Hb Nebraska [β86(F2)Ala→Ile (HBB:c.259G>A;260C>T)]: a unique high oxygen affinity hemoglobin variant with a double nucleotide substitution within the same codon

A new high oxygen affinity hemoglobin (Hb) variant, Hb Nebraska [β86(F2)Ala→Ile, GCC>ATC; HGVS: HBB: c.259G>A;260C>T] is reported. This variant was not identified by routine methods and was only suspected due to erythrocytosis and an abnormal p50 value. The variant was analyzed by DNA sequencing and mass spectrometry (MS). The β chain variant is unusual in that it has two nucleotide substitutions occurring at the same codon.     

Hb Lake Tapawingo [α46(CE4)Phe→Ser; HBA2:c.140T>C]: a new unstable α chain hemoglobin variant associated with low systemic arterial saturation

A new unstable α-globin variant was detected in a child with hypoxemia and anemia. The child's mother was found to carry the same mutation. The hemoglobin (Hb) variant co-eluted with Hb A(2) by cation exchange high performance liquid chromatography (HPLC) and appeared cathodal to Hb A and anodal to Hb F by isoelectric focusing. It represented less than 20% of the total Hb and was unstable by isopropanol testing. Gene sequencing identified a missense mutation on the α2 gene [HBA2:c.140T>C]. Oxygen dissociation and P(50) test results were normal.     

Hb Cambridge-MA [β144(HC1)-β146(HC3)Lys-Tyr-His→0 (HBB c.433 A>T)]: a new high oxygen affinity variant

A new β hemoglobin (Hb) variant, Hb Cambridge-MA [β144(HC1)β146(HC3)Lys-Tyr-His→0 (AAG>TAG) (HGVS: HBB c.433 A>T] is described. The variant was characterized by high performance liquid chromatography (HPLC), alkaline, acid, globin chain and capillary electrophoresis, isoelectric focusing (IEF), heat and isopropanol stability, p50 analyses, intact globin mass spectrometry (MS) and DNA sequencing. The new variant shows high oxygen (O?) affinity and is associated with mild polycythemia.     

Hb East Timor [β80(EF4)Asn→His, AAC>CAC (HBB c.241A>C)], a variant hemoglobin associated with normal hematology

Routine hemoglobin (Hb) analyses identified a new β-globin variant in a family from East Timor. The red cell indices were within normal limits for all affected family members. The variant is due to a missense mutation at amino acid codon 80 (AAC>CAC) which results in the substitution of histidine for asparagine.     

Hb Cemenelum [α92 (FG4) Arg→Trp]: A hemoglobin variant of theα1/β2 interface that displays a moderate increase in oxygen affinity

Summary Hb Cemenelum [92 (FG4) ArgTrp] carries a structural modification at the same position as Hb Chesapeake, a very high oxygen affinity variant. Hb Cemenelum was found in a French diabetic patient with no abnormal hematological features. The purified abnormal hemoglobin, like Hb J Cape Town, another variant of position 92(FG4), displayed only a 1.5-to 2-fold increased oxygen affinity and a reduced cooperativity. This hemoglobin demonstrates that, even for some key residues of the1/2 interface, the degree at which the functional properties are altered depends upon the specific residue occupying this position.     

Two new mutations in cis on <Superscript>G</Superscript>γ chain of fetal hemoglobin: Hb F-Madrid [Gγ50(D1)Ser→Cys] and [Gγ75(E19)Ile→Thr]

We describe a new structural hemoglobin variant of (G)gamma with two amino acid replacements in cis found in the umbilical cord blood of a neonate in Madrid, Spain. The substitutions were identified on exon 2 of the (G)gamma globin gene, at codon 50 (T CT-->T GT) and at codon 75 (A TA-->A CA). We have named it Hb F-Madrid. The father of the propositus was the carrier of the same (G)gamma chain variant and, moreover, molecular study of alpha genes revealed the loss of an alpha gene (-alpha(3.7)/alpha alpha) both in the propositus and his mother.     

