FIBRINOGEN LINCOLN - A NEW TRUNCATED ALPHA-CHAIN VARIANT WITH DELAYEDCLOTTING

A patient referred for preoperative investigation of prolonged bleedin g and easy bruising was found to have increased thrombin and reptilase times; however, the thrombin catalysed release of fibrinopeptides A a nd B was normal. Analysis of five other family members, spanning three generations, indicated that three had a similar defect and suggested autosomal dominant inheritance. Non-reducing SDS-PAGE of purified fibr inogen from affected individuals showed that the 340kD form of their f ibrinogen ran as a doublet. SSCP (single-stranded conformational polym orphism) analysis of exon 5 of the A alpha gene, which encodes the C-t erminal half of the chain, confirmed the presence of a mutation. Cycle sequencing of PCR amplified DNA revealed a 13 base pair deletion (nt 4758-4770), resulting in a frameshift at Ala 475, which translates as four new amino acids before terminating at a new stop codon (-(476)His -Cys-Leu-Ala-Stop). The presence of a circulating truncated Aa chain w as confirmed when SDS-PAGE gels were probed with an a chain specific a ntisera; which showed that the variant A alpha chain comigrated with g amma chains. The truncation results in a variant A alpha chain with a deletion of 131 amino acids (480-610), and four new amino acids at the C-terminal.