Hb Nijkerk: a new mutation at codons 138/139 of the beta-globin gene inducing severe hemolytic anemia in a Dutch girl

Newborn screening for hemoglobinopathies using capillary electrophoresis

This chapter reports the essential elements needed to understand basic laboratory diagnostics consisting of separation and measurement of the hemoglobin fractions. Although well established, basic diagnostics require some background and some degree of experience for application and interpretation. Last generation methods, consisting of automatic systems like high performance liquid chromatography and capillary electrophoresis (CE), allow high through put analysis in adults and newborns. Newborn screening using CE is presented in some details, using as an example the Capillarysâ Neonat Hb system (Sebia, France), as an upcoming alternative, explaining the method, the interpretation of the results, the objectives, the follow up, the advantages, and the pitfalls.

Strategies for basic laboratory diagnostics of the hemoglobinopathies in multi-ethnic societies: interpretation of results and pitfalls

The consistent multi-ethnic migrations of the last decades have considerably changed the epidemiology of the hemoglobinopathies. Healthy carriers of these conditions are present today in many nonendemic parts of the world, and severely affected children are now born where these diseases were previously rare or unknown. Improving the competence in carrier diagnostics at the laboratory level is one of the first concerns when introducing management and primary prevention of the severe conditions in nonendemic areas. This review describes how and when carriers should be correctly diagnosed and informed. The essential technologies needed for basic carrier diagnostics in different situations are summarized in some detail, and interpretation of the results and a number of related problems are discussed. The role of the hematology laboratory is essential, particularly in nonendemic areas where the first line of health care is often insufficiently aware of hemoglobinopathy management. Carriers living in nonendemic areas can be appropriately diagnosed and informed regarding genetic risk and prevention by well-organized laboratories. Both basic and specialized diagnostics are needed for the correct treatment for the anemic carriers, for primary prevention in couples at risk and for state-of-the art care of severely affected patients.

Hb Stara Zagora: A New Hyper-Unstable Hemoglobin Causing Severe Hemolytic Anemia

We describe a new hyper-unstable beta chain variant (codons 137-139, -6 bp) in a 2-year-old Bulgarian boy. The abnormal hemoglobin (Hb) is associated with severe hemolytic anemia as a consequence of its hyper instability. The child was admitted to the Pediatric Clinic (Faculty of Medicine, Stara Zagora, Bulgaria) at the age of 2 months. Because of anemia (Hb 6.9 g/dL) and high serum iron level (58 microM/L) the child was transfused. However, a month later his Hb level had dropped to 7.5 g/dL, and since then he has been on a regular monthly blood transfusion regimen. Hemoglobin analysis of a blood sample collected 2 months after the last transfusion at the age of 2 years, revealed no abnormalities except for the presence of inclusion bodies after incubation of peripheral blood with brilliant cresyl blue. Sequencing of the beta-globin gene revealed heterozygosity for a 6 bp deletion (-TGGCTA) at codons 137 [the second and third base pair (bp)], 138 and 139 (the first bp), forming a new codon at position 137 (GAT). This event eliminates three amino acids (Val-Ala-Asn) and introduces a new residue (Asp). It creates a new restriction site for HphI. The parents and his dizygotic twin brother had no history of hemolysis. The paternity of the child was confirmed by DNA analysis.

