Gene deletions in alpha thalassemia prove that the 5' zeta locus is functional

Hemoglobin Bart's hydrops fetalis: charting the past and envisioning the future

ABSTRACT

Hemoglobin Bart's hydrops fetalis syndrome (BHFS) represents the most severe form of α-thalassemia, arising from deletion of the duplicated α-globin genes from both alleles. The absence of α-globin leads to the formation of nonfunctional hemoglobin (Hb) Bart's (γ4) or HbH (β4) resulting in severe anemia, tissue hypoxia, and, in some cases, variable congenital or neurocognitive abnormalities. BHFS is the most common cause of hydrops fetalis in Southeast Asia; however, owing to global migration, the burden of this condition is increasing worldwide. With the availability of intensive perinatal care and intrauterine transfusions, an increasing number of patients survive with this condition. The current approach to long-term management of survivors involves regular blood transfusions and iron chelation, a task made challenging by the need for intensified transfusions to suppress the production of nonfunctional HbH-containing erythrocytes. Although our knowledge of outcomes of this condition is evolving, it seems, in comparison to individuals with transfusion-dependent β-thalassemia, those with BHFS may face an elevated risk of complications arising from chronic anemia and hypoxia, ongoing hemolysis, iron overload, and from their respective treatments. Although stem cell transplantation remains a viable option for a select few, it is not without potential side effects. Looking ahead, potential advancements in the form of genetic engineering and innovative therapeutic approaches, such as the reactivation of embryonic α-like globin gene expression, hold promise for furthering the treatment of this condition. Prevention remains a crucial aspect of care, particularly in areas with high prevalence or limited resources.

An international registry of survivors with Hb Bart's hydrops fetalis syndrome

Hemoglobin (Hb) Bart's hydrops fetalis syndrome (BHFS) resulting from α0-thalassemia is considered a universally fatal disorder. However, over the last 3 decades, improvements in intrauterine interventions and perinatal intensive care have resulted in increasing numbers of BHFS survivors. We have initiated an international registry containing information on 69 patients, of which 31 are previously unpublished. In this perspective, we analyze the available clinical information to document the natural history of BHFS. In the future, once we have accrued sufficient cases, we aim to build on this study and provide information to allow counseling of at-risk couples. To date, 39 patients have survived beyond the age of 5 years, 18 of whom are now older than 10 years. Based on the available cases, we find evidence to suggest that intrauterine therapy provides benefits during the perinatal and neonatal period; however, it may not provide additional benefits to long-term growth and neurodevelopmental outcomes. Growth retardation is a major adverse long-term outcome among BHFS patients with ∼40% being severely affected in terms of weight and ∼50% in terms of height. There is also an increased risk of neurodevelopmental delay as we find 20% (11/55) of BHFS survivors suffer from a serious delay of ≥6 months. Most patients in the registry require lifelong transfusion and often have associated congenital abnormalities and comorbidities. This perspective is a first step in gathering information to allow provision of informed counseling on the predicted outcomes of affected babies.

Introduction of novel α1-hemoglobin gene mutation with transfusion-dependent phenotype

OBJECTIVE AND IMPORTANCE

Thalassemia is the most frequently monogenetic disorders around the world that is inherited as a recessive single-gene disease, resulting from mutations in α- or β-globin gene clusters. The aim of this report was to present a new insertional mutation in the α₁ globin gene which causes transfusion-dependent anemia in α-thalassemic patients.

CLINICAL PRESENTATION

Two 5-year-old girls with blood transfusion-dependent α-thalassemia anemia and another girl with moderate α-thalassemia have been presented among patients who have been referred to Hematology and Thalassemia Research Center, Dastgheib Hospital, Shiraz, Iran. They were not relatives. All children were stunted and pale; they were put on regular blood transfusion every 14-21 days.

INTERVENTION

Sequencing of the β-globin gene was normal in all cases and their parents; but, α-globin gene sequencing results were remarkable. An insertion of 21 base pairs (IVS II+3ins (+21nt)(+GACCCGGTCAACTTCAAGGTG) in the α₁-globin gene was detected in all three cases and one of their parents. In two cases, this insertion was accompanied by MED deletion and in one child by POLY A₁ mutation. MED deletion was detected by gap-PCR.

CONCLUSION

This new 21 base pair insertion cannot affect blood parameters on its own, but can present as continuous blood transfusion-dependent α-thalassemia. Thus, it is important to take this point into account for detecting the carriers, like β-thalassemia carriers, which can present as transfusion-dependent children in parents with α-thalassemia trait.

Hemoglobin Constitution of Double Heterozygotes for α or β-Thalassemia and HB J Sardegna

In this study, we carried out alpha-globin gene mapping in 12 heterozygotes for Hb J Sardegna and in 5 double heterozygotes for this variant and beta-thalassemia. Then, we correlated the Hb pattern with the alpha and beta-globin genotype. In heterozygotes for Hb J Sardegna with a deletion of a single alpha-globin gene (alpha alpha/-alpha) the amount of the abnormal Hb was significantly (p much less than 0.001) higher than in heterozygotes for this variant with a full complement of 4 alpha-globin structural genes (27.5% versus 20.4%). Double heterozygotes for the abnormal hemoglobin and beta-thalassemia with a full complement of 4 alpha-globin structural genes tended to have lower amount of the abnormal Hb than heterozygotes for this variant who do not have beta-thalassemia.

