Hemoglobin H Disease-Constant Spring (HbH-CS) represents a severe variant of α-thalassemia characterized by a fundamental pathological mechanism involving inadequate synthesis of α-globin chains. This deficiency results in the formation of unstable Hemoglobin H (HbH) due to the aggregation of free β-globin chains, which subsequently induces an imbalance in oxidative stress within erythrocytes. This imbalance leads to an abnormal accumulation of reactive oxygen species (ROS), which in turn promotes lipid peroxidation, culminating in the production of malondialdehyde (MDA) and a significant depletion of glutathione (GSH). Concurrently, Nrf2 is translocated to the nucleus, where it activates the antioxidant response element (ARE) to mitigate cellular stress. Here, we report that NSUN3 (which, together with ALKBH1, maintains mitochondrial function through m5C→f5C modification) is abnormally overexpressed in reticulocytes from patients with HbH-CS, and an in vitro cellular model of NSUN3 overexpression/silencing was constructed using K562 cells, which have the potential for erythroid lineage differentiation and retain an intact cluster of bead protein genes. Functional assays indicated that the overexpression of NSUN3 significantly intensified the accumulation of intracellular ROS and MDA, led to a reduction in GSH levels, and diminished the overall cellular antioxidant capacity (T-AOC). This may be due to ROS accumulation resulting from inhibition of mitochondrial respiratory chain complex I, II, and IV synthesis through aberrant m5C→f5C modification. In addition, NSUN3 overexpression further exacerbates oxidative stress by inhibiting the phosphorylation of Nrf2 hindering its translocation into the nucleus and weakening the cellular antioxidant system. Moreover, we also observed that NSUN3 overexpression exacerbated intracellular DNA damage and inhibited cellular value-added activity, and silencing NSUN3 showed the opposite result. Our research offers initial insights into the molecular mechanisms through which NSUN3 modulates oxidative stress in erythrocytes via its role in epigenetic modifications. These findings contribute to a deeper understanding of the clinical management of patients with Hb H-CS.

Patients with unstable hemoglobin (Hb), caused by a qualitative abnormality in α- and β-globin genes, are often asymptomatic or mildly symptomatic. It is often difficult to diagnose unstable Hb patients with only mild hemolysis or low oxygen saturation. We herein report a case of a family with an unstable Hb, specifically, Hb Sydney (HBB: c.203T>C), an abnormal β-globin chain. A 5-year-old boy was referred to our hospital for low percutaneous oxygen saturation (SpO2) in the setting of bronchitis. During hospitalization, low SpO2 persisted despite the improvement in respiratory distress symptoms. As he had mild hemolysis and splenomegaly, his disease was diagnosed to carry Hb Sydney based on gene analysis. His mother and brother also carried Hb Sydney. In this case, bronchial asthma had been treated, but unstable Hb was not assessed. Low SpO2 may be tolerated and overlooked in cases of asthma and it took time to diagnose this patient. The present case suggests that unstable Hb should be considered in patients with bronchial asthma and prolonged low SpO2.

Unstable hemoglobins (Hbs) are often overlooked in the differential diagnoses of drug-induced hemolysis. Hb Peterborough [β111(G13)Val→Phe; HBB: c.334G>T] is a rare unstable Hb variant, predominantly found in individuals of Italian descent, due to a structural defect involving a single amino acid substitution (phenylalanine for valine at position 111 of the β-globin chain). Unstable Hb variants are often inherited in the heterozygous state with Hb A (α2β2) and rarely in compound heterozygosity with other Hb variants. The presence of another variant Hb often alters the phenotype, occasionally resulting in more severe disease. Using a combination of molecular techniques; multiplex ligation-dependent probe amplification (MLPA) and Sanger sequencing, we identified a compound heterozygosity for Hb Peterborough and Hb Lepore-Boston-Washington (Hb LBW) [δ87, β116; NG_000007.3: g.63632_71046del] in a middle-aged gentleman with a history of chronic microcytic anemia and splenomegaly, presenting with severe drug-induced hemolysis, which was managed conservatively. The clinical history and presentation reflect the dual pathology due to the presence of two variant Hbs and their associated phenotypes. In this article, we discuss the phenotype resulting from the interaction of Hb Peterborough and Hb LBW and emphasize the importance of molecular testing in the diagnosis of rare Hb variants.

Thalassemia and qualitative hemoglobinopathy are hereditary disorders of Hb synthesis that lead to change in the Hb conformation or a decrease in the synthesis of structurally normal Hb, and consequently, to erythron pathology. Many variants of Hb are unstable or have altered affinity for oxygen, and, in heterozygous form can be associated with clinical and hematological manifestations (hemolytic anemia, hypochromic microcytic anemia, erythrocytosis). HbD-Punjab [β121 (GH4) Glu → Gln; HBB: C.364G> C] is variant of Hb carrying the amino acid substitution in the 121 position of β-globin chain. In all cases reported so far, patients with HbD-Punjab/β+-thalassemia (IVSI+5 G-C) combination experienced typical thalassemia with hypochromic microcytosis. HbD-Punjab was detected by electrophoresis from 37 to 94% of total Hb. The article describes rare clinical case of the cohabitation of HbD-Punjab/β+-thalassemia (IVSI+5 G-C) in a patient with homozygous variant of Gilbert's syndrome observed in AS Loginov Moscow Clinical Scientific Center.

Unstable hemoglobin (Hb) variants are the result of sequence variants in the globin genes causing precipitation of Hb molecules in red blood cells (RBCs). Intracellular inclusions derived from the unstable Hb reduce the life-span of the red cells and may cause hemolytic anemia. Here we describe a patient with a history of hemolytic anemia and low oxygen saturation. She was found to be carrier of a novel unstable Hb variant, Hb Oslo [β42(CD1)Phe→Ile (TTT>ATT), HBB: c.127T>A] located in the heme pocket of the β-globin chain. Three-dimensional modeling suggested that isoleucine at position 42 creates weaker interactions with distal histidine and with the heme itself, which may lead to altered stability and decreased oxygen affinity. At steady state, the patient was in good clinical condition with a Hb concentration of 8.0-9.0 g/dL. During virus infections, the Hb concentration fell and on six occasions during 4 years, the patient needed a blood transfusion.