Haemoglobin Constant Spring--a chain termination mutant?

Erythropoiesis and Gene Expression Analysis in Erythroid Progenitor Cells Derived from Patients with Hemoglobin H/Constant Spring Disease

Hemoglobin H/Constant Spring (Hb H/CS) disease represents a form of non-deletional Hb H disease characterized by chronic hemolytic anemia that ranges from moderate to severe and may lead to transfusion-dependent thalassemia. To study the underlying mechanisms of this disease, we conducted an analysis of erythropoiesis and gene expression in erythroid progenitor cells derived from CD34+ hematopoietic stem/progenitor cells from patients with Hb H/CS disease and normal controls. Twelve patients with Hb H/CS disease and five normal controls were enrolled. Peripheral blood samples were collected to isolate CD34+ hematopoietic stem/progenitor cells for the analysis of cell proliferation and differentiation. Six samples from patients with Hb H/CS disease and three controls were subsequently studied for gene expression by next generation sequencing analysis. Erythroid progenitor cells derived from patients with Hb H/CS disease exhibited a trend towards increased rates of erythroid proliferation and decreased cell viability compared to those from controls. Moreover, erythroid progenitor cells derived from patients with Hb H/CS disease demonstrated delayed terminal differentiation. Gene expression profiling revealed elevated levels of genes encoding molecular chaperones, including the heat shock protein genes (HSPs) and the chaperonin containing TCP-1 subunit genes (CCTs) in the Hb H/CS disease group. In summary, erythroid progenitor cells derived from patients with Hb H/CS disease exhibit a trend towards heightened erythroid proliferation, diminished cell viability, and delayed terminal differentiation. Additionally, the increased expression of genes encoding molecular chaperones was observed, providing information on potential underlying pathophysiological mechanisms.

Effective screening of hemoglobin Constant Spring and hemoglobin Paksé with several forms of α- and β-thalassemia in an area with a high prevalence and heterogeneity of thalassemia using capillary electrophoresis

Background and aims

We aimed to evaluate the efficiency of identification and quantification of hemoglobin (Hb) Constant Spring (CS) and Hb Paksé by capillary electrophoresis (CE).

Materials and methods

Blood samples collected from 2057 patients were used for identifying and quantifying Hb by CE. Molecular analysis of α- and β-thalassemia, Hb CS, and Hb Paksé was performed.

Results

Hb CS and Hb Paksé were identified in 573 samples (27.86%) with diverse genotypes. Thirty-eight samples (6.6%) showed no Hb CS peak. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of Hb CS by CE were 93.37, 95.96, 89.92, 97.40, and 95.24%, respectively. The amount of Hb CS in those carrying Hb CS was 0.2-6.5% which showed an increasing trend according to the number of defective α-globin genes, in contrast to Hb A2 levels, which decreased. Hb CS level ≥1.0% accurately excluded heterozygotes and that of ≥2.0% could identify homozygotes.

Conclusion

CE has the high potential for identifying and quantifying Hb CS and Hb Paksé, especially in an area with a high prevalence of thalassemia. Hb CS levels can be used as a potential marker to distinguish the genotype of individuals carrying Hb CS.

Introduction to the Thalassemia Syndromes: Molecular Medicine's Index Case

Thalassemia is a heterogeneous group of inherited anemias having in common defective biosynthesis of one or more of the globin chain subunits of human hemoglobin. Their origins lie in inherited mutations that impair the expression of the affected globin genes. Their pathophysiology arises from the consequent insufficiency of hemoglobin production and the imbalance in the production of globin chains resulting in the accumulation of insoluble unpaired chains. These precipitate and damage or destroy developing erythroblasts and erythrocytes producing ineffective erythropoiesis and hemolytic anemia. Treatment of severe cases requires lifelong transfusion support with iron chelation therapy.

Stop codon usage as a window into genome evolution: mutation, selection, biased gene conversion and the TAG paradox

Protein coding genes terminate with one of three stop codons (TAA, TGA, or TAG) that, like synonymous codons, are not employed equally. With TGA and TAG having identical nucleotide content, analysis of their differential usage provides an unusual window into the forces operating on what are ostensibly functionally identical residues. Across genomes and between isochores within the human genome, TGA usage increases with G + C content but, with a common G + C → A + T mutation bias, this cannot be explained by mutation bias-drift equilibrium. Increased usage of TGA in G + C-rich genomes or genomic regions is also unlikely to reflect selection for the optimal stop codon, as TAA appears to be universally optimal, probably because it has the lowest read-through rate. Despite TAA being favored by selection and mutation bias, as with codon usage bias G + C pressure is the prime determinant of between-species TGA usage trends. In species with strong G + C-biased gene conversion (gBGC), such as mammals and birds, the high usage and conservation of TGA is best explained by an A + T → G + C repair bias. How to explain TGA enrichment in other G + C-rich genomes is less clear. Enigmatically, across bacterial and archaeal species and between human isochores TAG usage is mostly unresponsive to G + C pressure. This unresponsiveness we dub the TAG paradox as currently no mutational, selective, or gBGC model provides a well-supported explanation. That TAG does increase with G + C usage across eukaryotes makes the usage elsewhere yet more enigmatic. We suggest resolution of the TAG paradox may provide insights into either an unknown but common selective preference (probably at the DNA/RNA level) or an unrecognized complexity to the action of gBGC.