Haemoglobin GPhiladelphia and its interaction with haemoglobin S and alpha-thalassaemia in Nigerians

The diagnosis of Hb SS/GPhiladelphia disease was made in four young Nigerians from separate families. Their Hb electrophoretic patterns on cellulose acetate membrane at alkaline pH were similar to those obtained in sickle-cell haemoglobin C (HbSC) disease, but their clinical features and haematological data were consistent with the diagnosis of homozygous sickle-cell disease. Family studies also revealed that they had inherited an additional alpha-chain mutant haemoglobin. In one of the families, fingerprints of the globin peptides and amino acid analysis confirmed that the mutant haemoglobin was Hb GPhiladelphia (alpha 2 68 Asn----Lys beta 2 A). The results of the whole blood solubility test for sickle-haemoglobin provided firm support for the diagnosis of homozygous sickle-cell disease and distinguished clearly Hb SS/GPhiladelphia disease from Hb SC disease and Hb AS from Hb AGPhiladelphia heterozygotes. Restriction endonuclease mapping of the globin genes of the propositus and some relatives of one of the families revealed also that they were carriers of the alpha-thalassaemia-2 gene (deletion-type). The globin gene-analysis data indicate also that the alpha GPhiladelphia and alpha-thalassaemia genes are linked closely in Nigerians.

The phylogenetic and evolutionary history of a novel alpha-globin-type gene in orangutans (Pongo pygmaeus)

The alpha-globin genes are implicated in human resistance to malaria, a disease caused by Plasmodium parasites. This study is the first to analyze DNA sequences from a novel alpha-globin-type gene in orangutans, a species affected by Plasmodium. Phylogenetic methods show that the gene is a duplication of an alpha-globin gene and is located 5' of alpha-2 globin. The alpha-globin-type gene is notable for having four amino acid replacements relative to the orangutan's alpha-1 and alpha-2 globin genes, with no synonymous differences. Pairwise K(a)/K(s) methods and likelihood ratio tests (LRTs) revealed that the evolutionary history of the alpha-globin-type gene has been marked by either neutral or positive evolution, but not purifying selection. A comparative analysis of the amino acid replacements of the alpha-globin-type gene with human hemoglobinopathies and hemoglobin structure showed that two of the four replaced sites are members of the same molecular bond, one that is crucial to the proper functioning of the hemoglobin molecule. This suggested an adaptive evolutionary change. Functionally, this locus may result in a thalassemia-like phenotype in orangutans, possibly as an adaptation to combat Plasmodium.

Alpha-thalassaemia prenatal diagnosis by two PCR-based methods

In Cyprus all couples carrying alpha0-thalassaemia mutations are detected in the course of the thalassaemia carrier screening program and prenatal diagnosis is offered to all of them. Prenatal diagnosis for alpha-thalassaemia is routinely done by two independent molecular methods. With the first method, the mutations of the parents are directly determined by gap-PCR and then the chorionic villus sample (CVS) is examined for the presence of these mutations. With the other method, a (CA)n repeat polymorphic site located between the psialpha1- and alpha2-globin genes is used for determining the presence or absence of the normal and mutant alleles. In the period from 1995 to 1999, molecular analysis of 46 couples in which haematological data were consistent with deletion of two alpha-globin genes in both partners indicated that only 13 of them were actually at risk for haemoglobin (Hb) Bart's hydrops fetalis and prenatal diagnosis was provided in 16 pregnancies. The molecular diagnosis was possible in all cases with the use of both gap-PCR and (CA)n repeat polymorphisms analysis. No misdiagnosed cases for alpha-thalassaemia have been reported to date.

Hb Aghia Sophia [alpha62(E11)Val-->0 (alpha1)], an "in-frame" deletion causing alpha-thalassemia

In this report we describe a case of Hb H disease due to the interaction of the --(MED 1) deletion with a new alpha(+)-thalassemia determinant. The molecular analysis of the proband's genomic DNA was carried out by polymerase chain reaction amplification and sequencing of both alpha genes of the alpha(+)-thalassemia chromosome and revealed a deletion of codon 62 of the alpha1 gene. This DNA triplet codes for a valine residue at the E11 alpha helix, which is located in the interior of the heme pocket. Substitutions of valine E11 with other amino acid residues in the alpha as well as beta polypeptide chains lead, in the heterozygous carrier, either to Hb M disease or to congenital non-spherocytic hemolytic anemia. We assume that the deletion of valine at alpha62(E11) disrupts the conformation of the alpha chain to such an extent that the mutated subunit is rapidly removed by proteolysis. The final result is an alpha-thalassemia phenotype rather than an unstable hemoglobin syndrome. This conclusion is supported by the apparent absence of an abnormal alpha chain in the peripheral blood of the patient.

