Orosomucoid (ORM) typing by isoelectric focusing: evidence for an additional duplicated ORM1 locus haplotype and close linkage of two ORM loci.

Human serum orosomucoid (ORM) exhibits a high variability. Several alleles including a duplicated ORM1 gene (ORM12.1) have been identified at two functional ORM loci, ORM1 and ORM2. In this study a modified isoelectric focusing, in which glycerin was omitted from gels, was used to differentiate a new variant ORM1 5 from ORM2 3. The ORM1 5 band was always observed together with the ORM1 2 band. The simultaneous expression could be explained in terms of an additional duplicated ORM1 locus haplotype, ORM15.2, whose average frequency was .016 in two Japanese populations. The ORM26 found at a polymorphic frequency (.023) was demonstrated to be in association with ORM12, indicating the close proximity between ORM1 and ORM2 loci.