Variability in the fetal hemoglobin level of the normal adult

Transcriptional Repressor BCL11A in Erythroid Cells

BCL11A, a zinc finger repressor, is a stage-specific transcription factor that controls the switch from fetal (HbF, α2γ2) to adult (HbA, α2β2) hemoglobin in erythroid cells. While BCL11A was known as a factor critical for B-lymphoid cell development, its relationship to erythroid cells and HbF arose through genome-wide association studies (GWAS). Subsequent work validated its role as a silencer of γ-globin gene expression in cultured cells and mice. Erythroid-specific loss of BCL11A rescues the phenotype of engineered sickle cell disease (SCD) mice, thereby suggesting that downregulation of BCL11A expression might be beneficial in patients with SCD and β-thalassemia. Common genetic variation in GWAS resides in an erythroid-specific enhancer within the BCL11A gene that is required for its own expression. CRISPR/Cas9 gene editing of the enhancer revealed a GATA-binding site that confers a large portion of its regulatory function. Disruption of the GATA site leads to robust HbF reactivation. Advancement of a guide RNA targeting the GATA-binding site in clinical trials has recently led to approval of first-in-man use of ex vivo CRISPR editing of hematopoietic stem/progenitor cells (HSPCs) as therapy of SCD and β-thalassemia. Future challenges include expanding access and infrastructure for delivery of genetic therapy to eligible patients, reducing potential toxicity and costs, exploring prospects for in vivo targeting of hematopoietic stem cells (HSCs), and developing small molecule drugs that impair function of BCL11A protein as an alternative option.

Targeting fetal hemoglobin expression to treat β hemoglobinopathies

INTRODUCTION

Sickle cell disease and β thalassemia are the principal β hemoglobinopathies. The complex pathophysiology of sickle cell disease is initiated by sickle hemoglobin polymerization. In β thalassemia, insufficient β-globin synthesis results in excessive free α globin, ineffective erythropoiesis and severe anemia. Fetal hemoglobin (HbF) prevents sickle hemoglobin polymerization; in β thalassemia HbF compensates for the deficit of normal hemoglobin. When HbF constitutes about a third of total cell hemoglobin, the complications of sickle cell disease are nearly totally prevented. Similarly, sufficient HbF in β thalassemia diminishes or prevents ineffective erythropoiesis and hemolysis.

AREAS COVERED

This article examines the pathophysiology of β hemoglobinopathies, the physiology of HbF, intracellular distribution and the regulation of HbF expression. Inducing high levels of HbF by targeting its regulatory pathways pharmacologically or with cell-based therapeutics provides major clinical benefit and perhaps a "cure."

EXPERT OPINION

Erythrocytes must contain about 10 pg of HbF to "cure" sickle cell disease. If HbF is the only hemoglobin present, much higher levels are needed to "cure" β thalassemia. These levels of HbF can be obtained by different iterations of gene therapy. Small molecule drugs that can achieve even modest pancellular HbF concentrations are a major unmet need.

Association between Neutrophil Gelatinase-Associated Lipocalin and Fetal Hemoglobin Levels in Patients with Type 2 Diabetes Mellitus

The effect of neutrophil gelatinase-associated lipocalin (NGAL) on fetal hemoglobin (HbF) levels in diabetic patients is rarely investigated. This study is aimed at investigating the possible association between NGAL and HbF levels in type 2 diabetes mellitus (T2DM). A total of 160 patients with T2DM and 61 healthy individuals were evaluated. NGAL, HbF, tumor necrosis factor-α (TNF-α), interleukin-5 (IL-5), glycated hemoglobin (HbA1c), fasting plasma glucose (FPG), and urine albumin levels were measured. HbF levels were significantly higher in patients with elevated NGAL than in those without elevated NGAL (1.44% versus 0.94%, P = 0.001). High HbF was 2.3 times more prevalent in patients with elevated NGAL than in those without elevated NGAL. In addition, NGAL, TNF-α, and IL-5 levels were significantly higher in patients with high HbF than in those with low HbF; however, there was no significant difference in HbA1c and FPG levels between the two groups. HbF was positively correlated with NGAL (r = 0.275, P < 0.001), TNF-α (r = 0.256, P < 0.001), and IL-5 (r = 0.212, P < 0.001), but not with HbA1c and FPG. An elevated NGAL level led to a 1.27-fold increase in the prevalence of high HbF (odds ratio: 1.27, 95% CI: 1.03–2.51, and P < 0.001). The diagnostic efficacy of NGAL to identify an elevated HbF level was superior to that of HbA1c (area under the curve: 0.697, 95% CI: 0.609–0.786 versus 0.584, 95% CI: 0.488–0.681, and P = 0.022). In conclusion, enhanced NGAL production may be closely linked to elevated HbF in conjunction with proinflammatory cytokines in patients with T2DM.