A 3'-flanking NF-kappaB site mediates developmental silencing of the human zeta-globin gene

The central developmental event in the human (h)alpha-globin gene cluster is selective silencing of the zeta-globin gene as erythropoiesis shifts from primitive erythroblasts in the embryonic yolk sac to definitive erythroblasts in the fetal liver. Previous studies have demonstrated that full developmental silencing of the hzeta-globin gene in transgenic mice requires the proximal 2.1 kb of its 3'-flanking region. In the current report, we localize this silencing activity to a 108 bp segment located 1.2 kb 3' to the zeta-globin gene. Protein(s) in nuclear extracts from cell lines representing the fetal/adult erythroid stage bind specifically to an NF-kappaB motif located at this site. In contrast, this binding activity is lacking in the nuclear extract of an embryonic-stage erythroid line expressing zeta-globin. This complex is quantitatively recognized by antisera to the NF-kappaB p50 and to a lesser extent to p65 subunits. A two-base substitution that disrupts NF-kappaB site protein binding in vitro also results in the loss of the developmental silencing activity in vivo. The data suggest that NF-kappaB complex formation is a crucial component of hzeta-globin gene silencing. This finding expands the roles of this widely distributed transcriptional complex to include negative regulation in mammalian development.

Developmental silencing of the embryonic zeta-globin gene: concerted action of the promoter and the 3'-flanking region combined with stage-specific silencing by the transcribed segment

Globin gene switching is a well-described model of eucaryotic developmental control. In the case of the human alpha-globin gene cluster, migration of erythropoietic activity from the embryonic yolk sac to the fetal liver is parallaled by the zeta-globin gene silencing and enhanced expression of the alpha-globin genes. To map critical cis determinants of this switch, the human zeta-globin gene, the alpha-globin gene, and chimeric recombinants were introduced into the mouse genome. Consistent with previous studies, expression of the individual alpha- and zeta-globin transgenes was found to be developmentally appropriate. Contrary to current models, however, the alpha- and zeta-globin gene promoters were not sufficient to establish this control. Instead, full silencing of the zeta-globin gene required the combined activities of this promoter, transcribed region, and 3'-flanking sequences. Individually, the silencing activities of the zeta-globin gene promoter and 3'-flanking region were minimal but increased markedly when both regions were present. The zeta-globin transcribed region appeared to contribute to gene silencing by a mechanism specifically activated in definitive erythroblasts in the fetal liver. These data demonstrate that a complex set of controls, requiring at least three determinants and involving at least two independent mechanisms, is necessary for full developmental silencing of the human zeta-globin gene.

Rapid detection of point mutations and polymorphisms of the alpha-globin genes by DGGE and SSCA

We report the application of DGGE and SSCA for the identification of point mutations causing alpha-thalassemia. The alpha-globin genes were amplified in three overlapping fragments of 250 bp (I), 540 bp (II), and 600 bp (III), respectively. Fragments II and III were analysed by DGGE, while fragments I and II were analysed by SSCA. A panel of seven previously identified mutations was employed to test the combined DGGE/SSCA strategy: 5/5 and 6/7 mutations were detected by SSCA and DGGE, respectively. The same approach has also led to the identification of eight disease-causing mutations in a sample of 18 presumed non-deletional alpha-thalassemia carriers. During this pilot study, two novel mutations as well as three new polymorphisms were found. The combined application of SSCA and DGGE allows the rapid identification of mutations responsible for alpha-thalassemia and abnormal globin chain variants. Moreover, it will prove extremely useful for pre- and postnatal diagnosis and in screening programs for non-deletional alpha-thalassemias.

Alpha-thalassaemia and globin gene rearrangements in French Polynesia

The prevalence of alpha-thalassaemia and various globin gene rearrangements was determined in 1992 individuals living on 11 islands in French Polynesia. The gene frequencies for alpha(+)-thalassaemia (almost exclusively the -alpha 3.7III deletion form) range from 5.3% to 19.2%. Haematological indices on 177 heterozygotes and 27 homozygotes for the -alpha 3.7III variant showed considerable overlap with indices of normal individuals; although there was a broad correlation of average indices with alpha-globin genotype, individual values were a poor indication of genotype. A non-deletion form of alpha(+)-thalassaemia (alpha alpha Th), triplicated alpha genes (alpha alpha alpha) and single zeta gene (-zeta) chromosomes were present at low frequencies (< 1%), whereas triplicated gamma gene (gamma gamma gamma) and triplicated zeta (zeta zeta zeta) arrangements were more common (1.1-16.3%). alpha 0-thalassaemia, probably introduced from Southeast Asia in the early part of this century, was observed in a number of individuals of Chinese and Chinese/Polynesian ancestry. Because of the high frequency of alpha(+)-Thalassaemia on some islands, it therefore seems likely that haemoglobin H disease (resulting from the interaction between alpha 0 and alpha(+)-thalassaemia) must occur in parts of French Polynesia.

Prenatal diagnosis of unusual hemoglobinopathies

While analyzing 280 hemoglobinopathy kindreds with prescribed molecular tests, 3 unusual mutations were observed that required additional characterization. In the first case, the hypervariable region flanking the alpha-globin genes generated an intermediate length 8.2 kb psi zeta-globin gene fragment on a Southeast Asian chromosome with two deleted alpha-globin genes. Rehybridization of the Southern blot with alpha-globin probe distinguished the mutation unambiguously. In the second case, restriction enzyme analysis of a PCR amplified black beta-globin gene detected a novel beta-83 point mutation adjacent to a promoter element. In the third case, which was uninformative with available allele specific oligonucleotides (ASOs), total genomic PCR amplification and sequencing identified a single basepair insertion in codon 36/37 of an Iranian beta-globin gene that shifted the reading frame and obliterated gene activity. Developing additional region-specific ASOs will further diminish the number of cases that must be characterized by genomic PCR sequencing.

