Hb south Milwaukee [beta 105 (G7) Leu----Phe]: a newly-identified hemoglobin variant with high oxygen affinity

A Novel β-Globin Variant, Hb Odder [HBB: C.316C > G; CD105 (Leu > Val)]

We report the discovery of a novel β-globin gene variant, Hb Odder, characterized by a single nucleotide substitution; HBB:c.316C > G; CD105 (Leu > Val). This variant emerged incidentally during routine HbA1c measurements for diabetes monitoring. The patient exhibited no clinical or biochemical evidence of anemia or hemolysis. Our data on this variant suggest that Hb Odder is benign, regrettably limitations in our data make formal evaluations of stability and oxygen affinity impossible; additionally this emphasizes the importance of considering hemoglobin variants in the differential diagnosis of abnormal Hb A1c levels and suggest that laboratories should use alternative methods for the correct measurement of Hb A1c when hemoglobin variants interfere with diabetes monitoring. Notably, three other mutations have been described at codon 105 of the β globin chains and correspond to three Hb variants with different characteristics: Hb South Milwaukee, Hb Bellevue IV and Hb St. George.

High oxygen affinity hemoglobins

High oxygen affinity hemoglobins are responsible for rare and heterogeneous autosomic dominant genetic diseases. They cause pure erythrocytosis, sometimes accountable for hyperviscosity and thrombosis, or hemolysis. Differential diagnoses must be first ruled out. The diagnosis is based on the identification of a decreased P50, and their possible characterization by cation exchange-high performance liquid chromatography and capillary electrophoresis. Finally, genetic studies of the responsible globin chain gene will confirm the mutation. The prognosis mainly relies on the P50 decrease rate and on the hemoglobin cooperativity impairment. Disease management should be personalized, and it should primarily depend on smoking cessation and physical activity. Phlebotomy and platelet aggregation inhibitors' prescriptions can be discussed. There is no contraindication to flights, high-altitude conditions, or pregnancy. Nevertheless, blood donation must be prohibited.

Symptomatic Erythrocytosis Due to Homozygosity for Hb Luton [HBA2: c.269A>T (or HBA1)] and α-Thalassemia: A Clinical Update

A female proband homozygous for both Hb Luton [α89(FG1)His→Leu (CAC>CTC), HBA2: c.269A>T (or HBA1)], a high oxygen affinity hemoglobin (Hb), and for α(+)-thalassemia (α-thal), (-α(4.2), leftward deletion) was first described in 2012. This is a follow-up report of the same case. At the age of 18, the described patient presented with progressively worsening lethargy, headaches, dizziness, syncope and Raynaud's phenomenon. Following extensive cardiological and neurological investigation, it was felt that significant erythrocytosis was the most likely cause. Venesection followed by regular exchange transfusions were arranged with marked amelioration in symptomatology. In the vast majority of cases of high oxygen affinity Hbs, venesection is not recommended due to the asymptomatic phenotype and reduced oxygen delivery resulting from venesection. This update describes the evolving phenotype of this unique proband and, to the best of our knowledge, the first use of regular, long-term therapeutic red cell exchange transfusions in a case of high affinity Hb.

A new (G)γ-globin variant causing low oxygen affinity: Hb F-Brugine/Feldkirch [(G)γ105(G7)Leu→His; HBG2: c.317T>A]

In two unrelated families, several newborns developed cyanosis within the first days of life. For all of them, consecutive arterial blood gas analyses showed a right shift of the saturation curve, suggesting the presence of a hemoglobin (Hb) variant. A new (G)γ-globin variant was detected, namely (G)γ105(G7)Leu → His; HBG2: c.317T > A, that we named Hb F-Brugine/Feldkirch after the place of origin of the two families. This T to A conversion results in a leucine to histidine amino acid change at codon 105 of the (G)γ-globin gene and caused a Hb variant with lowered oxygen affinity. The γ to β switch proceeded normally.

Human fetal liver stromal cells expressing erythropoietin promote hematopoietic development from human embryonic stem cells

Blood cells transfusion and hematopoietic stem cells (HSCs) transplantation are important methods for cell therapy. They are widely used in the treatment of incurable hematological disorder, infectious diseases, genetic diseases, and immunologic deficiency. However, their availability is limited by quantity, capacity of proliferation and the risk of blood transfusion complications. Recently, human embryonic stem cells (hESCs) have been shown to be an alternative resource for the generation of hematopoietic cells. In the current study, we describe a novel method for the efficient production of hematopoietic cells from hESCs. The stable human fetal liver stromal cell lines (hFLSCs) expressing erythropoietin (EPO) were established using the lentiviral system. We observed that the supernatant from the EPO transfected hFLSCs could induce the hESCs differentiation into hematopoietic cells, especially erythroid cells. They not only expressed fetal and embryonic globins but also expressed the adult-globin chain on further maturation. In addition, these hESCs-derived erythroid cells possess oxygen-transporting capacity, which indicated hESCs could generate terminally mature progenies. This should be useful for ultimately developing an animal-free culture system to generate large numbers of erythroid cells from hESCs and provide an experimental model to study early human erythropoiesis.

