Coinheritance Of Alpha-thalassemia Research Articles

Growth Hormone/Insulin-like Growth Factor 1 Axis Associated with Modifier Factors in Children with Sickle Cell Anemia.

Sickle cell anemia is a disease that develops episodes of acute pain and multiple organ dysfunction that can affect the growth hormone/insulin-like growth factor 1 (GH/IGF-1) axis. The severity of sickle cell anemia is influenced by modifying factors, such as levels of fetal hemoglobin (HbF), the co-inheritance of alphathalassemia, or treatment with hydroxyurea. This cross-sectional study in children with sickle cell anemia evaluated bone age (BA), adult height prediction (AHP) using BA, a target height (TH) calculated as the mean SDS of the parents, and laboratory parameters. Children were grouped according to serum levels of HbF, co-inheritance of alpha-thalassemia, and hydroxyurea therapy.. The mean age of the 39 children was 8.2 ± 2.2 years old. The average height was -0.75 ± 0.30 SDS, and 10.3% (4/39) had short stature. Adjusted levels of IGF-1 or IGFBP- 3 were significantly higher in children with sickle cell anemia on hydroxyurea treatment, in children with HbF levels >10%, and in those without alpha-thalassemia. Using SDS, the growth potential of children with sickle cell anemia in relation to their parents calculated by the difference between AHP and TH as well as the difference between children's height and their TH, were lower in children with co-inheritance of alphathalassemia. The study showed an association between modifying factors and the GH/IGF-1 axis in children with sickle cell anemia. Additionally, the co-inheritance of alpha-thalassemia was associated with decreased height in these children when adjusted for their parents' height.

Microcytosis in children and adolescents with the sickle cell trait in Basra, Iraq

BackgroundMicrocytic anemia, the most common form of anemia in children and adolescents, is a heterogeneous group of diseases that is acquired or inherited. We assessed the frequency and causes of microcytosis in children and adolescents with the sickle cell trait (SCT).MethodsThis descriptive study included 95 subjects (49 males and 46 females) with SCT who attended Basra Center for Hereditary Blood Diseases for evaluation. Investigations included complete blood count, high performance liquid chromatography, capillary electrophoresis, and measurement of serum ferritin and transferrin levels.ResultsSCT subjects had a low hemoglobin (Hb) concentration (9.79±1.75 g/dL), low mean corpuscular volume (MCV, 67.43±9.22), low mean corpuscular Hb (21.15±3.64), and a normal red cell distribution width (RDW, 14.00±2.30). Among 95 SCT subjects, 81 (85.26%) had microcytosis, 12 (12.63%) had normal MCV, and 2 (2.11%) exhibited macrocytosis. Sixty-three (77.78%) SCT subjects with microcytosis were iron deficient, and 18 (22.22%) had normal iron levels. The mean serum ferritin and HbA2 levels were significantly lower, while the RDW, sickle Hb, and serum transferrin levels were significantly higher in patients with microcytosis and iron deficiency compared to non-iron deficient subjects (P<0.05). Correlation coefficients did not reveal a significant association between the MCV and iron status of SCT subjects (P>0.05).ConclusionDespite the frequent occurrence of iron deficiency in SCT subjects, co-inheritance of alpha-thalassemia seemed to be the cause of low MCV in non-iron deficient individuals with microcytosis. Genetic analysis is required to understand the genetic basis of this phenomenon.

Clinical and genetic predictors of renal dysfunctions in sickle cell anaemia in Cameroon.

