Fibrinogen Milano V: a congenital dysfibrinogenaemia with a gamma 275 Arg-->Cys substitution.

ABSTRACT

An abnormal fibrinogen was discovered in a clinically asymptomatic woman from Italy. Routine coagulation studies revealed prolonged thrombin and reptilase clotting times and a discrepancy between the plasma fibrinogen levels determined by the clotting assay and electroimmunoassay. Release of fibrinopeptides A and B from fibrinogen Milano V by thrombin was normal. Fibrin polymerization was strongly delayed in the presence of EDTA and was partially corrected at physiological calcium concentration. Normal migration of mercaptolysed polypeptide chains was observed 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 two-dimensional gel electrophoresis. A fragment of the gamma-chain gene coding for the amino acids 259-350 was amplified and cloned. The amino acid gamma 275 arginine was found to be substituted by cysteine. Immunoblotting analysis with a rabbit antiserum against human serum albumin indicated that albumin was not linked to the odd sulphydryl group of fibrinogen Milano V. Treatment of fibrinogen Milano V with cysteamine, that is surmised to convert the mutant cysteine to a positively charged lysine analogue, did not improve the clotting properties of fibrinogen Milano V.