Phenotypic effect of heterozygous alpha and beta 0-thalassemia interaction

In this study, we carried out restriction endonuclease mapping in order to characterize the alpha-globin genotype of 10 Sardinian beta 0- thalassemia heterozygotes, all of whom presented with normal red blood cell indices and increased HbA2 levels. In 8 of these subjects, we found the deletion of two alpha-globin genes (-alpha/-alpha), and in the remaining two the deletion of a single alpha-globin gene (- alpha/alpha alpha). In three of these carriers with the (-alpha/-alpha) alpha-globin genotype and in one with the (-alpha/alpha alpha) genotype, we also found the glucose-6-phosphate dehydrogenase (G6PD) defect of the Mediterranean type. On the basis of these findings, we may conclude that the interaction of heterozygous beta 0-thalassemia with alpha-thalassemia, due to the deletion of either one or two alpha- globin genes, may lead to the production of red blood cells with normal indices. The association of the G6PD defect with this thalassemia gene complex may eventually contribute to this effect. We suggest, therefore, that screening programs for heterozygous beta-thalassemia in populations where alpha-thalassemia is also prevalent, should incorporate the determination of HbA2 in the first set of tests.     

Alpha-thalassemia is related to prolonged survival in sickle cell anemia

We have determined the frequency of deletional alpha-thalassemia in black populations in the USA and Africa that harbor sickle cell anemia. In normals, the frequency of the chromosome bearing a deletion of one of the two normal alpha gene loci, designated (-alpha), ranged from 0.12 to 0.16, and in sickle trait subjects, the frequency ranged from 0.18 to 0.20. By contrast, in sickle cell anemia subjects, the frequency was significantly greater and ranged from 0.22 to 0.33. Analysis demonstrated that the greater frequency in the last group was primarily a result of an increased number of subjects with alpha- thalassemia trait (also called homozygous alpha-thalassemia-2). In addition, the frequency of the (-alpha) chromosome was found to increase progressively with age, supporting the hypothesis that alpha- thalassemia is favorable to the survival of subjects with sickle cell anemia. Thus, individuals who inherit alpha-thalassemia and sickle cell anemia may represent a subgroup of patients with a longer life expectancy.     

The diverse molecular basis and hematological features of Hb H and AEBart's diseases in Northeast Thailand

We defined the molecular basis and correlated the hematological phenotypes with the globin genotypes in 52 patients with Hb H disease and 29 patients with AEBart's disease of northeast Thailand. Among the former group, the most prevalent molecular defect was found to be the interaction of alpha-thalassemia 1 (SEA type) with the Hb Constant Spring (Hb CS; 35 of 52 patients), followed by the deletion of three alpha-globin genes with the SEA type alpha-thalassemia 1 and the 3.7- or 4.2-kb deletion of alpha-thalassemia 2 (14 of 52 patients) and the interaction of the SEA alpha-thalassemia 1 with the Hb Paksé which was found in the remaining 3 patients. Among the 29 patients of the latter group, in 18 disease was caused by interactions of Hb E heterozygotes with the SEA alpha-thalassemia 1 and Hb CS. Interaction of Hb E heterozygotes with a deletional form of Hb H disease was detected in 7 patients and the Hb Paksé AEBart's disease was found in another 3 patients. A remaining patient with an unusually severe form of AEBart's disease with a lower Hb E level and observable Hb H was associated with a hitherto undescribed condition, the interaction of Hb E heterozygote with alpha-thalassemia 1 and an alpha2 codon 30 (GAG) deletion. Hematological characterization of the patients demonstrated that although disease in most of them was associated with thalassemia intermedia phenotypes, it was apparent that association with the nondeletional form of alpha-thalassemia 2 produced a more severe phenotype than that of the deletional one. Therefore, alpha-globin gene analysis of Hb H and AEBart's disease patients would be useful for predicting the clinical outcome and improving genetic counseling.     

