Genetic studies of low-abundance human plasma proteins. IV. Improved typing of alpha-1 acid glycoprotein (orosomucoid) by isoelectric focusing and immunoblotting.

The sensitivity and specificity of isoelectric focusing (IEF) and immunoblotting have been combined for the routine typing of the plasma protein alpha-1 acid glycoprotein (Orosomucoid, ORM). Optimized conditions have been determined for a reliable classification of different ORM phenotypes. Phenotypic patterns of ORM in simple IEF gels correspond to those observed by other techniques. Addition of 6 M urea in a thin-layer IEF gel revealed additional, informative microheterogeneity in the ORM system, which cannot be detected in simple IEF gels. Applying the improved method, 239 White and 181 Black Americans have been screened to determine the distribution of ORM allele frequencies. Two common alleles, ORM1 and ORM2, have been observed and their frequencies are 0.5592 and 0.4408, and 0.6160 and 0.3840 in Whites and Blacks, respectively. Family studies confirm the genetic basis of this variation which is compatible with autosomal, codominant inheritance.