Unusual mammalian usage of TGA stop codons reveals that sequence conservation need not imply purifying selection

The assumption that conservation of sequence implies the action of purifying selection is central to diverse methodologies to infer functional importance. GC-biased gene conversion (gBGC), a meiotic mismatch repair bias strongly favouring GC over AT, can in principle mimic the action of selection, this being thought to be especially important in mammals. As mutation is GC→AT biased, to demonstrate that gBGC does indeed cause false signals requires evidence that an AT-rich residue is selectively optimal compared to its more GC-rich allele, while showing also that the GC-rich alternative is conserved. We propose that mammalian stop codon evolution provides a robust test case. Although in most taxa TAA is the optimal stop codon, TGA is both abundant and conserved in mammalian genomes. We show that this mammalian exceptionalism is well explained by gBGC mimicking purifying selection and that TAA is the selectively optimal codon. Supportive of gBGC, we observe (i) TGA usage trends are consistent at the focal stop codon and elsewhere (in UTR sequences); (ii) that higher TGA usage and higher TAA→TGA substitution rates are predicted by a high recombination rate; and (iii) across species the difference in TAA <-> TGA substitution rates between GC-rich and GC-poor genes is largest in genomes that possess higher between-gene GC variation. TAA optimality is supported both by enrichment in highly expressed genes and trends associated with effective population size. High TGA usage and high TAA→TGA rates in mammals are thus consistent with gBGC’s predicted ability to “drive” deleterious mutations and supports the hypothesis that sequence conservation need not be indicative of purifying selection. A general trend for GC-rich trinucleotides to reside at frequencies far above their mutational equilibrium in high recombining domains supports the generality of these results.

Effective Population Size Predicts Local Rates but Not Local Mitigation of Read-through Errors

In correctly predicting that selection efficiency is positively correlated with the effective population size (Ne), the nearly neutral theory provides a coherent understanding of between-species variation in numerous genomic parameters, including heritable error (germline mutation) rates. Does the same theory also explain variation in phenotypic error rates and in abundance of error mitigation mechanisms? Translational read-through provides a model to investigate both issues as it is common, mostly nonadaptive, and has good proxy for rate (TAA being the least leaky stop codon) and potential error mitigation via "fail-safe" 3' additional stop codons (ASCs). Prior theory of translational read-through has suggested that when population sizes are high, weak selection for local mitigation can be effective thus predicting a positive correlation between ASC enrichment and Ne. Contra to prediction, we find that ASC enrichment is not correlated with Ne. ASC enrichment, although highly phylogenetically patchy, is, however, more common both in unicellular species and in genes expressed in unicellular modes in multicellular species. By contrast, Ne does positively correlate with TAA enrichment. These results imply that local phenotypic error rates, not local mitigation rates, are consistent with a drift barrier/nearly neutral model.

Alpha thalassemia genotypes in Kuwait

Background

The frequency of the alpha thalassemia trait is approximately 40% in the Kuwaiti population, but there has been no comprehensive study of the prevalent alleles. This is a report of patients who were referred for molecular diagnosis over a 20-year period.

Methods

This is a retrospective study of the α-globin genotypes obtained in the Hemoglobin Research Laboratory of the Department of Pediatrics, Kuwait University from 1994 to 2015. Genotyping was performed by a combination of PCR, allele-specific oligonucleotide hybridization and reverse dot blot hybridization (Vienna Lab Strip Assay).

Results

Four hundred samples were characterized and analyzed from individuals aged < 1 month to 80 years, with a median of 6 years from 283 unrelated families. Most (90.8%) were Kuwaiti nationals. The commonest genotype was homozygosity for the polyadenylation-1 mutation (α^PA-1α/α ^PA-1α) in 33.3% of the samples, followed by heterozygosity (αα/α ^PA-1α) for the same mutation in 32.3%. PA-1 was therefore the most frequent allele (0.59). The frequency of the α⁰ (−-^MED) allele was 0.017. Rare alleles that were found in very low frequencies included α⁰ (−-^FIL) in a Filipino child, Hb Constant Spring, Hb Adana, and Hb Icaria.

Conclusion

There is a wide variety of alpha thalassemia alleles among Kuwaitis, but nondeletional PA-1 is by far the most common cause of the moderate to severe HbH (β4 tetramer) disease phenotype. The α⁰ (−^MED) allele is also encountered, which has implications for premarital counseling, especially for the possibility of having babies with alpha thalassemia major (Barts hydrops fetalis).