Kidney Function Decline among Black Patients with Sickle Cell Trait and Sickle Cell Disease: An Observational Cohort Study

BACKGROUND

Sickle cell trait and sickle cell disease are thought to be independent risk factors for CKD, but the trajectory and predictors of kidney function decline in patients with these phenotypes are not well understood.

METHODS

Our multicenter, observational study used registry data (collected January 2005 through June 2018) and included adult black patients with sickle cell trait or disease (exposures) or normal hemoglobin phenotype (reference) status (ascertained by electrophoresis) and at least 1 year of follow-up and three eGFR values. We used linear mixed models to evaluate the difference in the mean change in eGFR per year.

RESULTS

We identified 1251 patients with sickle cell trait, 230 with sickle cell disease, and 8729 reference patients, with a median follow-up of 8 years. After adjustment, eGFR declined significantly faster in patients with sickle cell trait or sickle cell disease compared with reference patients; it also declined significantly faster in patients with sickle cell disease than in patients with sickle cell trait. Male sex, diabetes mellitus, and baseline eGFR ≥90 ml/min per 1.73 m2 were associated with faster eGFR decline for both phenotypes. In sickle cell trait, low hemoglobin S and elevated hemoglobin A were associated with faster eGFR decline, but elevated hemoglobins F and A2 were renoprotective.

CONCLUSIONS

Sickle cell trait and disease are associated with faster eGFR decline in black patients, with faster decline in sickle cell disease. Low hemoglobin S was associated with faster eGFR decline in sickle cell trait but may be confounded by concurrent hemoglobinopathies. Prospective and mechanistic studies are needed to develop best practices to attenuate eGFR decline in such patients.

Relationship Between Some Single-nucleotide Polymorphism and Response to Hydroxyurea Therapy in Iranian Patients With β-Thalassemia Intermedia

OBJECTIVE

To evaluate the possible relationship between hydroxyurea (HU) response and some single-nucleotide polymorphism (SNP) in patients affected by β-thalassemia intermedia.

MATERIALS AND METHODS

In this cross-sectional study, 100 β-thalassemia intermedia patients who were taking HU with a dose of 8 to 15 mg/kg body weight per day for a period of at least 6 months were randomly selected between February 2013 and October 2014 in southern Iran. HU response was defined based on decrease or cessation of the blood transfusion need and evaluation of Hb level.

RESULTS

In univariate analysis, from all evaluated SNPs, only rs10837814 SNP of olfactory receptors (ORs) OR51B2 showed a significant association with HU response (P=0.038) and from laboratory characteristics, only nucleated red blood cells showed significant associations (116%±183%) in good responders versus (264%±286%) in poor responders (P=0.045). In multiple logistic regression, neither laboratory variables nor different SNPs, showed significant association with HU response. Three novel nucleotide variations (-665 [A→C], -1301 [T→G],-1199 delA) in OR51B2 gene were found in good responders.

CONCLUSIONS

None of the evaluated SNPs in our study showed significant association with HU response. Further larger studies and evaluation of other genes are suggested.

