Lipoprotein(a): identification of subjects with a superbinding capacity for fibrinogen

We have previously shown that the binding of lipoprotein(a) [Lp(a)] to immobilized fibrinogen involves the domain located in kringles IV-5 to IV-8, but not kringle IV-10. In extending those studies to subjects living in Chicago and in the island of Sardinia, we found that about 6% of them had an Lp(a) with Bmax values of 27.7+/-6.0 fmol, which were about 5-8-fold higher than those of controls (3.4+/-2.8 fmol) and in the range of those observed for free apo(a) derived from the Lp(a) of controls (36.6+/-2.9 fmol). This superbinding phenotype was unaffected by age, sex, type of lipid disorder and hypolipidemic agents, and also had a familial incidence. We are currently exploring the hypothesis that this fibrinogen superbinding phenotype is due to conformational changes of apolipoprotein(a) [apo(a)] resulting from the lipid content and composition of the Lp(a) particle and/or sequence anomalies in the kringle domain IV-5 to IV-8.