Nondeletional α-Thalassemia: Two New Mutations on the α2 Gene

About 10.0% of α-thalassemia (α-thal) cases are due to point mutations, small deletions, or insertions of one or more bases on the α genes that can alter mRNA processing at the transcription, translation, or post-translation level; these cases are called nondeletional α-thalassemias (α-thal). Most occur within the domain of the α2 gene without changes in the expression of the α1 gene. We present two new frameshift mutations on the HBA2 gene, associated with a nondeletional α-thal phenotype. The probands were referred to our clinic because of persistent microcytosis and hypochromia. The molecular characterization was performed by automatic sequencing of the α-globin genes. Two new mutations were detected on the HBA2 gene; HBA2: c.85delG, p.(Ala29fs*21), and HBA2: c.268_280delCACAAGCTTCGGG, p.(His90Trpfs*9). These new mutations cause a change of the reading frame, the first on codon 28 and the second from codons 89 to 93. In the first mutation, the result is an altered amino acid sequence and a premature termination codon at position 87, while the elimination of 13 bp generates a protein of 95 residues and in this case, the premature termination codon is at position 96. These types of mutation are among the most damaging changes to the coding of a protein. Not only do they lead to changes in the length of the polypeptide, but they also vary the chemical composition, which would result in a nonfunctional protein. The importance of identifying these new mutations lies in their possible association with α⁰-thal, which could lead to a severe thalassemia.

Trans-Species Polymorphism in Mitochondrial Genome of Camarodont Sea Urchins

Mitochondrial (mt) genomes of the sea urchins Strongylocentrotus intermedius and Mesocentrotus nudus demonstrate the identical patterns of intraspecific length variability of the ND6 gene, consisting of 489 bp (S variant) and 498 bp (L variant), respectively. For both species, the ND6 length difference is due to the 488A>G substitution, which changes the stop codon TAG in S variant for a tryptophan codon TGG in L variant and elongates the corresponding ND6 protein by three additional amino acids, Trp-Leu-Trp. The phylogenetic analysis based on mt genomes of sea urchins and related echinoderm groups from GenBank has shown the S and L ND6 variants as shared among the camarodont sea urchins; the rest of the echinoderms demonstrate the S variant only. The data suggest that the ND6 488A>G substitution can be the first example of the trans-species polymorphism in sea urchins, persisting at least since the time of the Odontophora diversification at the Eocene/Oligocene boundary (approximately 34 million years ago), which was characterized by an abrupt climate change and significant global ocean cooling. Alternative hypotheses, including the convergent RNA editing and/or codon reassignment, are not supported by direct comparisons of the ND6 gene sequences with the corresponding transcripts using the basic local alignment search tool (BLAST) of full sea urchin transcriptomes.

Potential limits of AAV-based gene therapy with the use of new transgenes expressing factor IX fusion proteins

INTRODUCTION

The variety of treatment for haemophilia B (HB) has recently improved with the emergence of both AAV-based gene therapy and bioengineered human factor IX (hFIX) molecules with prolonged half-life due to fusion to either albumin (Alb) or immunoglobulin Fc fragment (Fc).

AIM

Adeno-associated viral vectors (AAV) mediating expression of hFIX-Alb and hFIX-Fc fusion proteins was investigated for gene therapy of HB to explore if their extended half-life translates to higher plasma levels of FIX.

METHODS

Single-stranded cross-packaged AAV2/8 vectors expressing hFIX-Alb, hFIX-Fc and hFIX were evaluated in vitro, and in mice.

RESULTS

Both hFIX-Alb and hFIX-Fc fusion proteins were synthesized and expressed as single chains of expected size following AAV-mediated gene transfer in vitro and in vivo. The procoagulant properties of these hFIX-fusion proteins were comparable to wild-type hFIX. However, their expression levels were threefold lower than wild-type hFIX in vivo most likely due to inefficient secretion.

CONCLUSION

This, the first, evaluation of hFIX-fusion proteins in the context of AAV gene transfer suggests that the hFIX-fusion proteins are secreted inefficiently from the liver, thus preventing their optimal use in gene therapy approaches.

Identification of MYLK3 mutations in familial dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a primary cause of heart failure, life-threatening arrhythmias, and cardiac death. Pathogenic mutations have been identified at the loci of more than 50 genes in approximately 50% of DCM cases, while the etiologies of the remainder have yet to be determined. In this study, we applied whole exome sequencing in combination with segregation analysis to one pedigree with familial DCM, and identified a read-through mutation (c.2459 A > C; p.*820Sext*19) in the myosin light chain kinase 3 gene (MYLK3). We then conducted MYLK3 gene screening of 15 DCM patients (7 familial and 8 sporadic) who were negative for mutation screening of the previously-reported cardiomyopathy-causing genes, and identified another case with a MYLK3 frameshift mutation (c.1879_1885del; p.L627fs*41). In vitro experiments and immunohistochemistry suggested that the MYLK3 mutations identified in this study result in markedly reduced levels of protein expression and myosin light chain 2 phosphorylation. This is the first report that MYLK3 mutations can cause DCM in humans. The clinical phenotypes of DCM patients were consistent with MYLK3 loss-of-function mouse and zebrafish models in which cardiac enlargement and heart failure are observed. Our findings highlight an essential role for cardiac myosin light chain kinase in the human heart.