Current and future alternative therapies for beta-thalassemia major

Beta-thalassemia is a group of frequent genetic disorders resulting in the synthesis of little or no β-globin chains. Novel approaches are being developed to correct the resulting α/β-globin chain imbalance, in an effort to move beyond the palliative management of this disease and the complications of its treatment (e.g. life-long red blood cell transfusion, iron chelation, splenectomy), which impose high costs on healthcare systems. Three approaches are envisaged: fetal globin gene reactivation by pharmacological compounds injected into patients throughout their lives, allogeneic hematopoietic stem cell transplantation (HSCT), and gene therapy. HSCT is currently the only treatment shown to provide an effective, definitive cure for β-thalassemia. However, this procedure remains risky and histocompatible donors are identified for only a small fraction of patients. New pharmacological compounds are being tested, but none has yet made it into common clinical practice for the treatment of beta-thalassemia major. Gene therapy is in the experimental phase. It is emerging as a powerful approach without the immunological complications of HSCT, but with other possible drawbacks. Rapid progress is being made in this field, and long-term efficacy and safety studies are underway.

Effect of Cis Acting Potential Regulators in the β Globin Gene Cluster on the Production of HbF in Thalassemia Patients

The clinical presentation of β-thalassemia intermedia phenotypes are influenced by many factors. The persistence of fetal hemoglobin and several polymorphisms located in the promoters of γ- and β-globin genes are some of them. The aim of this study was to evaluate the combined effect of the -158 Gγ (C→T) polymorphism and of the (AT)x(T)y configuration, as well as their eventual association with elevated levels of HbF in β-thalassemia carriers, β-thalassemia intermedia, β-thalassemia major and normal controls of Indian origin. The -158 Gγ T allele was found to be associated with increased levels of HbF in β thalassemia carriers, and not in wild-type subjects. In the homozygous group, the -158 Gγ T allele was significantly higher in the thalassemia intermedia group (66%) as against the thalassemia major group (21%). The (AT)9(T)5 allele did not show any association with raised HbF levels. However 24% of milder cases showed presence of this allele. This study suggests that two regions of the β globin cluster, whether in cis or in trans to each other, can interact to enhance HbF expression when a β thalassemic determinant is present in heterozygosity and help in amelioration of the severity of the disease in homozygotes.

Detection of a Rare β-Globin Nonsense Mutation [Codon 59 (AAG→TAG)] in an Italian Family

In this study we report on the hematological and molecular findings of a family from Central Italy, whose 33-year-old male proband presented with a beta0-thalassemia (thal) trait associated to a relevant Hb F level. The proband and his family (parents and a sister) were investigated by hematological analysis. The two beta-thal carriers of the beta-globin nonsense mutation [codon 59 (AAG-->TAG)] (the proband and his father) showed the hematological picture of a beta0-thal trait: the only hematological difference between the two beta-thal carriers was in the Hb F level (3.3% in the proband and 1% in his father).

Identification and quantification of fetal red blood cells in maternal blood by a dual-color flow cytometric method: evaluation of the Fetal Cell Count kit

BACKGROUND

As an alternative to the cumbersome Kleihauer-Betke test (KBT), flow cytometry represents a powerful method for the identification and quantification of fetal red blood cells (RBCs) in maternal circulation.

STUDY DESIGN AND METHODS

The aim of this study was to evaluate the Fetal Cell Count kit (IQ Products), an innovative flow cytometric method, based on the combination of antibodies directed, respectively, against fetal hemoglobin (HbF) and carbonic anhydrase (CA), a marker expressed after birth, to discriminate fetal RBCs from adult F cells containing HbF. The investigation was performed by two French laboratories that compared the data obtained by flow cytometry and KBT in 455 pregnant or just-delivered women as well as in 124 artificial mixtures containing from 0.01 to 5.00 percent cord cells.

RESULTS

The FL1/FL2 histogram allowed distinction between fetal RBCs (HbF+, CA-), F cells (HbF+, CA+), and adult RBCs (HbF-, CA+). The limits of detection and quantification were determined at 0.03 and 0.10 percent or 0.02 and 0.05 percent when analyzing 100,000 or 200,000 events, respectively. Linearity was demonstrated between 0.01 and 5.00 percent fetal cells in the mixtures (r = 0.95, p < 0.01). A good correlation between fluorescence-activated cell sorting (FACS) and KBT results was obtained with artificial mixtures (r = 0.94, p < 0.01). From the 405 Kleihauer-negative samples, none were identified as positive by FACS. Among the 50 Kleihauer-positive samples, 6 were shown not to contain fetal cells but F cells by FACS.

CONCLUSION

With this new dual-color flow cytometric method, accurate evaluation of fetomaternal hemorrhage was achieved even in the face of HbF of maternal origin.

