Refractory Hypertension is Associated with the Haptoglobin 2-2 Phenotype

BACKGROUND: Many cases of refractory hypertension cannot be attributed to specific identifiable factors. Haptoglobin polymorphism has been suggested as a candidate genetic marker in essential hypertension. The aim of this study was to investigate the distribution of haptoglobin types in patients with refractory hypertension. METHODS: Haptoglobin polymorphism was studied in 383 patients with non-refractory and 62 patients with refractory hypertension. Haptoglobin was typed using starch gel electrophoresis of haemoglobin-supplemented serum. RESULTS: In the group of patients with refractory hypertension, the relative allele frequency of haptoglobin 1 (0.266) was lower than in the group with non-refractory hypertension (0.385: P < or = 0.05). The relative frequency of haptoglobin 2-2 was 39% in the non-refractory compared with 56% in the refractory group (P < or = 0.05). In the latter group, the relative frequency of haptoglobin 2-2 was highest (75%) in patients requiring medication with four classes of drug. CONCLUSION: Hypertension patients with the haptoglobin 2-2 phenotype are at higher risk of developing refractory hypertension than those with other haptoglobin phenotypes.