Functional Activity of the Triplicated ααα4.2/ Gene Rearrangement

Function of the triplicated ααα^4.2/ gene rearrangement was assessed by measurement of W Bart's and hematological phenotype including α/β biosynthesis ratio. Increased output of α globin chains in ααα^4.2 /– compared to αα/– was found in a cord blood. In contrast, hematological phenotypes in two family members with the ααα^4.2/.—genotype were consistent with that expected in αα/–. This would suggest that the additional α gene in the ααα^4.2 / rearrangement has variable expression.     

HbH disease in Sardinia: molecular, hematological and clinical aspects.

In this study we have defined the molecular basis and correlated the clinical phenotype with the alpha-globin genotype in a large series of patients of Sardinian descent with HbH disease. The most prevalent molecular defect was the deletion of 3 alpha-globin structural genes most commonly the (--/-alpha 3.7) genotype (83.6%) and rarely the (--/-alpha 4.2) genotype (1.4%), followed in decreasing order of incidence by the combination of deletion alpha zero-thalassemia and initiation codon mutation of the alpha 2-gene (--/alpha NcoI alpha = 9.8%), deletion alpha zero-thalassemia and pentanucleotide deletion of IVS-I of the alpha 2-globin gene, (--/alpha HphI alpha = 3.3%) deletion alpha zero-thalassemia and initiation codon mutation of the alpha 1-gene (--/alpha alpha NcoI = 1.3%), a homozygous state for initiation codon mutation of the alpha 2-gene (alpha Nco alpha/alpha NcoI alpha = 0.7%). Patients with the (--/alpha thal alpha) genotypes showed severer clinical and hematological features as compared to those with the (--/-alpha) or those with the (--/alpha alpha thal) genotypes. The single patient with the (alpha Nco alpha/alpha Nco alpha) genotype had a clinical phenotype intermediate between HbH disease and the alpha-thalassemia carrier status. This heterogeneity depends on the fact that the alpha 2-globin gene produces 2-3 times alpha-globin chains than the alpha 1-gene and the single remaining alpha 1-like globin gene in the -alpha 3.7 chromosome has a compensatory increase in the alpha-globin chain output. alpha-Globin gene mapping of HbH disease patients may be useful for predicting the clinical outcome and to improve genetic counseling.     

Hematological phenotype of the double heterozygous state for alpha and beta thalassemia

In this study, we have correlated the hematological phenotype of 56 Sardinian beta o-thalassemia heterozygotes with their alpha-globin genotype as defined by restriction endonuclease mapping. We found that the coinheritance of the deletion of one alpha-globin and, more obviously, two alpha-globin genes tend to normalize the thalassemia-like hematological phenotype commonly associated with the beta o-thalassemia carrier state. On the other hand, the association of the deletion of three alpha-globin genes caused a more severe phenotype. By globin chain synthesis analysis, those beta o-thalassemia heterozygotes with the (-alpha/alpha alpha) alpha-globin genotype had less deficiency of beta-chain synthesis than did those with the normal alpha-globin genotype (alpha alpha/alpha alpha). In heterozygotes with the (-alpha/-alpha) and in those with the (--/-alpha) alpha-globin genotype the imbalance was actually reversed with a mild or marked alpha-chain synthesis excess respectively.     

T-cell receptor delta/alpha rearrangements in lymphoid neoplasms

Rearrangements within the T-cell receptor (TCR)delta/alpha locus were analyzed in a wide variety of lymphoid neoplasms by eight DNA probes specific for TCR J delta, J alpha and C alpha segments. In all 11 T- cell malignancies, rearrangement and/or deletion of TCR delta was detected irrespective of the stage of maturation of the tumor. The organization of TCR delta correlated with the phenotype of the tumor: In "prethymic" T-cell acute lymphocytic leukemia (ALL), TCR delta was the only TCR gene to be rearranged. More mature T cell malignancies expressing CD4 together with CD3 showed deletion of both alleles of TCR delta, suggestive of TCR V alpha-J alpha rearrangement. All 43 B-cell tumors expressing surface immunoglobulin (sIg), including two cases of adult B-cell ALL, had germline configuration of TCR delta/alpha. In contrast, all 17 B-cell precursor ALLs (null, common, and pre-B-cell ALLs) had rearrangement and/or deletion of TCR delta/alpha. A single case of "histiocytic" lymphoma also showed biallelic deletion of TCR delta. Oligoclonal rearrangements of Ig and TCR genes were observed in two cases of B-cell precursor ALL and in one case of T-cell lymphoblastic lymphoma. Patterns of such "aberrant" TCR rearrangement were similar to those observed in T-lineage malignancies. In particular, seven of eight cases of B-cell precursor ALL and the histiocytic lymphoma which demonstrated biallelic TCR delta deletion, (suggestive of a V alpha-J alpha rearrangement) had clonal TCR beta rearrangement. These data support the hypothesis that supposedly aberrant rearrangements of the TCR genes may follow the same developmental controls as found in T-cell differentiation, despite the lack of evidence for further commitment to the T-cell lineage. TCR delta rearrangement is a useful marker of clonality of immature T-cell tumors which may have only this gene rearranged but is not specific to the T-cell lineage.     