Characterization of a new alpha-thalassemia-1 mutation in a Spanish family

A novel alpha-thalassemia-1 deletion of 14-15.4 kb that removes the alpha-2, alpha-1, theta-1 genes and pseudo-alpha-1 genes, has been detected in a father and 2 of his children from northern Spain.

Prenatal in situ hybridization test for deleted steroid sulfatase gene

X-linked ichthyosis results from steroid sulfatase (STS) deficiency; 90% of affected patients have a complete deletion of the entire 146 kb STS gene on the distal X chromosome short arm (Xp22.3). In these families prenatal diagnosis and carrier testing can be completed in 2 days by hybridizing simultaneously 2 different cosmid probes labeled with fluorescein or Texas red and counterstaining interphase nuclear DNA with DAPI. An STS gene probe labeled with Texas red hybridizes specifically to the steroid sulfatase gene on the X chromosome. A second flanking probe labeled with fluorescein hybridizes to both the normal Y chromosome and normal and STS deleted X chromosomes. In this fashion the interphase nuclei of normal males, affected males, normal females, and carrier females can be distinguished unambiguously. Because normal males and carrier females each show two yellow-green fluorescein spots and one Texas red STS spot, use of this test prenatally requires determining fetal sex independently with repetitive X and Y chromosome-specific probes. This procedure can be used with lymphocytes, direct and cultured chorionic villus cells, direct and cultured amniocytes, and fibroblasts. Similar methods are anticipated to be useful for rapid diagnostic assessment of other aneuploid gene disorders.

A PCR-based strategy to detect the common severe determinants of alpha thalassaemia

A rapid and inexpensive polymerase chain reaction (PCR) based strategy is described which detects the three common, severe alpha thalassaemia determinants observed in southeast Asia (--SEA) and the Mediterranean (--MED and -(alpha)20.5). Oligonucleotide primers have been chosen which allow specific identification of both normal (alpha alpha) and abnormal (--) chromosomes using identical conditions in either the same or parallel PCR reactions. This strategy should be useful in the development of screening programmes to identify carriers of alpha thalassaemia (--/alpha alpha) and prenatal diagnosis of the Hb Bart's hydrops fetalis syndrome (--/--) for those populations in which this represents a major cause of perinatal death.

Carrier detection and prenatal diagnosis of alpha-thalassemia of Southeast Asian deletion by polymerase chain reaction

Alpha-thalassemia of Southeast Asian deletion (-- SEA/) is very common in Southeast Asia. Homozygosity of this genotype is the major cause of Hb Bart's hydrops fetalis in Taiwan. With polymerase chain reaction using three oligonucleotide primers bridging the common deletion breakpoint, a DNA fragment of 194 basepairs (bp) was amplified in chromosomes with the -- SEA determinant and a DNA fragment of 287 bp was amplified in chromosomes without this deletion. In our pilot study including 8 normal subjects, 20 obligate carriers, and 11 homozygotes of the deletion, all the genotypes were determined and then confirmed by Southern blotting and DNA hybridization with phi zeta globin gene probe. For prenatal diagnosis, 55 at-risk pregnancies were collected. Chorionic villus sampling was done in 51 cases and early amniocentesis was done in 4 cases. Fourteen cases (25.5%) were diagnosed as normal, 25 (45.5%) as heterozygotes, and 16 (29%) as homozygotes of -- SEA. All of the diagnoses were also confirmed as aforementioned. With polymerase chain reaction, the determination of the -- SEA deletion is straightforward and is much quicker and easier than with conventional Southern blotting and DNA hybridization. In areas with a high prevalence of -- SEA deletion, this method provides a rapid tool for carrier detection and prenatal diagnosis.

A newly-characterized alpha-thalassaemia-1 deletion removes the entire alpha-like globin gene cluster in an Italian family

We describe a new deletional form of alpha thalassaemia which encompasses the entire alpha-like globin gene cluster in a 15-year-old boy of Southern Italian descent. The deletion removes approximately 31 kb, the 5'-end point is located approximately 4 kb upstream of the xi gene, while the 3'-end point maps between the alpha 1- and theta 1-globin genes. The interaction of this deletion with the common-alpha 3.7 form gives origin to a classical form of haemoglobin (Hb) H disease in the propositus of this study. Deletional forms of xi alpha-thalassaemia are uncommon in the Mediterranean basin; as for other unusual xi alpha-thalassaemia forms, heterozygotes for this mutation may escape detection in population surveys based on zeta and alpha probes.

Molecular characterization of severe alpha-thalassemias causing hydrops fetalis in Taiwan

alpha-Thalassemia hydrops fetalis is a common disorder in Taiwan. The condition causes perinatal death and many maternal obstetrical complications. In order to determine the molecular defects of this condition in Chinese, 87 unrelated families with this disorder were collected in the past 4 years. The molecular defects were studied by Southern blotting and DNA hybridization with phi zeta 1-globin gene and LO (a 0.4 kb BamHI/EcoRI fragment in the 5' flanking region of the zeta 2-globin gene) probes. Eighty-one (93.1%) fetuses had homozygous Southeast Asian deletion (- -SEA/- -SEA). Five (5.7%) fetuses were compound heterozygotes for the Southeast Asian deletion and Thailand deletion (- -SEA/- -THAI). The remaining fetus was a compound heterozygote for the Southeast Asian deletion and an uncharacterized nondeletional defect (- -SEA/(alpha alpha)Th). The molecular defects of alpha-thalassemia hydrops fetalis in Chinese are heterogeneous. This fact has important implications for genetic counseling and prenatal diagnosis.

