Hb F-Veleta or alpha 2 G gamma(2)40(C6)Arg-->Gly.
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Adult↗
Biomedical subjects
T H Huisman
Publications and source records attributed to T H Huisman.
Alpha-Thalassemia and fetal hemoglobin.
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Adolescent↗
The -158 (C-->T) promoter mutation is responsible for the increased transcription of the 3' gamma gene in the Atlanta type of hereditary persistence of fetal hemoglobin.
The Atlanta type of hereditary persistence of fetal hemoglobin (HPFH) is characterized by a mild elevation of Hb F (2% to 5% in heterozygotes), almost exclusively of the G gamma type (more than 90%). Gene-mapping analysis has identified this condition as a -G gamma-G gamma- arrangement with the -158 (C-->T) substitution in the promoters of both G gamma genes. We have reevaluated this condition in members of two families. Sequence analysis identified only two changes in the 3' gamma gene as compared with the A gamma gene from a chromosome with haplotype no. 3 (or Senegal), namely the -158 (C-->T) promoter mutation and the C-->G change in codon (CD) 136, which accounts for the -G gamma-G gamma- phenotype. The absence of any other nucleotide (nt) substitution provides genetic evidence that the -158 (C-->T) change is primarily responsible for the elevated Hb F levels associated with this condition. A quantitative reverse transcription/polymerase chain reaction (RT/PCR) procedure, presented in detail in this report, was developed to determine the effect of this mutation on the transcription of individual gamma genes in four individuals with the Atlanta type of HPFH. Both gamma-globin genes, ie, the (5') G gamma and the (3') G gamma-Atlanta genes of the Atlanta type of HPFH chromosome, expressed elevated amounts of transcripts, which were present in nearly equal amounts. This shows that the -158 (C-->T) mutation exerts its effect on the transcriptional rate of the gene with which it is associated.
Adolescent↗
The in vivo expression of the globin genes of the beta cistron in gamma-, delta-, and delta beta-thalassemia heterozygotes.
There is considerable evidence suggesting that the switch from gamma to delta and beta chain production after birth is due, in part, to silencing of the gamma genes by stage-specific factors which bind to their promoters and to the competition from the adult (delta and beta) genes for a common enhancer element located in the locus control region. As a consequence one can expect that the increased Hb F production in adults with hereditary persistence of fetal hemoglobin or delta beta-thalassemia is directed mainly by gamma-globin genes in cis to the deletion(s) responsible for these conditions. Here we review data on heterozygotes with gamma-, delta- or delta beta-thalassemia, who also had an A gamma T mutation, in cis or in trans, which was used as a marker of gamma gene expression. The results show that a deletion affecting adult beta genes favors the expression of gamma genes in cis, while the deletion of a single gamma gene does not affect the expression of the beta gene in cis but leads to a faster gamma-->beta switch postnatally.
Gene Deletion↗
A novel deletion of approximately 27 kb including the beta-globin gene and the locus control region 3'HS-1 regulatory sequence: beta zero-thalassemia or hereditary persistence of fetal hemoglobin?
A novel deletion of approximately 27 kb with the 5' breakpoint 1.5 to 2.2 kb upstream of the beta-globin gene, and the 3' breakpoint approximately 24 kb downstream of the beta-globin gene, has been found in five members of two families from Southeast Asia (Vietnam and Cambodia). Six members of another family from China, previously reported from our laboratory, have also been shown to carry this deletion. The patients presented with mild hypochromia and microcytosis, a hemoglobin (Hb) A2 level of approximately 4.0%, and a markedly increased, heterocellularly distributed, Hb F level (14.0 to 26.0%). In vitro globin-chain synthesis showed a mild imbalance with appreciable gamma-chain compensation (alpha/beta + gamma ratio of 1.46). The 3' end of this deletion includes the 3'HS-1, and we hypothesize that removal of this region results in the loss of its gamma-globin gene-silencing effect, which causes a markedly elevated Hb F level with a modest increase in Hb A2 levels, unlike the situation in other deletional beta zero-thalassemias. The possible influence of particular sequence variations in the locus control region 5'HS-2 and the G gamma promoter, present on the chromosome with this deletion, on the overall gamma-globin gene should also be considered.
Adolescent↗
Polymorphic pattern of the (AT)X(T)Y motif at -530 5' to the beta-globin gene in over 40 patients homozygous for various beta-thalassemia mutations.