Hemoglobin binding to A beta and HBG2 SNP association suggest a role in Alzheimer's disease

From a normal human brain phage display library screen we identified the gamma (A)-globin chain of fetal hemoglobin (Hb F) as a protein that bound strongly to A beta1-42. We showed the oxidized form of adult Hb (metHb A) binds with greater affinity to A beta1-42 than metHb F. MetHb is more toxic than oxyhemoglobin because it loses its heme group more readily. Free Hb and heme readily damage vascular endothelial cells similar to Alzheimer's disease (AD) vascular pathology. The XmnI polymorphism (C-->T) at -158 of the gamma (G)-globin promoter region can contribute to increased Hb F expression. Using family-based association testing, we found a significant protective association of this polymorphism in the NIMH sibling dataset (n=489) in families, with at least two affected and one unaffected sibling (p=0.006), with an age of onset >50 years (p=0.010) and >65 years (p=0.013), and families not homozygous for the APOE4 allele (p=0.041). We hypothesize that Hb F may be less toxic than adult Hb in its interaction with A beta and may protect against the development of AD.

Two beta-globin cluster-linked polymorphic loci in thalassemia patients of variable levels of fetal hemoglobin

OBJECTIVE

To correlate different polymorphisms of the beta-globin cluster with fetal hemoglobin (HbF) level in beta-thalassemia and E-beta thalassemia patients.

METHODS

Fifteen thalassemia patients, seven with high HbF and not requiring transfusion, eight with lower HbF and requiring transfusion were studied for beta-globin mutation, concurrent inheritance of alpha-thalassemia, RFLP haplotype, a C-->T polymorphism at -158 of Ggamma and configuration of an (AT)(x)T(y) motif at -540 of beta-globin gene.

RESULTS

Senegal 5'beta-haplotype and the polymorphism at -158 of G(gamma) was (P = 0.063) was linked to the high-HbF phenotype but the (AT)(9)T(5) configuration of the (AT)(x)T(y) motif was not (P = 0.6). Study of 30 chromosomes revealed 7 different configurations of the (AT)(x)T(y) motif. Association of these motifs with specific beta-globin mutations of this region has also been determined.

CONCLUSION

The senegal haplotype and the polymorphism at -158 of G(gamma) was linked to the high-HbF phenotype.

Spectrum of beta thalassemia mutations and HbF levels in the heterozygous Moroccan population

A comprehensive hematological and molecular analysis of 57 beta thalassemic heterozygotes, 28 homozygotes, 18 double heterozygotes, 3 compound heterozygotes beta thal/beta S and one compound heterozygote beta thal/Hb Newcastle, in 46 Moroccan families with at least one beta thalassemia patient is reported. Six major mutations: beta(0)39 (C-->T), beta(0)FsCD8(-AA), beta(+)IVS1,nt6 (T-->C) and beta(0)IVS1,nt1 (G-->A), beta(0)FsCD6 (-A) and beta(+)-29 (A-->G) cap site account for 75% of the 86 independent beta thal chromosomes studied. For the first time, an extensive mutation/haplotype study has been performed on the Moroccan population, and data are consistent with the geographical location of the country and historical links with both the Mediterranean and the Sub-Saharan Africa communities. Despite the heterogeneous spectrum of mutations, good genetic counseling can be offered to the carrier population. This study focuses on the analysis of fetal hemoglobin levels in beta thalassemic heterozygotes and its correlation with beta globin cluster polymorphic markers in this population. Fetal hemoglobin levels in heterozygotes vary from trace quantities to 17.9% (2.38 g/dl) of total hemoglobin in the adult. No statistically significant correlation was found, either between genders and HbF levels, or between the mutation and the HbF level, with the exception of mutation beta(0)FSCD6(-A). We have examined the alpha globin genotype and the beta globin genotype of heterozygotes, namely, the extended haplotype, which includes the XmnI site at -158 bp of the Ggamma gene and the microsatellite (AT)(x)T(y) at -540 bp of the beta globin gene. In this sample, we confirm the existence of linkage disequilibrium between the C-->T variation at -158 bp of Ggamma globin gene (XmnI(+)) and Orkin's haplotypes III, IV, or IX (the 5' subhaplotype class A). At 5' beta globin gene, we observe exclusively the allele (AT)(7)T(7). In the beta thalassemic heterozygotes studied, no correlation of those genetic markers with HbF levels is observed.

