Haptoglobin genotypes in sickle-cell disease

We compared the frequencies of the haptoglobin (Hp) genotypes of 775 Brazilian patients with sickle-cell disease divided into the following age groups: 3 months-5 years, 6-10 years, 11-15 years, 16-20 years, and over 20 years. The last group (>20 years) was also compared with a healthy control group and was further divided into subgroups including only subjects aged 21-30 years (V.a and Control.a) and over 30 years (V.b and Control.b). There was no significant difference in the frequencies of the Hp genotypes between the different patient groups or between the patients and controls. However, the Hp2-2 genotype was always less frequent than the Hp1-1 genotype in the patient groups, whereas the opposite was observed in healthy controls. The frequency of Hp2-2 was 25.0% in patients in the 21-30 years age group and fell to 19.5% in those over 30 years. In the controls, the corresponding frequency was around 28%. Although our results do not allow us to conclude that Hp genotypes on their own confer greater or lesser selective advantage on sickle-cell disease patients in the population studied, this polymorphism may, when combined with other genetic and environmental factors, contribute to the clinical diversity observed in this disease.