Prenatal diagnosis of alpha-thalassemia by polymerase chain reaction and dual restriction enzyme analysis

Asian couples at risk for a fetus with homozygous alpha-thalassemia (hydrops fetalis) are often identified by their low erythrocyte mean corpuscular volume (MCV) and normal hemoglobin electrophoresis when little time remains to test their genotypes by restriction enzyme analysis. DNA analysis is performed directly on chorionic villi or amniocytes remaining after an aliquot is used to establish a backup cell culture. The polymerase chain reaction (PCR) protocol quickly determines whether the fetus has hydrops fetalis without waiting for cultured cells to grow. Previously, growing cultured fetal cells to obtain more fetal material to establish unambiguously the fetal genotype with two independent restriction enzyme digests absorbed a significant portion of the time remaining to complete prenatal diagnosis. A dual restriction enzyme digestion protocol was development using a 3' zeta-globin probe to clearly distinguish the most common alpha-thalassemia deletions that represent nearly all the alpha-thalassemia haplotypes in Southeast Asia.

Identification of deletion and triple alpha-globin gene haplotypes in the Montreal beta-thalassemia screening program: implications for genetic medicine

We obtained blood samples in a screening program designed to detect beta-thalassemia heterozygotes in Montreal; additional samples were obtained from referred persons. We analyzed DNA for variant numbers of alpha-globin genes, notably the alpha-thalassemia2 (-alpha/), alpha-thalassemia1, (- -/), and triplicated alpha-globin gene (alpha alpha alpha/) haplotypes using restriction enzymes and probes for alpha-globin and zeta-globin gene sequences. We estimated the numbers of Montreal residents of Italian and Greek ethnic origin with -alpha/alpha alpha genotype. Thus, 4.3% of Italians and 1.5% of Greeks, or about 7,500 persons, are estimated to be alpha-thalassemia2, trait (silent carriers), largely (80%) in the -alpha 3.7/type I form. The triplicated alpha-globin gene haplotype was also found. The risk of a severe (alpha-thalassemia1) phenotype associated with inheritance of - -/alpha alpha or -alpha/-alpha genotypes was low and was found predominantly in this study, in persons of Asian ethnic origin. The sample of Asians was too small to estimate carrier frequencies; however, based on results from the beta-thalassemia screening program, we estimated that about 4% of Asians (about 1,300 persons) in Montreal are alpha-thalassemia carriers. We identified persons heterozygous for both beta-thalassemia and alpha-thalassemia mutations. In these double heterozygotes, the effect of the triplicated alpha-globin gene was to make the erythrocyte parameters used for screening (MCV and %HbA2) more deviant from normal whereas deletion of 2 alpha-globin genes tended to normalize the erythrocyte values. These findings have implications for the screening program and reproductive counseling.

Detection of specific DNA sequences by fluorescence amplification: a color complementation assay

We have developed a color complementation assay that allows rapid screening of specific genomic DNA sequences. It is based on the simultaneous amplification of two or more DNA segments with fluorescent oligonucleotide primers such that the generation of a color, or combination of colors, can be visualized and used for diagnosis. Color complementation assay obviates the need for gel electrophoresis and has been applied to the detection of a large and small gene deletion, a chromosomal translocation, an infectious agent, and a single-base substitution. DNA amplification with fluorescent oligonucleotide primers has also been used to multiplex and discriminate five different amplified DNA loci simultaneously. Each primer set is conjugated to a different dye, and the fluorescence of each dye respective to its amplified DNA locus is scored on a fluorometer. This method is valuable for DNA diagnostics of genetic, acquired, and infectious diseases, as well as in DNA forensics. It also lends itself to complete automation.

Positional effect of cis/trans alpha globin gene deletions on the formation of "H" bodies

Normal individuals have four alpha-globin genes, two on each member of the chromosome 16 pair (alpha alpha/alpha alpha). The alpha-thalassemia trait phenotype associated with deletions of two alpha-genes can be either on the same chromosome, the cis type (alpha alpha/--), or on opposite chromosomes, the trans type (alpha-/alpha-). Traditionally, the observation on vitally stained smears of occasional cells containing "H" bodies has been used as an important diagnostic criterion for alpha-thalassemia trait. These "H" bodies are thought to be precipitated beta tetramers because of the presence of excess beta-globin chains. Our study in patients with various alpha-genotypes indicates that normal subjects (alpha alpha/alpha alpha) and patients with silent alpha-thalassemia trait (alpha alpha/alpha-) generally have no "H" bodies. However, patients with the two-gene deletion of the cis type alpha-thalassemia (alpha alpha/--) show the occasional "H" body, and those with Hb "H" disease (alpha-/-- or alpha cs-/--) show many such bodies. On the other hand, patients with two-gene deletion of the trans type (alpha-/alpha-) do not show "H" bodies. The number of "H" bodies found does not appear to correlate directly with the degree of imbalance in alpha- and beta-chain production among the various alpha-genotypes examined. The chemical nature of "H" bodies is discussed, and an alternative hypothesis that embryonic zeta chains expressed in the cis type but not in the trans type of alpha-thalassemia are involved in the formation of "H" bodies is proposed.