T cell receptor (TCR) alpha/delta locus enhancer identity and position are critical for the assembly of TCR delta and alpha variable region genes

T cell receptor (TCR) delta and alpha variable region genes are assembled from germ-line gene segments located in a single chromosomal locus in which TCR delta segments are situated between TCR alpha segments. The TCR alpha enhancer (E alpha) located at the 3' end of the TCR alpha/delta locus functions over a long chromosomal distance to promote TCR alpha rearrangement and maximal TCR delta expression; whereas the TCR delta enhancer (E delta) is located among the TCR delta segments and functions with additional element(s) to mediate TCR delta rearrangement. We used gene-targeted mutation to evaluate whether the identity of E alpha and the position of E delta are critical for the developmental stage-specific assembly of TCR delta and alpha variable region genes. Specific replacement of E alpha with E delta, the core E alpha element (E alpha C), or the Ig heavy chain intronic enhancer (iE mu), all of which promote accessibility in the context of transgenic V(D)J recombination substrates, did not promote a significant level of TCR alpha rearrangement beyond that observed in the absence of E alpha. Therefore, the identity and full complement of E alpha-binding sites are critical for promoting accessibility within the TCR alpha locus. In the absence of the endogenous E delta element, specific replacement of E alpha with E delta also did not promote TCR delta rearrangement. However, deletion of intervening TCR alpha/delta locus sequences to restore the inserted E delta to its normal chromosomal position relative to 5' sequences rescued TCR delta rearrangement. Therefore, unlike E alpha, E delta lacks ability to function over the large intervening TCR alpha locus and or E delta function requires proximity to additional upstream element(s) to promote TCR delta accessibility.     

Concomitant T-cell receptor alpha and delta gene rearrangements in individual T-cell precursors.

A debate has recently surfaced concerning the degree of precommitment attained by alpha beta and gamma delta T-cell precursors prior to T-cell receptor (TCR) gene rearrangement. It has been suggested that precursors may be precommitted to rearrange either alpha or delta genes, but not both, thus giving rise to alpha beta- and gamma delta-producing T cells, respectively. Alternatively, the precursors may be flexible with regard to potential TCR gene rearrangements. To address this controversy, the gene rearrangements among a group of T-cell hybridomas from fetal, newborn, and early postnatal mouse thymi were examined. Six probes spanning the delta and alpha loci were used in Southern blot analyses to characterize the rearrangements which occurred on homologous chromosomes in each cell. Although homologous chromosomes often rearranged in synchrony within the alpha locus, a number of hybridomas were found which had retained a delta rearrangement on one chromosome and an alpha rearrangement on the second. Results show that a precommitment by T cells to rearrange delta or alpha genes in a mutually exclusive manner is not an absolute feature of mouse thymocyte development.     

Phenotype-genotype correlation in Sicilian patients with Hb H

We studied 15 Sicilian subjects with Hb H disease correlating clinical examinations with hematological and molecular data. Seven different alpha-tha1 mutations were identified: four deletion types (--MED --CAL, -alpha3.7, -alpha4.2) and three nondeletion types (alpha(Ncol)alpha, alpha(Hph)alpha, alphaCSalpha). All the patients had a zero-gene chromosome (--MED or --CAL), while the third alpha gene was deleted (-alpha3.7, -alpha4.2) or inactive (alpha(Ncol)alpha, alpha(Hph)alpha, alphaCSalpha). In patients with the nondeletion genotype the analysis of hematological values revealed lower levels of RBC and Hb A2 and significantly higher levels of Hb H. The clinical variability was remarkable, ranging from totally asymptomatic conditions, casually diagnosed, to severe thalassemia intermedia with marked hemolytic crises, liver and spleen enlargement and the necessity for frequent transfusions. The genotype did not justify the gravity of the phenotype in every case, and the differences in clinical manifestations, also notable, are not easily explainable in subjects who apparently have the same genotype.     

