Fibrinogen brescia - Hepatic endoplasmic reticulum storage and hypofibrinogenemia because of a gamma 284 Gly -> Arg mutation

The proposita suffered from liver cirrhosis and biopsy showed type 1 membra ne-bound fiberglass inclusions. The hepatic Inclusion bodies were weakly pe riodic acid-Schiff diastase-positive, and on immunoperoxidase staining reac ted specifically with anti-fibrinogen antisera, Coagulation investigations revealed low functional and antigenic fibrinogen together with a prolonged thrombin time of 37 seconds (normal, 17 to 22 seconds) suggestive of a hypo dysfibrinogenemia. DNA sequencing of all three fibrinogen genes showed a si ngle heterozygous mutation of GGG (Gly)->CGG (Arg) at codon 284 of the gamm a-chain gene. However, examination of purified fibrinogen chains by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, reverse-phase high-perf ormance liquid chromatography, ion-exchange high-performance liquid chromat ography, and isoelectric focusing, failed to show any evidence of the mutan t gamma(BR) chain in plasma fibrinogen. This finding was substantiated by e lectrospray ionization mass spectrometry, which showed only a normal gamma (and B beta) chain mass, but a large increase in the portion of their disia lo isoforms, We speculate that misfolding of the variant protein causes hep atic retention and the subsequent hypofibrinogenemia, and that the function al defect (dysfibrinogenemia) results from hypersialylation of otherwise no rmal B beta and gamma chains consequent to the liver cirrhosis, These concl usions were supported by studies on six other family members with hypofibri nogenemia, and essentially normal clotting times, who were heterozygous for the gamma 284 Gly->Arg mutation.