Serum transferrin receptor levels in beta-thalassemia trait

Increased levels of transferrin receptors (TfR) and soluble TfR (sTfR) are reliable indicators of iron deficiency anemia and conditions with enhanced erythropoietic activity. In this study we measured sTfR levels in the cases of beta-thalassemia trait (betaTT) and IDA to see whether it would be a diagnostic tool for the differentiation of betaTT and IDA. On the other hand STfR levels could give an idea about erythropoietic activity in betaTT. Serum transferrin receptor (sTfR) levels were measured with enzyme immune assay in 37 cases with betaTT, in 26 patients with iron deficiency anemia (IDA), in 17 patients with the coexistence of betaTT with IDA, and in 21 healthy controls. Mean sTfR in betaTT (6.54 +/- 1.88) were statistically higher than in controls (5.09 +/- 0.76) and lower than in IDA (11.46 +/- 5.03) and in IDA coexistence with betaTT (14.44 +/- 5.3, p < 0.05 in each comparison). However, in 17 cases with betaTT sTfR levels showed an overlap between the patients with IDA, and in 15 cases with betaTT it also showed an overlap with controls. The finding of higher sTfR levels in betaTT compared with controls suggested that there was a degree of ineffective hematopoiesis in betaTT. Although sTfR levels in IDA were higher than in betaTT, because of largely overlapping values in both groups, it was not satisfactory to distinguish betaTT from IDA.

An interplay of alleviating mutations in the clinical phenotype of beta-thalassaemia intermedia

Prediction of a beta-thalassaemia major phenotype from the beta-genotype is generally relatively straightforward. However, despite the ability to accurately define the beta-thalassaemia mutations, prediction of a beta-thalassaemia intermedia phenotype from the genotype sometimes remains problematic and this has important implications in genetic counselling and prenatal diagnosis. We report a 11-year-old Indian male child with a thalassaemia intermedia phenotype. beta-Globin gene analysis of the family showed that he was a compound heterozygote with the -88 (C-->T) beta+-mutation and the IVS1 nt 130 (G-->C) beta0-mutation. Both these mutations are rare among Indians. The propositus was also found to be heterozygous for the XmnI polymorphism and had a normal alpha-genotype. In this family interplay of two alleviating mutations (a milder promoter mutation along with a gene for raised HbF) might have synergistically compensated for lack of globin chains in the patient. Hence, the nature of the beta-genotype as well as the knowledge of the presence or absence of alleviating factors will help the clinician to decide whether early commencement of a regular transfusion regime is necessary.

[Studies on safety of cordocentesis guided by transabdominal ultrasound for prenatal diagnosis]

OBJECTIVE

To assess the safety and efficacy of diagnostic cordocentesis during pregnancy.

METHODS

During March 1990 to June 2003, 2403 consecutive cordocenteses were performed under transabdominal ultrasound guidance at Guangzhou Women and Children's Hospital. The results of each procedure was prospectively collected and subsequently analysed in terms of operational complications and pregnancy outcomes.

RESULTS

Success rate of cordocentesis: totally 2368 procedures (98.5%) were done successfully at the first attempt, and 35(1.5%) required repeated cordocentesis, 16 of which were performed successfully at second attempt. Duration of cordocentesis: In 75.5% cases, the procedure was completed in less than 5 min, and in 93.0% cases in less than 10 min.

COMPLICATIONS

Transient bleeding at puncture site was observed in 315 cases (13.1%), transient fetal bradycardia in 125 cases (5.2%), and chorioamnionitis in 2 cases (0.1%). Pregnancy outcomes: The total fetal loss rate was 0.8% (18 cases of abortions). The rate of premature birth after cordocentesis was 0.2% (4 cases).

CONCLUSION

Cordocentesis during pregnancy is a useful, relatively safe, and effective procedure for prenatal diagnosis.

[Accurate and rapid prenatal diagnosis of beta-thalassemia by a multiplex primer extension and denaturing high-performance liquid chromatography technique]

OBJECTIVE

To develop a primer-extension in combination with denaturing high-performance liquid chromatography (PE-DHPLC)-based assay for prenatal diagnosis of the five most common beta-thalassemia mutations in Chinese.

