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Genetic studies of low-abundance human plasma proteins. V. Evidence for a second orosomucoid structural locus (ORM2)
Abstract:
Orosomucoid (ORM) or alpha-1-acid glycoprotein is an acute-phase protein of human plasma whose function is suggested to be the competitive inhibition of cellular recognition by infective agents. Genetically determined variation in ORM has been reported, with two major alleles segregating in all populations studied to date. Isoelectric focusing-immunoblotting studies of ORM revealed the presence of isoprotein species that did not segregate with the predominant alleles at the ORM locus and suggested the expression of a second structural gene locus for orosomucoid (ORM2). Genetically independent variation consistent with expression of the ORM2 locus was observed in plasma samples from American blacks but was not observed in U.S. whites or sampled populations of North- and South-American Indians, Eskimos, Aleuts, or New Guinea Highlanders. The population allele frequencies for this locus were .958, .025, .006, and .011 for alleles ORM*1, ORM2*2, ORM2*3, and ORM2*4, respectively. Family studies confirm the autosomal codominant inheritance of the observed phenotypes.
Insights
Genetic variation in alpha-1-acid glycoprotein (orosomucoid, ORM) suggests a second structural gene locus, ORM2. This locus
Area of Science:
- Genetics
- Biochemistry
- Immunology
Background:
- Orosomucoid (ORM), also known as alpha-1-acid glycoprotein, is a key acute-phase protein in human plasma.
- Its proposed function involves inhibiting cellular recognition by infectious agents.
- Previous studies indicated genetically determined variation in ORM, with two major alleles found across populations.
Purpose of the Study:
- To investigate the presence and genetic basis of additional ORM variants.
- To identify potential new structural gene loci for orosomucoid.
- To determine the inheritance patterns and population frequencies of these variants.
Main Methods:
- Isoelectric focusing-immunoblotting techniques were employed to analyze ORM isoprotein species.
- Plasma samples from diverse ethnic and geographic groups were studied.
- Family studies were conducted to confirm inheritance patterns.
Main Results:
- Isoelectric focusing-immunoblotting revealed isoprotein species not linked to known ORM alleles, suggesting a second locus (ORM2).
- Genetically independent variation was observed in American black populations but not in other studied groups (U.S. whites, Indigenous Americans, Eskimos, Aleuts, New Guinea Highlanders).
- Population allele frequencies for ORM2 were determined: ORM2*1 (0.958), ORM2*2 (0.025), ORM2*3 (0.006), and ORM2*4 (0.011).
Conclusions:
- The findings support the existence of a second structural gene locus for orosomucoid, designated ORM2.
- The ORM2 locus exhibits genetically independent variation, particularly in American blacks.
- Autosomal codominant inheritance was confirmed for the observed ORM2 phenotypes.