Hb Sun Prairie: diagnostic pitfalls in thalassemic hemoglobinopathies

Effect of Mutations on mRNA and Globin Stability: The Cases of Hb Bernalda/Groene Hart and Hb Southern Italy

We identified two unstable variants in the third exon of α-globin genes: Hb Bernalda/Groene Hart (HBA1:c.358C>T), and Hb Caserta (HBA2:c.79G>A) in cis to Hb Sun Prairie (HBA2:c.391G>C), also named Hb Southern Italy. These mutations occurred in the H helix of the α-globin that is involved in heme contacting, specific recognition of α-hemoglobin-stabilizing protein (AHSP), and α₁β₁ interactions. The carriers showed α-thalassemia phenotype, but one also jaundice and cholelithiasis. Molecular identification of clusters of families in Southern Italy encouraged molecular characterization of mRNA, globin chain analyses, molecular modeling studies, and comparison with globin variants to understand the mechanisms causing the α-thalassemia phenotype. A normal amount of Hb Bernalda/Groene Hart mRNA were found, and molecular modeling highlighted additional H bonds with AHSP. For Hb Southern Italy, showing an unexpected α/β biosynthetic ratio typical of the β-thalassemia type, two different molecular mechanisms were shown: Reduction of the variant mRNA, likely due to the No-Go Decay for the presence of unused triplet ACG at cod 26, and protein instability due to the impairment of AHSP interaction. The UDP glucuronosyltransferase 1A (UGT1A1) genotyping was conclusive in the case of jaundice and cholelithiasis. Multiple approaches are needed to properly identify the mechanisms leading to unstable variants and the effect of a mutation.

Hb Sun Prairie: A rare cause of chronic hemolysis in an Indian patient

Haemolytic anaemia is a commonly encountered condition in clinical haematology practise. Dissecting the aetiology of haemolytic anaemia is of paramount importance for appropriate management. We describe a 29-years-old lady of Indian origin, who presented with fatigue and recurrent jaundice for 2 years. Examination revealed pallor, mild icterus, and splenomegaly. Blood tests showed anaemia, reticulocytosis, indirecthyperbilirubinemia, and high serum lactate dehydrogenase, consistent with haemolytic anaemia. Peripheral smear showed severely microcytic hypochromic red cells and polychromasia. Heinz bodies and inclusion bodies were seen with supravital staining. Haemoglobin high pressure liquid chromatography showed low HbA2 and normal HbF. Work-up for iron deficiency was negative. Polymerase chain reaction of the genomic DNA failed to identify common deletions in the HBA genes. Sangers sequencing of HBA2 gene revealed a homozygous missense mutation NM_000517.6: c.391G > C (p.Ala131Pro) leading to a highly unstable hemoglobin, Hb Sun Prairie. Mother was heterozygous for the same mutation, and father was unavailable for genetic testing. We highlight the role of sangers sequencing in unravelling the underlying aetiology of haemolytic anaemia. Pathophysiology and existing literature of Hb Sun Prairie has been discussed.

Characterization of Clinical and Laboratory Profiles of the Deletional α2-Globin Gene Polyadenylation Signal Sequence (AATAAA > AATA- -) in an Indian Population

α-Thalassemia (α-thal) is characterized by large deletions involving the variable regions of α2 and/or α1 genes. Nondeletional mutations and polyadenylation (polyA) signal sequence motif mutations are less common. In this retrospective study, we describe a fragment length analysis-based polymerase chain reaction (PCR) assay for screening the T(Indian) (AATAAA > AATA- -; HBA2: c.*93_*94delAA) polyA signal deletion along with its clinical and laboratory presentation in 21 patients. Most of the patients were diagnosed in early adulthood with a clinical presentation ranging from asymptomatic in the heterozygous state to severe Hb H disease with a prominent hemolytic component in the homozygous state. On genetic analysis, 14 patients were found to be homozygotes, five were compound heterozygotes and two were heterozygotes. Thus, the T(Indian) polyA signal deletion is common in the Indian population and should be screened for in patients with nondeletional α-thal mutations.