Molecular characterization of hereditary persistence of fetal hemoglobin in the Karen people of Thailand

Hereditary persistence of fetal hemoglobin (HPFH) is the condition whereby a continuously active gamma-globin gene expression leads to elevated fetal hemoglobin (Hb F) levels in adult life [Stamatoyannopoulos G, Grosveld F. Hemoglobin switching. In: Stamatoyannopoulos G, Majerus PW, Perlmutter RM, Varmus H, eds. The Molecular Basis of Blood Diseases. Philadelphia: W.B. Saunders, 2001:135-182; Wood WG. Hereditary persistence of fetal hemoglobin and delta(beta) thalassemia. In: Steinberg MH, Forget BG, Higgs DR, Nagel RL, eds. Disorders of Hemoglobin: Genetics, Pathophysiology, and Clinical Management. Cambridge: Cambridge University Press, 2001:356-388; and Weatherall DJ, Clegg JB. Hereditary persistence of fetal hemoglobin. In: Weatherall DJ, Clegg JB, eds. The Thalassaemia Syndromes. Oxford: Blackwell Scientific Publishers, 1981:450-507]. The condition is caused either by mutation of the beta- and gamma-globin genes, or the gamma-gene controlled region on other chromosomes. Several families with this condition have been reported from Vietnam, Cambodia and China, and the Southeast Asian mutation (or HPFH-6), a 27 kb deletion, was demonstrated. Here we report on a mother and her daughter of the Karen ethnic group with high levels of Hb F, living in the Suan Pueng District on the border of Thailand and Myanmar. Genotyping showed a heterozygosity for the 27 kb deletion of the beta-globin gene. Their conditions have been confirmed by gap polymerase chain reaction (PCR) with three oligonucleotide primers recently developed by Xu et al. [Xu X-M, Li Z-Q, Liu Z-Y, Zhong X-L, Zhao Y-Z, Mo Q-H. Molecular characterization and PCR detection of a deletional HPFH: application to rapid prenatal diagnosis for compound heterozygotes of this defect with beta-thalassemia in a Chinese family. Am J Hematol 2000; 65:183-188.], and a DNA sequencing method. Thus far there has been no official report of the HPFH-6 anomaly from Thailand. The compound heterozygosity of beta-thalassemia (thal) and hereditary persistence of Hb F causes the phenotype of thalassemia intermedia; in contrast, homozygotes for this anomaly show only mild microcytic anemia. Hence, genetic counseling for hereditary persistence of Hb F carriers is needed for family planning.

Effect of variability in anemia management on hemoglobin outcomes in ESRD

BACKGROUND

Hemoglobin (Hgb) levels fluctuate in patients with end-stage renal disease over time. This study quantified Hgb level variability and the likelihood of falling within the Hgb level goal range of 11 to 12 g/dL. Implications on the percentage of patients exceeding 3-month rolling average Hgb levels of 12, 12.5, and 13 g/dL were determined.

METHODS

Phase I (n = 65,009) tracked patients with Hgb values initially outside the goal range (<11 or >12 g/dL) during 2000. Correlation with facility-specific thresholds also was evaluated. Phase II (n = 48,133) quantified variation in 3-month rolling average Hgb levels in a subset with greater than 10 months of data (mean Hgb, 11.4 +/- 1.3 g/dL).

RESULTS

A total of 24,948 patients (38.4%) had Hgb levels between 11 and 12 g/dL. In only 8% did Hgb levels consistently remain less than 11 g/dL, and in 18%, greater than 12 g/dL all year. Twenty-nine percent (18,633 patients) moved from below to above target range or vice versa. Greater mean facility Hgb level correlated with a greater percentage of patients with Hgb levels greater than 10 g/dL (R2 = 0.49) and greater than 12.5 g/dL (R2 = 0.61). For facilities to have 90% or greater of patients with 3-month rolling average Hgb levels greater than 10 g/dL, 13% to 31% of patients will have 3-month rolling average Hgb values greater than 12.5 g/dL. The average individual patient is expected to have a +/-1.4-g/dL fluctuation in 3-month rolling average Hgb levels per year. Despite increased mean Hgb levels and erythropoietin (EPO) and iron use, the spread of the Hgb distribution curve remained unchanged in the last 6 years.