METHODS

The human beta-globin gene fragment was amplified by PCR, followed by a multiple PE reaction specific for each five mutations. Then the PE product mixtures were separated for genotyping of beta-globin gene mutations using fully-denaturing DHPLC analysis.

RESULTS

In a blind study, prenatal diagnosis was performed on thirty-six at-risk families for beta-thalassemia major. Reverse dot blot (RDB) analysis was used to validate each result, showing an accuracy rate of 100% for PE-DHPLC in a total of 108 samples tested. Overall, by PE-DHPLC analysis, the authors could identify the genotypes involving the five mutations and normal alleles corresponding to 94.4% (102/108) and actually make final decision for prenatal diagnosis covering 97.2% (35/36).

CONCLUSION

The PE-DHPLC protocol can be a simple, rapid, and highly accurate assay in the prenatal detection of common beta-thalassemia mutations.

Molecular defects in the β-globin gene identified in different ethnic groups/populations during prenatal diagnosis for β-thalassemia: a Malaysian experience

Beta-thalassemia is the most-common genetic disorder of hemoglobin synthesis in Malaysia, and about 4.5% of the population are heterozygous carriers of the disorder. Prenatal diagnosis was performed for 96 couples using the Amplification Refractory Mutation System and Gap-Polymerase Chain Reaction. We identified 17 beta-globin defects-initiation codon for translation (T-G), -29 (A-G), -28 (A-G), CAP +1 (A-C), CD 8/9 (+G), CD 15 (G-A), CD 17 (A-T), CD 19 (A-G), Hb E (G-A), IVS1-1 (G-T), IVS1-5 (G-C), CD 41/42 (-CTTT), CD 71-72 (+A), IVS2-654 (CT), poly A(A-G), 100-kb Ggamma(Agammadeltabeta) degrees and 45-kb Filipino deletions. The 192 beta-alleles studied comprised Chinese (151 patients), Malay (21), Orang Asli from East Malaysia (15), Filipino (1), Indian (1), Indonesian Chinese (2), and Thai (1). In the Chinese, 2 beta-globin defects at CD 41/42 and IVS2-654 were responsible for 74% of beta-thalassemia. beta-mutations at CD 19, IVS1-1 (G-T), IVS1-5, poly A, and hemoglobin E caused 76% of the hemoglobin disorders in the Malays. The Filipino 45-kb deletion caused 73.3% of bthalassemia in the Orang Asli. Using genomic sequencing, the rare Chinese beta-mutation at CD 43 (G-T) was confirmed in 2 Chinese, and the Mediterranean mutation IVS1-1 (G-A) was observed in a Malay beta-thalassemia carrier. The beta-globin mutations confirmed in this prenatal diagnosis study were heterogenous and 65 (68%) couples showed a different globin defect from each other. The use of specific molecular protocols has allowed rapid and successful prenatal diagnosis of beta-thalassemia in Malaysia.

The potential of electrospray ionization mass spectrometry for the diagnosis of hemoglobin variants found in newborn screening

Analytical procedures have been developed for the detection and diagnosis of sickle cell disease in newborn babies by analyzing the hemoglobin extracted from dried blood spots on Guthrie cards using electrospray ionization mass spectrometry (ESI-MS). An essential requirement is the ability to reliably differentiate two globin chains whose molecular weights differ by only 1 Da such as adult hemoglobin (Hb A) and Hb C. This has been achieved by improving the accuracy and precision of the molecular weight determination to a fraction of a dalton. We report the potential of mass spectrometry for screening neonates for these debilitating diseases by presenting results from 147 blood spots that had been characterized by phenotypic methods and which include samples from 20 sickle cell disease, 1 beta-thalassemia major, 57 sickle cell trait, and 39 normal babies. In all cases, the mass spectrometric results agreed with the results obtained using conventional analytical practice with high-performance liquid chromatography (HPLC) and isoelectric focusing (IEF). We show that mass spectrometry is a viable technique for the diagnosis of newborns with sickle cell disease or homozygous beta0-thalassemia.

