Alpha thalassemia

Clinical and genetic characteristics of hemoglobin H disease in Iran

Hemoglobin H (Hb H) disease is a subtype of α-thalassemia caused by deletional and/or non-deletional mutations in three alpha-globin genes in which the various genotypes determine the disease severity. This study was aimed to investigate the frequency of alpha gene mutations and genotypes and their correlation with hematological and clinical characteristics in Iran. Among 202 patients diagnosed with Hb H disease through a national study in Iran according to standard methods, we had access to the hematologic and clinical findings and genetic data of 101 patients in whom genetic study was performed. Genomic DNA from peripheral blood was extracted and analyzed for identification of α-globin gene mutations using Multiplex Gap Polymerase Chain Reaction, Reverse Hybridization Assay, and finally Direct DNA Sequencing method. Twenty-one different mutations and thirty genotypes were detected in 101 patients with Hb H disease. In total, 39 patients (38.6%) were deletional and 62 patients (61.4%) were non-deletional type of the disease. The _--^MED mutation was highly prevalent in almost half of the patients (56.4%). Among various genotypes, -^MED/-a^3.7 (29.7%) and -α^20.5/-α^5NT (6.9%) were the most prevalent genotypes found in the studied group. Patients with non-deletional type presented with more severe hematological and clinical findings. Hb H percentage and serum ferritin levels were significantly higher in non-deletional patients in comparison to the deletional group (p < 0.05). 12 (11.9%) and 40 (39.6%) out of 101 patients were on regular and occasional transfusions, respectively. 83% of those with regular transfusion belonged to the non-deletional group. Among transfusion-dependent patients, -^MED/α^CSα and α^20.5/-α^5NT were the most common genotypes. In this study, two patients with -α^20.5/α^CSα and -^MED/α^-5NT genotypes experienced thrombotic events. This study indicated that although non-deletional genotypes of Hb H disease were responsible for more clinical severity of the disease, due to the presence of severe phenotypes even in deletional types, no definite correlation was found between genotype and phenotype.

Alpha-Thalassemia Carrier due to -α3.7 Deletion: Not So Silent

BACKGROUND/OBJECTIVE

Alpha-thalassemia is one of the most prevalent genetic diseases, with the -α3.7 deletion being the most common mutation. Molecular studies have suggested mechanisms to explain the mild phenotype of "silent carrier" heterozygotes. However, the correlation between the clinical laboratory picture and the -α3.7 heterozygous state remains unclear, thus we chose to investigate.

METHODS

We analyzed the medical files of 192 children evaluated for microcytosis at our tertiary center between 2007 and 2017 and diagnosed as heterozygotes for the -α3.7 deletion. Additional α-thalassemia mutations, iron deficiency anemia, and β-thalassemia were ruled out. Laboratory parameters were compared to age- and sex-matched reference values.

RESULTS

The -α3.7 carriers had significantly lower Hb and mean corpuscular volume (MCV) than the reference population, and significantly higher red blood cell counts across all age groups. The greatest reduction in Hb level appeared among male adolescents, while MCV was consistently 2 SDs lower than normal in most patients older than 2 years.

CONCLUSION

Heterozygosity for the -α3.7 deletion was associated with clinically significant microcytosis and mild anemia in our pediatric population. In the absence of iron deficiency and β-thalassemia, this finding provides a diagnosis for mild microcytic anemia, making additional investigations of microcytosis unnecessary.

Detection of α-Thalassemia by Using Multiplex Ligation-Dependent Probe Amplification as an Additional Method for Rare Mutations in Southern Turkey

α-thalassemia is the most common single gene disorder in the Cukurova Region in Turkey. It is therefore routinely screened, including premaritally, in our region. The heterogeneous molecular basis of the disease makes α-thalassemia mutation detection difficult and complex. Besides well established methods, multiplex ligation dependent probe amplification (MLPA) is known as an effective, simple and specific method for the detection and characterization of deletions and duplications. We employed MLPA testing to 30 patients with hematological parameters suggestive of α-thalassemia carrier status but was negative for α-thalassemia with conventional reverse dot blot hybridization (RDB). We found α-globin gene deletions in 3 out of 30 (10 %) patients with MLPA. We propose that MLPA can be used as a second tier test in addition to other techniques such as RDB to identify α-thalassemia carriers in high prevalence regions such as ours, thereby allowing clinicians to provide accurate genetic counselling.