Hb Agrinio [alpha29(B10)Le-->uPro (alpha2)] in combination with --(MED I). Results in a severe form of Hb H disease

We report two cases of compound heterozygote patients for the --(MED I) and Hb Agrinio [alpha29(B10)Le-->uPro (alpha2)] anomalies in two unrelated Greek Cypriot families. The first patient had a serious form of Hb H disease and died at the age of 21 due to complications arising during an operation. The second patient showed a severe hematological picture and has been regularly transfused since an early age. This patient exhibits bone abnormalities as well as hepatosplenomegaly. The severity of these two incidences emphasizes the need for the inclusion of a screening test for the --(MED I)/alpha(Agrinio)alpha genotype among those already offered during prenatal diagnosis. Two homozygotes, as well as a number of simple, compound, and double heterozygotes for Hb Agrinio have been identified in Cyprus and their hematological indices are presented.     

The interaction of anti 3.7 type quadruplicated alpha-globin genes and heterozygous beta-thalassemia

Human alpha-globin gene mapping was carried out using a variety of restriction endonucleases (Bgl II, Bam HI, Hind III, Eco RI, Hpa I, Pvu II and Rsa I) on members of a family from El Salvador and a female from Hawaii, of Chinese descent, whose hematological and clinical parameters were those of beta-thalassemia intermedia. Southern blot DNA analysis showed that the beta-thalassemia intermedia patients from the above two families had the same anti 3.7 type quadruplicated alpha-genes on the one chromosome, and that they had the alpha genotype alpha 2, alpha 1 alpha 2, alpha 1 alpha 2, alpha 1/alpha 2, alpha 1. The alpha/beta globin synthesis ratios of the three affected Salvadoran patients were around 2.5, and the affected Hawaiian patient was 2.9. These ratios strongly suggest that the additional alpha-genes in the anti 3.7 type rearrangement are biologically active, thus accounting for the severity of the heterozygous beta-thalassemia observed among these patients.     

Hb Suan-Dok [alpha109(G16)Leu-->Arg; CTG-->CGG (alpha2)] described in a patient of African ancestry

A 58-year-old Black female from Cura?ao (West Indies) was recently referred to our Laboratory for a persistent microcytic hypochromic anemia. An analysis 13 years earlier had shown no abnormal hemoglobin (Hb) fractions and a balanced beta/alpha synthetic ratio. The hematological indices were again compatible with thalassemia and no abnormal fractions were observed on electrophoresis or high-performance liquid chromatography (HPLC). None of the seven common alpha-thalassemia (thal) deletion defects were present. Direct sequencing of the alpha2 gene revealed a CTG-->CGG single base substitution at codon 109. This mutation was previously described in a Thai patient (Hb Suan-Dok), inducing Hb H disease in association with a - -(SEA) allele. In contrast with earlier reports we were unable to identify any native Hb fraction. The balanced beta/alpha ratio indicated that alpha2-Suan-Dok is formed but does not form tetramer formation unless alpha-thal is present.     

Molecular and clinical features of Hb H disease in northern Thailand

Clinical assessment, hematological studies and molecular analyses were performed in 102 pediatric patients with Hb H disease in northern Thailand. A total of six mutations of the alpha-globin gene, which produced five genotypes, were detected. All patients had an alpha(0)-thalassemia (thal) deletion on one chromosome 16. All but one of these were of the South East Asian type (--SEA); one patient had the THAI deletion (--THAI). The deletional alpha(+)-thal mutations comprised 3.7 kb (-alpha(3.70) and 4.2 kb (-alpha(4.2)) deletions which were found in 34 (33.3%) and 10 (9.8%) alleles, respectively. The nondeletional alpha(+)-thal mutations comprised 55 (53.9%) alleles of Hb Constant Spring (CS) (alpha142, TAA --> CAA) and three (2.9%) alleles of Hb Pakse (alpha142, TAA --> TAT). Six patients with Hb H-CS disease also carried Hb E (AEBart's CS disease). The clinical features were diverse and the nondeletional genotypes were associated with more severe clinical and hematological features, including younger age at presentation, larger size of liver and spleen, lower hemoglobin (Hb) level, and higher transfusion requirements. The high proportion of nondeletional Hb H disease observed in this study was inconsistent with the previously reported gene frequencies of alpha-thal in the region, suggesting that many deletional Hb H patients with milder symptoms may have escaped recognition.     