An Additional Case of Hb Saint Nazaire [β103(G5)Phe→Ile; HBB: c.310T>A] Leading to Moderate Erythrocytosis in a French Family

We report two members of a French family who are carriers of a rare hemoglobin (Hb) variant leading to erythrocytosis: Hb Saint Nazaire [β103(G5)Phe→Ile; HBB: c.310T>A]. The proband is a 38-year-old woman referred to our institution for a moderate but persistent polycythemia without any clinical consequence. As her mother had a similar blood count, a diagnosis of a Hb variant with high oxygen affinity was proposed. The variant was difficult to detect by capillary electrophoresis (CE) and not distinguishable by high performance liquid chromatography (HPLC) and isoelectric focusing. Finally, a heterozygous mutation on the HBB gene corresponding to Hb Saint Nazaire was identified. This case report illustrates that this rare cause of erythrocytosis can be easily under or misdiagnosed unless several Hb separation techniques are used.     

A dyserythropoietic anemia associated with homozygous Hb Plasencia [α125(H8)Leu→Arg (α2)] (HBA2:c.377T>G), a variant with an unstable α chain

A female patient of Portuguese origin, who was born to consanguineous parents, presented with moderate anemia, mild jaundice and splenomegaly. Bone marrow aspiration showed an erythroid hyperplasia and binucleate erythroblasts, evoking a congenital dyserythropoietic anemia, type II (CDA II). Although microcytosis cast some doubt on the diagnosis, investigation was pursued along this line. The CDA II was finally ruled out as underglycosylation of band 3, remnants of endoplasmic reticulum cisternae and mutations in the SEC23B gene were all missing. On the other hand, analysis of the α-globin genes showed a base substitution at codon 125 (CTG→CGG) of the α2-globin gene, ascertaining a homozygosity for Hb Plasencia (HBA2:c.377T>G). This variant has an unstable α chain. In the absence of a thorough work-up, dyserythropoietic anemia associated with hemoglobin (Hb) variants having a moderately unstable α chain, may be mistaken for CDA II.     

Neonatal cyanosis due to a new (G)γ-globin variant causing low oxygen affinity: Hb F-Sarajevo [(G)γ102(G4)Asn→Thr, AAC>ACC

A baby girl, born at term, presented with severe cyanosis and received oxygen supplementation. Consecutive arterial blood gas analysis showed a pronounced right shift of the saturation curve, suggesting the presence of a hemoglobin (Hb) variant. A new (G)γ-globin variant was detected, namely HBG2:c.308G, which we have named Hb F-Sarajevo, the city from where the baby's parents originate. This A to C transversion exists in cis to the common (A)γ(T) and the resulting mutant Hb molecule exhibits very low oxygen affinity and cooperativity. Its analogue in the β-globin gene is Hb Kansas [β102(G4)Asn→Thr, AAC>ACC].     

Two new hemoglobin variants: Hb Aix-Les-Bains [β5(A2)Pro→Leu; HBB:c.17 C>T] and Hb Dubai [α122(H5)His→Leu (α2); HBA2:c.368 A>T

We report two new hemoglobin (Hb) variants; one causing an impairment of the N-terminal glycation of the β-globin chain and the other a hematological phenotype of α-thalassemia (α-thal). The first variant is Hb Aix-les-Bains [β5(A2)Pro→Leu] and the second Hb Dubai [α122(H5)His→Leu (α2)]. These two new Hb variants were detected by chromatographic and electrophoretic methods and characterized by molecular studies. Hb Dubai gives an α-thalassemic phenotype and should be routinely detected for preventing severe Hb H disease in couples at-risk for α-thal.     

Coinheritance of High Oxygen Affinity Hb Helsinki [HBB: c.248A>T; β82(EF6)Lys→Met] with Hb H Disease

Hb Helsinki [HBB: c.248A>T; β82(EF6)Lys→Met] is a high oxygen affinity hemoglobin (Hb) causing polycythemia, whereas Hb H (β4) disease causes mild to severe chronic hemolytic anemia. The clinical characteristics, gel electrophoresis, capillary electrophoresis (CE) and molecular genotyping of a case of Hb Helsinki coinherited with Hb H disease in an ethnic Malay is described, illustrating the interaction between the β-globin variant and coinheritance of three α gene deletions. The proband was asymptomatic, exhibited microcytosis and a normal with Hb value.     