Dominantly Inherited beta-Thalassemia

Dominantly inherited beta-thalassemia (thal) or "inclusion body beta-thalassemias" are heterogeneous at the molecular level and are due to mutations at or near the beta-globin gene locus. Many of these involve mutations of exon 3 of the beta-globin gene. They include frameshifts, premature chain termination (nonsense) mutations, and complex rearrangements that lead to the synthesis of truncated or elongated and highly unstable beta-globin gene products. The resulting beta chain variants are very unstable, and in many cases, the products of the dominantly inherited beta-thal are not detectable. Hematological and clinical observations made in several families with comparable forms of beta-thal and with certain highly unstable hemoglobin (Hb) variants, have indicated a striking overlap; many subjects with detectable unstable Hb variants and with a dominant type of beta-thal without a detectable abnormal Hb, have similar phenotypes. Here, a review of dominantly inherited beta-thal is given, and new examples of hyperunstable Hbs (Hb Stara Zagora and Hb Jambol) are presented. The first example is a hyperunstable variant named Hb Stara Zagora that was found in a 2-year-old Bulgarian boy. The abnormal Hb is associated with severe hemolytic anemia as a consequence of its hyper instability. The anemia was noticed at the age of 2 months and since then he has been on a regular monthly blood transfusion regimen. Hemoglobin analysis revealed no abnormalities, except the presence of inclusion bodies. Sequencing of the beta-globin gene revealed a heterozygosity for a 6 bp deletion (-TGGCTA) at codons 137 (the second and third bp), 138 and 139 (the first bp), thus forming a new codon at position 139 (GAT). This event eliminates three amino acids (Val-Ala-Asn) and introduces a new residue (Asp). It creates a new restriction site for HphI. The parents and his twin brother had no history of hemolysis. The paternity of the child was confirmed by DNA analysis. The second example is a new hyperunstable variant named Hb Jambol, found as a de novo mutation in a 2-year-old Bulgarian girl with severe hemolytic anemia. The mutation was detected through RNA/DNA analysis. It represents a complex genomic rearrangement involving an insertion of 23 nucleotides (nts) after IVS-II-535, a deletion of 310 nts extending from IVS-II-550 to the first nt of codon 108, and an insertion of 28 nts at the deletion junctions (derived from inverted sequence between nts +3707 and +3734 3' to the beta-globin gene termination codon). At the protein level, this mutation leads to a deletion of four amino acid residues (Leu-Leu-Glu-Asn) at positions 105, 106, 107 and 108, and an insertion of nine residues (Val-Pro-Ser-Val-Thr-Leu-Phe-Phe-Asp) at the same location, creating an abnormal elongated beta chain of 151 amino acid residues. The parents had no history of hemolysis. The paternity of the child was confirmed by DNA analysis.

Hb Jambol: a new hyperunstable hemoglobin causing severe hemolytic anemia

We describe a new hyperunstable beta-chain variant due to a complex genomic rearrangement. The abnormal hemoglobin (Hb) was found as a de novo mutation in a 2-year-old Bulgarian girl with severe hemolytic anemia. The mutation was detected through RNA/DNA analysis. It represents a complex genomic rearrangement involving an insertion of 23 nts after IVS-II-535 (derived by triplication of the 12-nts adjacent sequence and subsequent deletion of 1 nt), a deletion of 310 nts extending from IVS-II-550 to the first nt of Cd 108 and an insertion of 28 nts at the deletion junctions (derived from the inverted sequence between nts +3,707 and +3,734 3' to the beta-globin gene termination codon). At the protein level this mutation leads to a deletion of 4 amino acid residues (Leu-Leu-Glu-Asn) at positions 105-108 and an insertion of 9 residues (Val-Pro-Ser-Val-Thr-Leu-Phe-Phe-Asp) at the same location, creating an abnormal elongated beta-chain of 151 amino acid residues. This highly unstable variant was named 'Hb Jambol' after the geographic location in which the patient resides.

A deletion of 11 bp (CD 131–134) in exon 3 of the β-globin gene produces the phenotype of inclusion body β-thalassemia

Dominant inherited beta-thalassemias describe those beta-thalassemia variants that result in a thalassemia intermediate phenotype in individuals who have inherited only a single copy of the abnormal beta gene. This form of thalassemia is characterized by moderately severe anemia with jaundice and splenomegaly; it is also characterized by the presence of inclusion bodies in the red blood cell precursors and has, therefore, previously been referred to as inclusion body beta-thalassemia. We describe a case of inclusion body beta-thalassemia in a 51-year-old Spanish male caused by a deletion of 11 bp (CD 131-134) in exon 3 of the beta-globin gene. The deletion of 11 bp in exon 3 of the beta-globin chain is predicted to produce an anomalous chain of 134 amino acids instead of the normal 146 with an extremely altered amino acid sequence from residues 131-134. Although this shortened variant would lead to a missing H helix, which is involved in alpha1beta1 contact and alpha1beta2 subunit interactions, the variant chain can still be bound to the heme group and acquire a secondary structure that is not suitable for the formation of stable dimers or tetramers and also less susceptible to proteolytic degradation. This is the first report of such a beta-thalassemia mutation.

Two new variants with the same substitution at position beta122: Hb Bushey [beta122(GH5)Phe-->Leu] and Hb Casablanca [beta65(E9)lys-->Met; beta122(GH5)Phe-->Leu]

Hb Bushey, found in a Chinese baby and his father, is a new variant with a point mutation leading to the substitution Phe-->Leu at position beta122. Hb Casablanca, found in a family from Morocco, is a further example of a hemoglobin variant that carries two abnormalities in the same chain; the first is identical to that of Hb Bushey and the second to that of Hb J-Antakya [beta65 (E9)Lys-->Met]. Structural abnormalities of both Hbs were determined by protein chemistry methods including electrospray and tandem mass spectrometry. Their stability and oxygen binding properties were found to be identical to those of Hb A. Various mechanisms that may lead to two point mutations in the same chain are reviewed briefly.