG: c.902G>A λ: Arg301His impaired fiber interactions thrombosis relatively common

Diagnosis

The diagnosis of congenital dysfibrinogenmia is made by clinical laboratory studies that find normal levels of plasma fibrinogen but significant excess in the amount of immunologically detected compared to functionally detected (i.e. able to be clotted) fibrinogen. The ratio of functionally-detected to immunologically detected fibrinogen masses in these cases is <0.7. Partial thromboplastin time, activated partial thromboplastin time, thrombin time, and reptilase time tests are usually prolonged regardless of history of bleeding or thrombosis.[11] Where available, laboratory analyses of the fibrinogen genes and peptide chains solidify the diagnosis. Initial examination of these genes or protein chains should search specifically for "hot spot" mutations, i.e. the most common mutations (see Pathophysiology section) that comprise the large bulk of mutations in the disorder.[5] In cases of dysfibrinogenemia in which acquired disease is suspected, diagnosis requires a proper diagnosis of the presence of a causable disease.[4]

Congenital dysfibrinogenmia is initially distinguished form congenital hypodysfibrinogenemia by the finding of normal immunologically-detected levels of fibrinogen in congenital dysfibrinogenemia and sub-normal levels of immunologically-detected fibrinogen in congenital hypodysfibrinogenemia. Both disorders exhibit mass ratios of functionally-detected to immunologically-detected fibrinogen that are below <0.7. Genetic and protein analyses can definitively differentiate the two disorders.[9]

Treatment

In a study of 189 individuals diagnosed with congenital dysfibrinogenemia, ~33% were asymptomatic, ~47% experienced episodic bleeding, and ~20% experienced episodic thromboses.[9] Due to the rareness of this disorder, treatment of individuals with these presentations are based primarily on case reports, guidelines set by the United Kingdom, and expert opinions rather than controlled clinical studies.[5]

Asymptomatic individuals

Treatment of asymptomatic congenital dysfibrinogenemia depends in part on the expectations of developing bleeding and/or thrombotic complications as estimated based on the history of family members with the disorder and, where available, determination of the exact mutation causing the disorder plus the propensity of the particular mutation type to develop these complications.

prophylaxis therapy with fibrinogen replacement during pregnancy, delivery, and/or surgery.[5][9]

Symptomatic individuals

Individuals experiencing episodic bleeding as a result of congenital dysfibrinogenemia should be treated at a center specialized in treating

post-partum periods.[5]

Individuals experiencing episodic thrombosis as a result of congenital dysfibrinogenemia should also be treated at a center specialized in treating

low molecular weight heparin for a period that depends on personal and family history of thrombosis events. Prophylactic treatment prior to minor surgery should avoid fibrinogen supplementation and use prophylactic anticoagulation measures; prior to major surgery, fibrinogen supplementation should be used only if serious bleeding occurs; otherwise, prophylactic anticoagulation measures are recommended.[5]

Hereditary fibrinogen Aα-Chain amyloidosis

Presentation

Individuals with hereditary fibrinogen Aα-chain

end-stage kidney disease. They do not evidence pathological bleeding or thrombosis and their amyloidosis is non-systemic in that it is restricted to the kidney. In a report on 474 patients with renal amyloidosis, hereditary fibrinogen Aα chain disease represented only 1.3% of all cases whereas aberrant immunoglobulin-induced renal amyloidosis (e.g. AL amyloidosis) represented 86% of the cases).[17] Hereditary fibrinogen Aα-Chain amyloidosis is, however, the most common form of familial renal amyloidosis.[5][6]

Pathophysiology

Certain mutations in the fibrinogen Aα-chain gene cause a form of

frameshift viz., c.1622delT: Thr525Leu, is also a cause of the disorder. The fibrinogen bearing these mutant Aα-chains is secreted into the circulation and gradually accumulates in, and causes significant injury to, the kidney. The mutant fibrinogen does not appear to accumulate in, or injure, extra-renal tissues.[5][6][17]

