Benign FGB (148Lys→Asn, and 448Arg→Lys), and novel causative γ211Tyr→His mutation distinguished by time of flight mass spectrometry in a family with hypofibrinogenaemia

We describe a novel procedure for the direct analysis of plasma fibrinogen by HPLC time of flight (TOF) mass spectrometry and apply it to the investigation of a family with hypofibrinogenaemia. Electrospray TOF analysis provided much higher resolution than was possible with our previous quadrupole analyser and revealed three different mass changes within the fibrinogen 136 and gamma chains of the family. It also demonstrated the actual hypofibrinogenaemia phenotype was caused, by an aberrant gamma chain (-23 Da) which was expressed at a diminished ratio of 0.2:1 relative to gamma(A) and co-inherited with a second coequally expressed BP variant (B beta(M) /[B beta(A), 1:1). Co-segregation was confirmed by gene analysis that showed the affected father and son had a very rare B beta 148Lys -> Arg mutation (-14 Da) inherited together with a unique new gamma 211Tyr -> His mutation (-26 Da). This latter causative substitution occurs at a site that is absolutely conserved across all fibrinogen chains and preserved across all species. TOF analysis also identified a variant B beta chain (54,186 Da) that was coequally expressed with normal B beta chains (54,213 Da) in the unaffected mother.