Genotyping of the common haptoglobin Hp 1/2 polymorphism based on PCR

A genetically defined molecular heterogeneity of haptoglobin, characterized by the major phenotypic forms Hp 1-1, Hp 2-1, and Hp 2-2, has been associated with distinct clinical manifestations. To enable the use of DNA samples for the study of this polymorphism, we established a haptoglobin genotyping method based on PCR.

Taking advantage of the selectivity of PCR, we amplified DNA segments specifically representing haptoglobin alleles Hp 1 and Hp 2 from genomic DNA. The products were analyzed by agarose gel electrophoresis. Haptoglobin phenotyping of plasma samples was performed by polyacrylamide gel electrophoresis and peroxidase staining.

Exploiting the known size difference between Hp 1 and Hp 2, we amplified allele-specific DNA molecules with one pair of oligonucleotide primers. As an alternative, we used separate primer pairs to generate amplification products indicative of alleles Hp 1 and Hp 2. Because of the primer design, genotype determination was not compromised by sequence variations specifying haptoglobin allele subtypes S and F. For the same reason, the sequence similarity between the haptoglobin gene and the haptoglobin-related gene did not interfere with the accuracy of genotyping. Analysis with restriction enzymes demonstrated the authenticity of the allele-specific DNA products. Haptoglobin DNA genotyping and protein phenotyping, performed in parallel, yielded fully corresponding results. In a group of 249 individuals, the haptoglobin genotype distribution was as follows: 14.5% Hp 1-1, 48.2% Hp 2-1, and 37.3% Hp 2-2.

The new method can be used for genotyping of a common haptoglobin polymorphism.