THE RELATIVE ELECTROPHORETIC MOBILITY OF APO(A) ISOFORMS DEPENDS ON THE GEL SYSTEM - PROPOSAL OF A NOMENCLATURE FOR APO(A) PHENOTYPES

Genetic apo(a) isoforms were originally defined according to their rel ative mobility in SDS-PAGE compared to apoB-100 and were designated as F, B or S1-S4 isotypes, This widely accepted nomenclature does not ac commodate the broad spectrum of apo(a) isoforms (> 30) detected by hig h resolution SDS-agarose gel electrophoresis. Moreover we here show th at the relative mobilities of apo(a) isoforms depend on the SDS-gel sy stem used. Comparison of the SDS-PAGE system originally used for pheno typing with SDS-agarose gel electrophoresis and two commercial SDS-PAG E systems (PhastGel, Pharmacia, Sweden and NOVEX, USA) demonstrated ma rked differences in resolving power and resulted in very different R(f ) values for identical isoforms. Hence phenotyping results from labora tories using different systems are not comparable. We therefore propos e a nomenclature of apo(a) isoforms which reports the number of kringl e IV repeats in the apo(a) allele (e.g. apo(a) K-IV20 would designate an isoform with 20 K-IV repeats). This is achieved by using standards in which the number of kringle IV repeats has been determined by pulse d field gel electrophoresis of genomic DNA. The proposed nomenclature (i) accounts for the increased resolution of apo(a) phenotyping method s; (ii) is flexible to the introduction of smaller or larger isoforms; (iii) allows to report data from systems with lower resolution as 'bi nned' isoform categories; (iv) allows the comparison of phenotyping re sults between different investigators; and (v) can be applied on DNA a s well as on protein based apo(a) phenotyping.