Enhanced glucose transport in response to inhibition of respiration in Clone 9 cells

An acceleration of ATP synthesis by anaerobic glycolysis provides important compensation for interference with respiration in a variety of cells. Effective compensation for an inhibition of respiration, however, can occur in cells in which glucose entry is rate limiting only if sufficient glucose becomes available through an enhancement of transport. We present here a detailed study of the effects of inhibition of respiration in Clone 9 cells, a continuous cell line characterized by low internal glucose concentrations (less than 10% that of the external medium) and minimal stores of glycogen. Exposure of these cells to 5 mM cyanide results in a 90% fall in cell ATP and a twofold rise in cell Na+ within 20 min. By the end of 1 h, however, there is a 4.5- to 7-fold increase in cytochalasin B-inhibitable glucose transport that is accompanied by a parallel increase in the rate of lactate production, a partial recovery of cell ATP, and no further rise in cell Na+. The acute fall in ATP resulting from a submaximally effective concentration of cyanide (0.5 mM) is moreover followed by a time-dependent recovery of cell ATP to near-normal levels and subsequent resistance to challenge with even 5 mM cyanide. The stimulation of facilitative glucose transport resulting from exposure to cyanide is attributable to an increase in maximal velocity rather than to a change in Km and persists for more than 2 h after removal of the inhibitor. These results demonstrate that, in these cells characterized by low internal glucose concentrations, regulation of glucose entry is of central importance in ATP homeostasis and that a major component of the adaptive response to an inhibition of respiration is a time-dependent increase in glucose transport.

The levels of zeta, gamma, and delta chains in patients with Hb H disease

Details are given of a study of blood samples from 24 patients with Hb H disease from different Mediterranean countries and from the Far East. Four different types of alpha-thal-1 (--) were observed, namely -(alpha) (approximately 20.5-kb deletion); --MED-I (approximately 17.5-kb deletion); --MED-II (greater than 26.5-kb deletion); and --SEA (approximately 18-kb deletion, in Orientals only). The alpha-thal-2 was mainly of the deletion type (16 with the 3.7-kb deletion; 1 with the 4.2-kb deletion), while 4 of the 7 patients with a nondeletional type had the five-nucleotide deletion at the donor splice site of the first intron of the alpha 2 gene. All patients had a mild-to-moderate hemolytic anemia; no significant differences in hematology were observed between the groups. Hb A2 was decreased to about one-third of the normal level. The Hb H formation varied considerably and its quantitation was not always satisfactory. Patients with Hb H disease due to any alpha-thal-1 combined with a nondeletional alpha-thal-2 had the highest Hb H levels and a more marked anemia. The zeta chain production was small and absent in patients with the MED-II type of alpha-thal-1 because this deletion included the zeta and psi zeta genes. The highest zeta chain levels were present in the four patients with the SEA type of alpha-thal-1. The gamma chain production was increased, particularly in patients with a mutation of C----T at position -158 to the G gamma globin gene. This gamma chain was primarily present as Hb Bart's (or gamma 4) and only about 15% was recovered as Hb F or alpha 2 gamma 2. The evaluation of the rate of gamma chains produced in these patients was greatly facilitated by data from one patient who had Hb H disease and a heterozygosity for the A gamma-beta+-HPFH. The low levels of Hb A2 and of Hb F (relative to Hb Bart's) can be explained by a decreased affinity of alpha chains for delta and gamma chains as compared with beta chains in conditions of severe alpha chain deficiency.

The types of hemoglobins and globin chains in hydrops fetalis

Details are presented of analyses of hemoglobins in blood samples from four newborn babies with hydrops fetalis using reversed phase and anion exchange high performance liquid chromatographic methodology. Three were homozygous for the alpha-thalassemia-1 (SEA) deletion, and one was a compound heterozygote for the same deletion and the larger alpha-thalassemia-1 (Fil) deletion. All four babies had beta, G gamma, A gamma, and zeta chains; these chains were present in Hb Bart's or gamma 4, Hb Portland-I (zeta 2 gamma 2), and Hb Portland-II (zeta 2 beta 2). Hb H (beta 4) could not be detected. The level of zeta was directly related to the level of beta and, thus, the fetal age. A lower level of zeta chain was present in the baby with the compound heterozygosity because the large deletion (Fil) on one chromosome included the zeta and psi zeta genes. Circulating red cells, i.e. reticulocytes and nucleated red cells, were unable to synthesize zeta chains, indicating that this capability must have ceased a few months prior to birth. Quantitative data obtained by chromatographic procedures were greatly influenced by the condition of the blood sample and the way it was stored. Hb Portland-II (zeta 2 beta 2) and Hb Bart's (gamma 4) are rather unstable when a red cell lysate is stored at 4 degrees C; this is in contrast to Hb Portland-I (zeta 2 gamma 2) which appears to be stable. Samples can be stored as washed red cells or red cell lysates at -70 degrees C.

