A Rare Thalassemic Syndrome Caused by Interaction of Hb Adana [α59(E8)Gly→Asp] with an α+-Thalassemia Deletion: Clinical Aspects in Two Cases

Hb F-Wentzville [Gγ24(B6)Gly→Glu; HBG2: c.74G>A, p.Gly25Glu]: An Unstable Gγ-Globin Variant Associated with Neonatal Hemolytic Anemia

A novel unstable ^Gγ-globin variant, Hb F-Wentzville [^Gγ24(B6)Gly→Glu; HBG2: c.74G>A, (p.Gly25Glu)], was identified in a young infant who required a single transfusion of erythrocytes for hemolytic anemia. This is the first reported γ-globin variant affecting the highly conserved glycine residue at helical position B6. In the tertiary structure of hemoglobin (Hb), glycine at B6 is in close proximity to another invariant glycine residue at E8. Prior studies have shown that replacement of the B6 or E8 glycine residues with bulkier amino acids disrupts packing between the B and E helices, resulting in Hb instability. Thus, Hb F-Wentzville is analogous to the following unstable β-globin B6 variants: Hb Savannah (HBB: c.74G>T, p.Gly24Val), Hb Riverdale-Bronx (HBB: c.73G>C, p.Gly24Arg), and Hb Moscva (HBB: c.74G>A, p.Gly24Asp).

Thalassemia major phenotype caused by HB Zürich-Albisrieden [α2 59(E8) Gly > Arg (HBA2:C.178G > C)] in a Brazilian child

Hemoglobin (Hb) Zürich-Albisrieden (ZA) [α2 59(E8) Gly > Arg; HBA2:c.178G > C] is a rare and highly unstable α-chain variant. A few simple and compound heterozygotes (α^ZA α/αα and -/α^ZA α, respectively) have been described so far in Switzerland and China. We describe here a case of homozygosity for the Hb ZA mutation (α^ZA α/α^ZA α) in a Brazilian child with severe congenital hemolytic anemia and ineffective erythropoiesis.

Hb Adana (HBA2 or HBA1: c.179G > A) and alpha thalassemia: Genotype-phenotype correlation

Alpha thalassemia due to nondeletional mutations usually leads to more severe disease than that caused by deletional mutations. Devastating outcomes such as hydrops fetalis can occur with two nondeletional mutations, therefore warranting DNA-based workup for suspected carriers with subtle hematological abnormalities for family counseling purposes. We describe three cases with hemoglobin (Hb) Adana, a nondeletional alpha chain mutation, compounded with an alpha globin gene deletion resulting in thalassemia intermedia. We review the literature, draw genotype-phenotype correlations from published cases of Hb Adana, and propose that this correlation can be used by clinicians to help direct diagnostic studies and urge hematologists to thoroughly workup high-risk patients.

Compound Heterozygosity for Hb Adana (HBA2: c.179G>A) and the -α3.7/αα Thalassemia Deletion in Greece: Clinical Phenotype and Genetic Counseling

Hb Adana (HBA2: c.179G>A) is found worldwide but is extremely rare and carriers are asymptomatic, with red cell indices similar to α⁺-thalassemia (α⁺-thal) carriers. First line screening tests are unable to detect the unstable hemoglobin (Hb). Coinheritance with the α-thal (-α^3.7) deletion is herein presented and the challenges involving genetic counseling of couples carrying the mutations are discussed.

Molecular basis of α-thalassemia

α-Thalassemia is an inherited, autosomal recessive, disorder characterized by a microcytic hypochromic anemia. It is one of the most common monogenic gene disorders in the world population. The clinical severity varies from almost asymptomatic, to mild microcytic hypochromic, and to a lethal hemolytic condition, called Hb Bart's Hydrops Foetalis Syndrome. The molecular basis are usually deletions and less frequently, point mutations affecting the expression of one or more of the duplicated α-genes. The clinical variation and increase in disease severity is directly related to the decreased expression of one, two, three or four copies of the α-globin genes. Deletions and point mutations in the α-globin genes and their regulatory elements have been studied extensively in carriers and patients and these studies have given insight into the α-globin genes are regulated. By looking at naturally occurring deletions and point mutations, our knowledge of globin-gene regulation and expression will continue to increase and will lead to new targets of therapy.

DNA studies are necessary for accurate patient diagnosis in compound heterozygosity for Hb Adana (HBA2:c.179>A) with deletional or nondeletional α-thalassaemia