CONCLUSION

Variability caused by laboratory assays, biological factors, and therapeutic response determines patient Hgb level variability. Improving factors that can be manipulated (eg, standardizing EPO and iron algorithms) and adjustment of the target Hgb level range, specifically, by increasing the upper bound, likely will decrease the observed variability and further enhance the quality of anemia management.

Asymptomatic homozygous deletional beta(0)-thalassemia in an African individual

Homozygosity or compound heterozygosity for beta(0)-thalassemia mutations most commonly results in a transfusion-dependent thalassemia major phenotype. In this report, we describe a 55-year-old male, from Guinea-Bissau, that had been asymptomatic and never transfused until being admitted to hospital with anemia, fever, splenomegaly, and asthenia. Following hospital admission, HIV-2 and Mycobacterium tuberculosis infections were diagnosed, and biochemical and molecular studies revealed homozygosity for beta(0)-thalassemia. At the molecular level, this is the first description of homozygosity for the beta(0)-Black 1,393-bp deletion. In this case, the complete absence of beta-globin gene expression seems to be compensated by an unusually high fetal globin gene expression (Hb F 96%). Beta-globin haplotyping results were compatible with the propositus being homozygous for the Black 2 haplotype and for the absence of the XmnI polymorphism at -158 of (G)gamma-globin gene (-/-). Co-inheritance of genetic factors usually associated with high Hb F levels was not detected. Otherwise, the propositus is a heterozygote for the alpha-globin gene 3.7-kb deletion that is a beneficial modulating factor but not sufficient to explain this extremely mild phenotype. This unusual genotype/phenotype association is discussed in terms of the mechanisms underlying hemoglobin switching during development.

Foetal haemoglobin in normal healthy adults: relationship with polymorphic sequences cis to the beta globin gene

We evaluated the effects of polymorphic markers within the beta globin gene cluster on HbF expression in two groups. These groups were randomly selected from a survey of HbF distribution in a large population study of unrelated healthy Algerian adults (n=827). The first group contained individuals with normal HbF levels (0.1-0.5%) and the second group contained individuals with raised HbF levels (0.8-2.3%). Of the various polymorphic markers analysed, only the -309 G gamma A-->G, the -158 G gamma C-->T, the G gamma IVS2 TC (TG)(9) AG (TG)(2) (CG)(2) and the -540 beta (AT)(9) T(5) sequence configurations were significantly associated with increased HbF levels. More than 84% of the subjects with elevated HbF levels carried one or several of these four marker configurations, suggesting that the beta globin gene cluster exerts a significant effect on HbF expression in healthy individuals.

Fetal hemoglobin elevation in Hb Lepore heterozygotes and its correlation with beta globin cluster linked determinants

We have analysed, at the hematological and molecular level, 51 Hb lepore heterozygotes and three compound heterozygotes for Hb Lepore and HbS (HbLep/HbS) in 26 unselected Portuguese families. The Lepore Boston variant was present in one family, in association with classical haplotype V. All of the other Lepore alleles present haplotype III in association with XmnI (+)5' of (G)gamma gene, in tight linkage disequilibrium to the major mutation found in the Portuguese population, the Lepore Baltimore variant ( delta(68Leu)-beta(84Thr)). The three compound heterozygotes are the first HbLep/HbS individuals reported in the literature, with the Lepore Baltimore mutation linked to haplotype III. In agreement with other studies, these Lepore Baltimore heterozygotes have higher HbF (1.4-14.1% of total hemoglobin) than published cases of Lepore Boston (0.8-5.4%), which is associated with XmnI(-). Among the Lepore Baltimore heterozygotes, the (AT)xTy repeat region at -540 bp of the beta globin gene in trans to the Lepore chromosome, can account for much of the variability in HbF level. The allele (AT)7T7 is associated with lower HbF, and (AT)9T5 is associated with higher HbF. As we previously reported for beta thalassemic carriers, we observe in Lepore Baltimore carriers an effector in trans, linked to the (AT)xTy sequence, acting as an HPFH (Hereditary Persistence of Fetal Hemoglobin) determinant.