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.     

Prevalence of -alpha(3.7) and alpha alpha alpha(anti3.7) alleles in sickle cell trait and beta-thalassemia patients in Mexico

The aim of this study was to determine the frequency of alpha-globin gene mutations in three groups of Mexican unrelated individuals. The first two groups were normal and sickle cell trait individuals from the Costa Chica region, a place with a 12.8% frequency of HbS carriers, and the third group comprised of Mexican mestizo patients with beta-thalassemia. We searched for -alpha(3.7) and -alpha(4.2) alpha(+)-thalassemia deletion alleles, as well as the alpha alpha alpha(anti3.7) triplication through long-gap PCR. The alleles -alpha(3.7) and alpha alpha alpha(anti3.7) were found in the heterozygote state only; 19% of the normal subjects had the -alpha(3.7) allele, and 2% showed the alpha alpha alpha(anti3.7) allele. In individuals with the sickle cell trait, 17% had the -alpha(3.7) deletion, and the alpha alpha alpha(anti3.7) triplication was observed in 3% of these individuals. We revealed that 16% of the subjects with beta-thalassemia showed the -alpha(3.7) deletion and 28% the alpha alpha alpha(anti3.7) triplication. The -alpha(4.2) deletion was not detected in any individual. The frequency of the -alpha(3.7) allele was roughly the same in the three groups studied; this can be explained by the fact that the three groups have common genes from Africa and the Mediterranean, where a high prevalence of alpha(+)-thalassemia has been observed. To our knowledge, the frequency of alpha alpha alpha(anti3.7) triplication observed in the Mexican beta-thalassemia patients is the highest reported. As the -alpha(3.7) and alpha alpha alpha(anti3.7) alleles are very common in our selected populations, we believe that there is a need to investigate systematically the alpha-globin gene mutations in all hemoglobinopathies in the Mexican population.     

Role for rearranged variable gene segments in directing secondary T cell receptor alpha recombination

During the recombination of variable (V) and joining (J) gene segments at the T cell receptor alpha locus, a ValphaJalpha joint resulting from primary rearrangement can be replaced by subsequent rounds of secondary rearrangement that use progressively more 5' Valpha segments and progressively more 3' Jalpha segments. To understand the mechanisms that target secondary T cell receptor alpha recombination, we studied the behavior of a T cell receptor alpha allele (HYalpha) engineered to mimic a natural primary rearrangement of TRAV17 to Jalpha57. The introduced ValphaJalpha segment was shown to provide chromatin accessibility to Jalpha segments situated within several kilobases downstream and to suppress germ-line Jalpha promoter activity and accessibility at greater distances. As a consequence, the ValphaJalpha segment directed secondary recombination events to a subset of Jalpha segments immediately downstream from the primary rearrangement. The data provide the mechanistic basis for a model of primary and secondary T cell receptor alpha recombination in which recombination events progress in multiple small steps down the Jalpha array.     

Hb Zoetermeer: a new mutation on the alpha2 gene inducing an Ala-->Ser substitution at codon 21 is possibly associated with a mild thalassemic phenotype

A 52-year-old Dutch male was referred to our laboratory for hemoglobinopathy analysis because of persistent microcytic hypochromic parameters and moderate erythrocytosis in the absence of iron deficiency. The hemoglobin (Hb) pattern was normal and breakpoint polymerase chain reaction (PCR) excluded the six common deletion defects of the alpha gene cluster. Direct sequencing revealed a GCT-->TCT transversion at codon 21 of the alpha2 gene generating an Ala-->Ser single amino acid substitution. The hematological parameters observed in the presence of this mutation are consistent with a compensated heterozygous alpha(+)-thalassemia (thal). However, the neutral mutation and the external position of the residue do not explain an association with this phenotype. Nevertheless, we cannot exclude that the mutation could induce the observed hematological abnormalities and could eventually be considered as a mutation associated with a mild alpha-thalassemic phenotype.     