Secondary erythrocytosis due to compound homozygosity, but not compound heterozygosity, for Hb Luton and α-thalassemia: a family study

We describe the hematological and clinical features of homozygous Hb Luton (OMIM 141800.0172), a high affinity α-globin variant that has not been previously described in the homozygous state. The proband was found to have a high hemoglobin (Hb) concentration following a routine blood count prior to a planned appendectomy at the age of 16 years. Investigation showed that she was homozygous for both Hb Luton [α89(FG1)His→Leu (CAC>CTC), a high oxygen affinity Hb)] and homozygous for α(+)-thalassemia (α(+)-thal), while her mother, maternal aunt and half-brother were heterozygous for these conditions. Further investigation showed that she also had Gilbert's disease and Raynaud's syndrome. As far as we are aware, this is also the first reported family with a subject homozygous for both Hb Luton and α-thal so that the proband has no nomal α-globin. The parents of the proband are first cousins and originate from Pakistan.

Hb S-San Martin: a new sickling hemoglobin with two amino acid substitutions [β6(A3)Glu→Val;β105(G7)Leu→Pro] in an Argentinean family

A new sickling hemoglobin (Hb) detected in an Argentinean family from San Martín, Buenos Aires, Argentina, is hereby described. Two mutations were identified on the same β-globin gene resulting in a new variant named Hb San Martin. One mutation was found on exon 1, corresponding to Hb S [β6Glu→Val, GAG>GTG] and the second one on exon 3 at β105(G7)Leu→Pro, CTC>CCC. The replacement of leucine by proline will likely impair the structure breaking helix G and causing instability of the molecule and the clinical manifestations typical of unstable Hbs. The mutation at β105 seemed to be a de novo one in our patients, arising on a previously mutated gene, due to the fact that Hb S is the most frequent structural variant.

Production of erythriod cells from human embryonic stem cells by fetal liver cell extract treatment

BACKGROUND

We recently developed a new method to induce human stem cells (hESCs) differentiation into hematopoietic progenitors by cell extract treatment. Here, we report an efficient strategy to generate erythroid progenitors from hESCs using cell extract from human fetal liver tissue (hFLT) with cytokines. Human embryoid bodies (hEBs) obtained of human H1 hESCs were treated with cell extract from hFLT and co-cultured with human fetal liver stromal cells (hFLSCs) feeder to induce hematopoietic cells. After the 11 days of treatment, hEBs were isolated and transplanted into liquid medium with hematopoietic cytokines for erythroid differentiation. Characteristics of the erythroid cells were analyzed by flow cytometry, Wright-Giemsa staining, real-time RT-PCR and related functional assays.

RESULTS

The erythroid cells produced from hEBs could differentiate into enucleated cells and expressed globins in a time-dependent manner. They expressed not only embryonic globins but also the adult-globin with the maturation of the erythroid cells. In addition, our data showed that the hEBs-derived erythroid cells were able to act as oxygen carriers, indicating that hESCs could generate functional mature erythroid cells.

CONCLUSION

Cell extract exposure with the addition of cytokines resulted in robust erythroid -like differentiation of hEBs and these hEBs-derived erythroid cells possessed functions similar to mature red blood cells.

Biologic properties and enucleation of red blood cells from human embryonic stem cells

Human erythropoiesis is a complex multistep process that involves the differentiation of early erythroid progenitors to mature erythrocytes. Here we show that it is feasible to differentiate and mature human embryonic stem cells (hESCs) into functional oxygen-carrying erythrocytes on a large scale (10(10)-10(11) cells/6-well plate hESCs). We also show for the first time that the oxygen equilibrium curves of the hESC-derived cells are comparable with normal red blood cells and respond to changes in pH and 2,3-diphosphoglyerate. Although these cells mainly expressed fetal and embryonic globins, they also possessed the capacity to express the adult beta-globin chain on further maturation in vitro. Polymerase chain reaction and globin chain specific immunofluorescent analysis showed that the cells increased expression of beta-globin (from 0% to > 16%) after in vitro culture. Importantly, the cells underwent multiple maturation events, including a progressive decrease in size, increase in glycophorin A expression, and chromatin and nuclear condensation. This process resulted in extrusion of the pycnotic nuclei in up to more than 60% of the cells generating red blood cells with a diameter of approximately 6 to 8 mum. The results show that it is feasible to differentiate and mature hESCs into functional oxygen-carrying erythrocytes on a large scale.