Active stabilization of human endothelial nitric oxide synthase mRNA by hnRNP E1 protects against antisense RNA and microRNAs

Human endothelial nitric oxide synthase (eNOS) mRNA is highly stable in endothelial cells (ECs). Posttranscriptional regulation of eNOS mRNA stability is an important component of eNOS regulation, especially under hypoxic conditions. Here, we show that the human eNOS 3' untranslated region (3' UTR) contains multiple, evolutionarily conserved pyrimidine (C and CU)-rich sequence elements that are both necessary and sufficient for mRNA stabilization. Importantly, RNA immunoprecipitations and RNA electrophoretic mobility shift assays (EMSAs) revealed the formation of heterogeneous nuclear ribonucleoprotein E1 (hnRNP E1)-containing RNP complexes at these 3'-UTR elements. Knockdown of hnRNP E1 decreased eNOS mRNA half-life, mRNA levels, and protein expression. Significantly, these stabilizing RNP complexes protect eNOS mRNA from the inhibitory effects of its antisense transcript sONE and 3'-UTR-targeting small interfering RNAs (siRNAs), as well as microRNAs, specifically, hsa-miR-765, which targets eNOS mRNA stability determinants. Hypoxia disrupts hnRNP E1/eNOS 3'-UTR interactions via increased Akt-mediated serine phosphorylation (including serine 43) and increased nuclear localization of hnRNP E1. These mechanisms account, at least in part, for the decrease in eNOS mRNA stability under hypoxic conditions. Thus, the stabilization of human eNOS mRNA by hnRNP E1-containing RNP complexes serves as a key protective mechanism against the posttranscriptional inhibitory effects of antisense RNA and microRNAs under basal conditions but is disrupted under hypoxic conditions.

Neonatal anemia

Neonatal anemia and the need for red blood cell (RBC) transfusions are very common in neonatal intensive care units. Neonatal anemia can be due to blood loss, decreased RBC production, or increased destruction of erythrocytes. Physiologic anemia of the newborn and anemia of prematurity are the two most common causes of anemia in neonates. Phlebotomy losses result in much of the anemia seen in extremely low birthweight infants (ELBW). Accepting a lower threshold level for transfusion in ELBW infants can prevent these infants being exposed to multiple donors.

A laboratory strategy for genotyping haemoglobin H disease in the Chinese

BACKGROUND

The thalassaemias are the commonest blood disorders worldwide, with South East Asia and southern China as areas of high prevalence. Accurate diagnosis of these disorders helps in clinical management with improved outcome.

METHODS

The alpha-globin genotypes of 100 Chinese patients in Hong Kong with haemoglobin H (Hb H) disease were characterised. Single-tube multiplex gap-PCR was used to detect --(SEA), -alpha(3.7) and -alpha(4.2), while Hb CS, Hb QS and codon 30 (DeltaGAG) were identified by single-tube multiplex amplification refractory mutation system (ARMS). Automated direct nucleotide sequencing of the amplified alpha2- and alpha1-globin genes was performed to characterise other non-deletional alpha-thalassaemia determinants.

RESULTS

In the 100 cases studied, 99 cases had --(SEA) in combination with deletional alpha(+)-thalassaemia or non-deletional alpha-globin gene mutation involving the alpha2-globin gene. In 70 cases of the deletional form, 43 cases showed the genotype of (--(SEA)/-alpha(3.7)) and 27 cases of (--(SEA)/-alpha(4.2)). Three of the 27 cases of (--(SEA)/-alpha(4.2)) were found to have Hb Q-Thailand linked in-cis with -alpha(4.2). The remaining 30 cases were of non-deletional form with the following genotypes: 11 cases of (--(SEA)/alpha(HbCS)alpha), 9 cases of (--(SEA)/alpha(HbQS)alpha), 3 cases of (--(SEA)/alpha(cd30 (DeltaGAG))alpha), 3 cases of (--(SEA)/alpha(cd31)alpha), 2 cases of (--(SEA)/alpha(poly-A)alpha), 1 case of (--(SEA)/alpha(HbWestmead)alpha) and 1 case of (--(non-SEA)/alpha(HbQS)alpha).

CONCLUSIONS

Based on two rapid diagnostic tests, multiplex gap-PCR and multiplex ARMS, more than 90% of the cases were genetically characterised. This laboratory strategy should be widely applicable for genetic diagnosis of alpha-thalassaemia.

Chicken Egg Yolk Antibodies Specific for the γ Chain of Human Hemoglobin for Diagnosis of Thalassemia