Endocrinopathies in patients with thalassemias

Thalassemia major is a hereditary disorder of hemoglobin synthesis resulting in severe anemia. Treatment consists of multiple blood transfusions, a complication of which is iron overload. Excessive iron is then deposited in almost all tissues but primarily in the liver, heart and the endocrine glands. Lately, desferrioxamine has been used as a chelating agent in an attempt to prevent the complications of tissue damage by iron deposition. Early introduction of the chelating agent to combat iron overload in vulnerable organs leads to improved life expectancy. However, these patients often present with multiple endocrine dysfunction such as growth failure, hypogonadism, abnormalities in glucose metabolism, hypothyroidism, hypoparathyroidism and less frequently hypoadrenalism. We briefly review the current status of endocrine gland abnormalities in patients with thalassemia major.

Clinical and molecular aspects of haemoglobinopathies in Tunisia

BACKGROUND

For the last two decades, studies on the population genetics of Tunisians have focused on variations of protein and genetic markers. Results confirmed the genetic heterogeneity of Tunisians caused by the admixtures with migratory human groups arriving mainly from Africa, Europe, and Asia. These studies also allowed the screening of rare mutants and many haemoglobin variants.

METHODS

The present study delineates the incidence of the different haemoglobinopathies in Tunisia. Previously collected data and results obtained from epidemiological and clinical studies of 1238 blood donors and 276 patients were compared. The chromosomal backgrounds of different haemoglobinopathies were explored by molecular techniques (denaturing gradient gel electrophoresis (DGGE), amplification refractory mutation system (ARMS) polymerase chain reaction (PCR), and sequencing).

RESULTS

This study indicates that appropriate DNA methodologies required for a nationwide preventive program in Tunisia are available and that prenatal diagnosis is feasible. Additionally, analysis of sequence polymorphisms allowed a better understanding of the gene recombination events and their application for tracing back the origin and the diffusion of the mutations.

CONCLUSIONS

Molecular analysis techniques such as DGGE and ARMS PCR are socially and economically the most suitable techniques to be used in Tunisia for the detection and the identification of haemoglobin abnormalities. At present, their use is essential to conduct a clear and efficient screening program.

Reliable and High-Throughput Mutation Screening for β-Thalassemia by a Single-Base Extension/Fluorescence Polarization Assay

beta-thalassemia is one of the most common inherited diseases with incidence varying between 3% and 10% in the high-prevalence regions of South China. The molecular defects are mostly due to single-nucleotide substitutions, minor insertions, and deletions in the beta-globin gene. Large-scale population genetic screening combined with prenatal diagnosis is necessary for the effective prevention of this disease. We present a single base extension (SBE) method based on homogenous fluorescence polarization (FP) for simultaneous detection of the eight most common causative mutations [CDs 41-42 (-TCTT), IVS-2-654 (C-->T), -28 (A-->G), CD17 (A-->T), CD 71/72 (+A), CD26 (G-->A), -29 (A-->G), and CD43 (G-->T)] in the beta-globin gene in a Chinese population. This assay has been validated by a blind experiment with 100 clinical samples previously characterized by reverse dot-blot and direct sequencing. The results demonstrate that this high-throughput method is simple, reliable, and cost effective. We expect this approach can be used in large-scale genetic screening for beta-thalassemia.

Hemoglobinopathies in pregnancy

Hemoglobinopathies represent a unique set of genetic disorders. Formerly, many affected individuals did not survive to childbearing age. Affected women now commonly reach childbearing age and desire pregnancy. Successful pregnancy is possible in many cases with carefully coordinated obstetric and medical management. Genetic screening and prenatal diagnosis is an important aspect of prenatal care in these disorders. DNA mutation analysis offers rapid and accurate fetal diagnosis. Pregnancy also offers a unique situation in that cord blood has become a valuable source of stem cells for transplant. This allows the potential role of the unaffected fetus as a donor for affected siblings. In addition, it was proposed that the fetus may be able to act as a donor of stem cells for an affected mother. Despite current screening recommendations,many couples are not aware that they are carriers; it is common for a child to be born with an unexpected, serious hemoglobinopathies. For this reason, newborn screening programs have been introduced in most high-risk areas. Early diagnosis can facilitate implementation of proper preventive health measures, education of the parents regarding their carrier status, and provide the child with ongoing comprehensive care.

