Novel fibrinogen gamma-chain mutation p.Asp342Asn (fibrinogen Pisa) associated with hepatic fibrinogen storage disease and hypofibrinogenaemia

Background: Type I fibrinogen deficiencies (hypofibrinogenemia and afibrinogenemia) are rare congenital disorders characterized by low or unmeasurable plasma fibrinogen antigen levels. Their genetic bases are represented by mutations within the three fibrinogen genes, FGA, FGB, and FGG, coding for Aalpha, Bbeta, and gamma fibrinogen chains. So far, about 130 genetic defects have been reported to cause a- or hypofibrinogenemia, but only four mutations, all located in the fibrinogen gamma-chain gene, were shown to cause hepatic endoplasmic reticulum storage disease (ERSD). Aims: To find the genetic basis of hypofibrinogenemia and to investigate the possibility of hepatic fibrinogen storage disease in a 4-year-old female with elevated serum aminotransferases. Methods: Plasma functional and antigen fibrinogen levels were measured by an assay based on fibrin polymerisation time and by an enzyme-linked immunosorbent assay, respectively. Mutational screening was performed by direct sequencing of PCR products covering the coding sequence of FGA, FGB, and FGG genes. Liver histology was evaluated by light microscopy and immunocytochemistry. Results: The proband had concordantly reduced functional and immunologic fibrinogen levels (136 and 117 mg/dL, respectively), distinctive of hypofibrinogenemia. Molecular screening revealed the presence of a novel heterozygous transition (c.1024G>A) in exon 8 of FGG, leading to the p.Asp342Asn missense mutation (p.Asp316Asn, according to the mature protein numbering). This non-conservative amino acid substitution involves a highly conserved residue located in the C-terminal globular D-domain of the gamma chain. The same mutation was found also in the proband’s mother and grandfather, who also had similarly reduced plasma fibrinogen levels but no sign of liver disease. Histological analysis of hematoxylin-eosin stained sections of proband liver biopsy samples revealed hepatocyte cytoplasmic microvescicular steatosis and the presence of small globular and needle-like inclusions. These inclusions were negative with PAS-D and iron histochemical reactions, not refracting with polarized light and not auto fluorescent. All cytoplasmic inclusions of hepatocytes were strongly immunoreactive with anti-fibrinogen antibody. Conclusions: This work reports the identification of the fifth mutation in the FGG gene leading to hypofibrinogenemia and liver ERSD. As described in other families, our data confirm that the link between the FGG mutation and ERSD is not as strong as that with hypofibrinogenemia.