الفهرس 
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Abstract
Sickle cell disease (SCD) is a common haemoglobinopathy that results in chronic haemolytic anaemia, increased erythropoiesis and a chronic inflammatory state with endothelial activation and enhanced red cell and leukocyte adhesion. Patients with SCD are likely to be at extra risk for iron overload, because they are in a chronic hemolytic state and exhibit increased gastrointestinal absorption. Also, they may receive acute or chronic transfusions for treatment or prevention of the severe sickle cell-related complications such as stroke (Jeng et al., 2003).
Hepcidin, antimicrobial peptide produced in the liver, has been shown to play a central role in the homeostatic regulation of iron absorption and distribution (Park et al., 2001). Several studies suggest that there are strong genetic components that underlie hepcidin regulation beyond the usual suspects (i.e. infection, inflammation, erythropoiesis, hypoxia and iron), in a manner that could impinge on phenotypic differences in susceptibility to iron-overload or anaemia. Mouse genetics suggests epistatic interactions between the hepcidin gene (HAMP) and HFE, TfR2 and HJV. Polymorphisms or mutations at any of these loci or their upstream regulators could cause significant variability in hepcidin expression and differential iron-loading (Lee and Beutler, 2009).
In an attempt to shed light on the genetic determinants of iron overload in SCD patients, the aim of our work was to verify the influence of G71D of HAMP gene and H63D of HFE gene variants on iron overload in sickle cell disease patients. To achieve this aim, we studied the genes mutations frequencies in SCD patients as well as healthy controls.
Iron profile in the form of) serum iron, serum TIBC, transferrin saturation and steady-state serum ferritin level) was determined and genotyping of G71D of HAMP and of H63D of HFE variants was performed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) on a total of 92 subjects, 47 patients with SCD (39 patients with HbSS and 8 patients with HbS/β-thalassaemia) and Forty five age- and sex-matched healthy volunteers as a control group.
Genotyping of HAMP-G71D variant in the studied SCD patients revealed that 7 (14.9%) patients had a variation in HAMP-G71D, 6 (12.8%) in heterozygous state and one (2.1%) in homozygous state. Among the control group, nearly similar frequencies of HAMP-G71D variant were observed. Six out of 45 (13.3%) control subjects carried heterozygous G71D mutation.
As regards genotyping of HFE-H63D, the prevalence of heterozygous H63D genotype was (27.7%) among SCD patients and (8.9%) among controls. No homozygous H63D genotype was detected in patients or controls. Dual mutant genotype was detected in 4.3% of the patients and in 2.2% of the controls. Compared to controls, SCD patients showed a statistically significant higher frequency of H63D mutation (27.7% vs. 8.9%, p=0.02).
In the current study, the identification of either HAMP- G71D or HFE-H63D mutation in SCD patients did not determine which SCD patients were at risk for heavy iron overload since patients with either HAMP-G71D or HFE-H63D variants did not show statistically significant difference in their iron overload parameters in relation to wild type patients.
Our study confirmed the major impact of total lifetime transfusion on serum ferritin in frequently transfused SCD patients. Mean serum ferritin level was significantly higher in patients received >50 transfusions in lifetime than patients received ≤ 50 transfusions in lifetime (p=0.011). On the other hand, among the group of SCD patients who received > 50 transfusions in lifetime, the mean serum ferritin level was significantly higher in those carrying mutant genotype compared to wild type patients (p=0.017).
Among the group of SCD patients who are not compliant to iron chelation therapy, serum ferritin and serum TIBC were significantly higher in mutant genotype patients than those carrying the wild genotype (p=0.039 and 0.033, respectively).
Multivariate regression analysis of independent factors that may significantly affect serum ferritin level among the study sample revealed that only treatment with HU significantly reduces the serum ferritin level (p=0.020). The number of mutations harbored tends to affect serum ferritin level (p=0.054), however, this effect did not reach statistical significance. Our results may support the hypothesis that interaction between genetic determinants of iron regulating genes could in some cases be implicated in increasing iron storage.