A large deletion encompassing the entire alpha-like globin gene cluster in a family of northern European extraction

We describe a new deletional form of alpha thalassemia segregating in three generations of a family of northern European origin. A full-term female girl had hypochromic, microcytic anemia since early infancy associated with delayed language development, slow growth and weight gain. Hematologic studies suggested the presence of alpha thalassemia. Gene-blotting studies showed no abnormal alpha-like globin gene fragments; however, studies of inheritance of informative polymorphic restriction fragments using zeta, alpha and 3'-alpha-hypervariable region (3'-HVR) probes showed evidence for an extensive deletion encompassing the entire alpha-like globin gene cluster. The 3' breakpoint of this deletion maps beyond the 3'-HVR, a region implicated as a hot spot for the generation of other large deletional events within the alpha-like cluster. The 5' breakpoint maps at least 10 kilobases (kb) 5' to the zeta-globin gene. The minimum size estimate for this deletion is greater than 47 kilobases.

Characterization of a newly discovered alpha-thalassaemia-1 in two Spanish patients with Hb H disease

A new deletion of more than 27 kb, removing the psi zeta 1, psi alpha 2, psi alpha 1, alpha 2, alpha 1 and theta 1 globin genes has been found in four members of a Spanish family, including two patients with Hb H disease. The 5' end point of the deletion is located between the zeta and psi zeta genes, and the 3' end of the deletion is downstream of the 3' hypervariable region.

Interaction of heterozygous beta zero-thalassemia with single functional alpha-globin gene

In this study, we analyzed the phenotypic manifestations resulting from the interaction of heterozygous beta zero-thalassemia(beta zero-39 nonsense mutation) with the functional loss of three alpha-globin structural genes in six subjects, of whom four had the [-alpha/--]alpha-globin genotype and two the [--/alpha Th alpha] alpha-globin genotype. The beta-thalassemia defect was in all cases the nonsense mutation at codon 39. The nondeletion alpha-thalassemia alpha th was the initiation codon mutation (AUG----GUG) of the alpha-2 gene. In all these subjects hypochromia and microcytosis were more marked than in beta zero-thalassemia heterozygotes with a full complement of four alpha-globin genes. All but one had moderate anemia. The alpha:beta globin chain synthesis ratios were consistently decreased. No cases had Hb H on electrophoresis. Subjects with [--/alpha Th alpha] alpha-globin genotype had more severe thalassemia-like manifestations than those with [--/-alpha] alpha-globin genotype.

The molecular basis of HbH disease in Taiwan

We have determined the molecular characteristics of alpha-thalassemia in 12 HbH subjects from Taiwan by restriction endonuclease mapping with alpha- and zeta-specific probes. We have found four types of defects in the alpha-thalassemia-2 genetic determinant: -alpha 3.7 type I; -alpha 4.2; alpha CS alpha; and alpha alpha T. All HbH subjects carried the --SEA genotype in the alpha-thalassemia-1 determinant. At least two different subtypes of --SEA genotype were observed in this study.

Different forms of Hb H disease in the Chinese

A marked genetic and clinical variability of the Hb H syndrome occurs because of the molecular heterogeneity of alpha-thalassemia (thal). The hallmark is the presence of excess beta chains forming Hb H (beta tetramer). In the Chinese, classical Hb H disease presents as "alpha-thalassemia intermedia" and is due to a double heterozygosity for two deletional forms of alpha-thal, alpha-thal-1 and alpha-thal-2. The majority of cases with an alpha-thal-1 defect have a deletion of at least 18.1 kb starting 3' to the zeta 1 gene which includes the psi alpha and the two alpha genes; it is similar to that described in Thais. However, two families had a deletion of the entire zeta-alpha gene cluster, i.e. zeta-alpha-thal-1. Of 33 alpha-thal-2 defects studied, 26 were the rightward deletion (alpha -3.7 kb, all type I defects) and seven the leftward deletion (alpha -4.2 kb); one of the latter was associated with Hb Q. About 10% of the alpha-thal defects belong to the nondeletion type, the most common form being Hb Constant Spring (CS). This anomaly, when coinherited with alpha-thal-1, produces Hb H-CS disease which has a most marked anemia and splenomegaly due to the instability of the alpha-CS chain. Hb Quong Sze produces an alpha-thal-2 because of the unstable alpha-Quong Sze chain. One patient who inherited classical Hb H disease and Hb New York (NY) [alpha 113(G15)Val----Glu] had severe anemia, and required frequent blood transfusions due to the deleterious effect of an increased alpha-NY chain turnover.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha-thalassemia screening reveals quadruple zeta-globin genes in a Laotian family

In screening families for alpha-thalassemia (thal) by the Southern blot technique, several Laotian families were found which had anomalous zeta-globin haplotypes. The zeta-globin genes encode alpha-like embryonic hemoglobin subunits in the alpha-globin multigene complex on chromosome 16. There are normally two zeta-globin genes in this cluster: 5' zeta 2 and 3' psi zeta 1. In our study, six individuals in three families had triple zeta-globin genes. Another family revealed a novel quadruple zeta-globin arrangement. Two aberrant fragments were seen in Eco R1, Bam H1, Bgl II and Hind III digests using a zeta-globin gene probe. These anomalous bands were in the integral 10 kb range consistent with duplication of the zeta-globin region. This haplotype interpretation was confirmed by Southern blot analyses using double digestions hybridized to a cDNA zeta-gene probe, and Pvu II digests probed with a 5'-psi zeta 1 intergenic fragment. Proposed mechanisms of recombination and implications of this novel arrangement are discussed.