Simultaneous detection of alpha-thalassemia and beta-thalassemia by oligonucleotide microarray

In this study, we describe a reliable microarray-based assay for the simultaneous detection of alpha/beta-globin genotypes. The efficiency and specificity of this method were evaluated by blinded analysis of 1,880 samples. The assay provides unambiguous detection of complex combinations of heterozygous, compound heterozygous and homozygous alpha/beta-thalassemia genotypes.

β-Thalassemia Is a Modifying Factor of the Clinical Expression of Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is a codominant disorder due to a variety of mutations of the low-density lipoprotein (LDL) receptor gene that result in an elevation of plasma LDL-cholesterol (LDL-C). Plasma levels of LDL-C show large interindividual variation even in subjects carrying the same mutation of the LDL receptor gene. This variability may be due to genetic factors (modifier genes). Several surveys indicate that the overall contribution of common polymorphisms of modifier genes (such as the genes encoding apolipoproteins E and B) to this variability is less than 10%. In contrast, beta-thalassemia has a profound LDL-lowering effect. This was documented in FH patients identified on the island of Sardinia, in Italy, where 12% of the inhabitants are carriers of beta-thalassemia due to a single mutation (Q39X) of the beta-globin gene that abolishes the synthesis of beta-globin chain of hemoglobin (beta(o)-thalassemia). Plasma LDL-C in FH heterozygotes carrying the beta(o)-thalassemia trait is 25% lower than in noncarriers, regardless of the LDL receptor gene mutation. It is likely that this effect is due to two main mechanisms: (1) increased uptake of LDL by the bone marrow to provide cholesterol for the increased proliferation of erythroid progenitor cells and (2) increased production of inflammatory cytokines that reduce the hepatic secretion and increase the catabolism of LDL. In view of its LDL-C-lowering effect, beta-thalassemia trait may protect FH heterozygotes against premature coronary atherosclerosis.

Molecular genetic analyses of β-thalassemia in South India reveals rare mutations in the β-globin gene

beta-Thalassemia is the most prevalent single-gene disorder. Since no viable forms of treatment are available, the best course is prevention through prenatal diagnosis. In the present study, the prevalence of beta-thalassemia was extensively investigated in the South Indian population, especially from the state of Andhra Pradesh. Screening for causal mutations was carried out on genomic DNA isolated from patient blood samples by using the routine reverse dot blot (RDB) and amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) techniques. DNA sequencing was performed wherever necessary. Among the nine mutations identified, four, including IVS-1-5 (G-C) (IVS1+5G>T), codon 41/42 (-TTCT) (c.124_127delTTCT), codon 15 (G-A) (c.47G>A), and HbS (sickle mutation) (c.20A>T) mutations, accounted for about 98% of the total positive cases. Two mutations viz. codon 8/9 (+G) (c.27_28insG) and HbE (codon 26 G-A) (c.79G>A) exhibited a very low frequency of occurrence, whereas the IVS-1-1 (G-T) (IVS1+1G>T) and the 619 bp deletion (c.366_494del) mutations were absent. We also identified certain rare mutations during the diagnostic evaluation. Gene sequencing confirmed the codon 30 (G-C) (c.92G>C) mutation and the rare codon 5 (-CT) (c.17_18delCT) and IVS-II-837 (T-G) (IVSII-14T>G) mutations. This is the first report of the IVS II 837 mutation in the Indian population. We also report a novel diagnostic application during RDB-based screening for the detection of the (c.92G>C) mutations. Such a comprehensive mutation screening is essential for prenatal diagnosis of beta-thalassemia and control of this highly prevalent monogenic disorder in the Indian population.