Hb Kurosaki [alpha7(A5)Lys -->Glu (AAG --> GAG)]: an alpha2-globin gene mutation found in Thailand

Hb Kurosaki [alpha 7(A5)Lys --> Glu (AAG --> GAG)], has been found for the first time in Thailand. The 30-year-old Thai male had a normal hematological profile at the steady state, but showed an abnormal hemoglobin (Hb) present at a level of 28%. Protein characterization was performed by automated sequencer analysis of the abnormal alpha-globin chain and amino acid analysis of the abnormal alphaT-1,2 peptide. Direct DNA sequence analysis of selectively amplified segments of the alpha1 and alpha2 genes showed that codon 7 of the alpha2-globin gene was heterozygous for AAG (Lys) and GAG (Glu). This was confirmed by restriction endonuclease digestion with Eco31I.     

Proportion of hemoglobin G Philadelphia (alpha 268 Asn leads to Lys beta 2) in heterozygotes is determined by alpha-globin gene deletions.

In humans the alpha-globin genes are duplicated and closely linked. Whereas individuals heterozygous for most alpha-chain mutations possess approximately 25% abnormal hemoglobin, heterozygotes for the alpha-chain variant Hb G Philadelphia synthesize either 33% or 50% Hb G. Both variable gene dosage and interaction with alpha-thalassemia have been proposed to explain this observation. To differentiate between these models, we have performed restriction endonuclease mapping and hematological studies on individuals with Hb G from four families. In every case the alpha G locus was carried on an EcoRI or EcoRI + BamHI fragment approximately 4 kilobases shorter than that bearing the two linked alpha A loci of hematologically normal individuals. Bgl II digestion revealed that the alpha G gene is the only alpha locus on the affected chromosome. Erythrocyte indices and alpha/beta synthesis ratios indicated that the alpha G chromosome confers alpha-thalassemia. In addition to the alpha G gene, subjects who synthesized 33% Hb G possessed two alpha A genes on the homologous chromosome and exhibited the mild form of alpha-thalassemia trait ("silent carrier"). Subjects who synthesized 50% Hb G possessed a single alpha A gene trans to the alpha G locus and displayed the more pronounced form of alpha-thalassemia trait. One subject, who synthesized 100% alpha G chains and had Hb G-Hb H disease, was found to have a single nonfunctional alpha gene trans to the alpha G gene. Thus the proportion of Hb G synthesized by heterozygotes is determined by interaction with alpha-globin gene deletions cis and trans to the alpha G locus.     

Compound heterozygosity for two genotypes of alpha-thalassemia-2: hematological, biosynthetic and DNA studies

Hemoglobin and DNA gene analyses were carried out in two Black Canadian families. In Family Q, both the parents and the brother were found to be heterozygotes for alpha-thalassemia-2 with the following alpha-genotypes: -alpha 3.7/alpha alpha, -alpha 4.2/alpha alpha and -alpha 4.2/alpha alpha, respectively. In Family C, the mother was found to be a homozygote for alpha-thalassemia-2 with the alpha-genotype of -alpha 3.7/-alpha 3.7. In both families, the propositi were compound heterozygotes for alpha-thalassemia-2 with the alpha-genotype of -alpha 3.7/-alpha 4.2. The propositus in Family C was also a sickle cell trait carrier. The usefulness of DNA gene analyses in family studies of hemoglobinopathy was discussed.     

Recombinant interferon alpha can induce rearrangement of T-cell antigen receptor alpha-chain genes and maturation to cytotoxicity in T-lymphocyte clones in vitro.

T-cell receptor genes are found in the germ-line configuration as well as in rearranged forms, as detected in T lymphocytes by different patterns in Southern blot analysis. We have recently shown that cytotoxic T-lymphocyte (CTL) "precursor" clones, in which rearrangements are not detected in the gene encoding the T-cell receptor alpha-chain (TCRA), acquire specific lytic function induced by treatment with recombinant interferon alpha or gamma. We now report that, coincident with the acquisition of cytotoxic function by the precursor CTL clone; recombinant interferon alpha appears to induce a rearrangement of TCRA. In addition, in a mature CTL clone (i.e., one already showing lytic function) in which one TCRA allele is rearranged, treatment with recombinant interferon alpha appears to induce a new rearrangement of a TCRA gene.