Evidence for multiple structural genes for the gamma-chain of human fetal hemoglobin in hereditary persistence of fetal hemoglobin

The gamma-chain heterogeneity of haemoglobin F in German infants

gamma-chain heterogeneity of haemoglobin F was studied in German full-term and preterm infants up to 12 months old. The A gamma T-gene frequency calculated was about 19%. In most cases with A gamma I-/A gamma T-chain heterogeneity A gamma I-chains predominated over A gamma T-chains. There was no difference between infants with or without the A gamma T-chain concerning haemoglobin F-concentration, F-cell percentage or G gamma-chain percentage. The G gamma-chains accounted for 69.2% +/- 3.3% (SD) of the total gamma-chains in full-term newborn infants with a decrease to 42.5% +/- 6.5% during the first 6 months. Comparison of the G gamma-chain decrease in preterm and in full-term newborn infants suggests a more pronounced decrease during extrauterine life than during the intrauterine course.

The Greek A gamma beta+-HPFH observed in a large black family

Several members of a Black family with a heterozygosity for an A gamma beta+-HPFH, shown in 1969 to have relatively low levels of Hb F and a low glycine to alanine ratio in the gamma chain of this Hb F, were reinvestigated. Thirteen of 30 available family members in two generations had the heterozygous form of this condition, which was characterized by a decreased level of Hb A2, an average Hb FAD value of 13.3%, an equal distribution of Hb F over the red cells, and normal hematological values. The gamma chain composition of isolated Hb F was determined by reversed phase high performance liquid chromatography for all 13 heterozygotes and showed an average A gamma value of 84.5%. Hybridization with synthetic oligonucleotides, specific for normal and mutant sequences at positions 111-129 5' to the A gamma globin gene, identified a G----A base substitution at position 117, similar to that seen in subjects with the Greek A gamma-HPFH. Our data support conclusions by others that this replacement is causative of the increased A gamma chain synthesis in this condition. Haplotype analysis supported the suggestion that the G----A substitution occurred as an independent event in this Black family.

Heterogeneity in the molecular basis of three types of hereditary persistence of fetal hemoglobin and the relative synthesis of the G gamma and A gamma types of gamma chain

Restriction endonuclease analyses of DNA from one Black G gamma A gamma-HPFH homozygote and four Black and one Indian G gamma A gamma-HPFH heterozygotes have identified three different HPFH types which are the result of large deletions including the delta and beta genes. Two of the types are comparable to those characterized previously, but the third, which is present in the Indian heterozygote, shows a distinct difference in the size of the deletion. The 5' end point of the deletion in this type III G gamma A gamma-HPFH extends 0.5-1.0 kb beyond the 5' end point of one of the Black types of HPFH (type I). Each of the three types is associated with a distinct ratio between the G gamma and the A gamma chains, an observation supported by family data. The highest ratio is found in the heterozygote with the Indian type III G gamma A gamma-HPFH, with 69.3% G gamma chains, while the averages for the other types were 50.7% G gamma (type I) and 32.3% G gamma (type II).

Hemoglobin abnormalities in a black family with HB S, hereditary persistence of HB F, and a gamma chain variant; a reevaluation through gene mapping

Members of a Black family from Georgia who were investigated for the first time in 1960 and several times thereafter were reinvestigated through DNA restriction endonuclease analyses and haplotyping, while the gamma chain heterogeneity of the Hb F was reevaluated using a newly developed HPLC procedure. Four different abnormalities were present. (a) Heterozygosity for G gamma A gamma-HPFH type II characterized by a large deletion involving the delta and beta globin genes with a 5' end within the psi beta gene. (b) Heterozygosity for an -epsilon-G gamma-G gamma-psi beta-delta-beta S-chromosome, thus carrying a beta S globin gene and two G gamma genes instead of one G gamma and one A gamma gene. (c) Heterozygosity for an -epsilon-G gamma-A gamma T-psi beta-delta-beta S-chromosome, carrying the beta S globin gene and an allele of the A gamma (or A gamma I) gene. These three chromosomes occurred in combination with each other, resulting in SS and S-HPFH conditions, and with a normal -epsilon-G gamma-A gamma-psi beta-delta-beta A-chromosome resulting in the HPFH and Hb S heterozygosities. The presence of the -G gamma-G gamma- and -G gamma-A gamma T-chromosomes in the one SS patient was responsible for the high G gamma value (average 75%), 25% A gamma T chain, and for the absence of the A gamma I chain. (d) An alpha-thalassemia-2 heterozygosity in one member.