Nucleotide sequence analysis of the 5' beta-globin gene flanking region has been carried out for numerous homozygous beta-thalassemia patients with different mutations and of various ethnic backgrounds. Four different rearrangements were found associated with numerous beta-thalassemia mutations. The (AT)X(T)Y repeat motif at -530 showed polymorphic patterns among these patients as follows: All ten IVS-II-1 (G-->A) chromosomes and the two with the -87 (C-->G) mutation are associated with the (AT)9(T)5 rearrangement, while the 30 IVS-I-6 (T-->C), the 16 codon 39 (C-->T), the six codon 8 (-AA) chromosomes, and 12 chromosomes with different promoter mutations had the (AT)7(T)7 motif. Six chromosomes with the promoter mutation at position -29 (A-->G) had the (AT)8(T)6 motif, while an (AT)8(T)4 motif appears characteristic for two IVS-I-5 (G-->A and G-->T). No direct association between any of the (AT)X(T)Y arrangements and an increased gamma gene expression [G gamma and fetal hemoglobin (Hb F)] levels could be demonstrated, suggesting that variations in the (AT)X(T)Y motif are common polymorphisms.
Adult↗
Quantities of alpha Q chain variants in heterozygotes with and without a concomitant beta-thalassemia trait.
We have analyzed the quantities of alpha x chain-containing hemoglobins (alpha 2 x beta 2 and alpha 2 x delta 2) in 14 heterozygotes for Hb Q-India [alpha 64(E13)Asp-->His] or Hb Q-Thailand [alpha 74(EF3)Asp-->His]; both amino acid replacements are the result of mutations in the alpha 1-globin gene. Five of these persons (three with Hb Q-India and two with Hb Q-Thailand) had an additional beta(0)-thalassemia heterozygosity. The average quantities for Hb Q + Hb Q2 in the four groups were 17.2% (alpha alpha Q/alpha alpha; beta A/beta A), 9.5% (alpha alpha Q/alpha alpha; beta A/beta(0) Th), 26.8% (-alpha Q/alpha alpha; beta A/beta A), and 16.95% (-alpha Q/alpha alpha; beta A/beta(0) Th). These variations can best be explained by a posttranslational control mechanism; an imbalance in the alpha A, alpha Q, and beta A chain ratio will favor the alpha 2 Q beta 2 formation when an alpha-thalassemia is present and will reduce its formation in the presence of a beta-thalassemia heterozygosity.
Adolescent↗
Two different mutations in codon 68 are observed in Hb G-Philadelphia heterozygotes.
Through sequencing of amplified DNA containing the appropriate alpha-globin genes we have identified the base substitution leading to the formation of Hb G-Philadelphia [alpha 68(E17)Asn Lys]. Three subjects (approximately 25% Hb G) had an ACC AAA change at codon 68 of the alpha 2-globin gene; the chromosome with this mutation carried two alpha genes (alpha alpha). Six subjects (approximately 33% Hb G) had an AAC AAG change at the same codon of the alpha 2 alpha 1 hybrid gene on a chromosome with the 3.7 kb deletion (-alpha 3.7). These results indicate two independent mutations which likely occurred in different populations; increase in the level of Hb G is primarily dependent upon the loss of one or more alpha-globin genes.
Adult↗
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.
Base Sequence↗
Compound heterozygosity for two alpha-globin gene defects, Hb Taybe (alpha 1; 38 or 39 minus Thr) and a poly A mutation (alpha 2; AATAAA-->AATAAG), results in a severe hemolytic anemia.
We have identified two alpha-globin gene variations in an Arabian male with severe hemolytic disease through sequencing of amplified DNA of his alpha 2- and alpha 1-globin genes. One of the abnormalities involves a CAC (ACC or CCA) deletion between codons 36 and 41 of the alpha 1-globin gene. This leads to the synthesis of an abnormal alpha chain with one instead of two threonine residues at positions 38-39 and to the formation of the unstable Hb Taybe. The second variation is a mutation located in the poly A site of the alpha 2-globin gene (AATAAA-->AATAAG) which is common among Arabian people. Family studies have shown that the two variations are located on opposite chromosomes. The hemolytic disease in this man, resembling Hb H disease, is likely the result of a severe downregulation of both alpha-globin genes on the chromosome with the alpha 2 poly A mutation, and the instability of the alpha-Taybe chain being the product of an alpha 1-globin gene; this leaves only one alpha 2-globin gene normally active.
Adult↗
Sickle cell anemia, sickle cell beta-thalassemia, and thalassemia major in Albania: characterization of mutations.