Translation readthrough mitigation

A fraction of ribosomes engaged in translation will fail to terminate when reaching a stop codon, yielding nascent proteins inappropriately extended on their C termini. Although such extended proteins can interfere with normal cellular processes, known mechanisms of translational surveillance are insufficient to protect cells from potential dominant consequences. Here, through a combination of transgenics and CRISPR–Cas9 gene editing in Caenorhabditis elegans, we demonstrate a consistent ability of cells to block accumulation of C-terminal-extended proteins that result from failure to terminate at stop codons. Sequences encoded by the 3′ untranslated region (UTR) were sufficient to lower protein levels. Measurements of mRNA levels and translation suggested a co- or post-translational mechanism of action for these sequences in C. elegans. Similar mechanisms evidently operate in human cells, in which we observed a comparable tendency for translated human 3′ UTR sequences to reduce mature protein expression in tissue culture assays, including 3′ UTR sequences from the hypomorphic ‘Constant Spring’ haemoglobin stop codon variant. We suggest that 3′ UTRs may encode peptide sequences that destabilize the attached protein, providing mitigation of unwelcome and varied translation errors.

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.

Hemoglobin Constant Spring among Southeast Asian Populations: Haplotypic Heterogeneities and Phylogenetic Analysis

Background

Hemoglobin Constant Spring (Hb CS) is an abnormal Hb caused by a mutation at the termination codon of α2-globin gene found commonly among Southeast Asian and Chinese people. Association of Hb CS with α°-thalassemia leads to a thalassemia intermedia syndrome commonly encountered in the region. We report chromosome background and addressed genetic origins of Hb CS observed in a large cohort of Hb CS among Southeast Asian populations.

Materials and Methods

A study was done on 102 Vietnamese (aged 15–49 year-old) and 40 Laotian (aged 18–39 year-old) subjects with Hb CS and results compared with 120 Hb CS genes in Thailand. Hematological parameters were recorded and Hb analysis was performed using capillary electrophoresis. Hb CS mutation and thalassemia genotypes were defined by DNA analysis. Six DNA polymorphisms within α-globin gene cluster including 5’Xba I, Bgl I, Inter-zeta HVR, AccI, RsaI and αPstI 3’, were determined using PCR-RFLP assay.

Results

Nine different genotypes of Hb CS were observed. In contrast to the Thai Hb CS alleles which are mostly linked to haplotype (+—S + + -), most of the Vietnamese and the Laotian Hb CS genes were associated with haplotype (+—M + + -), both of which are different from that of the European Hb CS.

Conclusions

Hb CS is commonly found in combination with other thalassemias among Southeast Asian populations. Accurate genotyping of the cases requires both hematologic and DNA analyses. At least two independent origins are associated with the Hb CS gene which could indirectly explain the high prevalence of this Hb variant in the region.

Identification of Hb Constant Spring (HBA2: c.427T > C) by an Automated High Performance Liquid Chromatography Method

Laboratory investigation of hemoglobinopathies includes complete blood count (CBC), hemoglobin (Hb) typing by high performance liquid chromatography (HPLC) and DNA analysis. DNA analysis is the most reliable method but requires a manually laborious procedure and is time consuming. A more practical method of detecting abnormal Hbs is the HPLC technique, because it is more rapid and easier to interpret. Hb Constant Spring (Hb CS; HBA2: c.427T > C) is an abnormal variant that is labile and difficult to detect using conventional methods. To evaluate the efficiency of Hb CS determination by HPLC, blood samples from 578 subjects were analyzed using an automated cell analyzer for hematological parameters, automated HPLC for Hb identification, and polymerase chain reaction (PCR) for α-thalassemia (α-thal) and Hb CS confirmation. These included 169 normal, 119 heterozygous α-thal-2, 30 homozygous α-thal-2, 177 heterozygous α-thal-1, 59 heterozygous Hb CS, seven homozygous Hb CS and 17 compound heterozygous α-thal-2 and Hb CS subjects. The results showed that sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of Hb CS by HPLC were 93.78, 99.80, 98.73 and 99.00%, respectively. The mean of misdiagnosis value of the three groups of Hb CS subjects (total 83) was 6.02% (n = 5), with percentages for heterozygous Hb CS, homozygous Hb CS, and compound heterozygous α-thal-2 and Hb CS being 6.8, 0.0 and 5.9%, respectively. The HPLC method yielded good results, although it may also lead to misdiagnosis of Hb CS due to the relatively small amount and lability.

Hemoglobin Constant Spring exhibits prolonged ex vivo stability when assessed by HPLC

OBJECTIVES

1) To investigate the presence of hemoglobin Constant Spring (HbCS) in a patientwith severe microcytic anemia who had previously been diagnosed with alpha thalassemia minor. 2) To assess the stability of HbCS post blood collection by high performance liquid chromatography (HPLC).