Immunoglobulin Y (IgY) technology was used to generate anti-hemoglobin Bart's (Hb Bart's) IgY antibodies (Abs) for development into an enzyme-linked immunosorbent assay (ELISA) test for thalassemia diagnosis. Hb Bart's purified from the hemolysate of a patient with Hb Bart's hydrops fetalis (homozygous alpha-thalassemia) was used to immunize a chicken via the pectoralis muscle. After water dilution and sodium sulfate precipitation, 40 to 70 mg of IgY could be extracted from an egg. IgY, first detected in sera 2 weeks after immunization, reached the highest titer at week 4, and the titer remained stable for at least 2 weeks before declining. The pattern of Ab response in the yolk was the same as in the serum but was somewhat delayed. The IgY Abs produced reacted with gamma globin, Hb Bart's, Hb F, normal cord hemolysate (Hbs F plus A), and Hb Bart's hydrops fetalis (Hbs Bart's plus Portland) and to a lesser degree with beta globin, Hb A, Hb A2 and adult hemolysate (Hbs A plus A2), but the Abs did not react with alpha globin. Immunoaffinity purification with Hb A coupled to Sepharose was used to isolate an unbound IgY that reacted with Hb F, Hb Bart's, and gamma globin, and this IgY was used to develop an ELISA test for thalassemia diagnosis. The results of direct ELISA analyses of 336 hemolysate samples from individuals with various known thalassemia genotypes and phenotypes and from healthy individuals confirmed the specificity of the polyclonal Abs for Hbs containing Hb F and Hb Bart's. This specificity, which was due to the Abs' strong reactivity in cases of pathologic thalassemic diseases and weak reactivity in cases of nonpathologic thalassemic diseases, depended on the levels of Hb Bart's and Hb F.

Differential diagnosis and management of anemia in the newborn

Neonatal anemia is a condition with a diverse etiologic spectrum.Therefore, in order to form a focused differential diagnosis, it is important for the caregiver to have some knowledge of the more common causes of low hemoglobin and hematocrit concentrations in the neonate. Proper history taking, physical examination, and interpretation of diagnostic tests can narrow this focus and aid in establishing an accurate diagnosis and in directing the appropriate therapeutic interventions.

Identification of two new alpha-thalassemia mutations in exon 2 of the alpha1-globin gene

The most common causes of alpha-thalassemia are deletions that remove one or both of the functional alpha-globin genes. In addition, more than 30 different point mutations and small deletions/insertions have been reported for the alpha-globin genes. Here, we describe two new mutations occurring in exon 2 of the alpha1-globin gene. One mutation is an insertion of 21 bp that gives rise to a predicted alpha-globin chain containing a duplication of amino acid residues 93-99. The second mutation is a 33 bp deletion resulting in a predicted alpha-globin chain that is missing amino acid residues 64-74. Neither mutation results in a detectable hemoglobin variant, indicating that the variant alpha-globin chains are highly unstable. Carriers of these mutations have mild microcytosis and the phenotype of alpha+-thalassemia trait.

Hemoglobin H (Hb H) disease in Canada: molecular diagnosis and review of 116 cases

Over the past decade, we have characterized at the DNA level a total of 116 hemoglobin H (Hb H) disease patients living in Canada. The majority of patients were of southeast Asian descent (Chinese, Filipino, Laotian, Vietnamese), with a small number being of Mediterranean, Middle Eastern or East Indian background. A total of 15 distinct genotypes were detected, all but one being compound heterozygotes for a two-gene cis deletion and a single-gene deletion (-alpha/-) or a non-deletion mutation of the alpha2-globin gene (alpha(T) alpha/-). Seven different two-gene cis deletions were encountered, along with nine single-gene deletions and point mutations. The wide range of mutations associated with Hb H disease in Canada is a reflection of the population heterogeneity. The diagnosis of Hb H disease at the molecular level is important with respect to genetic counseling and the identification of families at risk for having pregnancies affected with Hb Bart's hydrops fetalis syndrome and/or Hb H disease. Six of the Hb H disease patients in our cohort had spouses who carried single-gene deletions, making these couples at risk for having children with Hb H disease. More important, seven patients had partners who carried two-gene cis deletions. These couples are at reproductive risk for both Hb Bart's hydrops fetalis syndrome and Hb H disease.

Rapid differentiation of five common alpha-thalassemia genotypes by polymerase chain reaction

The alpha-thalassemias are common genetic disorders that arise from reduced synthesis of the alpha-globin chains. At present, large-scale carrier screening and clinically valuable antenatal detection programs have not been established for the congenital disorder alpha-thalassemia (alpha-thal). We have developed a simple nonradioactive polymerase chain reaction (PCR) approach that can detect and differentiate several common alpha-globin gene deletional alpha-thals regardless of the break points. When three primer sets were used--two gene-specific sets for the alpha1- and alpha2-globin genes and one set for the beta-actin gene (serving as an internal control)--PCR products from genomic DNA were simultaneously amplified and analyzed after coamplification and gel electrophoresis. The number of alpha-globin genes present in the subjects was determined by the intensity of alpha1 and alpha2 bands normalized with that of beta-actin when using densitometry. Our results demonstrate that five common genotypes of deletional alpha-thal are differentiated by the ratios of alpha1/beta-actin and alpha2/beta-actin. We also examined the feasibility of coupling this allele-specific amplification to a color-complementary assay. This easy and reproducible PCR assay is suitable for identifying alpha-thal carriers in screenings of large populations and improving genetic counseling.