Gamma-chain heterogeneity of fetal hemoglobin in nonblack beta- and delta beta- thalassemia and HPFH heterozygotes and homozygotes

The fetal hemoblobin (Hb F) of a few hundred nonblack patients with a heterozygosity or homozygosity for β‐thalassemia (β‐thal), δβ‐thalassemia (δβ‐thal), and some forms of the hereditary persistence of Hb F (HPFH) was isolated by DEAE‐cellulose chromatography and further characterized by high‐pressure liquid chromatography. Quantitative data for the three types of γ chain (AγT, AγI, and G‐γ) were compared with those obtained for the Hb F from black patients with similar conditions.

The Gγ chain levels in nonblack β‐thal heterozygotes varied greatly and did not fall into two distinct groups with high or low levels, as has been observed in blacks. The level of the AγT chain in AγT heterozygotes did not differ significantly when this anomaly was in cis or in trans to the β‐thal determinant. Beta‐thalassemia homozygotes from Turkey and Yugoslavia, had Gγ values varying between 40% and 80%. Only 13 of 34 patients carried the AγT gene. Nine were AγT heterozygotes with an AγT/total Aγ level averaging 39% and four were AγT homozygotes.

The Gγ chain levels in nonblack δβ‐thal heterozygotes varied between 28% and 46%. An additional AγT chain heterozygosity in cis to the δβ‐thal determinant demonstrated that over 90% of the γ chains is produced by genes in cis to this anomaly. Analyses of members of two relatively large families with β‐thal, δβ‐thal, and the AγT chain heterozygosities and homozygosities occurring in different combinations allowed a more or less quantitative evaluation of the production of γ‐chain genes in cis or in trans to either of the two types of thalassemia determinants. Such calculations were possible both in simple heterozygotes and in persons with the β‐δβ‐thalassemia condition.

Greek (A gamma) variant of hereditary persistence of fetal haemoglobin: globin gene organization and studies of expression of fetal haemoglobins in clonal erythroid cultures

Individuals heterozygous for the Greek (A gamma) variant of hereditary persistence of fetal haemoglobin (HPFH) synthesize Hb F whose gamma-globin chains are predominantly of the A gamma type. DNA obtained from Greek HPFH heterozygotes was used to test for abnormalities in the organization of non alpha-globin genes. In addition, gamma- and beta-globin expression was studied in BFUe cultures. Restriction endonuclease mapping showed that the G gamma, delta and beta genes in cis to the Greek HPFH determinant are intact. Overproduction of gamma-globin chains synthesis was observed in the BFUe cultures. A significant portion of the gamma chain synthesis was of the G gamma type, suggesting that the G gamma genes cis and trans to the HPFH chromosome are active in culture. DNA mapping data indicate that in contrast to G gamma A gamma HPFH and the G gamma (delta beta) thalassaemia, the Greek (A gamma) HPFH is not due to a large deletion in the non-alpha globin gene region. It is possible that the anomaly may result either from a small deletion or point mutation which influences non alpha-globin transcription. The in vitro synthesis data suggest that the low level of G gamma-globin chain synthesis in vivo is not the result of transcriptional inactivation of the G gamma gene, since this gene appears to be expressed in erythroid cell cultures. We speculate that the genetic lesion in Greek (A gamma) HPFH is in regulatory sequences which control the level of G gamma and A gamma expression during development.

The use of globin chain electrophoresis in polyacrylamide gels for the quantitation of the G gamma to A gamma ratio in fetal hemoglobin

Polyacrylamide gel electrophoresis (PAGE) in the presence of urea, acid, and Triton X-100 was used for determination of the G gamma to A gamma ratio in human Hb F. The data compared most favourable with results obtained by a HPLC procedure and by a chemical procedure. Moreover, its accuracy and reproducibility was determined. The presence of Hb A2 in a sample with Hb F level below 10% interferes with the determination because of the nearly identical electrophoretic mobilities of the delta and G gamma chains. Thus, the removal of Hb A2 is required. Samples free fo Hb A2 but with a Hb F level as low as 2% can be analyzed with an accuracy of about 5%. The PAGE method has been applied to the Hb F of 63 subjects with beta thalassemia and related conditions, and the results of these analyses are included in this communication.

Clinical implications of recent advances in hemoglobin disorders

The greater availability of sophisticated diagnostic procedures has led to the discovery of more than 350 abnormal human hemoglobins. Whereas most are clinically silent, in a sizeable number of variants, function anomalies and disease states. Their more clinically relevant aspects are discussed.

