Congenital structural and functional fibrinogen disorders: a primer for internists.

Congenital qualitative and quantitative fibrinogen disorders represent heterogeneous rare abnormalities caused by mutations in one of the 3 genes encoding individual fibrinogen polypeptide chains, located on chromosome 4q28. It is estimated that congenital fibrinogen disorder accounts for 8% of rare coagulation factor deficiencies. Most of congenital fibrinogen disorders are suspected in individuals with bleeding tendency or coincidentally discovered, for instance prior to surgery. Fibrinogen disorders could be also found in patients with thrombotic events, impaired wound healing, and recurrent spontaneous abortions. Afibrinogenemia manifests as mild to severe bleeding, while hypofibrinogenemia is often asymptomatic. Dysfibrinogenemia, a qualitative fibrinogen disorder, is associated with bleeding, thrombosis, or with no symptoms. Recent recommendations issued by the International Society on Thrombosis and Haemostasis in 2018 do not encourage routine evaluation of thrombin time or other coagulation tests in patients with suspected congenital fibrinogen disorders, highlighting the value of fibrinogen antigen measurement and genetic analysis, added to the key finding, that is, reduced fibrinogen concentration determined with a coagulometric assay. The current review summarizes practical issues in diagnostic workup and clinical management of patients with afibrinogenemia, hypofibrinogenemia, dysfibrinogenemia, and hypodysfibrinogenemia from a perspective of internists who may encounter patients with reduced fibrinogen concentration in everyday practice. Despite the fact that hematologists are in front line for the management of patients with bleeding tendency, internists should be aware of the clinical and laboratory findings in patients with inherited fibrinogen disorders including the risk of thromboembolism and management prior to invasive procedures.

Clot waveform analysis in Clauss fibrinogen assay contributes to classification of fibrinogen disorders.

BACKGROUND: Clauss fibrinogen assay (CFA) is widely used as a screening test to detect fibrinogen disorders. However, CFA alone cannot distinguish quantitative and qualitative defects because it depends on functional fibrinogen activity (Ac), and fibrinogen antigen (Ag) determination is required to classify fibrinogen disorders. OBJECTIVES: To establish a novel approach to classify fibrinogen disorders, we investigated the potential of clot waveform analysis (CWA) of CFA and searched for a surrogate marker for fibrinogen Ag. MATERIALS AND METHODS: We analyzed CWA parameters obtained from CFA using plasma from normal patients (n = 91) and those with fibrinogen disorders (n = 27, including 15 hypofibrinogenemia, 6 dysfibrinogenemia and 6 hypodysfibrinogenemia) with a CS-5100 autoanalyzer. RESULTS: We found that maximum coagulation velocity (Min1) levels were most strongly correlated with fibrinogen Ag in both normal and fibrinogen disorders. Hence, Min1 appeared to function as a surrogate for fibrinogen Ag. Although the Ac/Min1 ratio did not simply reflect the measured Ac/Ag ratio, we found that the Ac/Min1 ratio was significantly higher than normal in hypofibrinogenemia and hypodysfibrinogenemia, but not in dysfibrinogenemia. On the other hand, we could distinguish type II deficiency from type I using estimated fibrinogen Ag (eAg) predicted from Min1. The Ac/eAg ratios of dysfibrinogenemia and hypodysfibrinogenemia were significantly lower than those of normal and hypofibrinogenemia. CONCLUSION: The CWA of CFA could distinguish fibrinogen disorders using a combination of Ac/Min1 and Ac/eAg values. This analysis allows the qualitative detection of fibrinogen disorder easily and represents a novel screening test for fibrinogen disorders.

[Analysis of molecular pathogenesis and clinical phenotypes in 10 probands with inherited fibrinogen deficiency].

OBJECTIVE: To explore the molecular pathogenesis and clinical phenotypes in 10 probands with inherited fibrinogen (Fg) deficiency. METHODS: The diagnosis of hereditary Fg deficiency was validated by prothrombin time (PT), thrombin time (TT), Fg activity (Fg:C) and Fg antigen (Fg:Ag) in plasma. All of the exons and their flanking sequences of the Fg gene were analyzed by direct sequencing. Detected mutations were confirmed by reverse sequencing. RESULTS: The ranges of Fg:C and Fg:Ag in the 10 probands were 0.52-0.91 g/L and 0.62-2.98 g/L, respectively. Five of the probands had type I disorders, and 5 had type II disorders. Seven point mutations were identified, among which 6 have located in the D region. γThr277Arg, γAsp316His, γTrp208Leu and Lys232Thr were novel mutations, and αArg19Ser was first reported in Chinese. Four probands had the same mutation site (γArg275). As to the clinical manifestation, probands with type I disorders were asymptomatic or with mild or medium symptoms, while those belonged to type II disorders had moderate or serious symptoms. Two probands have carried an Arg275Cys mutation but had different clinical manifestations. CONCLUSION: Mutations of the Fg gene seem to aggregate to the D region of FGG in our region, and Arg275 is a common mutation. However, no correlation has been found between the mutation site and clinical manifestations.