Micro-albuminuria and glomerular hyperfiltration are primary indicators of renal dysfunctions in Sickle Cell Disease (SCD), with more severe manifestations previously associated with variants in APOL1 and HMOX1 among African Americans. We have investigated 413 SCD patients from Cameroon. Anthropometric variables, haematological indices, crude albuminuria, albumin-to-creatinine ratio (ACR) and estimated glomerular filtration rate (eGFR) were measured. Patients were genotyped for 3·7kb alpha-globin gene (HBA1/HBA2) deletion, and for variants in APOL1 (G1/G2; rs60910145, rs73885319, rs71785313) and HMOX1 (rs3074372, rs743811). The median age was 15years; the majority presented with micro-albuminuria (60·9%; n=248), and approximately half with glomerular hyperfiltration (49·5%; n=200). Age, male sex, haemoglobin level, leucocyte count, mean corpuscular volume, blood pressure, body mass index and creatinine levels significantly affected albuminuria and/or eGFR. Co-inheritance of alpha-thalassaemia was protective against macro-albuminuria (P=0·03). APOL1 G1/G2 risk variants were significantly associated with the ACR (P=0·01) and borderline with eGFR (P=0·07). HMOX1 - rs743811 was borderline associated with micro-albuminuria (P=0·07) and macro-albuminuria (P=0·06). The results revealed a high proportion of micro-albuminuria and glomerular hyperfiltration among Cameroonian SCD patients, and support the possible use of targeted genetic biomarkers for risks assessment.

Alpha thalassemia deletions found in suspected cases of beta thalassemia major in Pakistani population.

Background & Objective:Alpha (α) thalassemia is a hereditary disorder and is caused by deletions or mutations in globin genes. It is present in two clinically significant forms: hemoglobin Bart hydrops fetalis (Hb Bart) syndrome and hemoglobin H (HbH) disease. It is highly prevalent in South-East Asia or Mediterranean countries. The most common deletion reported in alpha thalassemia in Pakistani population was –α3.7 with a frequency of 8.3%, and the rare forms were –α4.2 (0.2%) and αααanti3.7 (0.9%). In our study, diagnosis of severe anemia cases without any α and β mutations or deletions were made by using extended alpha thalassemia deletions panel. The main objective of this study was to determine the prevalence and to study the spectra of alpha thalassemia gene deletions in beta thalassemia patients with the use of an extended panel including −−SEA, −−FIL, −−MED, −−20.5, −−THAI in addition to –α3.7, –α4.2 & -αααanti3.7.Methods:The samples were collected in ethylenediaminetetraacetic acid (EDTA) vacutainers. A total of 156 samples were analyzed for alpha thalassemia mutations. This cohort included 121 samples of beta thalassemia major, nine samples of beta thalassemia minor and 26 without any evidence of beta thalassemia mutations. DNA was extracted with Qiagen extraction kit. The primers for determination of different subsets of alpha thalassemia deletions were included. PCR amplification was performed and result interpreted on agarose gel.Results:Co-inheritance of alpha thalassemia (–α3.7, –α4.2) with homozygous beta thalassemia was detected in 30% cases of studied cohort (37 out of 121). The most common found was –α3.7 deletion (35/37) as single/double deletions or in combination with -αααanti3.7. In undiagnosed cases screened for beta thalassemia major, we found Mediterranean (–αMED) deletion at specifically 875 bp on agarose gel. This is distinctive finding in case of detecting –αMED instead of any other deletion from Pakistan.Conclusion:Alpha thalassemia deletions (–α3.7, –α4.2) are the common co-inherited deletions found in beta thalassemia major patients. On the basis of results, we propose an extended alpha thalassemia genetic mutation panel should be used for screening of children presenting with anemia with suspicion of haemoglobinopathy.

The co-inheritance of alpha-thalassemia and sickle cell anemia is associated with better hematological indices and lower consultations rate in Cameroonian patients and could improve their survival.