Hemoglobin F in beta thalassemia and related conditions

Further examination of the Hb F in beta thalassemia has substantiated earlier conclusions that the Hb F of heterozygotes has a bimodal distribution of the G gamma to A gamma ratio whereas that of homozygotes does not. Although the T gamma chain is present in the Hb F of beta thalassemia and delta beta thalassemia, it occurs also in cord blood Hb F without thalassemia and it, therefore, is not a special feature of the thalassemia condition. The T gamma chain has not been detected in the Hb F from HPFH. Because studies of genomic DNA have detected single G gamma and A gamma genes instead of pairs of both, some explanations of the observed heterogeneity and control of Hb F production must be reconsidered. On the other hand, experiments with DNA agree with the suggestion that a different extent of deletion leads to HPFH or to delta beta thalassemia. As further studies of genomic DNA are made, a search should be made for the means by which the G gamma to A gamma ratio is controlled at the newborn or adult level, for the manner in which the quantity of Hb F is regulated, and for the determinants that may influence the production of Hb F in trans.

The chemical heterogeneity of human hemoglobin F. Direct evidence for the existence of three types of gamma chain, the G gamma I, A gamma I, and A gamma T chains

Direct evidence is presented for the existence of three types of gamma chain of human hemoglobin F. A modification of a CM-cellulose chromatographic method has allowed the incomplete separation of these gamma chains while high pressure liquid chromatography and fingerprint analyses of tryptic peptides of zones of the isolated gamma chains, and amino acid analyses of isolated peptides were used to identify the chains. These studies have shown that the presence of a glycyl residue in position 136 (G gamma chain) is directly related to that of an isoleucyl residue in position 75 (I gamma chain), thus indicating the existence of an G gamma I chain, and that the presence of an alanyl residue in position 136 (A gamma chain) can be related to that of an isoleucyl residue in position 75, thus suggesting the existence of an A gamma I chain. When the isoleucyl residue at positive 75 is replaced by a threonyl residue, invariably it is related to the alanyl substitution at position 136 (A gamma T chain). These data support indirect evidence from case analyses and family studies which were published before, and indicate that the T gamma chain is an allele of the A gamma which should be renamed the A gamma T chain.

Heterogeneity of hemoglobin gamma chains in normal newborns and in cases of alpha and beta thalassemia

The ratio of Ggamma to Agamma was studied in 13 normal healthy newborns and in eight neonates with hydrops fetalis due to homozygous alpha-thalassemia. The findings in the normal healthy newborns agreed with those of earlier reports. In homozygous alpha-thalassemia the Ggamma and Agamma ratio appeared generally lower than in healthy control newborns, but one of the hydrops fetalis cases had a very high Ggamma value. In all 13 normal healthy newborns, in 8 patients with homozygous alpha-thalassemia, and in 4 patients with homozygous beta-thalassemia, Tgamma chains with threonine at position 75 were detected in addition Igamma chains with isoleucine at position 75. In homozygous alpha-thalassemia, the Tgamma-to-Igamma ratio seemed lower and in homozygous beta-thalassemia higher than in normal newborns.

Genes for gamma-globin in human adult erythroid DNA

Purified gamma-globin specific complementary DNA has been used to demonstrate the presence of the gene for gamma-globin in DNA from human adult red blood cells. This finding sheds doubt on any theory involving looping-out excision of genes to explain the switch over from synthesis of gamma-globin to beta-globin at birth.

G gamma delta beta thalassaemia and g gamma HPFH (Hb Kenya type): comparison of 2 new cases

Two new cases of G gamma delta beta thalassaemia and G gamma HPFH (Hb Kenya type) have been characterised in detail and compared with regard to haematological data, globin chains biosynthesis, and intracellular distribution of Hb F. The similarities and differences between these two conditions are discussed in relation to the possible underlying defects at the molecular level and to the control of the gamma delta beta gene complex in general.

Fluctuation of fetal hemoglobin in sickle-cell anemia

A reduction of morbidity and mortality rates in homozygous sickle-cell patients was found in those with high fetal hemoglobin (HbF) levels. This factor would lead one to believe that an adequate amount of this substance would be protective to a patient with this hemoglobinopathy. This study utilizing pregnant and nongravid females, as well as males, followed for long periods of time indicates that the HbF level fluctuates with crisis. Some patients had low HbF levels with many crises and others had high amounts of HbF with no crises. However, many patients with high levels on one occasion demonstrated a decrease in HbF levels when crisis occurred. More importantly, no patient had high levels of HbF during a crisis although the amount was elevated before and after the episodes. The possible explanation and ramifications of this finding are discussed.