The switch from fetal to adult erythropoiesis

The story of the developmental changes in erythropoiesis is the history of oxygenation in the developing organism. The individual components of the switch from embryonic to adult erythropoiesis are developmentally regulated, and their interaction with one another is complex. Basic defects, such as absence of Epo production, lead to early embryonic or fetal death. Other defects, such as abnormalities in the switch from the fetal to adult erythropoiesis, are less catastrophic but result in hematologic abnormalities. Understanding the many aspects of the switch from embryonic to fetal to adult erythropoiesis can lead to an improved awareness of many of the problems typical of preterm infants, inborn errors resulting in hematologic diseases, and aspects important for transplantation medicine.

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.

An mRNA stability complex functions with poly(A)-binding protein to stabilize mRNA in vitro

The stable globin mRNAs provide an ideal system for studying the mechanism governing mammalian mRNA turnover. alpha-Globin mRNA stability is dictated by sequences in the 3' untranslated region (3'UTR) which form a specific ribonucleoprotein complex (alpha-complex) whose presence correlates with mRNA stability. One of the major protein components within this complex is a family of two polycytidylate-binding proteins, alphaCP1 and alphaCP2. Using an in vitro-transcribed and polyadenylated alpha-globin 3'UTR, we have devised an in vitro mRNA decay assay which reproduces the alpha-complex-dependent mRNA stability observed in cells. Incubation of the RNA with erythroleukemia K562 cytosolic extract results in deadenylation with distinct intermediates containing a periodicity of approximately 30 nucleotides, which is consistent with the binding of poly(A)-binding protein (PABP) monomers. Disruption of the alpha-complex by sequestration of alphaCP1 and alphaCP2 enhances deadenylation and decay of the mRNA, while reconstitution of the alpha-complex stabilizes the mRNA. Similarly, PABP is also essential for the stability of mRNA in vitro, since rapid deadenylation resulted upon its depletion. An RNA-dependent interaction between alphaCP1 and alphaCP2 with PABP suggests that the alpha-complex can directly interact with PABP. Therefore, the alpha-complex is an mRNA stability complex in vitro which could function at least in part by interacting with PABP.

Double heterozygosity for the codon beta 39 C-to-T nonsense mutation and a triplicate alpha-globin gene locus can cause "dominantly" inherited beta-thalassemia intermedia

BACKGROUND

A beta-thalassemia intermedia phenotype can be caused by multiple genotypes.

METHODS

We studied a family where the mother was hematologically normal and both father and daughter had beta-thalassemia intermedia.

RESULTS

Both affected individuals were heterozygous for a codon 39 CAG-to-TAG mutation. They also were heterozygous for a triplicate alpha-globin gene locus (alphaalphaalpha(anti 3.7)).

CONCLUSIONS

This compound heterozygous condition of a beta39 C-to-T mutation and triplicate alpha-globin gene increases alpha:beta-globin chain imbalance and accounts for the presence of beta-thalassemia intermedia. The proband received both an abnormal beta-globin gene and a triplicate alpha-globin locus from her father. Although the phenotype seems to be dominantly inherited, because of independent segregation of the alpha- and beta-globin genes, it is more accurately an example of polygenic inheritance.

Expression and developmental control of the human alpha-globin gene cluster

The human alpha-globin gene cluster contains three functional genes zeta, alpha 2 and alpha 1. The zeta-globin gene is expressed exclusively in the primitive erythroblasts of the embryonic yolk sac and is selectively silenced during the transition from primitive to definitive erythropoesis. The two alpha-globin genes are expressed through development; they are expressed at equivalent levels in embryonic cells at a 2.6:1 ratio of alpha 2:alpha 1 in fetal and adult cells. The dominant contribution of the alpha 2-globin locus to overall expression of adult alpha-globin is reflected in the more severe phenotype resulting from mutations that affect this locus. Developmental silencing of the zeta-globin gene reflects both transcriptional and posttranscriptional mechanisms. Transcriptional silencing is mediated by an interaction between the zeta-globin gene promoter and a silencer located in the 3' flanking region. This transcriptional silencing is only partial, and residual levels of zeta-globin mRNA are subject to subsequent degredation. This instability of zeta-globin mRNA relative to that of alpha-globin mRNA reflects differences in their respective 3'UTR segments; the zeta-globin mRNA 3'UTR has a lower affinity for a sequence-specific mRNP stability complex which assembles at this site. The alpha-globin mRNA assembles this complex at a higher efficiency and mutations which interfere with 3'UTR function result in corresponding loss of alpha-globin gene expression. These data outline a developmental pathway for the alpha-globin gene cluster which reflects transcriptional and posttranscriptional controls.

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.

