Case Report: Unmasked Inherited Dysfibrinogenemia After Everolimus Therapy

A previously hemostatically asymptomatic patient with common variable hypogammaglobulinemia was given everolimus to prevent growth of her liver. Within several months, the patient developed a severe bleeding disorder. The bleeding was due to fibrin polymerization defect that upon sequencing was shown to be dysfibrinogenemia Krakow III. Elimination of the mTor inhibitor ameliorated the clinical bleeding state.

A 45 yo woman with a history of common variable immunodeficiency (CVID) was referred for a bleeding disorder. In 2009, this patient was diagnosed with common variable hypogammaglobulinemia. In 2011, the disorder manifested with immune thrombocytopenia and a splenectomy was performed. At that time, she had a normal prothrombin time (PT) and activated partial thromboplastin time (aPTT) and had no abnormal bleeding at surgery. In 2013, she developed hepatomegaly. In 2016, the hepatomegaly was symptomatic and she was started on everolimus by her liver immunologists as part of a protocol to reduce her liver size.
In general, a normal reptilase time with an abnormal thrombin time suggests a fibrinopeptide B release defect (1,2). However, fibrinopeptide B defects are not associated with bleeding (2). Therefore the combined clinical and laboratory data suggest a fibrin polymerization defect. In a fibrin polymerization assay, the patient required 4-fold greater concentrations of human alpha-thrombin (32 vs. 8 nM) to achieve complete fibrin polymerization (Figure 1B). Since recognizing this fibrin polymerization defect, the patient's bleeding episodes have been controlled by cryoprecipitate infusions to raise her baseline fibrinogen values by 150-250 mg/dl with normal fibrinogen.
Sequencing of fibrinogen coding regions following PCR amplification of leukocyte genomic DNA revealed that the patient was heterozygous for a mutation in fibrinogen gamma chain exon 3 [FGGc.124G>A, p.Gly42Ser (Gly16Ser in the mature protein without the signal peptide)] (Figure 1C). This defect was previously described in a bleeding patient with similar blood coagulation studies as Fibrinogen Krakow III (3). Neither a control DNA sample from a normal donor nor the patient's father have this mutation. However, the patient's mother has the identical heterozygous mutation. The patient's mother, who is otherwise healthy, has no bleeding history. Our patient also is heterozygous for Fibrinogen Krakow III but never had a bleeding problem until everolimus treatment was instituted to manage her CVID.
The original hypothesis for these investigations was that treatment with everolimus caused an "acquired" bleeding state. Everolimus is an mTor inhibitor and mTor is a major regulator of protein synthesis (4). Further, mTor inhibition itself blocks fibrin clot retraction (5). Later, the patient also was found to have a heterozygous genetic polymorphism in her fibrinogen's gamma chain that interferes with fibrin polymerization. Thus, the patient's congenital fibrinogen mutation and everolimus treatment combined to give this patient a serious bleeding disorder. Upon urging the patient and treating physicians, the everolimus therapy was stopped and she has not had a major bleeding incident in 18 months. She does, however, have frequent minor mucous membrane bleeding (e.g., epistaxis). She persists in having an abnormal thrombin time and reduced fibrinogen activity/antigen ratio of 0.7.

DATA AVAILABILITY STATEMENT
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ETHICS STATEMENT
The studies involving human participants were reviewed and approved by University Hospitals Cleveland Medical Center IRB. The patients/participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

AUTHOR CONTRIBUTIONS
AM, SMi, SMe, AW, and MN-A contributed experimental studies. AS conceived the project. AS, AW, and MN-A wrote the manuscript. All authors contributed to the article and approved the submitted version.

FUNDING
This study was not supported by any specific grants, but laboratory operations and PI support to AHS was through NIH grants AI130131, HL144113, HL143402, and CA223301. MN-A was supported by a grant from the Swiss National Science Foundation (grant #31003A_172864).