BackgroundCo-inheritance of α-thalassemia was reported to be associated with a delayed age of disease onset among Cameroonian Sickle Cell Anemia (SCA) patients. The present study aimed to explore the correlation between α-thalassemia, hematological indices, and clinical events in these patients.Methods and FindingsWe studied 161 Cameroonian SCA patients and 103 controls (59.1% HbAA) with median ages of 17.5 and 23 years. RFLP-PCR was used to confirm SCA genotype and to describe haplotypes in the HBB-like genes cluster. Multiplex Gap-PCR was performed to investigate the 3.7 kb α-globin gene deletions. SNaPshot PCR, capillary electrophoresis and cycle sequencing were used for the genotyping of 10 SNPs in BCL11A, HMIP1/2, OR51B5/6 and HBG loci, known to influence HbF levels. Generalised linear regression models adjusted for age, sex and SNPs genotypes was used to investigate effects of α-thalassemia on clinical and hematological indices. The median rate of vaso-occlusive painful crisis and hospitalisations was two and one per year, respectively. Stroke was reported in eight cases (7.4%). Benin haplotype was the most prevalent (66.3%; n = 208 chromosomes). Among patients, 37.3% (n = 60) had at least one 3.7 kb deletion, compared to 10.9% (n = 6) among HbAA controls (p<0.001). Among patients, the median RBC count increased with the number of 3.7 kb deletions [2.6, 3.0 and 3.4 million/dl, with no, one and two deletions (p = 0.01)]. The median MCV decreased with the number of 3.7 kb deletion [86, 80, and 68fl, with no, one and two deletions (p<0.0001)], as well as median WBC counts [13.2, 10.5 and 9.8×109/L (p<0.0001. The co-inheritance of α-thalassemia was associated with lower consultations rate (p = 0.038).ConclusionThe co-inheritance of α-thalassemia and SCA is associated with improved hematological indices, and lower consultations rate in this group of patients. This could possibly improve their survival and explain the higher proportion of α-thalassemia among patients than controls.

Effect Of Genetic Modifiers Of Baseline Fetal Hemoglobin On Hydroxyurea Response In Children With Sickle Cell Disease

Hydroxyurea is a safe and effective therapy for sickle cell disease (SCD), with the majority of its benefit correlating with the amount of fetal hemoglobin (HbF) produced at maximum tolerated dose, or MTD. There is substantial individual variability in HbF response to hydroxyurea, with baseline HbF levels accounting for approximately 40% of the observed variability in final HbF at MTD. Several genetic modifiers of baseline, or endogenous, HbF levels have previously been identified by genome wide association studies. These include certain beta-globin haplotypes, and polymorphisms at the BCL11A and HBS1L-MYB gene loci. The effect of these known genetic modifiers of baseline HbF on drug response has been investigated in a small (n=38) cohort of pediatric patients treated with hydroxyurea in several centers with different treatment guidelines. In this limited group, no association was found between the BCL11A or HBS1L-MYB variants and the change in HbF at MTD (ΔHbF; final HbF minus baseline HbF). Co-inheritance of alpha thalassemia has been reported to have a negative effect on HbF response to hydroxyurea. To independently verify these findings in a larger sample size, we tested the effect of four BCL11A single nucleotide polymorphisms (SNPs), three HBS1L-MYB SNPs, the XmnI polymorphism, and co-inheritance of α-thalassemia on ΔHbF at MTD in a cohort of 171 pediatric SCA patients, treated prospectively and uniformly on HUSTLE (NCT NCT00305175) and SWiTCH (NCT 00122980) protocols. These patients represent the most accurate hydroxyurea phenotypes available, as all were meticulously titrated to MTD, and had complete laboratory data demonstrating compliance, such as absolute neutrophil count and absolute reticulocyte count within the therapeutic range. In our cohort, the BCL11A SNPs rs1427407, rs4671393 and rs11886868 were significantly associated with baseline HbF (Table 1). We saw no association between baseline HbF and any of the HBS1L-MYB SNPs, XmnI, α-thalassemia or BCL11A SNP rs7599488. In contrast to other reports, we found that coinheritance of α-thalassemia did not affect hydroxyurea treatment response (p=0.088). We found that BCL11A SNPs rs1427407, rs4671393 and rs11886868 were significantly associated with reduced ΔHbF following hydroxyurea treatment (Table 1), where individuals with the BCL11A SNPs had a smaller ΔHbF compared to individuals without the polymorphisms, as shown by the negative baseline β-value. For example, one BCL11A rs1427407 SNP is associated with a ΔHbF 3.46 percentage points lower than individuals without the SNP at MTD, with an additive, dose effect of the SNP at the second allele; homozygous individuals have higher baseline HbF, lower ΔHbF compared to heterozygotes or wild-type individuals (Figure 1). The other variants HBS1L-MYB SNPs, XmnI, α-thalassemia or BCL11A SNP rs7599488 did not significantly impact ΔHbF. None of the tested polymorphisms, including the BCL11A SNPs, were associated with a significant difference in final HbF levels. Individuals with higher baseline HbF due to BCL11A polymorphisms demonstrate a statistically significant lower rise in HbF in response to hydroxyurea than individuals without these polymorphisms. Identification of more variants associated with baseline and ΔHbF through next generation sequencing will help elucidate whether the negative effect of high baseline on ΔHbF is a BCL11A specific effect, or a manifestation of a general threshold effect, that there is a maximum amount of HbF an individual is able to achieve through hydroxyurea induction.Table 1Association between BCL11A SNPs and response to hydroxyurea.GeneSNP IDBaseline β-value (lnHbF)Baseline p-valueΔHbF β-value (%HbF)ΔHbF p-valueBCL11Ars14274070.3569.05x10-5-3.461.02x10-3BCL11Ars46713930.272.17x10-3-2.627.21x10-3BCL11Ars118868680.131.61x10-4-3.007.86x10-4BCL11Ars75994880.080.30-0.780.33 [Display omitted] Disclosures:Off Label Use: Hydroxyurea is not FDA approved for use in pediatric sickle cell patients.