Screening for clinically significant non-deletional alpha thalassaemia mutations by pyrosequencing

Non-deletional α(+)-thalassaemia is associated with a higher degree of morbidity and mortality than deletional forms of α(+)-thalassaemia. Screening for the common deletional forms of α-thalassaemia by Gap-PCR is widely practiced; however, the detection of non-deletional α-thalassaemia mutations is technically more labour-intensive and expensive, as it requires DNA sequencing. In addition, the presence of four very closely homologous alpha globin genes and the frequent co-existence of deletional forms of α-thalassaemia present another layer of complexity in the detection of these mutations. With growing evidence that non-deletional α-thalassaemia is relatively common in the UK, there is a demand for technologies which can quickly and accurately screen for these mutations. We describe a method utilising pyrosequencing for detecting the ten most common clinically significant non-deletional α-thalassaemia mutations in the UK. We tested 105 patients with non-deletional α-thalassaemia and found 100% concordance with known genotype as identified by Sanger sequencing. We found pyrosequencing to be simpler, more robust, quicker, and cheaper than conventional sequencing, making it a good choice for rapid and cost-effective diagnosis of patients with suspected non-deletional α-thalassaemia. The technique is also likely to help expedite prenatal diagnosis of pregnancies at risk of α-thalassaemia major.

Hb Southern Italy: coexistence of two missence mutations (the Hb Sun Prairie alpha2 130 Ala --> Pro and Hb Caserta alpha2 26 Ala --> Thr) in a single HBA2 gene

This study describes a new molecular condition in the alpha(2)-globin gene (HBA2) found in six unrelated families from Southern Italy (Campania and Sicily). This new double mutant form of haemoglobin is called Hb Southern Italy and originated from the coexistence of two known mutations occurring in the same globin gene, HBA2 26 G-->A (Hb Caserta) and HBA2 130 G-->C (Hb Sun Prairie). Hb Sun Prairie was originally observed in Indian patients in either the homozygous state, with severe hemolytic anemia, and in the heterozygous state with microcytosis, or in asymptomatic cases as an alpha-thalassemia carrier phenotype. Hb Caserta was observed for the first time in a Casertian family (South Italy) that displayed a slowmigrating haemoglobin upon investigation. We report the clinical phenotype and molecular study of this new double mutant form of haemoglobin in heterozygous and homozygous subjects, as well as in association with alpha degrees delectional thalassemia.

Co-inheritance of the Hb Sun Prairie mutation with a point mutation at 5'-UTR in the eastern Indian population

Haemoglobin (Hb) Sun Prairie (alpha2-globin cd130, GCT-->CCT, Ala-->Pro) is detected in three unrelated chromosomes, in association with a C-->T transition in the 5'-untranslated region (UTR), two bases upstream from the translation start site. Reported inversion of alpha/beta-mRNA ratio observed in Hb Sun Prairie mutants might stem from the second mutation and should be investigated. Molecular modelling studies indicate that the 130th residue of alpha-globin faces primarily the central cavity of the molecule and is not in contact with any beta-chain residue; further, no significant disruption of the Hb structure because of the Sun Prairie mutation is discernible. Depression of translation because of the second mutation of a conserved base in the 5'-UTR might explain the observed clinical severity.

Hb Bronte or alpha93(FG5)Val-->Gly: a new unstable variant of the alpha2-globin gene, associated with a mild alpha(+)-thalassemia phenotype

We report a new unstable variant identified in three carriers of a family from East Sicily; it was named Hb Bronte after the place from which the family originated. DNA sequencing from nucleotides -181 to +894 (alpha1) and to +884 (alpha2) revealed a GTG-->GGG substitution at codon 93 of the alpha2-globin gene. The MCV and MCH values were at the lower end of the normal range in the carriers. On cation exchange high performance liquid chromatography (HPLC), the Hb A2 level was apparently increased to around 6%, and a small abnormal peak (0.3-0.4%) was detected after Hb A2. Two abnormal bands were detected by cellulose acetate electrophoresis: a major band (about 3-4%) migrated between Hb A and Hb F; a minor band (<1%) migrated between Hb A2 and carbonic anhydrase. Normal values of Hb A2 were detected by DEAE microchromatography. On reversed phase HPLC the variant chain was not detected, and most likely it was eluted with the alpha chain peak. The isopropanol stability test was very slightly positive in the carriers. Hemolytic symptoms were absent with the exception of indirect bilirubin, which was at high borderline in 2/3 carriers. In biosynthesis in vitro, the specific activity of the alpha chains was much higher than that of the beta-globin chains, and the alpha/beta biosynthetic ratio in the mother and proband was of the beta-thalassemia (thal) type (2.24 and 2.54, respectively). Time course experiments showed that the increase of the 3H-specific activity of the peak containing normal and variant alpha chains was not linear and was much higher than that of beta chains; moreover, the alpha/beta biosynthetic ratio varied during the 2 hours incubation.

