Anemia, Hypochromic Microcytic, With Iron Overload

Iron-overloaded patients are recognized as presenting an increased risk of osteoporosis. However, studies on the correlation between osteoporosis and organ iron overload are controversial or scarce. The aim of this study is to assess bone mineral density (BMD) and trabecular bone score (TBS) in correlation with hepatic and pancreatic iron overload.

Forty-one patients diagnosed with hemoglobinopathies, were studied. BMDs of the lumbar spine (LS), femoral neck (FN), and total hip (TH) were analyzed by Dual-energy X-ray absorptiometry (DXA) scan. LS bone quality was derived from each spine DXA examination using the TBS analysis. Hepatic and pancreatic iron overload were obtained with a multi-echo gradient echo T2* technique.

Abnormal microarchitecture and abnormal bone mass were observed in 19/41 (46.3%) and 9/41 (22.0%) patients, respectively. For 26 males, BMD, T-score and Z-score of LS were significantly lower among subjects with moderate-severe hepatic iron-overload than their counterparts, as it is between no- and pancreatic iron-overload groups. For 15 females, patients with moderate-severe hepatic iron-overload had significantly lower BMD and T-score of FN and TH, and patients with pancreatic iron-overload had significantly lower BMD, T-score of FN, and lower BMD, T-score and Z-score of TH than their counterparts. Moreover, pancreatic T2*-value was positively correlated with BMD and T-score at all analyzed sites and Z-score at TH.

These data showed lower bone mass in patients with organ iron overload, particularly for LS in males, FN and TH in females. TBS may well represent a complementary tool for the evaluation of bone quality and the risk of fracture in iron-overloaded patients.

Divalent metal-iron transporter 1 (DMT1) is a mammalian iron transporter encoded by the SLC11A2 gene. DMT1 has a vital role in iron homeostasis by mediating iron uptake in the intestine and kidneys and by recovering iron from recycling endosomes after transferrin endocytosis. Mutations in SLC11A2 cause an ultra-rare hypochromic microcytic anemia with iron overload (AHMIO1), which has been described in eight patients so far. Here, we report two novel cases of this disease. The first proband is homozygous for a new SLC11A2 splicing variant (c.762 + 35A > G), becoming the first ever patient reported with a SLC11A2 splicing mutation in homozygosity. Splicing studies performed in this work confirm its pathogenicity. The second proband harbors the previously reported DMT1 G75R mutation in homozygosis. Functional studies with the G75R mutation in HuTu 80 cells demonstrate that this mutation results in improper DMT1 accumulation in lysosomes, which correlates with a significant decrease in DMT1 levels in patient-derived lymphoblast cell lines (LCLs). We also suggest that recombinant erythropoietin would be an adequate therapeutic approach for AHMIO1 patients as it improves their anemic state and may possibly contribute to mobilizing excessive hepatic iron.

Beta-thalassaemia is an inherited blood disorder characterised by ineffective erythropoiesis and anaemia. Consequently, hepcidin expression is reduced resulting in increased iron absorption and primary iron overload. Hepcidin is under the negative control of transmembrane serine protease 6 (TMPRSS6) via cleavage of haemojuvelin (HJV), a co-receptor for the bone morphogenetic protein (BMP)-mothers against decapentaplegic homologue (SMAD) signalling pathway. Considering the central role of the TMPRSS6/HJV/hepcidin axis in iron homeostasis, the inhibition of TMPRSS6 expression represents a promising therapeutic strategy to increase hepcidin production and ameliorate anaemia and iron overload in β-thalassaemia. In the present study, we investigated a small interfering RNA (siRNA) conjugate optimised for hepatic targeting of Tmprss6 (SLN124) in β-thalassaemia mice (Hbb^th3/+ ). Two subcutaneous injections of SLN124 (3 mg/kg) were sufficient to normalise hepcidin expression and reduce anaemia. We also observed a significant improvement in erythroid maturation, which was associated with a significant reduction in splenomegaly. Treatment with the iron chelator, deferiprone (DFP), did not impact any of the erythroid parameters. However, the combination of SLN124 with DFP was more effective in reducing hepatic iron overload than either treatment alone. Collectively, we show that the combination therapy can ameliorate several disease symptoms associated with chronic anaemia and iron overload, and therefore represents a promising pharmacological modality for the treatment of β-thalassaemia and related disorders.