We have analyzed the hemoglobin abnormalities in nearly 50 Albanian patients with a significant hemoglobinopathy and included 37 relatives in this study. Sickle cell anemia (SS) is a common disorder; all 15 sickle cell anemia patients had the complications expected for this disease. The beta S haplotype was type 19 (Benin); alpha-thalassemia-2 was rare. Three beta-thalassemia alleles (IVS-I-110, G-->A; codon 39, C-->T; IVS-I-6, T-->C) were present in nearly 85% of the beta-thalassemia alleles; their frequencies were intermediate between those observed in the populations of neighboring countries. A few rare mutations were also found, which might have originated in India, Turkey, Macedonia, and Greece. Nearly all patients with Hb S-beta-thalassemia had the IVS-I-110 (G-->A) mutation. The frequencies of 11 beta-thalassemia mutations in 17 mostly Mediterranean countries have been reviewed.
Adolescent↗
The T-->C mutation at position +96 of the untranslated region 3' to the terminating codon of the beta-globin gene is a rare polymorphism that does not cause a beta-thalassemia as previously ascribed.
We have observed a T-->C mutation at position +96 of the untranslated region 3' to the terminating codon of the beta-globin gene in members of two Czech families and one black family. Data from initial studies suggested that this change was the cause of a beta-thalassemia, but continued analyses have provided convincing evidence that this mutation is a simple polymorphism.
Adult↗
Haemoglobin Hammersmith precludes monitoring with conventional pulse oximetry.
We report a case of a 15-yr-old North American Indian female with haemoglobin Hammersmith, scheduled for elective tonsillectomy, whose arterial oxygen saturation could not be reliably monitored perioperatively because of technical limitations of conventional dual wavelength pulse oximetry. The patient was chronically icteric. She had an atrial septal defect with a small L-->R shunt demonstrated by echocardiography. On arrival in the operating room pulse oximetry (Nellcor-Model N100) demonstrated a saturation of 45% whilst breathing room air. Her oxygen saturation increased to 60% whilst breathing 100% oxygen via a face mask. An arterial blood gas performed whilst breathing 100% oxygen revealed a PaO2 of 418 mmHg. Tonsillectomy was completed uneventfully under general anaesthesia. The pulse oximeter did not provide any clinically useful information throughout the case. In conclusion, conventional dual wavelength pulse oximeters cannot give an accurate estimate of oxygenation in patients with haemoglobin Hammersmith. Assessment of oxygenation in these patients requires alternative monitoring techniques.
Adolescent↗
Factors associated with hypochromia and microcytosis among high school students in the southeastern United States.
We studied hematologic findings in 617 apparently healthy Georgia elementary, middle, and high school students, aged 10 to 19 years, and examined the influence of several parameters (race, sex, iron status, and genetic hemoglobin [Hb] abnormalities) on hypochromia and microcytosis, with or without anemia. Fourteen students (2%) (6 male, 8 female; 4 white, 10 black) were found to be anemic (Hb < 11.8 g/dL in boys or < 11.3 g/dL in girls). Hypochromia (mean corpuscular Hb < 25 pg) with or without microcytosis (mean corpuscular volume < 78 fL) was found in 26 students (4%). Iron deficiency was the main associated factor in white students, but in blacks genetic Hb abnormalities, especially alpha-thalassemia trait, were other predisposing factors. The overall prevalence of iron deficiency (serum ferritin < or = 12 ng/mL) was 32.4% in the entire sample population, 30.5%, among blacks, and 33.2% among whites.
Adolescent↗
Alpha and beta thalassaemia among Chinese children in Guangxi Province, P.R. China: molecular and haematological characterization.
We have studied nearly 100 patients with beta-thalassaemia major and 60 patients with Hb H disease who were attending the Haematology Clinic of Guangxi Medical College. Treatment of the patients was limited and only a few patients with beta-thalassaemia major received blood transfusion(s). As a result, the severe anaemia has led to early death at 3-4 years for beta zero-thalassaemia homozygotes, and 8-12 years for beta(+)-thalassaemia homozygotes. Four beta-thalassaemia alleles are responsible for nearly 90% of all beta-thalassaemia chromosomes. This information has resulted in the initiation of a prenatal testing programme at the local level. The patients with Hb H disease maintained a haemoglobin level of 6-10 g/dl and early death was infrequently observed. The --SEA deletion was the major type of alpha-thalassemia-1, while three smaller deletions (-2.7, -3.7 and -4.2 kb) and two nondeletional alpha-thalassaemia determinants (Hbs Constant Spring and Quong Sze) were the alpha-thalassaemia-2 types.
Alleles↗
The relative levels of beta A and beta S mRNAs in Hb S heterozygotes and in patients with Hb S-beta(+)-thalassaemia or Hb S-beta(+)-HPFH combinations.