A direct estimate of the number of human gamma-globin genes

The number of genes specifying human gamma-globin has been determined directly by hybridization of complementary DNA to total human DNA. The complementary DNA was enriched in sequences specific for gamma-globin genes by transcribing globin mRNA isolated from fetal reticulocytes with viral reverse transcriptase, and collecting the material which does not back-hybridize to adult globin mRNA. When hybridized in cDNA excess to DNA, very similar values are found for gamma-gene number as for beta-gene number, suggesting two or at most three gamma-globin genes per haploid human genome. This indicates that the non-Mendelian ratios of gamma-chain mutants found in heterozygotes are due to transcriptional or post-transcriptional regulation rather than to gene dosage. The number of each major human globin gene has now been determined directly by molecular methods.

Variations in globin chain synthesis in hereditary persistence of fetal haemoglobin

Globin synthesis was studied in four Negro families including 10 members with Hb A-HPFH and four with Hb S-HPFH. The beta/alpha specific activity ratios in 10 of these HPFH heterozygotes were similar to those of the control group. In two patients with Hb A-HPFH, the beta/alpha ratio was slightly decreased in one (0.84) and clearly decreased in another (0.78). In two of the patients with Hb S-HPFH the ratios were clearly decreased (0.71 and 0.75). The extended range of beta/alpha ratios in these 14 patients is similar to that of Negro patients with beta-thalassaemia trait. These studies indicate that a decreased beta/alpha ratio may be found in HPFH, as well as in beta-thalassaemia. Bone marrow globin synthesis was measured in two patients with Hb S-HPFH and decreased peripheral blood beta/alpha ratios, and in one with Hb A-HPFH and a normal peripheral blood beta/alpha ratio. In each patient the (beta+gamma)/alpha ratio of radioactivities as well as the beta/alpha specific activity ratio was close to 1 and therefore balanced, indicating more rapid decay of beta-chain synthesis relative to alpha-chain during red cell maturation or extremely rapid destruction of newly synthesized excess alpha-chains in the bone marrow.

The Kenya form of hereditary persistence of fetal haemoglobin: structural studies and evidence for homogeneous distribution of haemoglobin F using fluorescent anti-haemoglobin F antibodies

Several members of a Ugandan family were heterozygous for the gamma beta fusion gene of Haemoglobin Kenya. Levels of Hb Kenya were significantly higher than those in subjects of previous reports, ranging from 20.68 to 23.35% of the total haemoglobin. The individuals had also 5-8% Hb F, consisting solely of alpha and Ggamma chains. Investigation of the distribution of Hb F among the red cells of Hb Kenya heterozygotes, using monospecific antibodies absorbed against pure Hb Kenya and rendered fluorescent by conjugation with fluorescein isothiocyanate, showed the presence of fetal haemoglobin in all red cells. The data suggest that the phenotype of the Hb Kenya trait resembles that of the Ggamma form of hereditary persistence of fetal haemoglobin rather than that of thalassaemia.

Recent developments in foetal haemoglobin research

There have been numerous new contributions to the knowledge of foetal haemoglobin over the last few years. It is, therefore, timely to review them together. They throw light on the arrangement on the chromosome of non-alpha chain genes, and on the condition generally known as Hereditary Persistence of Foetal Haemoglobin (HPFH) and have contributed to other aspects of human ontogeny and physiology.

A form of hereditary persistence of fetal haemoglobin characterized by uneven cellular distribution of haemoglobin F and the production of haemoglobins A and A2 in homozygotes

Thirteen members of a British family were found to have elevated levels of haemoglobin F (Hb F) which segregated into two groups with mean values of 19.8+/-0.52% and 8.9+/-3.1% respectively. Genetic data indicate that the individuals in the former group are probably homozygous, and those in the latter group heterozygous, for the gene causing persistent Hb-F production. There is a significant reduction in the level of Hb A2 in the homozygotes. The Hb F is heterogeneously distributed among the red cells of each of the affected family members. In each case the haematological findings are normal and biosynthetic studies indicate balanced globin-chain synthesis. Chemical studies indicate that the Hb F consists mainly of the Agamma type together with a small (c 10%) but significant amount of the Ggamma type in both homozygotes and heterozygotes. The other red-cell proteins and antigens are of the adult variety in all affected family members. The condition differs from previously described forms of hereditary persistence of fetal haemoglobin by virtue of the heterogeneous distribution of the Hb F and the presence of beta and delta-chain synthesis in homozygotes. Its possible basis as a controller-gene mutation is discussed.

