Study on the Association between different haptoglobin gene polymorphisms and the severity of sickle cell anemia complications in Sudanese children

Abstract

Introduction: Sickle cell anemia is an inherited hemoglobin disorder caused by a single mutation in hemoglobin gene and has various severe complications, mainly the hemolytic anemia. Haptoglobin gene is a polymorphic gene that codes for haptoglobin protein which has the main role in binding the free hemoglobin that is result from the destruction of RBCs during the hemolytic anemia in order to protect the blood vessels from the oxidative stress caused by this protein which may lead to more severe complications in sickle cell anemia patients. Aim: This study aimed to investigate the relationship between the Haptoglobin gene polymorphism and the severity of the clinical symptom in Sudanese sickle cell anemia children. Methodology : Hospital based case control study was conducted in which sixty blood samples were collected from Gaffer Ibn Ouf hospital and the sickle cell anemia center in Al- obied , including thirty samples from sickle cell anemia children and thirty samples from normal subjects. Demographic data including age, gender, ethnicity and hematological parameters were collected using a structured questionnaire.The DNA was extracted using Guanidine hydrochloride method and the quantity of DNA was determined using gel electrophoresis. Genotyping was done using allele specific PCR targeting Haptoglobin gene polymorphism.

Results: From demographic data, the highest incidence of sickle cell anemia is found in 1-6 years age group representing 63.3 % in which males and females were equally distributed and most of them were Afro –Asiatic representing 60 %. Regarding to disease severity, 50% of cases have moderate disease severity and 47 % have mild severity while only small percentage have the severe form of the disease (3%). When comparing the mean of hematological parameters in cases and controls , there was a significant difference only on the mean of HB (P.value =0.001 ) , Whereas non-significant differences found in the mean of RBCs ( P.value = 0.516 ) , WBCs ( P.value =0.510 ) , and in platelets P.value =(0.204 ). Regarding Hp genotype frequency, this study showed that the homozygous Hp 2-2 was significantly the most common genotype (P.value =0.001) in both cases and controls representing 90.5 % in cases and 78.3 % in controls. On the other hand, Hp1-1 was less common representing 9.5 % in cases and 21.7 % in controls. No heterozygous Hp 2-1 was detected in this study. Also, there was no significant difference between cases and controls regarding Hp genotype. (P.value =0.269) Conclusion: From demographic data, the highest incidence of sickle cell anemia found in 1-6 years age group, most of them were Afro –Asiatic. From the genetic analysis results of this study, Hp 2-2 genotype appear to be common in both sickle cell anemia patients and in normal subjects, this may conclude no strong association between Hp gene polymorphism and the severity of complications in sickle cell anemia. The difference in Hp gene polymorphism between different populations is mainly due to ethnic variation.