Interaction between Hb SS and alpha thalassemia (3.7 kb deletion)

Both the clinical course and molecular alterations of sickle cell anemia (Hb SS) are highly distinct. Possible modulators of phenotypical variability have been documented, including alpha-thalassemia and beta S-globin gene cluster haplotypes.(1) The possible benefits of alpha thalassemia co-inheritance also affect hematological parameters.(2) The Hb S intracellular concentration seems to present direct dependence on the alpha-globin genotype. Thus, the association of alpha thalassemia and Hb SS minimizes the physiopathological effects in carriers of hemoglobinopathy S. Alpha thalassemia caused by the deletion of 3.7 kb of DNA (-α3.7) is the most common in Brazil.(3) The present article reports the observation of different clinical and hematological profiles in two individuals from the same familial nucleus with Hb SS, one heterozygosis (-α/αα) and the other homozygosis (-α/-α) for alpha thalassemia(3.7 kb deletion). Patient 1, a 10-year-old boy (-α/αα) and Patient 2, a 22-year-old woman (-α-α) are both mulattos. The diagnostic confirmation of Hb SS and for alpha thalassemia (3.7 kb deletion) were achieved by polymerase chain reactionrestriction fragment length polymorphism (PCR-RFLP)(4) and multiplex PCR,(5) respectively. The concentrations of hemoglobinic fractions were determined by HPLC Variant™ equipment using the Beta Thal Short Program (Bio-Rad). Hematological parameters were obtained using a BC-300 PLUS automatic analyzer (Mindray). Blood samples were collected after receiving informed consent and according to the ethical principles established by Resolution 196/96 of the National Health Council. Clinical data, obtained from an evaluation of medical records, are shown in Table 1. Patient 1 had been transfused 130 days prior and Patient 2, 3204 days prior to the blood collection for this study. They did not take hydroxyurea but took folic acid. Quantitative laboratorial data are shown in Table 2. As for the morphologic evaluation of red blood cells, hypochromia was only present in the Hb SS interaction with the α/-α genotype, and polychromatophilic macrocytes only in the interaction between Hb SS and the -α/αα genotype. Other alterations such as microcytosis, macrocytosis, polychromatophilic cells, drepanocytes, Howell-Jolly bodies, codocytes and erythroblasts were common in both. The haplotypes of both individuals were characterized as Bantu/Benin by PCR-RFLP. Table 1 Clinical characteristics of the Hb SS-α3.7 thalassemia coexistence observed Table 2 Hematological data of the Hb SS-α3.7 interaction of Patients 1 and 2 with deletion of 1 and 2 alpha-genes, respectively Both hepatobiliary complications and vasculopathy were seen in Patient 1 (-α/αα), and splenomegaly were only observed in Patient 2 (-α/-α). As for the hematological effect, the homozygous patient for alpha thalassemia (-α/-α) showed a lower level of hemolysis, milder anemia, lower red blood cell indices as well as inflammation cell markers (granulocytes and monocytes) compared to the heterozygous patient (-α/αα). Co-inheritance of alpha thalassemia and Hb SS is associated to lower risk of cholelithiasis(6) and a higher frequency of splenomegaly.(7) The benefits of this epistatic effect seem to increase with the number of -α3.7 gene deletions. The results corroborate published data which report that the coexistence of homozygosis for alpha thalassemia (3.7 kb deletion) with sickle cell anemia is a factor that modulates the clinical variability and hematological severity, demonstrating a diversity of manifestations even within a single family nucleus.

