Sandra G.J. Arkesteijn

Occurrence of common and rare δ-globin gene defects in two multiethnic populations: thirteen new mutations and the significance of δ-globin gene defects in β-thalassemia diagnostics

Introduction:  The aim of this review is to study the frequency of common and the occurrence of rare and novel mutations of the delta‐globin gene and of Hb Lepore defects that might interfere with thalassemia diagnostics and to report the rationale of HbA2 estimation in the presence of delta‐ or alpha‐gene mutations.

A brief review on newborn screening methods for hemoglobinopathies and preliminary results selecting beta thalassemia carriers at birth by quantitative estimation of the HbA fraction

OBJECTIVES We present in a brief summary the basic aspects of the most rational technologies used for new born screening (NBS) of the hemoglobinopathies and we report the preliminary results for the identification of beta-thalassemia carriers at birth by measuring the expression of the HbA fraction. DESIGN AND METHODS Separation and measurement of the Hb fractions in 1.500 cord blood samples collected among the multi-ethnic Dutch population using different methods. RESULTS By using a cut of <15% HbA we have found 4 carriers of point mutations defects 3 of which among a group of 34 newborns of ethnic origin and one among 120 north Europeans. DISCUSSION All methods for NBS summarized in this paper provide identification at practically 100% sensitivity and high specificity. However, all methods should be followed by routine parents analysis to confirm the provisional results. Taking into consideration the gestation age and the HbA expression, we believe that carriers of beta-thalassemia can be preselected at birth with a reasonable degree of sensitivity and be confirmed by parent analysis.

The First Case of Hb Groene Hart [α119(H2)Pro→Ser, CCT→TCT (α1)] Homozygosity Confirms That a Thalassemia Phenotype Is Associated with this Abnormal Hemoglobin Variant

Hb Groene Hart [α119(H2)Pro→Ser, CCT→TCT (α1)] has been reported in heterozygotes of Moroccan origin and also in association with the common −α3.7 deletion. In all cases, the mutated protein was not detectable but was apparently associated with a mild α-thalassemia (thal) phenotype, presumably due to a modification of the α-globin chain domain that is recognized by the a hemoglobin stabilizing protein (AHSP). The present case of Hb Groene Hart homozygosity, confirms that the α-thal phenotype is associated with this α-globin chain. Hb Groene Hart must be quite frequent not only in Morocco but probably also among the northern African coastal population.

A new alpha(0)-thalassemia deletion found in a Dutch family (--(AW)).

Alpha-thalassemia is an inherited hemoglobin disorder characterized by a microcytic hypochromic anemia caused by a quantitative reduction of the alpha-globin chain. The majority of the alpha-thalassemias is caused by deletions in the alpha-globin gene cluster. A deletion in the alpha-globin gene cluster, which was found in a Dutch family, was characterized by MLPA, long-range PCR and direct sequencing. We describe the molecular characterization of a novel 8.2kb deletion (--(AW)), involving both alpha-globin genes in cis. The deletion is caused by a non-homologous recombination event between an Alu and an L1-repeat sequence. This deletion is the third example of a non-homologous recombination event involving an Alu and an L1 repeat, and the first described in the human alpha-globin gene cluster. Because of a 25% risk of Hb Barts with hydrops foetalis in the offspring when in combination with another alpha(0)-thalassemia allele, it is important to diagnose this deletion.

Hb Lepore-Leiden: A New δ/β Rearrangement Associated with a β-Thalassemia Minor Phenotype

The Lepore hemoglobins (Hbs) are a group of structural defects resulting from different recombination events between the δ- and β-globin genes. They may come with different β-thalassemia (β-thal) minor-like phenotypes in the carrier and with variably severe phenotypes in the rare homozygote, and in the common compound heterozygote with β-thal. The most seriously affected patients are those of Yugoslavian origin presenting with severe transfusion-dependent hemolytic anemia, dyserythropoiesis, hepatosplenomegaly and skeletal malformations. Because of genetic risk, couples where both partners are carriers of these combinations may require prognosis and prenatal diagnosis. In these cases, recognition of the defect must be done with particular care. We report a case of Hb Lepore induced by a yet unknown crossover event found in a 24-year-old Turkish male and compare the novel mutation with those previously reported.