DESIGN AND METHODS

Hemoglobin fractionation was performed by HPLC immediately after specimen collection using the β-thalassemia Short Program on the BioRad Variant II. To assess HbCS stability, the patient's specimen was re-analyzed over a 17 day period.

RESULTS

HPLC analysis showed a low abundance peak with chromatographic properties consistent with HbCS. Presence of this hemoglobin variant was confirmed by electrophoresis and gene sequencing. HbCS remained detectable by HPLC for 17 days after specimen collection, with minimal degradation.

CONCLUSIONS

Our results suggest that HbCS is stable many days after blood collection. Consequently, it is not necessary to analyze specimens immediately after collection when assessing the potential presence of this hemoglobin variant.

AUF-1 and YB-1 independently regulate β-globin mRNA in developing erythroid cells through interactions with poly(A)-binding protein

The normal expression of β-globin protein in mature erythrocytes is critically dependent on post-transcriptional events in erythroid progenitors that ensure the high stability of β-globin mRNA. Previous work has revealed that these regulatory processes require AUF-1 and YB-1, two RNA-binding proteins that assemble an mRNP β-complex on the β-globin 3'UTR. Here, we demonstrate that the β-complex organizes during the erythropoietic interval when both β-globin mRNA and protein accumulate rapidly, implicating the importance of this regulatory mRNP to normal erythroid differentiation. Subsequent functional analyses link β-complex assembly to the half-life of β-globin mRNA in vivo, providing a mechanistic basis for this regulatory activity. AUF-1 and YB-1 appear to serve a redundant post-transcriptional function, as both β-complex assembly and β-globin mRNA levels are reduced by coordinate depletion of the two factors, and can be restored by independent rescue with either factor alone. Additional studies demonstrate that the β-complex assembles more efficiently on polyadenylated transcripts, implicating a model in which the β-complex enhances the binding of PABPC1 to the poly(A) tail, inhibiting mRNA deadenylation and consequently effecting the high half-life of β-globin transcripts in erythroid progenitors. These data specify a post-transcriptional mechanism through which AUF1 and YB1 contribute to the normal development of erythropoietic cells, as well as to non-hematopoietic tissues in which AUF1- and YB1-based regulatory mRNPs have been observed to assemble on heterologous mRNAs.

A journey in science: early lessons from the hemoglobin field

Real innovations in medicine and science are historic and singular; the stories behind each occurrence are precious. At Molecular Medicine we have established the Anthony Cerami Award in Translational Medicine to document and preserve these histories. The monographs recount the seminal events as told in the voice of the original investigators who provided the crucial early insight. These essays capture the essence of discovery, chronicling the birth of ideas that created new fields of research; and launched trajectories that persisted and ultimately influenced how disease is prevented, diagnosed, and treated. In this volume, the Cerami Award Monograph is by David J Weatherall, Founder, Weatherall Institute of Molecular Medicine, Oxford University, John Radcliffe Hospital. A visionary in the field of hemoglobin, this is the story of Professor Weatherall's scientific journey.

Alpha-thalassemia mutations in adana province, southern Turkey: genotype-phenotype correlation

To look over the distribution of the mutations in a large series from Adana province, Southern Turkey, and determine the genotype-phenotype correlation of the frequent mutations. Among the 2500 individuals with mild or moderate anemia, microcytosis, and normal iron levels that were referred to our Genetic Diagnosis Center, a population consisting of 539 individuals were included in the study and tested for alpha-thalassemia mutations by using reverse dot blot hybridization technique. Twelve different mutations were detected in 539 patients. Among the 12 different mutations found, the most frequent mutations were the -α(3.7) (63.3 %), --(MED) (11.7 %), --(20.5) (10.7 %), α2(IVS1(-5nt)) (3.9 %), and α2(polyA-2) (3.5 %). The most frequent genotypes were -α(3.7)/αα (35.8 %), -α(3.7)/-α(3.7)(18.9 %), -(20.5)/αα (11.5 %), and --(MED)/αα (10.4 %), respectively. There were statistically significant differences in hematological findings between -α(3.7)/-α(3.7) and --(MED)/αα, even though both have two mutated genes in the genotype. Our results show that alpha-thalassemia mutations are highly heterogeneous as well as deletional and -α(3.7) single gene deletion is particularly prevalent at Adana province in agreement to other studies from Turkey.

Acute haemolytic crisis in a Thai patient with homozygous haemoglobin Constant Spring (Hb CS/CS): a case report

Acute haemolysis associated with mild upper respiratory tract infection was observed in a Thai boy who presented with a rapid decline in haemoglobin (Hb) levels, haemoglobinuria and evidence of intravascular haemolysis. Several possible causes giving rise to such a condition were excluded including G6PD deficiency, which is extremely common in Thailand. Subsequent haematological and molecular analyses demonstrated that the patient was homozygous for Hb Constant Spring (Hb CS/CS), an a globin haemoglobinopathy. It has been shown previously that patients with homozygous Hb CS had mild haemolytic anaemia secondary to an accumulation of alpha(CS) chains, which are toxic to red blood cell membrane cytoskeletons. Increased body temperature might induce more precipitation of this a globin variant. This report highlights the importance of Hb CS/CS as a potential predisposing cause of acute haemolysis in children that might be aggravated by acute bacterial or viral infections. This is particularly relevant for patients of Southeast Asian descent where this abnormal haemoglobin is highly prevalent.