Effect Alpha Globlin Gene Deletion And Gamma Globin Gene -158 (C/T) Polymorphism In Beta-Thalassemic Patients

The beta-thalassemias (&#946;- thalassemias) are among the most common autosomal recessive disorders. They have a remarkably high frequency in the Mediterranean region and represent one of the most common genetic diseases in Egypt. In this study, the spectrum of &#946;- thalassemia mutations and genotype-to-phenotype correlations were defined in 32 &#946;- thalassemic patients (&#946;- thlassemias major and intermedia) with varying disease severity in two cities of the Suez Canal region. Ten different mutations were identified and the most frequent ones were: IVSI-6 (T-C) (37.5%), IVSI-110 (G-A) (34.4%) and both IVSI-1 (G-A), IVSII-745 (C-G) and -102 (C-G) (12.5% each). There was a wide spectrum of phenotypic severity in all patients. We studied the Xmn1 polymorphism (C/T) in &#947;- globin gene position -158 of &#946;- thalassemia as a modulating factor of the disease severity. Presence of the polymorphism was found in two patients and this was not sufficient to explain the diversity of the phenotype encountered. Co-inheritance of alpha thalassaemia as a modulating factor was not evident in our patients. In conclusion, we have been unable to find a molecular basis for the benign clinical course in all our patients. Other genetic or acquired factors must be hypothesized which ameliorate the clinical condition. Keywords: &#946;- thalassemia, Xmn1 polymorphism, &#945-globin gene deletion. Egyptian Journal of Biochemistry and Molecular Biology Vol. 26 (2) 2008: pp. 85-100

Thalassemia intermedia in HbH-CS disease with compound heterozygosity for .BETA.-thalassemia: Challenges in hemoglobin analysis and clinical diagnosis

Co-inheritance of alpha-thalassemia with homozygosity or compound heterozygosity for beta-thalassemia may ameliorate beta-thalassemia major. A wide range of clinical phenotypes is produced depending on the number of alpha-thalassemia alleles (-alpha/alphaalpha --/alphaalpha, --/-alpha). The co-inheritance of beta-thalassemia with alpha-thalassemia with a single gene deletion (-alpha/alphaalpha) is usually associated with thalassemia major. In contrast, the co-inheritance of beta-thalassemia with two alpha-genes deleted in cis or trans (--/alphaalpha or -alpha/-alpha) generally produces beta-thalassemia intermedia. In Southeast Asia, the most common defect responsible for alpha-thalassemia is the Southeast Asian (SEA) deletion of 20.5 kilobases. The presence of the SEA deletion with Hb Constant Spring (HbCS) produces HbH-CS disease. Co-inheritance of HbH-CS with compound heterozygosity for beta-thalassemia is very rare. This study presents a Malay patient with HbH-CS disorder and beta degrees/beta+-thalassemia. The SEA deletion was confirmed in the patient using a duplex-PCR. A Combine-Amplification Refractory Mutation System (C-ARMS) technique to simultaneously detect HbCS and Hb Quong Sze confirmed HbCS in the patient. Compound heterozygosity for CD41/42 and Poly A was confirmed using the ARMS. This is a unique case as the SEA alpha-gene deletion in cis (--SEA/alphaalpha) is generally not present in the Malays, who more commonly possess the two alpha-gene deletion in trans (-alpha/-alpha). In addition, the beta-globin gene mutation at CD41/42 is a common mutation in the Chinese and not in the Malays. The presence of both the SEA deletion and CD41/42 in the mother of the patient suggests the possible introduction of these two defects into the family by marriage with a Chinese.