Double Heterozygosity for Hb Durham-N.C. (HBB: c.344T>C) [β114(G16)Leu→Pro] and the IVS-I-110 (HBB: c.93-21G>A) Causing a Severe β-Thalassemia Phenotype

Abstract

The evaluation of a 10-month-old girl of Sicilian origin with a clinical phenotype of severe thalassemia led to the identification of two β-globin gene defects, a β-thalassemia (β-thal), mutation at IVS-I-110 (HBB: c.93-21G>A) and a variant hemoglobin (Hb) mutation at codon 114 (HBB: c.344T>C) on the other allele, reported as Hb Durham-N.C. (also known as Hb Brescia) [β114(G16)Leu→Pro] in the HbVar database. A very low Hb level (Hb 3.5?g/dL), microcytosis [mean corpuscular volume (MCV) 63.2 fL] and hypocromia [mean corpuscular Hb (MCH) 19.6?pg], increased red blood cell (RBC) distribution width (RDW) (36.0%), higher reticulocytes (6.2%), anisocytosis, poikilocytosis, hypocromia, basophilic stippling and inclusion body formation, were present in the affected subject. Analysis of other family components showed the presence of HBB: c.93-21G>A defect in the mother and in her brother, while Hb Durham-N.C. was absent in all other relatives, thus, this mutation has arisen as a de novo defect. This is the first case described as a severe thalassemic phenotype in a compound heterozygote carrier of this unstable Hb and a common β-thalassemic allele. The important information gained from this case is that a rare dominant or recessive mutation may arise in every individual, even if this is a very rare event.     

Hb Agenogi [β90(F6)Glu→Lys (GAG>AAG) HBB: c.271G>A)] in a Pregnant Thai Woman

Hb Agenogi [β90(F6)Glu→Lys (GAG>AAG) HBB: c.271G>A)] is a very rare β-globin chain variant. We report for the first time this hemoglobinopathy in a pregnant 20-year-old Thai woman. She was seen by an obstetrician at her 14th week of gestation. She was pale and had an inflammatory lesion of her lower left leg. The hemoglobin (Hb) analysis by high performance liquid chromatography (HPLC) and low pressure liquid chromatography (LPLC) showed a peak of abnormal Hb at the C window. On capillary electrophoresis (CE), the abnormal Hb peak was observed at electrophoretic zone 4 that corresponded to the Hb E (HBB: c.79G>A) peak. Direct DNA sequencing revealed a GAG>AAG mutation at codon 90 of the β-globin gene. Thus, even though Hb Agenogi is very rare, it can be found in Thai people. The knowledge and understanding of this hemoglobinopathy will be used to assist in diagnosis, management and counseling for patients.     

Severe Thalassemia Caused by Hb Zunyi [β147(HC3)Stop→Gln; HBB: c.442T>C)] on the β-Globin Gene

Hemoglobinopathies are caused by genetic defects on the globin genes. To date, more than 900 β-globin variants have been recorded worldwide. These gene alterations often cause either a decrease in β-globin synthesis or completely block synthesis, leading to a hemoglobinopathy. While most of these causative mutations are inherited, de novo mutations are quite rare. Here, we investigated three hemoglobinopathy cases. These patients developed severe hemolytic anemia at 3-5?months of age and were transfusion-dependent. In patient 1, a novel β variant, Hb Zunyi [β147(HC3)Stop→Gln; HBB: c.442T>C] was identified. This de novo mutation results in a stop codon substitution to a glutamine residue at codon 147 of the β-globin gene, and leads to severe thalassemia. In patient 2, we discovered the rare Hb Southampton mutation [β106(G8)Leu→Pro; HBB: c.320T>C], while in patient 3, the rare Hb Alesha mutation [β67(E11)Val→Met (GTG>ATG); HBB: c.202G>A] was detected. The identification of the novel β variant, Hb Zunyi, has added to the human globin database and will shed light on future diagnosis of hemoglobinopathy/thalassemia and genetic counseling.     

Hb Oslo [β42(CD1)Phe→Ile; HBB: c.127T>A]: A Novel Unstable Hemoglobin Variant Found in a Norwegian Patient

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.     

Hb Ullevaal [β78(EF2)Leu→Val; HBB: c.235C>G], a New Hemoglobin Variant Interfering with Hb A1c Measurement Using a Cation Exchange High Performance Liquid Chromatography Method

A new hemoglobin (Hb) variant was detected during Hb A_1c measurement. DNA sequencing showed heterozygosity for the single nucleotide substitution (C?>?G) on the β-globin gene causing an amino acid change [β78(EF2)Leu→Val; HBB: c.235C?>?G]. The new Hb variant was designated Hb Ullevaal after the hospital at which it was discovered. Heterozygosity for Hb Ullevaal appears to have no clinical significance. However, it interferes with Hb A_1c measurement by cation exchange high performance liquid chromatography (HPLC), causing falsely low Hb A_1c concentration when using the Tosoh G7 apparatus in variant mode.