Identification of an uncommon haptoglobin type using DNA and protein analysis

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Abstract
The inherited variations in haptoglobin phenotypes are attributed to the homozygous and heterozygous combinations of three common autosomal alleles:HP * 1F,HP * 1S andHP * 2.HP * 1F andHP * 1S encode polypeptides that differ by two amino acids at positions 51 and 53. The formation ofHP * 2 is postulated to have resulted from a breakage and subsequent reunion event at non-homologous positions of twoHP * 1 alleles. The most common form ofHP * 2 isHP * 2FS in which the 5′ end ofHP * 2 resemblesHP * 1F and the 3′ end resemblesHP * 1S. Homologous crossing over betweenHP * 2 and either anHP * 1F orHP * 1S allele inHP * 2/HP * 1 heterozygotes can change the usual type ofHP * 2 to three other forms:HP * 2SS,HP * 2FF orHP * 2SF. We describe a nuclear family in which the uncommon genotypeHP * 2SS in one parent caused initial confusion in assigning genotypes to the rest of the nuclear family. The data demonstrate the need for a cautious approach when deducing haptoglobin genotypes from molecular analysis alone.