Globin chain synthesis in the greek type (A gamma) of hereditary persisitence of fetal haemoglobin

Globin chain synthesis was studied in a family with both the Greek (Agamma) type of hereditary persistence of fetal haemoglobin and beta thalassaemia. The ratio of alpha/(gamma+beta+delta) chain synthesis in the hereditary persistence of fetal haemoglobin (HPFH) heterozygotes was 0.97 while in the HPFH/beta-thalassaemia heterozygote it was 2.14. However, calculation of the amounts of haemoglobin synthesized per cell suggests that in the HPFH/beta-thalassaemia heterozygote, the beta- and Agamma-chain genes in cis to the HPFH determinant are unable to compensate for the deficiency of chains imposed by the beta-thalassaemia gene in trans and that the increased synthesis of Hb F is directed by the gamma-chain genes located on the beta-thalassaemia chromosome. The data suggest that synthesis of beta and Agamma chains in the Greek HPFH is fixed at a 'preset' level and indicate that the defect might be due to an abnormality in the rate of transcription of the closely linked beta-, delta- and gamma-chain genes.

A homozygote for the Hb G type of foetal haemoglobin in India: a study of two Indian and four Negro families

Summary. The haemoglobin of a 9‐yr‐old boy from the area of Bombay has only haemoglobin F. The γ‐chains of this haemoglobin F are solely of Gγ type, and the child is considered to be a homozygote for hereditary persistence of foetal haemoglobin of the Gγ type. The same kind of haemoglobin F is also present in a second Indian family and in four American Negro families. One Negro family has an appreciably lower percentage of haemoglobin F in heterozygotes than the other five families. In some of the families certain individuals also have haemoglobin E or haemoglobin S in trans to the other condition and haemoglobin A is absent. Although it has been concluded that the hereditary persistence of foetal haemoglobin is present the condition is not expressed uniformly in all these families. Some of them have certain characteristics of F‐thalassaemia. It is possible that two conditions are, in reality, represented: perhaps some families have the hereditary persistence of foetal haemoglobin and others have F‐thalassaemia.

Genetic determination of phenotypic variation in sickle cell trait

Two genetic sources of variation influence the percentage of sickle cell hemoglobin found in heterozygotes. One factor is strongly related to the percentage of hemoglobin S in the carrier parent and appears to be determined by sickle hemoglobin isoalleles, whereas the other is related to racial background and may well be polygenic.

Gene selection in hemoglobin and in antibody-synthesizing cells

Close linkage of mutually exclusive genes occurs in the non-alpha chain hemoglobin genes and in the immunoglobulin genes of man and other mammals. The expression of one gene in the cluster precludes the expression of any other linked gene. A simple, testable theory of gene selection called "looping-out excision"which was designed only to explain this mutual exclusivity in the hemoglobin system is described. The theory is closely concordant with a wide range of previously unexplained findings concerning hematopoiesis- including the developmental changes of hemoglobins, the increases in immature or fetal forms of hemoglobin that accompany anemia, and with the distribution of adult and fetal hemoglobins among erythrocytes during normal embryogenesis and in various pathological conditions. One corollary of this theory is that erythroid tissue in the normal adult bone marrow is constantly recapitulating the developmental stages of its embryogenesis. Another corollary is that the selection from among the linked globin genes occurs independently on the two chromosomes of the diploid organism. Both of these corollaries are supported by the available data. The same theory of gene selection is also remarkably consistent with known data for immunoglobulin synthesis; it could explain not only the mutually exclusive activation of linked variable genes but also the splicing which occurs between genetically linked variable and constant region genes for the immunoglobulin polypeptide chains. The agreement between these two different tissues is considered to be strong evidence that the proposed mechanism is correct at least in broad outline. Evidence from the genetics of maize and of drosophila also supports this theory of somatic tissue variegation. On the basis of these comparisons, I suggest that looping-out excision probably occurs also in other tissues and may be one means of gene selection and activation in differentiating cells.

Chimpanzee foetal haemoglobin: structure and heterogeneity of the gamma chain

The amino acid compositions of soluble tryptic and chymotryptic peptides of the gamma chain of chimpanzee foetal haemoglobin have been determined. The peptides, accounting for all 146 residues of the gamma chain, were found to be identical in composition to the corresponding human gamma chain peptides. As in man, position gamma 136 can be occupied by glycine (G gamma chain) as well as alanine (A gamma chain). The ratio of G gamma to A gamma chains in the infant chimpanzee is approx. 2:1, and in the adult approx. 1:2.