Hemoglobin variants: biochemical properties and clinical correlates

Diseases affecting hemoglobin synthesis and function are extremely common worldwide. More than 1000 naturally occurring human hemoglobin variants with single amino acid substitutions throughout the molecule have been discovered, mainly through their clinical and/or laboratory manifestations. These variants alter hemoglobin structure and biochemical properties with physiological effects ranging from insignificant to severe. Studies of these mutations in patients and in the laboratory have produced a wealth of information on hemoglobin biochemistry and biology with significant implications for hematology practice. More generally, landmark studies of hemoglobin performed over the past 60 years have established important paradigms for the disciplines of structural biology, genetics, biochemistry, and medicine. Here we review the major classes of hemoglobin variants, emphasizing general concepts and illustrative examples.

The spectrum of α-thalassemia mutations in the Kurdish population of Northeastern Iraq

In an attempt to determine the spectrum of α-thalassemia (α-thal) mutations in the Kurdish population of Northeastern (NE) Iraq, a total of 101 unrelated adults with unexplained hypochromia and/or microcytosis were enrolled. α-Thalasssemia mutations were characterized by gap polymerase chain reaction (gap-PCR), multiplex PCR (m-PCR) and reverse hybridization and sequencing for both α genes. A total of nine α-thal mutations were characterized including four deletional ones: -α(3.7) (rightward), - -(MED-I), -(α)(20.5), -α(4.2) (leftward) and five nondeletional ones: α(polyA1)α, αα(Adana), α(-5 nt)α, α(CS)α and α(polyA2)α. These determinants were arranged in 12 different genotypes, the most frequent of which were: -α(3.7)/αα, - -(MED-I)/αα, -α(3.7)/-α(3.7), α(polyA1)α/αα, αα(Adana)/αα and -(α)(20.5)/αα. This pattern is similar to that reported in Turkey, western (W) Iran, Cyprus and Greece, and to some extent, different from the pattern observed in the Arabian Peninsula.

First case of Hb Fontainebleau with sickle haemoglobin and other non-deletional α gene variants identified in neonates during newborn screening for sickle cell disorders

OBJECTIVE

To evaluate the significance of non-deletional α gene variants identified in neonates during newborn screening for sickle cell disorders.

METHODS

1534 newborn babies were screened in the last 2 years for sickle cell disease using a targeted screening approach. Investigations included a complete blood count, high performance liquid chromatography analysis, cellulose acetate electrophoresis (pH 8.9), heat stability test, restriction digestion and Amplified Refractory Mutation System for confirmation of sickle haemoglobin (Hb S), α genotyping by multiplex PCR and DNA sequencing.

RESULTS

Three non-deletional α gene variants, Hb Fontainebleau, Hb O Indonesia and Hb Koya Dora, were identified in heterozygous condition in newborns. This is the first report of Hb Fontainebleau in association with Hb S. The baby had anaemia at birth (Hb 11.4 g/dl) with no cyanosis, icterus or need for transfusion. She had occipital encephalocoele and was operated on day 24 to remove the mass. The baby diagnosed with Hb O Indonesia in combination with Hb S also had a low haemoglobin level of 12.7 g/dl.

CONCLUSION

Newborn screening for sickle cell disorders also enabled us to identify three α globin chain variants. Two babies who inherited Hb Fontainebleau and Hb O Indonesia along with Hb S had reduced Hb levels at birth and need to be followed up.

An RNA-protein complex links enhanced nuclear 3' processing with cytoplasmic mRNA stabilization

Post-transcriptional controls are critical to gene regulation. These controls are frequently based on sequence-specific binding of trans-acting proteins to cis-acting motifs on target RNAs. Prior studies have revealed that the KH-domain protein, αCP, binds to a 3' UTR C-rich motif of hα-globin mRNA and contributes to its cytoplasmic stability. Here, we report that this 3' UTR αCP complex regulates the production of mature α-globin mRNA by enhancing 3' processing of the hα-globin transcript. We go on to demonstrate that this nuclear activity reflects enhancement of both the cleavage and the polyadenylation reactions and that αCP interacts in vivo with core components of the 3' processing complex. Consistent with its nuclear processing activity, our studies reveal that αCP assembles co-transcriptionally at the hα-globin chromatin locus and that this loading is selectively enriched at the 3' terminus of the gene. The demonstrated linkage of nuclear processing with cytoplasmic stabilization via a common RNA-protein complex establishes a basis for integration of sequential controls critical to robust and sustained expression of a target mRNA.