Distinct phenotypic expression associated with a new hyperunstable alpha globin variant (Hb heraklion, alpha1cd37(C2)Pro>0): comparison to other alpha-thalassemic hemoglobinopathies

Clinical phenotypes associated with abnormal globin chain biosynthesis may result in thalassemia (deficient quantity) or hemolytic anemia (abnormal hemoglobins). However, the phenotypic expression of hyperunstable hemoglobin variants often includes features of thalassemia, along with variable peripheral hemolysis. Hemoglobinopathies caused by highly unstable beta-chain variants have a dominant thalassemia-like phenotype, in which carriers have a clinical expression of thalassemia intermedia, but highly unstable alpha-globin variants are usually only phenotypically apparent when they interact with other alpha-thalassemia mutations. In a child with clinical and hematological features consistent with beta-thalassemia intermedia, DNA analysis excluded any beta-globin gene mutations but characterized a novel deletion cd37(C2)Pro>0 (Hb Heraklion) in the alpha1 globin gene, in trans to a common Mediterranean nondeletion alpha-thalassemia mutation (alpha(Hph)alpha). The deletion of proline at alpha37(C2) is predicted to result in severe instability of the variant hemoglobin, which on interaction with a synthesis-deficient alpha-thalassemia mutation causes a relatively severe dyserythropoietic anemia, representing an alternative phenotype associated with highly unstable alpha-chain variants. Hb Heraklion is the fourth highly unstable alpha-globin variant that we have observed in patients from Greece and Albania. Two variants involve the alpha2-globin gene: Hb Agrinio (alpha29(B10)Leu>Pro) and Hb Adana (alpha59(E8)Gly>Asp), and two the alpha1-gene: Hb Aghia Sophia (alpha62(E11)Val>0) and (Hb Heraklion a37(C2)Pro>0). Each has been observed on interaction with a different alpha-thalassemia mutation and the phenotypes associated with these highly unstable alpha-variants are presented.

Interaction of an alpha(+)-thalassemia deletion with either a highly unstable alpha-globin variant (alpha2, codon 59, GGC-->GAC) or a nondeletional alpha-thalassemia mutation (AATAAA-->AATAAG): comparison of phenotypes illustrating "dominant" alpha-thalassemia

Thalassemia syndromes and unstable hemoglobins traditionally represent two phenotypically separate disorders of hemoglobin synthesis. Highly unstable hemoglobin variants, however, often have phenotypic characteristics associated with both ineffective erythropoiesis (thalassemias) and peripheral hemolysis (unstable hemoglobins). Many highly unstable beta chain variants cause a dominant thalassemia-like phenotype, in which simple heterozygotes for such mutations have a clinical expression similar to thalassemia intermedia. The phenotypic expression of highly unstable alpha-globin variants is usually less severe, due mainly to a gene dosage effect, and they are often only characterized on interaction with other alpha-thalassemia mutations, whence they are classified as nondeletional alpha-thalassemia determinants. This study reports the clinical and hematological findings in five cases with rare alpha-thalassemia genotypes: a single patient with the thalassemic alpha2-globin gene codon 59 Gly-->Asp hemoglobin variant in trans to an alpha(+)-thalassemia deletion, and four compound heterozygotes for the nondeletional alpha-thalassemia polyadenylation mutation (alpha2 gene AATAAA-->AATAAG or alpha(T-Saudi)alpha/-alpha) and an alpha(+)-thalassemia deletion. Evaluation of the clinical and hematological features in these two analogous genotypes clearly demonstrates the more severe clinical expression associated with the alpha-thalassemic unstable hemoglobin variant. In addition, the case in this study with the codon 59 alpha chain variant provides a further example illustrating the spectrum of phenotypes associated with the alpha-thalassemic hemoglobinopathies.

An alpha-thalassemic hemoglobinopathy: homozygosity for the HB Agrinio alpha 2-globin chain variant

This report describes the first case of homozygosity for the Hb Agrinio [alpha 29(B10)Leu-->Pro] alpha 2-globin gene variant (codon 29, CTG-->CCG) in a Greek patient. At 12 months of age, the proband presented with a marked hypochromic, microcytic anemia, a very low level of Hb H (< 2.5%), rare Hb H inclusions, and a balanced alpha/non-alpha biosynthesis ratio. The mother had hematological findings and globin biosynthesis consistent with heterozygous beta-thalassemia, but paradoxically, red cell morphology demonstrated very rare Hb H inclusions. The father had mild microcytosis and hypochromia. Analysis of alpha- and beta-globin genotypes demonstrated that the patient was homozygous for the highly unstable Hb Agrinio variant, caused by a T-->C mutation in codon 29 of the alpha 2-globin gene. At the age of 13 years, the proband had a clinical phenotype compatible with mild thalassemia intermedia with moderate anemia (Hb 7-8 g/dL), normal growth and development, slight splenomegaly, and minimal bone changes, while Hb H and inclusion bodies were not detected.