Hematologic disorders and nonimmune hydrops fetalis

Hematologic disorders are implicated in approximately 10% to 27% of cases of nonimmune hydrops fetalis. In almost all of these disorders, anemia leading to heart failure, edema, ascites, and anasarca is the final common denominator. The etiology of the anemia in these cases can be conveniently divided into two categories: (1) excessive erythrocyte loss by hemolysis or hemorrhage, and (2) erythrocyte underproduction. The former include intrinsic erythrocyte abnormalities such as alpha-thalassemia and glucose-6-phosphate dehydrogenase deficiency, and conditions with excessive fetal blood loss such as fetomaternal hemorrhage and twin-twin transfusion. The latter include bone marrow replacement syndromes and conditions associated with failure of erythrocyte production. The presentation, diagnosis, and management of hematologic disorders associated with nonimmune hydrops fetalis are reviewed.

Lethal alpha-thalassaemia created by gene targeting in mice and its genetic rescue

Mutations at the alpha-globin locus are the most common class of mutations in humans, with deletion of all four adult alpha-globin genes resulting in the perinatal lethal condition haemoglobin Barts hydrops fetalis. Using gene targeting in mice, we have deleted a 16 kilobase region encompassing both adult alpha-globin genes. Animals homozygous for this deletion become hydropic and die late in gestation mimicking humans with hydrops fetalis. Introduction of a human alpha-globin transgene rescued these animals from perinatal death thus demonstrating the utility of this murine model in the development of cellular and gene based approaches for treating this human genetic disease.

Molecular characterization of a new family with alpha-thalassemia-1 (--MA mutation)

A Spanish family with alpha-thalassemia-1 (alpha-Thal-1), deletion (--MA), is described. In addition to the loss of 22 kb of DNA with a deletion of the alpha 1, alpha 2, psi alpha 2, and psi zeta 1 genes, a triplication of the zeta gene cluster in "cis" is produced. The structure of this triplication is formed by the psi zeta 1 gene, the interzeta region, and, possibly, the insertion of the psi alpha 2 fragment.

Molecular basis of alpha-thalassemia in Portugal

We have estimated the incidence and molecular basis of alpha-thalassemia in a Portuguese population, mostly from the Greater Lisbon area. In a group of 100 consecutive cord blood samples, the gene frequency of the rightward deletion (-alpha 3.7) was 0.035, and the leftward deletion (-alpha 4.2) was 0.015. In this group, we have also found four heterozygotes for the triple alpha-globin gene rearrangement (alpha alpha alpha anti 3.7. gene frequency 0.020). We have characterized the subtypes of -alpha 3.7 and alpha alpha alpha anti 3.7 rearrangements. On the whole, these results give an incidence of 10% for deletional alpha-thalassemia carriers in the studied Portuguese population. In a group of 342 subjects presenting beta-thalassemia, or Hb S trait, beta-thalassemia major sickle cell disease or low red blood cell indices, the -alpha 3.7, -alpha 4.2, -SEA, -MED, (alpha alpha)MM, and alpha alpha alpha anti 3.7 haplotypes were found in different combinations. Only one nondeletional alpha-thalassemia determinant (a 5 nucleotide deletion in the alpha 2-globin gene in the second intervening sequence donor site) was detected, which might suggest a low incidence of these defects in the Portuguese population.

Rapid detection of -alpha 4.2 deletion of alpha-thalassemia-2 by polymerase chain reaction

We sequenced part of the X boxes of alpha-thalassemia-1 of Southeast Asia type (- -SEA) with -alpha 4.2, -alpha 3.7, -alpha G-Taichung, and alpha CS alpha. We found the X box of -alpha 3.7 belonged to the X box of alpha 2 globin gene and the X box of alpha CS alpha contained X boxes of both alpha 1 and alpha 2 globin gene, whereas the X box of -alpha 4.2 and -alpha G-Taichung was a hybrid of X boxes of alpha 2 and alpha 1 globin gene. We also found there are two types of -alpha 4.2 deletion; type 1 is a common type of -alpha 4.2 deletion and type 2 is linkage to -alpha G-Taichung. We used a combination of two methods, the amplification refractory mutation system (ARMS) and the amplified created restriction sites (ACRS), to amplify the hybrids of X boxes specifically. The upstream primer for X box of alpha 2 globin gene was designed following the standard ARMS procedure to amplify the X segment of the alpha-globin gene. The downstream primer was designed according to the ACRS method to check the specificity of PCR products. Using this approach, we can diagnose the different types of -alpha 4.2 deletion. This kind of approach can also be used to amplify the specific region from the cluster of highly homologous genes.