Molecular screening of the Hbs Constant Spring (codon 142, TAA>CAA, α2) and Paksé (codon 142, TAA>TAT, α2) mutations in Thailand

Hb Constant Spring [Hb CS, α142(H19)Term] and Hb Paksé [α142(H19)Term] occur from the mutation in the termination codon of the α2-globin gene, TAA>CAA (→Gln) and TAA>TAT (→Tyr), respectively. They are the most common nondeletional α-thalassemia (α-thal) variants causing Hb H disease in Southeast Asia. In this study, 587 cord blood samples were screened for the Hb CS and Hb Paksé mutations by a dot-blot hybridization technique using oligonucleotide probes specific for each mutation. The results showed that the prevalence of Hb CS and Hb Paksé in Central Thailand are 5.80 and 0.51%, respectively, which is in concordance with the results from previous studies.

Control of human beta-globin mRNA stability and its impact on beta-thalassemia phenotype

Messenger RNA (mRNA) stability is a critical determinant that affects gene expression. Many pathways have evolved to modulate mRNA stability in response to developmental, physiological and/or environmental stimuli. Eukaryotic mRNAs have a considerable range of half-lives, from as short as a few minutes to as long as several days. Human globin mRNAs constitute an example of highly stable mRNAs. However, a wide variety of naturally occurring mutations that result in the clinical syndrome of thalassemia can trigger accelerated mRNA decay thus controlling mRNA quality prior to translation. Distinct surveillance mechanisms have been described as being targeted for specific defective globin mRNAs. Here, we review mRNA stability mechanisms implicated in the control of β-globin gene expression and the surveillance pathways that prevent translation of aberrant β-globin mRNAs. In addition, we emphasize the importance of these pathways in modulating the severity of the β-thalassemia phenotype.

Alpha-thalassaemia

Alpha-thalassaemia is inherited as an autosomal recessive disorder characterised by a microcytic hypochromic anaemia, and a clinical phenotype varying from almost asymptomatic to a lethal haemolytic anaemia.

It is probably the most common monogenic gene disorder in the world and is especially frequent in Mediterranean countries, South-East Asia, Africa, the Middle East and in the Indian subcontinent. During the last few decades the incidence of alpha thalassaemia in North-European countries and Northern America has increased because of demographic changes. Compound heterozygotes and some homozygotes have a moderate to severe form of alpha thalassaemia called HbH disease. Hb Bart's hydrops foetalis is a lethal form in which no alpha-globin is synthesized. Alpha thalassaemia most frequently results from deletion of one or both alpha genes from the chromosome and can be classified according to its genotype/phenotype correlation. The normal complement of four functional alpha-globin genes may be decreased by 1, 2, 3 or all 4 copies of the genes, explaining the clinical variation and increasing severity of the disease. All affected individuals have a variable degree of anaemia (low Hb), reduced mean corpuscular haemoglobin (MCH/pg), reduced mean corpuscular volume (MCV/fl) and a normal/slightly reduced level of HbA₂. Molecular analysis is usually required to confirm the haematological observations (especially in silent alpha-thalassaemia and alpha-thalassaemia trait). The predominant features in HbH disease are anaemia with variable amounts of HbH (0.8-40%). The type of mutation influences the clinical severity of HbH disease. The distinguishing features of the haemoglobin Bart's hydrops foetalis syndrome are the presence of Hb Bart's and the total absence of HbF. The mode of transmission of alpha thalassaemia is autosomal recessive. Genetic counselling is offered to couples at risk for HbH disease or haemoglobin Bart's Hydrops Foetalis Syndrome. Carriers of alpha⁺- or alpha⁰-thalassaemia alleles generally do not need treatment. HbH patients may require intermittent transfusion therapy especially during intercurrent illness. Most pregnancies in which the foetus is known to have the haemoglobin Bart's hydrops foetalis syndrome are terminated due to the increased risk of both maternal and foetal morbidity.

Novel hemoglobin alpha chain elongation resulting from a 15-residue insertion and tandem duplication of the F helix

OBJECTIVES

To determine the cause of an unusual hemoglobin pattern with two novel components eluting after HbA(2) on cation exchange HPLC. This variant was detected during HbA1c measurement and was associated with a normal blood count and a positive isopropanol test.

DESIGN AND METHOD

Whole hemolysate and isopropanol precipitates were analysed by ESI MS, and individual components were purified by reverse phase and cation exchange HPLC. Tryptic peptide mapping of isopropanol precipitates was used to detect the molecular lesion and DNA sequencing was used to characterise the precise rearrangement.

RESULTS

ESI MS showed a mass increase of 1614Da in 9% of the alpha globin chains and sequence analysis of the alpha2 gene revealed the heterozygous insertion of 45 nucleotides after codon 93. The predicted in phase incretion of ALSALSDLHAHKLRV (+ 1613Da) is a direct repeat of residues alpha79-93 and signature ions from the new peptide were clearly visible in peptide maps of the unstable hemoglobin.