Genetic modifiers of the β‐haemoglobinopathies

Identification of the molecular basis of the beta-thalassaemias and sickle cell disease (SCD) has made it clear that patients with the same beta-globin genotypes can have very variable patterns of clinical expression. Extensive biochemical and pathophysiological studies over the last 50 years have derived two major modifiers--innate ability to produce fetal haemoglobin and co-inheritance of alpha-thalassaemia, subsequently validated by family and population studies. However, these two modifiers do not explain the full clinical spectrum. Genetic studies have been successful in identifying modifiers if the loci have a major clinical effect and if the genetic variants are common. It is possible that additional modifiers could be uncovered using genetic approaches but success will depend on large sample sizes of well-characterised patients with well-defined phenotypes. Since some of the complications, such as overt stroke in SCD, are relatively rare events, intermediate end-points that contribute to the phenotype, such as Transcranial Doppler velocity (a major predictor of stroke in SCD), could be integrated within the genetic analysis. Integrating multiplex genetic testing with clinical and laboratory data to generate predictive models shows potential, but such genetic approaches also require large datasets.

Coinheritance of the different copy numbers of α-globin gene modifies severity of β-thalassemia/Hb E disease

beta-Thalassemia/Hb E patients show a range of clinical severities, from nearly asymptomatic to transfusion-dependent thalassemia major. This study investigated the clinical heterogeneity and hematologic parameters obtained in the large cohort of 925 Thai beta 0-thalassemia/Hb E patients. Coinheritance of alpha-thalassemia with beta 0-thalassemia/Hb E produces a milder clinical phenotype in contrast to an interaction of alpha-globin gene triplication in severe thalassemia. The mean steady-state Hb was also higher, whereas the mean corpuscular volume and the percentage of Hb F were markedly lower in the former group. This finding demonstrates that the genetic combination leading to the more/less degree of alpha- to non-alpha-globin chains imbalance is indeed the cause of the severe/mild thalassemia phenotype.

The role of heterocellular hereditary persistence of fetal haemoglobin in beta(0)-thalassaemia intermedia.

Beta(0)-thalassaemia intermedia (beta(0)-TI) describes patients who lack beta-globin synthesis yet manifest a non-transfusion-dependent form of beta-thalassaemia. Co-inheritance of alpha-thalassaemia, certain variants of the beta-like globin gene cluster and elevated fetal haemoglobin (HbF) production are all associated with beta(0)-TI. However, the mild phenotypes of many beta(0)-TI patients are unexplained. Genetically determined HbF levels in beta-thalassaemia are difficult to assess because erythrocytes containing HbF (F cells) preferentially survive over erythrocytes without HbF. To evaluate the importance of genetically elevated HbF in beta-thalassaemia, F-cell levels of 19 TI patients' relatives were compared with relatives of transfusion-dependent beta-thalassaemia major patients and those of beta-globin genotype-matched controls. The beta-globin and alpha-globin genotypes, as well as their Ggamma promoter were also examined. Using this approach, in all but one patient the mild phenotype was attributable to either alpha-globin genotype, gamma-globin promoter polymorphism or inherited elevated F-cell levels. The findings of this study establish the F-cell levels required to modify the degree of disease severity significantly and demonstrate that F-cell level is a crucial parameter in the understanding of phenotypic variation in beta-thalassaemia.

Relationship between genotype and phenotype. Thalassemia intermedia.

