Results

The investigated population was 60 BTM patients including 28 female and 32 men who were on regular red blood cell transfusion at intervals of 2–4 weeks. The mean ages of the BTM patients were 17.5±9.1 years. The rate of splenectomy in the study population was 25.0% (15 out of 60 BTM patients). Of the 60 patients, 10 (16.6%) had developed alloantibody with anti-K the most common. All patients were transfused with leukoreduced packed red blood cells. All patients received regular iron chelation therapy from early childhood. Thirty-five patients were under regular iron chelation therapy with desferrioxamine (30–50 mg/kg/day), which was administered subcutaneously. The 25 patients that had an intolerance to desferrioxamine were chelated with oral iron chelator deferasirox (30–40 mg/kg/day). Abnormal hepatic iron load (T2*MRI < 6.3 ms) and abnormal cardiac iron load (T2*MRI < 20 ms) was detected in 25 (41.6%) and 23 (38.3%) patients with BTM, respectively. Detailed information regarding the cardiac and hepatic T2*MRI values in the BTM patients are presented in Table 1. The comparison of BTM patients with and without hemosiderosis revealed that plasma ferritin levels, iron levels, and transferrin saturation index were significantly higher in BTM patients with hepatic hemosiderosis than those without hepatic hemosiderosis (p = 0.021; p = 0.001; p = 0.010, respectively). Similarly, these values were significantly higher in BTM patients with cardiac hemosiderosis than those without cardiac hemosiderosis (p = 0.008; p = 0.001; p = 0.012, respectively) [Table 2].

The correlation between plasma ferritin levels and hepatic T2*MRI values indicated a statistically significant inverse correlation (r = -0.631, p = 0.001) [Figure 1a]. Plasma ferritin levels showed a strong direct correlation with LIC (r = 0.701, p = 0.007). A strong inverse correlation was seen between the hepatic T2*MRI values and LIC (r = -0.812, p < 0.001) [Table 3]. However, the inverse correlation between plasma ferritin levels and cardiac T2*MRI values was poor (r = -0.297, p = 0.044) [Figure 1b]. Also, the inverse correlation between cardiac T2*MRI values and LIC was poor and insignificant (r = -0.285, p = 0.270). Moreover, the correlation between cardiac T2*MRI and hepatic T2*MRI values was also weak and insignificant (r = 0.287, p = 0.058) [Table 3]. The correlation of age with cardiac T2*MRI values in patients with BTM indicated a significant and moderate inverse correlation (r = -0.519, p = 0.017). However, the correlation of age with hepatic T2*MRI values (r = -0.167, p = 0.312) and LIC (r = 201, p = 0.075) was poor and statistically insignificant [Table 4].

We investigated the genotype distribution of HFE C282Y and H63D mutations in our cohort. The HFE C282Y mutation was not detected in any patients in our study. However, the HFE H63D mutation was detected in 12 (20.0%) patients. The genotype distribution of HFE H63D mutation (HH = 48, HD = 10, DD = 2) was in accordance with the Hardy-Weinberg equilibrium (p = 0.138), indicating the absence of selection bias in our study. As shown in Table 5, the carrier frequency of HFE H63D mutation did not differ significantly between patients with and without hepatic hemosiderosis [odd ratio (OR) = 2.33; 95% confidence interval (CI): 0.64–8.45; p = 0.190] as well as between patients with and without cardiac hemosiderosis [OR = 1.82; 95% CI: 0.50–6.52; p = 0.350] [Table 5]. However, comparing patients with and without HFE H63D mutation indicated significantly higher plasma ferritin levels (1 903±993 vs. 992±683, p < 0.001) and iron levels (214.56±39.46 vs. 167.83±58.61, p = 0.008) in carriers of HFE 63D allele relative to carriers of HFE 63H allele. No significant differences were seen regarding the mean transfused blood (mL/kg/year) (215.9±54.6 vs. 208.4±60.2, p = 0.190), mean age (17.8±9.7 vs. 17.4±9.6 years) and splenectomy rate (33.3% vs. 22.9%, p = 0.270) between the two patient subgroups.

Discussion

Cardiac and hepatic hemosiderosis are the main causes of morbidity and mortality in patients with BTM. The results of our study indicated cardiac and hepatic hemosiderosis in 38.3% and 41.6% of the patients, respectively. Different rates of cardiac and hepatic hemosiderosis were reported in previous studies.20,22,24 Mean age differences of the studied populations, variations in sample size, and of chelation regimes may considerably affect the incidence of cardiac and hepatic hemosiderosis in different studies.19,24 Interestingly, it is known that deferiprone results in preferential cardiac chelation whereas deferoxamine may be more effective for hepatic chelation.19 Also, our results are in accordance with some previously published studies that demonstrated a statistically significant inverse correlation between plasma ferritin levels and hepatic T2*MRI values (p = 0.001, r = -0.631) and indicated that plasma ferritin levels could accurately and thoroughly estimate hepatic iron load.20–22 This result may be of great importance in unequipped centers where T2*MRI is unavailable. However, other studies have reported different correlation strengths ranging from no correlation to moderate correlation.18,25,26