ζ-, ε-, and γ-Globin mRNA in Blood Samples and CD71+ Cell Fractions from Fetuses and from Pregnant and Nonpregnant Women, with Special Attention to Identification of Fetal Erythroblasts

Background: Information about the appearance of γ-, ε-, and ζ-globin mRNAs in fetal erythroblasts during gestation and about the presence and amounts of these mRNAs in pregnant and nonpregnant women is important from the perspective of using these molecules as a marker of fetal erythroblasts. A specific marker is necessary for isolation and identification of fetal nucleated red blood cells from maternal blood samples for use in antenatal diagnosis of fetal genetic or chromosomal abnormalities.

Methods: We used a very sensitive reverse transcription-PCR (RT-PCR) method, coamplification analysis of γ- and ε-globin cDNA, and quantitative analysis of γ-globin mRNA based on competitive RT-PCR to investigate these aspects.

Results: All adult whole-blood samples were negative for ε- and ζ-globin mRNA. Analyses of CD71+ cell fractions showed that specimens from 19 of 20 nonpregnant and 10 of 14 pregnant women (at 9–13 weeks of gestation) were positive for γ-globin mRNA (Fisher’s exact test, P = 0.13), and those from 3 of 20 nonpregnant and 5 of 14 pregnant women were positive for ζ-globin mRNA (Fisher’s exact test, P = 0.23). No ε-globin mRNA was detected in CD71+ cell fractions from 1-mL blood samples from adults. CD71+ cell fractions from eight fetal blood samples (at 17–20 weeks of gestation) were positive for all three globin mRNAs. We found no statistically significant difference between the amounts of γ-globin mRNA in pregnant and nonpregnant women.

Conclusions: This study indicates that ε-globin mRNA might function as a marker for fetal CD71+ cells early in pregnancy. Although γ-globin mRNA can be detected in CD71+ cell fractions from most adults, these transcripts also may be of use because of a marked difference between adult and fetal values.

Molecular studies of beta-thalassemia heterozygotes with raised Hb F levels

Hb F levels in beta-thalassemia heterozygotes are usually less than 2%, but amongst 1,059 patients studied, 73 (7%) had Hb F levels above 2.5% (2.6-14.0%). To investigate factors that may influence the increase of Hb F levels in these heterozygotes, we characterized the beta-thalassemia mutations and their chromosomal background, gamma-globin gene promoter variations, and alpha-globin genotypes. All 73 beta-thalassemia heterozygotes carried beta-thalassemia point mutations previously observed in the Greek population; gene mapping excluded b gene cluster deletions; only two cases had an additional gamma-globin gene (gammagammagamma/gammagamma). Five alpha-globin genes (alphaalphaalpha/alphaalpha) were detected in 17/73 cases (23%) as compared to a carrier rate of 1.76% in the general population. Molecular, hematological, and biosynthetic findings in these compound heterozygotes indicated that the raised Hb F levels were caused by cell selection due to ineffective erythropoiesis. In the remaining 56 simple beta-thalassemia heterozygotes, 11 beta-thalassemia mutations were observed, each on the expected haplotype(s), and analysis of the gamma gene promoters revealed three known polymorphisms (in linkage disequilibrium), with minimal influence on gamma-globin levels. However, the overall distribution of beta-thalassemia mutations in the 56 simple beta-thalassemia heterozygotes was significantly different (P<0.0002) compared to that in 986 simple beta-thalassemia heterozygotes with <2.5% Hb F, implicating an association between beta-thalassemia mutations and moderately increased Hb F levels, most notably codon 39 (C-->T), IVS-II-1 (G-->A), codon 6 (-A), and codon 8 (-AA), which accounted for 41/56 (73%) cases with >2.5% Hb F. In the remaining 15/56 (27%) cases, no common underlying globin genotypes could explain the raised Hb F levels. Overall, this study indicates that the control of Hb F levels in beta-thalassemia heterozygotes is heterogeneous and multi-factorial.