Detection of common deletional alpha-thalassemia-2 determinants by PCR

We have developed a rapid approach to detect the two most common alpha-thalassemia-2 (alpha-thal-2) determinants by the polymerase chain reaction (PCR) technique, which takes a few hours to complete. Specific oligonucleotides selectively amplify appropriate segments of the chromosome with the deletion and the normal chromosome under identical experimental conditions, and the products are identified by electrophoresis on 1.5% agarose. Characterization of the two most prevalent types of the -alpha 3.7 determinant [-alpha 3.7(I) and -alpha 3.7(II)] can be made by Apa I digestion of the PCR product. Two types of alpha-thal-2 determinants, -alpha 3.7 and -alpha 4.2, were tested in numerous samples from various parts of the world. This approach is believed to provide a cost-effective way to screen large numbers of blood samples in a relatively short time and can be used to identify alpha-thal-2 heterozygotes and homozygotes and compound heterozygotes (-alpha 3.7/-alpha 4.2) in populations where such alpha-gene defects are shown to exist at high frequencies.

Genotype-phenotype correlations in beta-thalassemias

In this paper we review the molecular basis of the marked heterogeneity of the thalassemia syndromes as well as the relative implications for carrier screening and prenatal diagnosis. The classical phenotype of heterozygous beta-thalassemia may be modified by a number of environmental and genetic interacting factors--among which the most relevant are: (1) coinheritance of alpha-thalassemia, which may normalize the red blood cell indices; (2) the presence of a mild beta-thalassemia mutation; (3) cotransmission of delta-thalassemia which may reduce the increase of HbA2 typical of heterozygous beta-thalassemia to normal values and (4) the presence of a silent mutation which can be defined only by imbalanced beta-globin chain synthesis. A number of molecular mechanisms are able to produce the non transfusion dependent attenuated forms of thalassemia syndromes referred to as thalassemia intermedia. The most common are homozygosity for mild beta-thalassemia mutations, coinheritance with homozygous beta-thalassemia of alpha-thalassemia or genetic determinants able to sustain a continuous production of HbF in adult life or the presence of heterozygosity for hyperunstable globin variants.

Detection of the (--SEA) double alpha-globin gene deletion by a simple immunologic assay for embryonic zeta-globin chains

Homozygous alpha-thalassemia [alpha-thal-1], with loss of all four alpha-globin genes, causes lethal hydrops fetalis. The most common mutation producing this syndrome is the Southeast Asian (--SEA) double alpha-globin gene deletion. Erythrocytes from adults heterozygous for the (--SEA) deletion have minute amounts of embryonic zeta-globin chains detectable by anti-zeta-globin monoclonal antibodies. Among 225 peripheral blood samples tested by a simple anti-zeta-immunobinding tetrazolium dye test, 81 were positive and 144 were negative. The majority of subjects were of Filipino, Chinese, or Laotian ancestry. All 81 positive samples were confirmed by Bam HI digests and a zeta-cDNA probe to have the (--SEA) mutation. The (--SEA) double alpha-deletion was the only abnormality in 58. In the others, it was combined with alpha-globin or beta-globin mutations, or coincidental iron deficiency. Four other samples from (--SEA) heterozygotes were negative by this immunologic assay. Anti-zeta negative samples included 78 deletions of the total alpha-globin region, (--Tot), 23 single alpha-globin deletions, and a variety of beta-globin mutations; 16 normocytic samples with normal alpha-genes were also negative. Ten anti-zeta positive and 25 anti-zeta negative samples had benign triplicated zeta-globin genes. In this population, the sensitivity of this test was 95%; and specificity for the (--SEA) mutation was 100%. Anti-zeta immunobinding testing provides rapid, simple, and reliable screening for the (--SEA) double alpha-globin deletion, although it does not detect the (--Tot) total alpha-deletions.

An IVS-I-117 (G-->A) acceptor splice site mutation in the alpha 1-globin gene is a nondeletional alpha-thalassaemia-2 determinant in an Indian population

In 1991 we reported the identification of two deletional alpha-thalassaemia-2 determinants (-3.7 kb and -4.2 kb) and one nondeletional alpha-thalassaemia-2 determinant (Hb Koya Dora alpha 2 codon 142, TAA-->TCA) in a tribal population in Central India (Gupta et al, 1991). Evidence was obtained at that time for the possible presence of an additional nondeletional alpha-thalassaemia-2 because of low levels of Hb S (< 28%) in some Hb S heterozygotes with a simple alpha-thalassaemia-2 heterozygosity (-alpha/alpha alpha). This abnormality has now been identified as a G-->A mutation at IVS-I-117 of the alpha 1-globin gene (acceptor splice site) which makes this gene nonfunctional. Its frequency was established at approximately 6% which raises the total frequency of alpha-thalassaemia determinants in this population to approximately 60%. Subjects with a deletional alpha-thalassaemia-2 and the newly discovered alpha 1 acceptor splice junction mutation in trans appear to have an alpha chain deficiency similar to that of an alpha-thalassaemia-2 homozygote (-alpha/-alpha). An additional change (C-->G) at the Cap -4 site was observed in six alpha 1- and one alpha 2-globin genes; this polymorphism is not associated with a decrease in alpha chain synthesis and is not linked to the IVS-I-117 (G-->A) mutation.