MS analysis of single-nucleotide differences in circulating nucleic acids: Application to noninvasive prenatal diagnosis

The analysis of circulating nucleic acids has revealed applications in the noninvasive diagnosis, monitoring, and prognostication of many clinical conditions. Circulating fetal-specific sequences have been detected and constitute a fraction of the total DNA in maternal plasma. The diagnostic reliability of circulating DNA analysis depends on the fractional concentration of the targeted sequence, the analytical sensitivity, and the specificity. The robust discrimination of single-nucleotide differences between circulating DNA species is technically challenging and demands the adoption of highly sensitive and specific analytical systems. We have developed a method based on single-allele base extension reaction and MS, which allows for the reliable detection of fetal-specific alleles, including point mutations and single-nucleotide polymorphisms, in maternal plasma. The approach was applied to exclude the fetal inheritance of the four most common Southeast Asian beta-thalassemia mutations in at-risk pregnancies between weeks 7 and 21 of gestation. Fetal genotypes were correctly predicted in all cases studied. Fetal haplotype analysis based on a single-nucleotide polymorphism linked to the beta-globin locus, HBB, in maternal plasma also was achieved. Consequently, noninvasive prenatal diagnosis in a mother and father carrying identical beta-thalassemia mutations was accomplished. These advances will help in catalyzing the clinical applications of fetal nucleic acids in maternal plasma. This analytical approach also will have implications for many other applications of circulating nucleic acids in areas such as oncology and transplantation.

Molecular basis and hematologic characterization of deltabeta-thalassemia and hereditary persistence of fetal hemoglobin in Thailand

BACKGROUND AND OBJECTIVES

Hereditary persistence of fetal hemoglobin (HPFH) and deltabeta-thalassemia are heterogeneous disorders characterized by increased levels of Hb F in adult life. The distinction between these two conditions is not always possible from routine hematologic analyses. This study investigated the hematologic and molecular characteristics of high HbF determinants in Thailand, and describes a rapid DNA-based assay to facilitate diagnosis in a routine laboratory.

DESIGN AND METHODS

A multiplex allele-specific polymerase chain reaction (PCR) system for rapid detection of three common DNA deletions causing (deltabeta)0-thalassemia and HPFH in South-east Asians was developed and used to examine the molecular basis for the high Hb F phenotypes in 273 unrelated Thai individuals. Hematologic data were recorded and correlated to the molecular findings.

RESULTS

The multiplex PCR system was validated and results were completely concordant with those of other established methods. DNA analysis identified GgAg(deltabeta)0-thalassemia in 148 cases (54.2%), deletional HPFH-6 in 83 (30.4 %) and the deletion-inversion Ggamma(Agammadeltabeta)0-thalassemia in 22 (8.1 %) cases, while another 20 (7.3 %) subjects remained uncharacterized. Genotype-phenotype relationships are discussed.

INTERPRETATION AND CONCLUSIONS

These data emphasize the high frequencies of deltabeta-thalassemia and HPFH in Thailand and the need for differential diagnostic methods since the hematologic parameters associated with the conditions are very similar and overlap. The multiplex allele-specific PCR approach should prove useful in complementing routine Hb analysis for the differential diagnosis of these three common causes of high Hb F determinants and should facilitate a program of hemoglobinopathy screening in the region.

Real-time multiplex analysis of four beta-thalassemia mutations employing surface plasmon resonance and biosensor technology

In this paper, biospecific interaction analysis (BIA) employing surface plasmon resonance (SPR) and biosensor technologies was applied to the analysis of multiple mutations of the human beta-globin gene. To this aim, large target polymerase chain reaction (PCR) products were immobilized on sensor chips and then probes detecting beta degrees 39 (C>T), beta degrees IVSI-1 (G>A), beta(+)IVSI-6 (T>C) and beta(+)IVSI-110 (G>A) thalassemia mutations were sequentially injected. In this study, a total of ten normal and seven heterozygous subjects, and six homozygous patients were considered. The results obtained allow to conclude that discrimination between normal subjects, heterozygous, and homozygous patients is readily achieved for all the four mutations by PCR amplification of genomic DNA containing all the regions corresponding to the same mutations, immobilization of the same PCR products, and hybridization. To our knowledge the procedure described here is the first reported on the use of SPR-based BIA and biosensor technology for multiple detections of point mutations.

