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.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. 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. 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.Congenital dysfibrinogenemia is distinguished from a similar inherited disorder, congenital hypodysfibrinogenemia.
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). Hereditary fibrinogen Aα-Chain amyloidosis is, however, the most common form of familial renal amyloidosis. Pathophysiology
Certain mutations in the fibrinogen Aα-chain gene cause a form of familial renal amyloidosis termed hereditary fibrinogen Aα-Chain amyloidosis. The disorder is due to autosomal dominant inheritance of Aα chain mutations the most common of which is hemoglobin Indianopolis, a heterzyogus missense (c.1718G>T: Arg554Leu) mutation. Other missense mutations causing this disorder are unnamed; they include 1634A>T: Glu526Val; c.1670C>A: Thr538lys; c.1676A.T:Glu540Val; and c1712C>A:Pro552His. A deletion mutation causing a 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. 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.