Haemoglobin (Hb) Adana (HBA2:c.179>A) interacts with deletional and nondeletional α-thalassaemia mutations to produce HbH disorders with varying clinical manifestations from asymptomatic to severe anaemia with significant hepatosplenomegaly. Hb Adana carriers are generally asymptomatic and haemoglobin subtyping is unable to detect this highly unstable α-haemoglobin variant. This study identified 13 patients with compound heterozygosity for Hb Adana with either the 3.7 kb gene deletion (-α^3.7), Hb Constant Spring (HbCS) (HBA2:c.427T>C) or Hb Paksé (HBA2:429A>T). Multiplex Amplification Refractory Mutation System was used for the detection of five deletional and six nondeletional α-thalassaemia mutations. Duplex-PCR was used to confirm Hb Paksé and HbCS. Results showed 84.6% of the Hb Adana patients were Malays. Using DNA studies, compound heterozygosity for Hb Adana and HbCS (α^{codon 59}α/α^CSα) was confirmed in 11 patients. A novel point in this investigation was that DNA studies confirmed Hb Paksé for the first time in a Malaysian patient (α^{codon 59}α/α^Pakséα) after nine years of being misdiagnosis with Hb Adana and HbCS (α^{codon 59}α/α^CSα). Thus, the reliance on haematology studies and Hb subtyping to detect Hb variants is inadequate in countries where thalassaemia is prevalent and caused by a wide spectrum of mutations.

A case series of α-thalassemia intermedia due to compound heterozygosity for Hb Adana [HBA2: c179G>A (or HBA1); p.Gly60Asp] with other α-thalassemias in Malay families

Hb Adana [HBA2: c179G>A (or HBA1); p.Gly60Asp] is a rare hemoglobin (Hb) variant due to a mutation at codon 59 of the α2- or α1-globin gene resulting in a glycine to aspartic acid substitution. Two siblings with a unique coinheritance of Hb Adana and Hb Constant Spring (Hb CS, α142, Term→Gln, TAA>CAA; HBA2: c.427 T>C) (α(codon 59)α/α(CS)α), were compared phenotypically with another two siblings carrying the Hb Adana mutation and a 3.7 kb deletion (α(codon 59)α/-α(3.7)). Although they all had α-thalassemia intermedia (α-TI), the former were clinically more severe than the latter. The first pair of siblings presented at a much younger age than the second pair and showed lower Hb levels and significant extramedullay hemopoiesis. Another case of a hydropic fetus as a result of Hb H/Hb Adana is also described. Their clinical phenotypes and hematological parameters are all presented for comparison.

Severe α-thalassemia intermedia due to a compound heterozygosity for the highly unstable Hb Adana (HBA2: c.179G>A) and a novel codon 24 (HBA2: c.75T>A) mutation

HBA2

We report a novel mutation at codon 24 of the α2-globin gene (HBA2: c.75T > A) found in a Sundanese family. This novel mutation was detected during prenatal diagnosis. The couple already had a 7-year-old boy who exhibited clinically severe α-thalassemia intermedia (α-TI), and he was found to be a compound heterozygote for the novel mutation at codon 24 and the previously described Hb Adana (HBA2: c.179G > A) at codon 59 of the α2-globin gene. The father was a carrier of the novel point mutation and showed normal hemoglobin (Hb) and a low mean corpuscular volume (MCV) and mean corpuscular Hb (MCH) value.

Interaction of Hb adana (HBA2: c.179G>A) with deletional and nondeletional α(+)-thalassemia mutations: diverse hematological and clinical features

We describe 27 cases of mild-to-severe α-thalassemia (α-thal) syndrome caused by interaction of Hb Adana [α59(E8)Gly→Asp, GGC>GAC (α2)] with deletional and nondeletional α(+)-thal mutations in Indonesian patients. Hematological profiles and clinical manifestations of all patients were assessed by routine procedures. The genotypes were generated by a multiplex-polymerase chain reaction (m-PCR), PCR-RFLP (restriction fragment length polymorphism)-based method, and DNA sequencing. The α-thal patients who had Hb Adana in combination with the 3.7 kb deletion mostly have mild-to-moderate anemia. In contrast, patients who were compound heterozygotes for Hb Adana and nondeletional mutations, generally showed a more severe anemia and it mostly presented in childhood. Thus, accurate diagnosis of α-thal disorders is not only important for future management of these patients but also for providing proper genetic counseling to the family.

A severe alpha thalassemia case compound heterozygous for Hb Adana in alpha1 gene and 20.5 kb double gene deletion

We report a 6-year-old boy diagnosed as transfusion dependent chronic nonspherocytic hemolytic anemia since 40 days old. Hemoglobin H inclusions were detected with brilliant cresyl blue preparation. His parents were found to be normal on physical examination. His mother had hemoglobin level of 9.34 g/dL, accompanied by typical thalassemic changes of the red cells, and inclusion bodies were also detected with brilliant cresyl blue staining. His father had normal hemoglobin level and borderline red cell indices. Mutation analysis using strip assay capable of detecting 22 mutations within the alpha genes was performed for the proband and the parents which revealed that the case was compound heterozygous for Hb Adana in alpha1 gene and 20.5 kb double gene deletion. The father was found to be heterozygous for Hb Adana alpha1 gene whereas the mother was found to be compound heterozygous for 20.5 kb double gene deletion and 3.7 kb single gene deletion. It is well known that non deletional forms of HbH disease are more severe than the deletional forms. This case represents another example of the nondeletional mutation underlying Hb Adana, which is rarely seen in alpha1 gene, and illustrates the distinctive phenotypes of both the deletional and nondeletional forms of hemoglobin H disease within the same family.