Human beta 2-glycoprotein I has recently been identified as a component of several human plasma lipoprotein fractions and therefore termed as apolipoprotein H. Its metabolic function in lipid metabolism is not known with certainty, though it may be involved in very-low-density-lipoprotein metabolism. Previously, inherited quantitative variation in beta 2-glycoprotein I has been suggested in man. In this investigation, we document the evidence of genetically determined structural polymorphism of apolipoprotein H or beta 2-glycoprotein I by using thin-layer polyacrylamide isoelectric focusing gels followed by immunological identification by double antibody staining. The apolipoprotein H structural locus is characterized by the occurrence of three common alleles in U.S. whites and blacks. The frequency distributions of the three alleles designated APO H1, APO H2, and APO H3 are .059, .882, and .059 in whites and .017, .902, and .068 in blacks, respectively. In addition, the gene product of a fourth allele, APO H4, has been observed at polymorphic frequency in black individuals and may represent a black marker variant. Family data confirm the hypothesis of four alleles at a single APO H gene locus with an autosomal codominant pattern of inheritance.
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