CONCLUSION

The insertion probably results from replication slippage during DNA synthesis and the 15-residue repeat results in full repetition of the heme-linked F helix. The nature of the inserted sequence explains the molecular instability and the electrophoretic mobility, but not the twin peaks observed on cation exchange HPLC. These components had the same chain composition, (alpha(L) beta), the same number of heme groups per chain, were not in rapid equilibrium with each other, and probably represent hemoglobin species with different conformers of the elongated alpha(L) chain.

A cell type-restricted mRNA surveillance pathway triggered by ribosome extension into the 3' untranslated region

The accuracy of eukaryotic gene expression is monitored at multiple levels. Surveillance pathways have been identified that degrade messenger RNAs containing nonsense mutations, harboring stalled ribosomes or lacking termination codons. Here we report a previously uncharacterized surveillance pathway triggered by ribosome extension into the 3' untranslated region. This ribosome extension-mediated decay, REMD, accounts for marked repression of protein synthesis from a human alpha-globin gene containing a prevalent antitermination mutation. REMD can be mechanistically distinguished from other surveillance pathways by its functional linkage to accelerated deadenylation, by its independence from the NMD factor Upf1 and by cell-type restriction. This unusual pathway of mRNA surveillance is likely to act as a modifier of additional genetic defects and may reflect post-transcriptional controls particular to erythroid and other differentiated cell lineages.

The 3' untranslated region complex involved in stabilization of human alpha-globin mRNA assembles in the nucleus and serves an independent role as a splice enhancer

Posttranscriptional controls, mediated primarily by RNA-protein complexes, have the potential to alter multiple steps in RNA processing and function. Human alpha-globin mRNA is bound at a C-rich motif in the 3' untranslated region (3'UTR) by the KH domain protein alpha-globin poly(C)-binding protein (alphaCP). This "alpha-complex" is essential to cytoplasmic stability of alpha-globin mRNA in erythroid cells. Here we report that the 3'UTR alpha-complex also serves an independent nuclear role as a splice enhancer. Consistent with this role, we find that alphaCP binds alpha-globin transcripts prior to splicing. Surprisingly, this binding occurs at C-rich sites within intron I as well as at the 3'UTR C-rich determinant. The intronic and 3'UTR alphaCP complexes appear to have distinct effects on splicing. While intron I complexes repress intron I excision, the 3'UTR complex enhances splicing of the full-length transcript both in vivo and in vitro. In addition to its importance to splicing, nuclear assembly of the 3'UTR alphaCP complex may serve to "prepackage" alpha-globin mRNA with its stabilizing complex prior to cytoplasmic export. Linking nuclear and cytoplasmic controls by the action of a particular RNA-binding protein, as reported here, may represent a modality of general importance in eukaryotic gene regulation.

Anemia and hydrops in a fetus with homozygous hemoglobin constant spring

Hemoglobin Constant Spring (Hb CS) is an unstable hemoglobin (Hb) variant that results from a nucleotide substitution at the termination codon of the alpha2-globin gene. The compound heterozygosity of alpha-thalassemia and Hb CS (--/alphaCSalpha) results in a Hb H/CS disease which is clinically more severe than deletional Hb H disease. Homozygosity of Hb CS (alphaCSalpha/alphaCSalpha) is generally characterized with mild hemolytic anemia, jaundice, and splenomegaly. The authors report 1 case with Hb CS homozygosity who presented with fetal anemia and hydrops. Intrauterine transfusions were given which rendered a favorable outcome. This report demonstrates an unusual and serious in utero complication in a fetus with Hb CS/CS.

Shared stabilization functions of pyrimidine-rich determinants in the erythroid 15-lipoxygenase and alpha-globin mRNAs

The poly(C)-binding proteins, alphaCPs, comprise a set of highly conserved KH-domain factors that participate in mRNA stabilization and translational controls in developmental and viral systems. Two prominent models of alphaCP function link these controls to late stages of erythroid differentiation: translational silencing of 15-lipoxygenase (Lox) mRNA and stabilization of alpha-globin mRNA. These two controls are mediated via association of alphaCPs with structurally related C-rich 3'-untranslated region elements: the differentiation control elements (DICE) in Lox mRNA and the pyrimidine-rich motifs in alpha-globin mRNA. In the present report a set of mRNA translation and stability assays are used to determine how these two alphaCP-containing complexes, related in structure and position, mediate distinct posttranscriptional controls. While the previously reported translational silencing by the DICE is not evident in our studies, we find that the two determinants mediate similar levels of mRNA stabilization in erythroid cells. In both cases this stabilization is sensitive to interference by a nuclear-restricted alphaCP decoy but not by the same decoy restricted to the cytoplasm. These data support a general role for alphaCPs in stabilizing a subset of erythroid mRNAs. The findings also suggest that initial binding of alphaCP to target mRNAs occurs in the nucleus. Assembly of stabilizing mRNP complexes in the nucleus prior to export may maximize their impact on cytoplasmic events.