Diagnosis

The diagnosis of this disorder depends on demonstrating: 1) a dysfunctional plasma fibrinogen, i.e. significantly less functionally-detected compared to immunologically-detected fibrinogen; b) presence of signs and/or symptoms of kidney disease; and c) histological evidence of often massive obliteration of renal glomeruli by amyloid as detected by Congo red staining. There also should be no evidence for systemic amyloidosis. Specialized centers use immunological and genetic studies to define the nature of the renal amyloid deposits, the presence of FGA gene mutations, and the occurrence of these mutations in family members. The disorder exhibits a highly variable penetrance among family members.[17][6] Hereditary fibrinogen Aα-Chain amyloidosis shows variable penetrance among family members, a distinctive histological appearance, proteinuria, progressive renal impairment, and markedly better survival rates than other forms of systemic renal amyloidosis.[6]

Treatment

Treatment of hereditary fibrinogen Aα-Chain amyloidosis has relied on chronic maintenance hemodialysis and, where possible, kidney transplantation. While recurrence of amyloidosis in the transplanted kidney occurs and is to be expected, transplant survival rates for this form of amyloidosis are significantly better than those for transplants in other forms of systemic renal amyloidosis. Relatively healthy individuals with hereditary fibrinogen Aα-Chain-related renal amyloidosis may be considered for kidney and liver bi-transplantation with the expectation that survival of the transplanted kidney will be prolonged by replacing the fibrinogen Aα-Chain-producing liver with a non-diseased donor liver.[6]

Acquired dysfibrinogenemia

Presentation

Acquired dysfibrinogenemia commonly present with signs, symptoms, and/or prior diagnoses of the underlying causative disease or drug intake in an individual with an otherwise unexplained bleeding tendency or episode. Bleeding appears to be more prominent in acquired compared to congenital dysfibrinogenemia; pathological thrombosis, while potentially occurring in these individuals as a complication of their underlying disease, is an uncommon feature of the acquired disorder.[4]

Pathophysiology

Acquired dysfibrinogenemia occurs as a known or presumed consequence of an underlying disease which directly or indirectly interferes with the clotting function of fibrinogen. Individuals with acquired dysfibrinogenemias have a greater tendency for bleeding complications than those with congenital fibrinogenemia.[4][18][19] The following Table gives some abnormalities, causes, and apparent pathophysiology along with some comments on examples of acquired dysfibrinogenemia.[3][4]

Abnormality Cause Pathophysiology Comment
incorrect post-translational modification of fibrinogen severe liver disease abnormal fibrinogen
sialylation
 most common cause of acquired dysfibrinogenemia
monoclonal antibody
plasma cell dyscrasias such as multiple myeloma
and MGUS		 monoclonal antibody interferes with clotting uncommon
polyclonal antibody
systemic lupus erythematosus, rheumatoid arthritis, ulcerative colitis
 polyclonal antibody interferes with clotting uncommon
production of abnormal fibrinogen by cancer cervical cancer of epithelium, renal cell carcinoma, others
paraneoplastic
effect of cancer		 extremely rare
Drug effect
mithramycin, isoniazid, direct thrombin inhibitors (e.g. heparin, dabigatran, bivalirudin, argatroban
)		 unclear extremely rare
case reports

Diagnosis

Diagnosis of acquired dysfibrinogenemia uses the same laboratory tests that are used for congenital dysfibrinogenemia plus evidence for an underlying causative disease.[4]

Treatment

Treatment of acquired dysfibrinogenemia follows the guidelines recommended for congenital dysfibrinogenemia.[4] In addition, treatment of any disease thought to be responsible for the dysfibrinogenemia might be useful. For example, therapeutic plasma exchange and chemotherapy to reduce monoclonal antibody levels has been used successfully to reverse otherwise uncontrollable bleeding in cases of multiple myeloma-associated dysfibrinogenemia.[20][21]

References

  1. ^ "Dysfibrinogenemia". Genetic and Rare Diseases (GARD). NIH. Retrieved 19 March 2019.[permanent dead link]
  2. ^ Dysfibrinogenemia at eMedicine
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External links

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