Alpha-thalassemia among tribal populations of Eastern India

Five hundred and thirteen unrelated subjects belonging to various tribes of West Bengal, Arunachal Pradesh and Assam in Eastern India, were screened for the presence of alpha-thalassemia (thal) gene deletion(s) as a possible cause of unexplained anemia (Hb < 11 g/dL and/or MCH <28 pg, MCV < 78 fL). As reported earlier, beta-globin gene mutant alleles were found with a frequency of up to 20% in some tribes. In the present study, alpha-globin gene deletion alleles were found in 18% of subjects from West Bengal, 3.9% from Arunachal Pradesh and 3.84% from Assam tribesmen. Coexistence of alpha- and beta-globin gene abnormalities was observed in up to 18% of some tribal groups. The high inbreeding rate and lack of appropriate medical care make these populations particularly vulnerable.     

The effect of Hb F and alpha-thalassemia on the red cell indices in sickle cell anemia

This study examines the effect of different levels of fetal hemoglobin (Hb F) and the presence or absence of genes for alpha-thalassemia on the red cell indices and degree of anemia among 102 patients with homozygous sickle cell disease (S/S) between the ages of 15 and 62 years. Patients were divided into those with an average Hb F of less than 10 gm/L ("low" Hb F group) and those with greater than 10 gm/L ("high" Hb F group). alpha-Thalassemia was assessed by restriction enzyme analysis of DNA by the Southern blotting technique. Homozygosity for the beta(s) gene was confirmed by restriction enzyme analysis of DNA using the enzyme Mst II. There were 51 patients with four alpha-globin genes, 28 of whom had "high" and 23 "low" Hb F levels. Fifty-one patients had alpha-thalassemia, 38 of whom were heterozygous and 13 homozygous for the 3.7 kb alpha-thalassemia deletion. Nine had "high" and 31 had "low" Hb F. Irrespective of alpha-globin genotype, patients in the high Hb F group had a higher mean Hb, Hct, MCV, and MCH than those in the low HB F group. In patients without alpha-thalassemia Hb F was positively correlated with MCV and MCH (p less than 0.001), patients with high Hb F levels having macrocytosis confirmed by microhematocrit studies. Patients with alpha-thalassemia had a lower MCHC than patients with four alpha-globin genes and this was not significantly affected by the level of Hb F. The combination of alpha-thalassemia and high levels of Hb F appears to result in a distinctive S/S phenotype that is similar to the type of S/S disease described in Southern India.     

Hb Bart's levels in cord blood and alpha-thalassemia mutations in Cyprus

The purpose of this study was to examine the frequency of alpha-thalassemia in the population of Cyprus using cord blood samples. The levels of Hb Bart's were compared with the hematological indices and the results correlated with the presence of alpha-thalassemia mutations. The protocols for the polymerase chain reaction detection of the six most common alpha-globin mutations encountered in Cyprus were optimized, and the frequency of each mutation was determined through the screening of 495 random cord blood samples. The total allele frequency for the mutations examined was 10.6%, of which 1% is due to the triplication of the alpha-globin genes. The -alpha(3.7 kb) deletion accounts for 72.8% of all detectable mutations, while the--MED-I and -(alpha)-20.5 kb mutations account for 7.8%. The level of Hb Bart's and the MCV and MCH values in cord blood samples were found to correlate closely with the severity of alpha-thalassemia, although the -alpha(3.7 kb) deletion and perhaps other mild alpha-thalassemia mutations may not give detectable Hb Bart's levels. A reasonably accurate estimate of the alpha-thalassemia carrier frequency may be obtained from cord blood studies if Hb Bart's estimates are combined with hematological indices. When molecular methods are added, these give the best way to use cord bloods to survey populations for alpha-thalassemia.     

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.     