Screening and prenatal diagnosis of the haemoglobinopathies

In this paper we have reviewed the social and technical aspects of carrier screening and prenatal diagnosis of the inherited haemoglobinopathies. The characteristics of programmes based on carrier screening and prenatal diagnosis ongoing in a number of at-risk Mediterranean populations have been described. The most relevant and common aspects of these programmes are the continuous educational campaign directed to the population at large, the voluntary basis and non-directive counselling. The target population has been most commonly couples before or after marriage. The vast majority of couples counselled accepted prenatal diagnosis. All programmes have encountered a high degree of success as indicated by the marked reduction in the birth rate of infants with thalassaemia major. No significant adverse effects have been reported. A programme with similar characteristics and for which the preliminary results are encouraging, is operating for sickle cell anaemia in the Cuban population. In a population with high frequency of hydrops fetalis, screening for deletion alpha-thalassaemia is recommended to prevent the negative effects on a pregnant woman of the presence of an hydropic fetus. Thalassaemia carrier screening is now carried out by automatic red cell indices and HbA2 determination. Definition of atypical cases may require iron studies, globin chain synthesis determination and/or alpha, beta- and delta-globin gene analysis. Identification of the carrier state is followed by definition of the mutation on enzymatically amplified DNA. Known mutations may be detected by restriction endonuclease analysis, non-denaturing polyacrylamide gel electrophoresis, allele-specific primers or allele-specific probes. The most promising procedures, which are also amenable to complete automation are reverse oligonucleotide hybridization and primer-specific amplification. Unknown mutations are defined by denaturing gradient gel electrophoresis, single-strand conformation polymorphism analysis, and chemical mismatch cleavage analysis followed by direct sequencing. The same methods on enzymatically amplified chorionic villus DNA are used for prenatal diagnosis. The potential pitfall resulting from maternal contamination can be avoided by careful dissection of the maternal decidua from the chorion and by the simultaneous amplification of a suitable polymorphism.

DNA polymorphisms associated with Hb D-Los Angeles [beta 121(GH4)Glu-->Gln] in southern Italy

We detected Hb D-Los Angeles [beta 121(GH4)Glu-->Gln], the most common hemoglobin variant after Hb S and Hb Lepore-Boston, in six unrelated families in Southern Italy. Ten patients were studied; eight patients were heterozygotes and two were compound heterozygotes for the hemoglobin variant and the beta-thalassemia codon 39 (C-->T) nonsense mutation. The beta-globin gene sequence was characterized by polymerase chain reaction direct sequencing; restriction fragment length polymorphisms were defined by Southern blot analysis. The gene variant, due to the GAA-->CAA substitution at codon 121, was found in association with the 5' subhaplotype [+ - - - -] and the beta-globin gene framework 1; in addition, it was found to be associated with the absence of Ava II/phi beta and Xmn I/5'G gamma, and with the presence of Hpa I/3' beta. This restriction fragment length polymorphism haplotype is common in the Mediterranean area as well as in other populations. The findings are equally compatible with an independent origin in the Mediterranean area or with origin in Asia and subsequent spread to Italy.

Hb F in sickle cell anemia

We have reviewed the methodology for an accurate quantitation of Hb F in the blood of patients with sickle cell anemia, values observed in hundreds of patients of different (racial or ethnic) backgrounds and with differences in severity of the disease, and the various factors that affect the level of Hb F. The latter include sex, age, genetic background or chromosomal haplotypes, variations in the sequences of the locus control region(s) 5' to the epsilon-globin gene, and the presence of an alpha chain deficiency or alpha-thalassemia. Finally, a few remarks about agents effective in increasing the in vivo Hb F synthesis are also included.

Postnatal changes in the quantities of globin chains and hemoglobin types in two babies with Hb H disease

We have studied two babies with Hb H disease from birth to about six months of age and analyzed the changes in the relative quantities of the five globin chains (zeta, alpha, beta, G gamma, A gamma) and the four hemoglobins (Hb F, Hb A, Hb Bart's, Hb H) using different high performance liquid chromatography procedures. The types of Hb H disease were -(SEA)/-alpha(3.7 kb) and -(Fil)/-alpha(3.7 kb); the larger -(Fil) deletion includes the functional zeta 2-globin gene, explaining the higher zeta chain level in the baby with the -(SEA)/-alpha(3.7 kb) type. The functional hemoglobin level at birth (Hb A+Hb F) was 11 to 12 g/dl with 3 to 4 g/dl Hb Bart's (gamma 4). Only 5% of the "fast-moving" hemoglobin was Hb H (beta 4). The level of Hb F at birth was low (less than 50% of the total Hb A+Hb F). After birth, the alpha and gamma chain production decreases rapidly resulting in a severe anemia (total functional hemoglobin approximately 7 g/dl) at 30 to 60 days postnatally, improving gradually to 8.5-9.5 g/dl at age of three months. The preferential formation of Hb A over Hb F at birth, and presumably prenatally, has the advantage that the level of the highly unstable Hb H is kept low; it also results in low levels of Hb F impairing the oxygen transfer capability of the fetal blood.