Our study indicated a weak correlation between plasma ferritin levels and cardiac T2*MRI values that was in accordance with previous studies.21,26,27 However, in contrast to our result, Yang et al,19 in a recently published study reported a statistically significant strong correlation between serum ferritin levels and cardiac T2*MRI values. This may be explained by the fact that the vast majority of patients (97.5%) included in their study received poor chelation therapy. Similar to previous studies,18,26,28 our study indicated a poor and statistically insignificant correlation between cardiac and hepatic T2*MRI values (p = 0.058, r = 0.287). The poor correlation of cardiac T2*MRI values with plasma ferritin levels as well as with hepatic T2*MRI values strongly suggest that plasma ferritin levels and hepatic T2*MRI values cannot thoroughly predict cardiac iron content. This finding emphasizes the importance of using cardiac T2*MRI as a non-invasive and precise procedure for estimating of cardiac iron overload instead of relying solely on ferritin levels or hepatic T2*MRI values. The possible mechanisms for poor or insignificant correlation between hepatic and cardiac T2*MRI values may be related to the organ-specific mechanisms of iron uptake and release.29 Also chelation therapy is usually more effective in eliminating iron from the liver than heart.19 Another important aspect of our study was that a statistically significant moderate correlation was seen between age and cardiac T2*MRI values while the correlation of age with hepatic T2*MRI values was weak and insignificant. Similar results have been reported previously.18,19,28 Since the liver is the first organ to store iron in the body, most patients develop hepatic iron overload earlier in life. However, cardiac iron overload develops slowly in a time-dependent manner so that it progresses as the patient ages. Therefore, the age of patients has a more pronounced impact on the development of cardiac hemosiderosis relative to the development of hepatic hemosiderosis. The study by Yang et al,19 proposed that cardiac hemosiderosis should be assessed using T2*MRI in patients with BTM at six years of age. Iron overload cardiomyopathy (IOC) is the serious manifestation of iron deposition in the heart. The spectrum of symptoms of IOC ranges from asymptomatic in the early stage of disease to terminal heart failure in severely overloaded patients. Early diagnosis and adequate medical therapy can reverse IOC and has a crucial role in the prevention and treatment of this disorder.30 Our results showed that MRI is more sensitive and more precise than analysis of routine biochemical markers and we would like to reemphasize the advantage of using this technique for the early detection of cardiac iron overload in patients with BTM.

HFE H63D and C282Y gene mutations are the common causes of genetic hemosiderosis. Interestingly, some previous studies have reported an increased frequency of HFE gene mutations in BTM patients.8,31 Our study investigated for the first time the role of HFE H63D and C282Y mutations in the development of cardiac and hepatic hemosiderosis in Iranian patients with BTM. According to our results, the difference in genotype and allele distribution of HFE H63D mutation in patients with and without cardiac or hepatic hemosiderosis did not reach a significant level, indicating the futility of these mutations in conferring increased risk of cardiac and hepatic hemosiderosis. Similar results were reported by Turedi et al,13 in a recently published study of 33 Turkish patients with BTM. However, in our study, an elevated plasma ferritin level was found in the carriers of HFE H63D mutation, which indicated the modulating effects of the HFE H63D mutation on biochemical iron markers. Coinheritance of HFE H63D mutation may enhance the iron overload in patients with BTM, which may necessitate a more intensive iron chelation therapy in these patients to prevent hemosiderosis development. Our recent results were in accordance with the results of some previously published studies that indicated a positive association between HFE H63D mutation and serum ferritin levels.4,6,11 However, some other studies have not reported such an association.32,33 The possible reasons for these contradictory results may be related to variation in the study design (i.e., sample size, sample selection criteria) and the presence of gene-gene and gene-environment interactions in various studied populations.34 The present study has some limitations: (i) the cross-sectional design of the study limited the inclusion of control group, (ii) the other polymorphisms of HFE gene were not investigated, and (iii) the study population was relatively small.

Conclusions

Cardiac T2*MRI should be done for all patients with BTM regardless of their serum ferritin levels or hepatic T2*MRI values. HFE H63D and C282Y mutations are not major causes for development of cardiac and hepatic hemosiderosis in patients with BTM from the Zanjan province of Iran. However, a large-scale multi-center study in Iran is required to confirm these preliminary results.

Disclosure

The authors declared no conflicts of interest. The study was funded by a grant from Zanjan University of Medical Sciences (ZUMS), Deputy of Research and Technology (grant number A-12-104-1) Zanjan, Iran.

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