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

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

The leftward deletion alpha-thal-2 haplotype in a black subject with hemoglobin SS

We have identified a black individual with homozygous sickle cell anemia who is the silent carrier of alpha-thalassemia (genotype - alpha/alpha alpha) due to heterozygosity for the leftward deletion alpha-thal-2 haplotype. This deletion has not been described previously in a black subject and is the only leftward deletion that we have found among 255 alpha-thal-2 chromosomes from sickle cell subjects. Its effects on the clinical, hematologic, biosynthetic, and cellular pathology of sickle cell anemia resemble those reported for the common alpha-thalassemia genotypes of the black population.     

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)     

A newly identified deletion of 970 bp at the alpha-globin locus that removes the promoter region of the alpha1 gene

The most common causes of alpha-thalassemia (thal) are deletions that remove a part, or one or both of the functional alpha-globin genes. These deletions cause diminished expression of the alpha-globin protein, which may result in relatively low hemoglobin (Hb) and/or mean corpuscular volume (MCV) values. We here report the identification of a 970 bp deletion in the alpha1-globin gene that encompasses the entire promoter region of the alpha1-globin gene and 26 bp encoding the 5' end of the mRNA. Thus, the affected alpha1-globin gene is prone to be nonfunctional. We therefore nominated the newly identified deletion allele alpha-alphaDelta970. The MCV values of four related carriers of the alpha-alphaDelta970 allele were slightly lowered, consistent with the presence of three functional alpha-globin genes.     

Three new alpha-thalassemia point mutations ascertained through newborn screening

We report three new alpha-thalassemia (thal) point mutations detected during newborn screening for hemoglobinopathies. The first mutation is a single nucleotide deletion (-A) that abolishes the translation initiation codon of the alpha2-globin gene, detected in a newborn of Hmong ethnicity who carried the Southeast Asian alpha(0)-thal deletion (alpha(T)alpha/- -(SEA)). The second mutation, a frameshift caused by a single nucleotide deletion in exon 2 of the alpha1-globin gene [codon 78 (-C)], was detected in a Black/Chinese newborn who also carried the Southeast Asian alpha0-thal deletion (alphaalpha(T)/- -(SEA)). The third mutation was a frameshift in exon 3 of the alpha2-globin gene, codons 113/114 (-C). This mutation was detected in a newborn who carried the 3.7 kb alpha(+)-thal deletion (alpha(T)alpha/-alpha(3.7)).     

A human complement receptor 1 polymorphism that reduces Plasmodium falciparum rosetting confers protection against severe malaria

Parasitized red blood cells (RBCs) from children suffering from severe malaria often adhere to complement receptor 1 (CR1) on uninfected RBCs to form clumps of cells known as "rosettes." Despite a well documented association between rosetting and severe malaria, it is controversial whether rosetting is a cause or a correlate of parasite virulence. CR1-deficient RBC show greatly reduced rosetting; therefore, we hypothesized that, if rosetting is a direct cause of malaria pathology, CR1-deficient individuals should be protected against severe disease. In this study, we show that RBC CR1 deficiency occurs in up to 80% of healthy individuals from the malaria-endemic regions of Papua New Guinea. This RBC CR1 deficiency is associated with polymorphisms in the CR1 gene and, unexpectedly, with alpha-thalassemia, a common genetic disorder in Melanesian populations. Analysis of a case-control study demonstrated that the CR1 polymorphisms and alpha-thalassemia independently confer protection against severe malaria. We have therefore identified CR1 as a new malaria resistance gene and provided compelling evidence that rosetting is an important parasite virulence phenotype that should be a target for drug and vaccine development.     

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

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

Inactivation of human alpha-globin gene expression by a de novo deletion located upstream of the alpha-globin gene cluster.

Synthesis of normal human hemoglobin A, alpha 2 beta 2, is based upon balanced expression of genes in the alpha-globin gene cluster on chromosome 16 and the beta-globin gene cluster on chromosome 11. Full levels of erythroid-specific activation of the beta-globin cluster depend on sequences located at a considerable distance 5' to the beta-globin gene, referred to as the locus-activating or dominant control region. The existence of an analogous element(s) upstream of the alpha-globin cluster has been suggested from observations on naturally occurring deletions and experimental studies. We have identified an individual with alpha-thalassemia in whom structurally normal alpha-globin genes have been inactivated in cis by a discrete de novo 35-kilobase deletion located approximately 30 kilobases 5' from the alpha-globin gene cluster. We conclude that this deletion inactivates expression of the alpha-globin genes by removing one or more of the previously identified upstream regulatory sequences that are critical to expression of the alpha-globin genes.     

