Hb Hradec Kralove (Hb HK) or alpha 2 beta 2 115(G17)Ala-->Asp, a severely unstable hemoglobin variant resulting in a dominant beta-thalassemia trait in a Czech family

[Rare thalassemia caused by novel nucleotide variants in the globin gene: four case reports and literature review]

目的

分析4例少见地中海贫血（地贫）患者的DNA序列、临床表型，提高对地贫的认识。

方法

对2014年5月至2019年12月4例少见地贫患者的临床及DNA序列特征进行回顾性分析并复习相关文献。

结果

地贫基因常规检测显示，例1～3均未检测到常见的3种α株蛋白1/2（HBA1/A2）基因缺失及其3种点突变和16种β株蛋白（HBB）基因点突变，例4检测到αα^--SEA缺失。HBA1/A2和HBB基因全序列Sanger测序示：例1～4分别存在HBB:c.347C>A、HBB:c.1A>G、HBB:c.393T>G及HBA2:c.301-1G>A（IVS-II-142 G>A）突变。同时，例2的祖父、父亲和姑姑均为HBB:c.1A>G杂合突变。

结论

本研究发现了新的珠蛋白基因突变，HBB:c.347C>A、HBB:c.1A>G和HBB:c.393T>G以及HBA2:c.301-1 G>A（IVS-II-142 G>A）突变在中国地贫患者中为首次报道，HBB:c.393T>G突变为全球首次报道，丰富了地贫基因突变数据库。

Novel dominant β-thalassemia: Hb Boston-Kuwait [codon 139/140(+T)]

Dominant β-thalassemias exhibit a hybrid phenotype of unstable hemoglobin and ineffective erythropoiesis. Most arise from heterozygous β-globin gene mutations in exons 3 or 2 and present in adulthood as thalassemia intermedia. We report a novel, de novo β-globin mutation presenting in a toddler with features of thalassemia major and chromaturia. Hemoglobin Boston-Kuwait is an elongated β-chain variant (163 amino acids) that results from a frameshift mutation caused by a thymidine insertion in codons 139/140. Hematopoietic stem cell transplant provided a successful alternative therapy for this severe form of dominant β-thalassemia.

A new beta-chain haemoglobin variant with increased oxygen affinity: Hb Roma [beta115(g17)Ala-->Val]

BACKGROUND

Haemoglobin Roma [beta115(G17)Ala-->Val] is a new adult haemoglobin variant found in a patient presenting a mild hypochromia and microcytosis. We studied this previously uncharacterised variant in order to evaluate the effect on the structural and funcional properties of the Ala-->Val substitution at the alpha1beta1 interface.

METHODS AND RESULTS

The variant chain was identified by direct DNA sequencing of the beta-globin gene, which revealed a GCC-->GTC mutation in codon 115. This mutation was confirmed by mass spectrometric analysis of the tetramers and peptides. The oxygen-binding properties of the haemoglobin A/haemoglobin Roma mixture, in which the variant makes up 25% of the haemoglobins, showed a significant increase in oxygen affinity with respect to normal haemoglobin A, both in the absence and presence of 2,3-bisphosphoglycerate. The role of the betaG17 position, situated at the alpha(1)beta(1) interface, has been examined using computational models of haemoglobin Roma and other known betaG17 variants, in comparison with normal haemoglobin A.

CONCLUSIONS

This study suggests that the beta115(G17)Ala-->Val substitution at the alpha1beta1 interface is responsible for increased oxygen affinity and mild destabilisation of the haemoglobin Roma.

GENERAL SIGNIFICANCE

An amino acid substitution at the G17 position of the alpha1beta1 interface may result in stabilisation of the high affinity R-state of the haemoglobin molecule.

A young girl with hemolytic anemia and elevated hemoglobin F

The non-immune, non-spherocytic anemias result from multiple potential etiologies. We report a 16-year-old girl, who was presented with a long-standing anemia and normal blood screening tests except an elevated hemoglobin F. Her diagnosis of unstable hemoglobinopathy was made only after gene sequencing of the beta-globin chain.

Dominant beta-thalassemia with hemoglobin Hradec Kralove: enhanced hemolysis in the spleen

We describe a 6-year-old girl and her mother with dominant beta-thalassemia due to hemoglobin Hradec Kralove (Hb HK). Both patients presented microcytic anemia, jaundice, splenomegaly, cholelithiasis, and recurrent hemolytic bouts. Osmotic resistance tests using saline and coiled planet centrifugation revealed the increased fragility of the red cell membrane. On the other hand, the glycerol lysing time was prolonged, and results of the isopropanol test were weakly positive. Despite mimicking the features of hereditary spherocytosis, the results of the genetic analyses verified the second reported family with Hb HK (codon 115, GCC [Ala] --> GAC [Asp]). Splenectomy was effective for the amelioration of hemolysis. Of 7 reported patients with Hb variants at beta-globin codon 115 (Hb Madrid and Hb HK), 5 underwent splenectomy. Because of the variable augmentation of extramedullary hemolysis in dominant beta-thalassemias, genotyping is necessary for determining the clinical indication of splenectomy.

Hb Madrid [beta115(G17)Ala-->Pro] in a Korean family with chronic hemolytic anemia

Hb Madrid, in which the alanine residue at beta115 (G17) is replaced by proline, results in a moderately severe hemolytic anemia due to the disruption of an alpha helical region and the weakening of an alpha1 beta1 contact (1,2). It was first discovered in a single Spanish patient, by protein structural analysis, whose parents did not carry the abnormality (1). The second observation of Hb Madrid was in an American Black teenager by DNA analysis, who had the family history of chronic hemolytic anemia, but none of family members were available for evaluation (3).

Priapism following splenectomy in an unstable hemoglobin: hemoglobin Olmsted beta 141 (H19) Leu-->Arg

We report a case of severe priapism occurring in a patient with an unstable hemoglobin, Hb Olmsted (beta 141 Leu-->Arg) This is a rare hemoglobin variant, which until now has been reported only once. The clinical course of the 12-year-old boy was characterized by severe hemolytic anemia leading to splenectomy and cholecystectomy at the of 3.5 years. The priapism occurred 8 years after splenectomy, during a hemolytic febrile episode and required aspiration of the corpora cavernosa. This report raises the question of the benefit of splenectomy in patients suffering from a chronic hemolytic anemia such as that due to an unstable hemoglobin. This treatment lowers the frequency and the severity of acute hemolytic attacks, but several cases of vascular complications have been reported after splenectomy.

Hb Nottingham or alpha 2 beta 2 98 (FG5) Val-->Gly in a Czech child

We report a fourth case of Hb Nottingham [alpha 2 beta 2 98 (FG5) Val-->Gly] observed in an 8-year-old girl in the Czech Republic with clinical and laboratory symptoms of severe hemolytic anemia. The unstable hemoglobin probably represents a de novo mutation, since the parents of the patient and the two siblings do not exhibit any hematological abnormalities. Splenectomy had a beneficial effect on the degree of hemolysis, as well as on the Hb level.