Thalassemia intermedia encompasses a number of clinical conditions ranging in severity from beta-thalassemia carrier state to transfusion-dependent thalassemia major. The molecular bases of thalassemia intermedia, only partially defined, are very heterogeneous, but in general any factor able to reduce the globin-chain imbalance results in a milder form of thalassemia. These factors are the presence of a silent or mild beta-thalassemia allele, associated with a high residual beta-globin production, and the coinheritance of alpha-thalassemia or of genetic determinants that increase the gamma-chain production. Less frequent mechanisms are double heterozygosity for beta-thalassemia and triplicated alpha genes, and the presence of a hyperunstable hemoglobin variant. However, for a consistent number of beta zero-thalassemia homozygotes with a thalassemia intermedia phenotype the modifying factor has not been defined yet. In contrast, there are simple beta-thalassemia carriers who, for unknown reasons, have an unusually severe clinical phenotype.

Severity differences in beta-thalassaemia/haemoglobin E syndromes: implication of genetic factors.

Genetic factors determining the difference in severity of anaemia in beta-thalassaemia/HbE disease were studied in 90 patients who had haemoglobin levels, at steady state, ranging from 4.2 to 12.6 g/dl. Co-inheritance of alpha-thalassaemia 2 and haemoglobin Constant Spring could significantly decrease the severity of the disease. Inheritance of a beta-thalassaemia chromosome with Xmn I cleavage site at position -158 of the G gamma-globin gene which was linked to the haplotype -+-++ or ++-++, was associated with a milder anaemia. Two copies of these alleles were necessary to produce a significant clinical effect. Increased expression of the G gamma-globin gene and higher production of haemoglobin F, which could reduce the overall globin chain imbalance, were also associated with homozygosity for the Xmn I cleavage site and thus with less severe anaemia. However, this effect was not seen in Xmn I site heterozygotes. Whether the effects of the Xmn I polymorphism, HbF concentration and G gamma/A gamma ratio act separately or through common mechanisms in reducing anaemia remains to be ascertained.

β-Thalassämie: Molekulare Pathogenese und klinische Variabilität

Clinically, homozygous beta-thalassaemia is characterised by a severe anaemia requiring regular transfusion therapy in most patients. However, there is a marked clinical variability ranging from this severe picture to the virtual absence of symptoms and haematological abnormalities. Biochemically, beta-globin synthesis in the erythroid precursors of the bone marrow is reduced or absent resulting in a relative excess of insoluble alpha-globin chains and dyserythropoiesis. The molecular genetics of this disorder is highly variable involving a multitude of different mutations of the beta-globin gene. These mutations can inactivate gene expression at all levels on its way from DNA to mature haemoglobin. The clinical picture is largely determined by the type of mutations inherited. Additionally the degree of alpha-globin chain excess can be influenced by the co-inheritance of alpha-thalassaemia or mutations resulting in the hereditary persistence of fetal globin synthesis (HPFH). This review discusses the relationship between the molecular defect and the clinical picture of patients with beta-thalassaemia.

Thalassemia intermedia resulting from a mild beta-thalassemia mutation

We investigated the molecular basis for a mild phenotype in a group of patients with beta + thalassemia originating from Northern Sardinia by definition of the beta-thalassemia mutation, alpha-globin mapping and beta-globin haplotype determination. In nine patients, we detected the compound heterozygous state for the -87 promoter mutation and the codon 39 nonsense mutation; in one patient, we detected the combination of the codon 39 nonsense mutation and beta + IVS-1 nt 6 mutation. These patients were either nontransfusion dependent for survival or became transfusion dependent later. We did not detect the -87 promoter mutation in any of 115 thalassemia major patients originating from the same part of Sardinia, investigated as controls. Heterozygotes for the - 87 promoter mutation showed statistically higher hemoglobin (Hb) levels and larger and better hemoglobinized RBCs as compared with heterozygotes for the codon 39 nonsense mutation. From these data, we conclude that the -87 promoter mutation is a mild thalassemia allele, able to produce a phenotype of intermediate severity even in combination with a beta degree-thalassemia mutant. The coinheritance of alpha-thalassemia or the -++-- 5′ subhaplotype in several cases may have contributed to development of the mild clinical picture. Characterization of the beta-thalassemia mutation in combination with alpha-globin mapping and haplotype analysis may allow a better estimate of the probability of a given clinical phenotype, thus permitting more accurate counseling.