A simplified screening for alpha-thalassemia 1 (SEA type) using a combination of a modified osmotic fragility test and a direct PCR on whole blood cell lysates

In order to provide a rapid method for identifying alpha-thalassemia 1 in a region with massive population and limited resources, we have tested a rapid screening strategy. Preliminary screening was done using a modified one tube osmotic fragility test (OF test) followed by RBC indices; Hb analysis and detection of alpha-thalassemia 1 with the Southeast Asian deletion (SEA type) were performed by PCR. One hundred and seventy-five adult Thai subjects were studied. Fifty-one of the 175 subjects (29.1%) were positive for a modified OF test. They all had significantly lower MCV and MCH but higher RDW-CV values as compared to the OF negative group. A successful identification of alpha-thalassemia 1 deletion using a direct PCR on cell lysates was demonstrated. Among the 51 OF-test-positive subjects, 7 were found to be alpha-thalassemia 1 carriers, 3 of whom were also carriers of Hb E. No alpha-thalassemia 1 was detected in the OF-test-negative group. A combination of a modified OF test and a direct PCR analysis on whole blood cell lysates would therefore provide an effective screening for alpha-thalassemia 1 in the regions where a program of prevention and control of the disease remains underserved.     

Sickle cell disease due to compound heterozygosity for Hb S and a novel 7.7-kb beta-globin gene deletion

A young woman originally from Cape Verde islands presented with mild sickle cell disease. Her blood counts and hemoglobin analysis results initially suggested that she might be either homozygous for the sickle cell hemoglobin (Hb S) with concomitant alpha-thalassemia, or compound heterozygous for Hb S and beta0-thalassemia, deletional deltabeta-thalassemia or hereditary persistence of fetal hemoglobin (HPFH). We utilized a novel polymerase chain reaction (PCR)-based screening technique and found a hitherto unrecognized 7.7-kb deletion, starting from the HBB IVSII to 3' downstream of the beta-globin gene. This diagnostic approach can be applied to decipher other similar deletional mutations. This is the second known deletion that removes the 3'-end but preserves the integrity of the 5'-end of the beta-globin gene. Furthermore, the identification of the deletion allows proper genetic counseling for affected families.     

Thalassemia intermedia due to co-inheritance of beta0/beta(+)-thalassemia and (- -SEA) alpha-thalassemia/Hb Westmead [alpha122(H5)His > Gln (alpha2)] in a Chinese family

Two brothers from a Chinese family with beta-thalassemia intermedia who harbor both alpha- and beta-globin gene defects are described. They are both compound heterozygous for codons 41/42 (-CTTT) beta0-thalassemia and nt - 28 (A > G) beta(+)-thalassemia mutations together with concurrent (- -SEA) alpha-thalassemia (SEA) deletion. One sibling also harbors Hb Westmead, giving an unusual genotype of beta0/beta(+)-thalassemia and (- -SEA) alpha-thalassemia/Hb Westmead. With respect to the age at presentation and transfusion requirement, this subject shows a milder clinical phenotype than his brother, most probably explainable by the presence of Hb Westmead in addition to the SEA deletion, which causes a further amelioration of the alpha-chain excess and hence a less severe disease. For areas with high prevalence of both alpha- and beta-thalassemia mutations, their interactions should always be considered in genotype phenotype correlation. Moreover, routine laboratory diagnostic strategy for non-deletional alpha-globin gene mutations in the Chinese may need to include Hb Westmead, as it is a common alpha-globin gene mutation in our population apart from Hb Constant Spring and Hb Quong Sze.