We have used a quantitative reverse transcription/polymerase chain reaction (RT/PCR) procedure to evaluate the relative amounts of beta A and beta S mRNA transcripts in eight subjects with a simple Hb S heterozygosity, in six with Hb S-beta(+)-thalassaemia (thal), and in three individuals with Hb S-beta(+)-HPFH [hereditary persistence of fetal haemoglobin (Hb)] [two with the Atlanta type and one with the G gamma-202 (C-->G) substitution]. A balanced synthesis of beta A and beta S mRNAs was observed in all Hb S heterozygotes, whereas the beta A mRNA levels were reduced to approximately 16% of that of the beta S mRNA in the six Hb S-beta(+)-thal compound heterozygotes, to approximately 43% in the two subjects with Hb S-beta(+)-HPFH (Atlanta type), and to 23.8% in the one individual with Hb S-beta(+)-HPFH [G gamma-202 (C-->G) substitution]. The higher Hb A versus Hb S levels observed in all groups of the patients studied, further confirm a post-translational control mechanism in determining the levels of Hb A and Hb S in the peripheral blood of these individuals. The procedure described here provides an accurate and easy method for studying the relative expression of particular globin genes at the transcriptional level in patients with various haemoglobinopathies.
Adolescent↗
The differences in quantities of alpha 2- and alpha 1-globin gene variants in heterozygotes.
We have identified through sequencing of amplified DNA the mutations in the alpha 2- and alpha 1-globin genes in 63 individuals with a heterozygosity for an alpha chain abnormal haemoglobin (Hb). Moreover, we developed a reverse transcription/polymerase chain reaction (RT/PCR) based procedure for the determination of the alpha 2- and alpha 1-mRNA ratio in normal individuals. The numbers of alpha 2 and alpha 1 variants were nearly the same. The average percentage of the abnormal Hb in heterozygotes with alpha 2 mutations (23.5%) was slightly higher than that in heterozygotes with alpha 1 mutations (19.7%) (stable Hbs only). These percentages correspond to a ratio of alpha 2 to alpha 1 of 1.19 to 1 at the protein level. Variations in the number of active alpha-globin genes and in the stability of the variants (greatly) affected the percentages of the abnormal protein. The average ratio between the alpha 2- and alpha 1-mRNAs in 12 normal individuals was 2.6-2.75 to 1, about as expected from published data, and 2.0 to 1 for two persons with an alpha-thalassaemia-2 (alpha-thal-2) (-3.7 kb) heterozygosity. The high relative mRNA (alpha 2) level which is about twice the relative level of the alpha 2 protein suggests a less efficient translation of the alpha 2-mRNA.
Base Sequence↗
gamma-mRNA and Hb F levels in beta-thalassaemia.
The Hb F levels in beta-thalassaemia can be affected by factors both linked and unlinked to the beta-globin gene cluster. We have recently analysed a group of patients with a homozygosity for the IVS-I-6 (T-->C) mutation, showing a wide variation in Hb F levels (2-47%) which could not be accounted for by any sequence variation within regulatory elements of the beta-globin gene cluster. In order to further investigate factors underlying this phenotypic difference we have developed a competitive reverse transcription/polymerase chain reaction procedure and used this method to determine the relative amounts of gamma- and beta-mRNAs in 10 patients with the IVS-I-6 homozygosity and 15 heterozygous parents, two IVS-I-6/delta beta-thalassaemia compound heterozygotes, five homozygotes for the beta(+) IVS-I-110 (G-->A) mutation, and in two with a homozygosity for the beta(0) codon 39 (C-->T) mutation. Three heterozygotes were also included. The percentages of gamma/(gamma(+) beta) mRNA were 10-73% in the IVS-I-6 homozygotes and < 2% to 10% in their heterozygous parents. A direct relationship existed between the level of mRNA and the % Hb F. However, the relative gamma-mRNA levels in the IVS-I-6 homozygotes were higher than their Hb F levels, indicating a possible competition between the gamma and beta transcripts for translational factors with a less efficient initiation of protein synthesis on the gamma-mRNA or a preferential survival of cells with mainly beta-globin gene expression at the post-reticulocyte stage. The gamma-mRNA levels in the two IVS-I-6/delta beta-thalassaemia compound heterozygotes were 71% and 62%, similar to their Hb F levels (63% and 59%), and averaged 82% (range 65-91%) in the five IVS-I-110 homozygotes, and 97.5% in the two codon 39 homozygotes. The correlation between these values and the % Hb F could not be evaluated because of the transfusion regimens; however, the levels of gamma-mRNA were as expected for patients with these beta-thalassaemia alleles.
Adolescent↗