Dysfunctional alpha-globin genes in hemoglobin H disease in blacks: variation in restriction fragment size permits the detection of the -alpha/-alpha T genotype

Hemoglobin H (HbH) disease is most often due to deletion of three of the four alpha-globin genes (genotype --/--alpha). In black subjects although the -alpha/chromosome is common, the --/haplotype is very rare and few examples of HbH disease have been detected. We have studied three black siblings with HbH by restriction endonuclease mapping of the alpha-like gene complex (5'-zeta-psi zeta-psi alpha 2-psi alpha 1-alpha 2-alpha 1-3') using zeta- and alpha- specific probes. The presence of size differences in the previously described hypervariable region between the zeta and psi zeta genes results in a restriction fragment length polymorphism which permitted the detection of single alpha genes on both number 16 chromosomes in these subjects. Quantitative DNA hybridization by a slot-blot technique confirmed that their genomes contained two alpha-globin genes. The results establish that in these black subjects HbH disease is associated with dysfunctional alpha-globin genes (genotype: -alpha/-alpha T).

DNA polymorphisms in human population studies: a review

The use of restriction endonucleases and DNA probes to expand the range of informative polymorphisms should be of immense value in the study of human populations. To date, this approach has been only minimally used, but results are available for markers in the major histocompatibility complex and the globin gene clusters. In addition, isolated studies using other probes have been published. The ease of the techniques involved, the rate at which new DNA polymorphisms are being found and the range of information provided should ensure that use of this approach expands rapidly.

HB Q-Thailand-HB H disease in a Chinese living in Geneva, Switzerland: characterization of the variant and identification of the two alpha-thalassemic chromosomes

Data on a 24-year-old Chinese male with Hb Q-Thailand-Hb H disease are presented. The hemoglobin variant was characterized by fast microprocedures, mainly by reverse-phase high-performance liquid chromatography. Gene mapping analyses identified the alpha-thalassemia-2, which is associated with the alpha-Q chain, as caused by a 4.2-kb deletion involving the alpha 2 globin gene, while the alpha-thalassemia-1 anomaly was the common Southeast Asian type in which part of the psi zeta, the psi alpha, and the alpha 2 and alpha 1 globin genes are deleted.

Alpha-thalassemia haplotypes in the Algerian population

DNA mapping was performed in seven unrelated Hb H patients and nine carriers for alpha-thalassemia trait originating from Algeria. This study has allowed us to identify four alpha-thalassemia haplotypes: the (-alpha 3.7) haplotype, which is the most frequent (18 of 23 alpha-thalassemic chromosomes), the (-(alpha)20.5) haplotype, a (--) haplotype, and an (alpha alpha)T haplotype. Our results also show that the (-alpha 3.7) haplotypes encountered in the Algerian population are heterogeneous and differ by the site of the unequal crossover responsible for the 3.7-kb deletion and the size of the interzeta fragment. In addition, during this survey we observed that normal chromosomes bearing a polymorphic BglII site are associated with different interzeta fragments.

Alpha-thalassemia in Papua New Guinea

A study of the distribution of alpha-thalassemia in Papua New Guinea (PNG) was carried out by DNA analysis. A total of 664 DNA samples were screened for alpha-thalassemia 2 and alpha-thalassemia 1 caused respectively by either deletion of one or both of the duplicated alpha-globin genes. alpha-Thalassemia 2 was detected in high frequencies in coastal and lowland regions where malaria has been holo- to hyperendemic but in low frequencies in non-malarious highland regions. The highest frequency was observed in the north coast of PNG. The distribution of alpha-thalassemia 2 seems to be in accordance with other conditions such as ovalocytosis and G6PD deficiency which are also prevalent in this population, suggesting that they may interact in protection against malaria. However, it appears to be negatively correlated with beta-thalassemia and alpha-thalassemia 1, the latter being extremely rare in this population. Analysis of the types and subtypes of the single alpha-globin gene deletion revealed a predominance of the -alpha 4.2 type in general, except in some regions in the south where the -alpha 3.7 type is prevalent. The -alpha 3.7 I subtype is the common form of the -alpha 3.7 deletion in the PNG mainland. The -alpha 3.7 III subtype, previously reported to be unique in Melanesians and Polynesians, was detected in an offshore island of PNG. However, this subtype is very rare in Melanesians from the PNG mainland.

An elongated segment of DNA observed between two human alpha globin genes

Detailed restriction enzyme analysis of the DNA from a Chinese female showed that one of her chromosomes had a greater than 17.5 kb deletion of DNA, including the psi alpha, alpha 2, and alpha 1 globin genes, which is present in many Southeast Asians with an alpha-thalassemia-1 chromosome. Her "normal" chromosome had the expected cluster of alpha-like globin genes (5'-zeta-psi zeta-psi alpha-alpha 2-alpha 1-3'), but the segment of DNA between the two alpha globin genes was elongated by some 0.5-0.7 kb. Analyses of various restriction sites suggested that this normal variant of the human alpha globin gene complex is due to a crossover between a normal chromosome with (alpha alpha) and a chromosome with an alpha-thalassemia-2 (-alpha 3.7) and an -alpha 2 alpha 1-hybrid gene.