FIBRINOGEN MILANO-V - A CONGENITAL DYSFIBRINOGENEMIA WITH A GAMMA-275ARG-]CYS SUBSTITUTION

An abnormal fibrinogen was discovered in a clinically asymptomatic wom an from Italy. Routine coagulation studies revealed prolonged thrombin and reptilase clotting times and a discrepancy between the plasma fib rinogen levels determined by the clotting assay and electroimmunoassay . Release of fibrinopeptides A and B from fibrinogen Milano V by throm bin was normal. Fibrin polymerization was strongly delayed in the pres ence of EDTA and was partially corrected at physiological calcium conc entration. Normal migration of mercaptolysed polypeptide chains was ob served in polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. Moreover, there was no apparent abnormality in the charge of the reduced chains of the variant fibrinogen, as judged by t wo-dimensional gel electrophoresis. A fragment of the gamma-chain gene coding for the amino acids 259-350 was amplified and cloned. The amin o acid gamma 275 arginine was found to be substituted by cysteine. Imm unoblotting analysis with a rabbit antiserum against human serum album in indicated that albumin was not linked to the odd sulphydryl group o f fibrinogen Milano V. Treatment of fibrinogen Milano V with cysteamin e, that is surmised to convert the mutant cysteine to a positively cha rged lysine analogue, did not improve the clotting properties of fibri nogen Milano V.