HbF production in beta thalassaemia heterozygotes for the IVS-II-1 G-->A beta(0)-globin mutation. Implication of the haplotype and the (G)gamma-158 C-->T mutation on the HbF level

We studied the presence of the XmnI site and the beta-globin haplotype in 24 individuals, carriers of the IVSII-1 G-->A beta(0)-globin mutation, of whom fourteen had no detectable levels of HbF, while ten coming from 5 families, presented HbF levels ranging from 1.7 to 9% of the total Hb. Of these beta-thalassaemia heterozygotes with fetal hemoglobin, 6 were females and 4 were males with median HbF levels of 4.85% and 4% respectively, and an excess of (G)gamma chains (range (G)gamma/(A)gamma: 55/45-70/30). Of the group of carriers of beta-thalassaemia with HbF < 0.1, in all cases except one, IVSII-1 mutation was found associated with XmnI polymorphic site. Haplotype analysis in these individuals revealed that in 10 cases IVSII-1 was linked with haplotype IIIb, in 1 case with haplotype IIIa, and in 3 cases with haplotype IX. On the other hand, in the group of carriers with measurable levels of HbF, IVSII-1 was always associated with haplotype IIIa and the XmnI site was either in-homozygous or the heterozygous state in-cis or in-trans with the mutated beta-globin gene. In conclusion the results of the study of these families seem that XmnI site in-cis with the IVSII-1 does not induce HbF production when this beta(0)-thalassaemia mutation is associated with IIIb or IX haplotype. On the other hand the (G)gamma -158 C-->T mutation is associated with small amounts of HbF in IVSII-1 heterozygotes, when the beta-globin mutation is linked to haplotype IIIa.

Combined effect of two different polymorphic sequences within the beta globin gene cluster on the level of HbF

Beta thalassemia and Hb Lepore heterozygotes included in this study exhibit fetal hemoglobin levels varying from trace quantities to 14% (1.74 g/dl) of total hemoglobin in the adult. In this work, we have examined the correlation of DNA sequence polymorphisms with the observed HbF level. The analysis of polymorphic markers within the beta globin cluster in 39 individuals heterozygous for beta thalassemia or Hb Lepore confirms the previous findings for homozygous beta thalassemia: the presence of both an (AT)9 T5 sequence configuration at position -540 of the beta globin gene and a (C --> T) variation at -158 of the Ggamma globin gene is associated with elevated expression of HbF. However, at least one defective beta globin gene is required to reveal this association. The best evidence is from the study of individuals heterozygous for Hb Lepore with various levels of HbF. In these individuals it was possible to explore the effect of a single (AT)x Ty motif (the other being absent from the rearranged Lepore chromosome) on HbF expression. The presence of the (AT)9 T5 configuration increases HbF level from a median of 0.515 g/dl observed in (AT)7 T7 subjects, to 1.39 g/dl. We confirm the existence of linkage disequilibrium between the (C --> T) variation at -158 of Ggamma gene and the (TG)13 configuration at the second intervening sequence (IVS-2) of Agamma gene and identify two new polymorphisms in this region: (TG)7 (CG)5 (TG)8 linked to haplotype V and (TG)8 (CG)5 (TG)10 linked to haplotype II. This study suggests that two distinct regions of the beta cluster, whether in cis or in trans to each other, can interact to enhance HbF expression when a beta thalassemic determinant is present in heterozigosity.

Fetal hemoglobin in sickle cell anemia: examination of phylogenetically conserved sequences within the locus control region but outside the cores of hypersensitive sites 2 and 3

Regulatory elements linked to the beta-globin gene cluster modulates gamma-globin gene expression. The location of all of these elements and their mechanisms of action are still incompletely defined. Phylogenetically conserved DNA within the beta-globin gene cluster locus control region (LCR), but outside the core sequences of its hypersensitive sites (HS), were identified and we searched for any differences between HS 3 and HS 2, and HS 2 and HS 1, among patients with sickle cell anemia with different levels of Hb F who were homozygous for the common haplotypes. DNA was amplified with and without GC clamps, digested with restriction endonucleases, and examined by denaturing gradient gel electrophoresis (DGGE). We found limited fragment size diversity. However, the type of differences found and their distribution among haplotypes did not suggest that they represented distinctive changes that might explain the differential expression of the gamma-globin genes in sickle cell anemia.