Thalassemia Intermedia Resulting From a Mild β-Thalassemia Mutation

We investigated the molecular basis for a mild phenotype in a group of patients with beta(+) thalassemia originating from Northern Sardinia by definition of the beta-thalassemia mutation, alpha-globin mapping and beta-globin haplotype determination. In nine patients, we detected the compound heterozygous state for the -87 promoter mutation and the codon 39 nonsense mutation; in one patient, we detected the combination of the codon 39 nonsense mutation and beta(+) IVS-1 nt 6 mutation. These patients were either nontransfusion dependent for survival or became transfusion dependent later. We did not detect the -87 promoter mutation in any of 115 thalassemia major patients originating from the same part of Sardinia, investigated as controls. Heterozygotes for the -87 promoter mutation showed statistically higher hemoglobin (Hb) levels and larger and better hemoglobinized RBCs as compared with heterozygotes for the codon 39 nonsense mutation. From these data, we conclude that the -87 promoter mutation is a mild thalassemia allele, able to produce a phenotype of intermediate severity even in combination with a beta(0)-thalassemia mutant. The coinheritance of alpha-thalassemia or the -++-- 5' subhaplotype in several cases may have contributed to development of the mild clinical picture. Characterization of the beta-thalassemia mutation in combination with alpha-globin mapping and haplotype analysis may allow a better estimate of the probability of a given clinical phenotype, thus permitting more accurate counseling.

EF Bart's disease: interaction of the abnormal alpha- and beta-globin genes.

EF Bart's disease is an uncommon form of thalassaemia intermedia resulting from the co-inheritance of alpha-thalassaemia and haemoglobin E in the same subject. Starch-gel electrophoresis revealed two phenotypes in 19 patients with EF Bart's. 16 patients had Hbs CS + E + F + Bart's and the remainder had Hbs E + F + Bart's. DNA mapping and haemoglobin electrophoresis indicated that there are four genotypes, involving 5 abnormal globin genes, responsible for this thalassaemia syndrome.

Organization of the zeta-alpha genes in Chinese.

Analysis of alpha and zeta genes in 101 healthy normals and hospitalized patients with non-haematological diseases revealed a 3% incidence of alpha thalassaemia in the local Chinese population of Hong Kong. Triple alpha genes were found in only one person while triple zeta genes were more prevalent, occurring in 13 subjects. Studies of 28 unselected patients with Hb H disease indicated a predominance of the rightward alpha gene deletion. The extent of alpha gene deletion in homozygous alpha thalassaemia 1 was at least 18.1 kb, beginning from the BamH I site 3' to the zeta 1 gene and includes the psi alpha, alpha 2 and alpha 1 genes. Nineteen of the 20 chromosomes bearing the alpha thalassaemia 1 deletion had identical zeta-intergenic hypervariable region suggesting a common origin of this mutation. The co-inheritance of alpha thalassaemia in beta thalassaemia subjects was 8%, but did not ameliorate the clinical features of those with homozygous beta thalassaemia.

Alpha-thalassemia in two Mediterranean populations

We used restriction endonuclease analysis to determine the incidence of alpha-thalassemia in two Mediterranean islands. In a random population sample, the gene frequency of deletion-type alpha-thalassemia-2 (-alpha) was 0.18 in Sardinians and 0.07 in Greek Cypriots. All cases were the rightward crossover type. From these frequencies and the known incidence of hemoglobin-H disease in these populations, we calculated the frequency of the alpha-thalassemia-1 genotype (--) and determined that it was low. We also found that beta-thalassemia homozygotes in sardinia have a higher incidence of alpha-thalassemia than normals and beta thalassemia heterozygotes because a significantly greater number of these homozygotes are also homozygous for the alpha-thalassemia-2 lesion. These findings support the theory that coinheritance of alpha-thalassemia mitigates the severity of beta-thalassemia and suggest that the protection is most pronounced when two alpha-globin genes are deleted.