Two New α1-Globin Gene Point Mutations: Hb Nedlands (HBA1:c.86C>T) [α28(B9)Ala→Val] and Hb Queens Park (HBA1:c.98T>A) [α32(B13)Met→Lys]

We report two new point mutations of the α1-globin gene found in a Greek and a Burmese patient, both living in Western Australia. The patients were initially selected for their microcytic hypochromic parameters as belonging to a group suspected for uncommon (deletion) defects. Gap-polymerase chain reaction (gap-PCR) and multiplex ligation-dependent probe amplification (MLPA) technologies were applied, and in those cases not showing deletions, direct sequencing was performed. We have found 1) HBA1:c.86C>T, Hb Nedlands [α28(B9)Ala→Val] which, based on the red cell indices and phenotype prediction scores, is presumed to be clinically silent, and 2) HBA1:c.98T>A, Hb Queens Park [α32(B13)Met→Lys] which seems to be associated with a mild α-thalassemia (α-thal) phenotype. The phenotype/genotype correlation is briefly described.

Hb Zoeterwoude [β23(B5)Val → Ala)]: A New β-Globin Variant Found in Association with Erythrocytosis

We describe the characterization of a new hemoglobin (Hb) variant found in a 77-year-old Dutch woman, suspected of hypoxia-mediated erythrocytosis. The typical blood parameters (Hb 17.3 g/dL; PCV 0.525 L/L; RBC 5.82 × 1012/L) could not be explained by any of the pathological or physiological conditions causing erythrocytosis. The patient was preventively phlebotomized because of intermittent claudication and erythrocytosis. At the hematological and biochemical levels, no anemia or hemolysis were present and no abnormal Hb fractions were detectable on alkaline electrophoresis or high performance liquid chromatography (HPLC). Molecular analysis revealed intact α-globin genes and a heterozygosity for a GT T → GC T transition at codon 23 of the β-globin gene, causing a Val → Ala amino acid substitution. The P50 measured in full blood indicated that this mutant has an elevated oxygen affinity. This is the fourth single nucleotide substitution at codon 23 of the β gene and the second associated with erythrocytosis. Because the family was not available for investigation no information was obtained as to whether the mutation represents a de novo event or was inherited, and might be a more common cause of erythrocytosis in Dutch patients. Considering the relatively high frequency of β-thalassemia (thal) in the large allochthonous population in The Netherlands, combinations of Hb Zoeterwoude and β-thal traits may lead to hemizygosity, with severe hypoxia and erythrocytosis from a few months after birth.

Hb Haaglanden: a new nonsickling β7Glu>Val variant. Consequences for basic diagnostics, screening, and risk assessment when dealing with HbS-like variants.

Introduction:  To report a new hemoglobin variant undistinguishable from the common HbS on HPLC. To show the efficiency of the simplest confirmation method for HbS and to discuss the implications that may occur if HbS‐like variants are wrongly reported as HbS.

α‐thalassaemia masked by β gene defects and a new polyadenylation site mutation on the α2‐globin gene

We report three examples of chronic anaemia involving complex combinations of α‐ and β‐globin gene defects. The first case had a potential Hb H disease caused by the classic SEA/RW deletions masked by Hb E [β26(B8)Glu→Lys] in the homozygous state. The second had an unusual Hb H disease caused by compound heterozygosity for two different α2 polyadenylation site mutations masked by a β‐thalassaemia heterozygosity. The third had an intermediate α‐thalassaemia with considerable anaemia caused by an as yet unknown polyadenylation site (AATAAA>AATAAC) mutation in combination with a common RW deletion masked by a common Hb C [β6(A3)Glu→Lys] heterozygosity. Diagnostic methods, genotype/phenotype correlations and the chance of overlooking these combinations during risk assessment in a multiethnic society are discussed.

Hb Geldrop St. Anna [β94(FG1)Asp→Tyr]: a New Hemoglobin Variant Observed in a Diabetic Patient

An abnormal hemoglobin (Hb) fraction was observed during a high performance liquid chromatographic (HPLC) Hb A1c control for diabetes mellitus in a 56-year-old north European woman. Family analyses revealed the abnormal fraction in three of her five siblings and in her son. Elevated Hb and packed cell volume (PCV) values and red blood cell (RBC) counts were present in all carriers. No histories of anemia, hemolytic or circulatory episodes were reported. The abnormal Hb fraction estimated at 40%, migrated just below Hb F on alkaline electrophoresis and overlapped the Hb A2 peak on cation exchange HPLC. Direct sequencing of the β-globin genes revealed a new GAC→TAC transversion in heterozygous form at codon 94 of the β-globin gene. Based on the hematological/biochemical data and the decreased P50 value, we conclude that the new variant is a stable Hb associated with a slightly elevated oxygen affinity.