Human alpha-globin gene expression is silenced by terminal truncation of chromosome 16p beginning immediately 3' of the zeta-globin gene

The high level expression of the human alpha-globin genes in erythroid tissue appears to require a set of DNaseI hypersensitive sites located upstream of the human alpha-globin gene cluster. These sequences, termed the locus control region (LCR), include two erythroid specific and a number of less restricted DNaseI hypersensitive sites. In this report we describe an individual with alpha-thalassemia associated with a truncation of the short arm of chromosome 16 that removes the LCR region and inactivates the adjacent intact alpha-globin genes. This genetic study supports the critical role of the LCR in the transcriptional activation of the human alpha-globin gene cluster and substantiates the importance of LCR deletions in the etiology of alpha-thalassemia.

ααααanti-3.7 type II: a new α-globin gene rearrangement suggesting that the α-globin gene duplication could be caused by intrachromosomal recombination

We report here a new human alpha-globin gene rearrangement carrying the two normal, alpha 2 and alpha 1, and two hybrid, alpha 1/alpha 2, globin genes in the order 5'-alpha 2-alpha 1/alpha 2-alpha 1/alpha 2-alpha 1-3'. Both the hybrid genes, subtyped with ApaI and RsaI restriction enzymes, were found to be of the uncommon anti 3.7 type II. The hybrid genes were expressed at the biosynthetic level and their interaction with the beta-thalassaemia IVS 1 nt 1 G----A mutation caused thalassaemia intermedia. We also report a case of an alpha alpha alpha-globin gene rearrangement in the twin of one of the alpha alpha alpha alpha-globin gene carriers; the duplicated gene was of the anti 4.2 type and was associated with the absence of RsaI polymorphism. The singular finding of an alpha alpha alpha alpha-anti 3.7 cluster with two identical rare hybrid genes suggests that the reciprocal unequal recombination causing the alpha-globin gene rearrangements could be of the intrachromosomal rather than the interchromosomal type.

A new gene deletion involving the alpha 2-, alpha 1-, and theta 1-globin genes in a black family with Hb H disease

A new deletion of approximately 8.5 kb that includes the alpha 2-, alpha 1-, and theta 1-globin genes was detected in a father and newborn son of a black family from Georgia. In the newborn baby the chromosome with the deletion occurred together with a rightward (-alpha 3.7) deletion chromosome. The resulting Hb H disease was detected at birth by the high level of Hb Bart's; a moderate anemia with severe microcytosis and hypochromia was present at the age of 5 months. A review of cord blood testing results for a period of over 20 years, involving at least 200,000 black newborns, indicated that this baby was the first with a level of Hb Bart's in excess of 10-15%; this underscores the rarity of alpha-thalassemia-1 in this population.

The nondeletional types of Hb H disease in Guangxi

Three primers were designed, one specific for alpha 1-globin DNA, a second for alpha 2-globin DNA, and a third that is common for both alpha 1- and alpha 2-globin DNA. These three primers can be applied for selective amplification of the two globin DNA fragments, which is useful for identification of nondeletional types of Hb H disease. Fifty-nine DNA samples of Hb H patients from Guangxi were studied by selective amplification, and 27 cases (45.8%) were confirmed as nondeletional types. Of these, 22 (81.5%) had the Hb Constant Spring (CS) mutation and one had the Hb Quong Sze (QS) mutation; both were identified by hybridization with synthesized oligonucleotide probes. Nondeletional Hb H disease in Guangxi seems to be more severe than the deletional types. The average hemoglobin level of the nondeletional Hb H/CS (--/alpha alpha) is 6.8 g/dl, which is lower than that of the deletional types (7.9 g/dl), while the levels of Hb H and Hb Bart's were much higher in the patients with Hb H/CS than in those with the deletional types.

A novel alpha-thalassemia-2 (-2.7-kb) observed in a Chinese patient with Hb H disease

We describe a newly detected alpha-thalassemia-2 (alpha-thal-2) deletion characterized by a small -2.7-kb deletion involving the alpha 1 globin gene. This deletion has thus far been observed in only one Chinese subject with Hb H disease.