Fast and sensitive diagnosis of thalassemia by capillary electrophoresis

This paper demonstrates the diagnosis of beta-thalassemia by capillary electrophoresis in conjunction with laser-induced fluorescence using poly(ethylene oxide) (PEO) solutions in the presence of electroosmotic flow (EOF). During the electrophoretic separation, PEO solution entered a capillary from the anodic vial by EOF. The separation of a mixture of the polymerase chain reaction (PCR) products (330 and 334 base pairs) from a healthy person and a beta-thalassemia patient was accomplished within 15 min at 15 kV using 1.5% PEO containing 2 M urea at 30 degrees C. The electropherogram patterns instead of migration times were used to diagnose beta-thalassemia, with an accuracy of 100% for the analyses of 11 blood samples from suspected patients. After injecting a large volume of the mixture to the capillary filled with 800 mM Tris-borate buffer (pH 10.0), the DNA fragments stacked due to increases in viscosity and sieving when migrating into 1.5% PEO solution. As a result of improved sensitivity, only 15 PCR cycles were required when using 500 ng of DNA templates. The results shown in this study indicate the potential of this simple, rapid, and cost-effective method for the diagnosis of beta-thalassemia.

Early prenatal diagnosis by celocentesis

BACKGROUND

Celocentesis is the ultrasound-guided aspiration of fluid from the extra-amniotic cavity at 7-8 weeks of gestation. This paper reports on the clinical application of celocentesis for early prenatal diagnosis.

METHODS

Celocentesis was successfully performed in nine pregnancies and 1-2 mL of fluid were obtained after one needle insertion. The indications were prenatal diagnosis of beta-thalassemia or sickle cell disease (n = 6), Marfan syndrome (n = 1) and paternity testing (n = 2). Molecular biological techniques were used to analyze the celomic fluid and this was successfully carried out in all cases.

RESULTS

In two cases pregnancy termination was performed at the request of the mother because in one case the fetus was found to have sickle cell anemia and in the second case paternity testing demonstrated that the father was not the woman's husband. In both cases the results were confirmed using the placental samples collected after pregnancy termination. In six of the seven pregnancies with desirable results, amniocentesis was performed at 16 weeks and the results were concordant with those obtained from celocentesis. All pregnancies were uneventful and resulted in the delivery of healthy and appropriately grown babies.

CONCLUSION

Celocentesis may be a viable alternative to the currently used tests of chorionic villus sampling and amniocentesis.

Evaluation of alpha hemoglobin stabilizing protein (AHSP) as a genetic modifier in patients with β thalassemia

Although β thalassemia is considered to be a classic monogenic disease, it is clear that there is considerable clinical variability between patients who inherit identical β globin gene mutations, suggesting that there may be a variety of genetic determinants influencing different clinical phenotypes. It has been suggested that variations in the structure or amounts of a highly expressed red cell protein (alpha hemoglobin stabilizing protein [AHSP]), which can stabilize free α globin chains in vitro, could influence disease severity in patients with β thalassemia. To address this hypothesis, we studied 120 patients with Hb E-β thalassemia with mild, moderate, or severe clinical phenotypes. Using gene mapping, direct genomic sequencing, and extended haplotype analysis, we found no mutation or specific association between haplotypes of AHSP and disease severity in these patients, suggesting that AHSP is not a disease modifier in Hb E-β thalassemia. It remains to be seen if any association between AHSP and clinical severity is present in other population groups with a high frequency of β thalassemia. (Blood. 2004;103:3296-3299)

[Diagnosis of beta-thalassemia]

The purpose of the case study was to evaluate the potentialities of using the data found by hematology analyzers in the diagnosis of beta-thalassemia. Eighty (80) persons with homozygous beta-thalassemia, 180 carriers of the beta-thalassemia gene and 50 healthy subjects were examined. Counts of erythrocytes, content of hemoglobin, hematocrit and erythrocytes indices (MCV, MCH, MCHC) were determined in all of them. Besides, also in all cases, the osmotic erythrocyte resistance was investigated; the content of fetal hemoglobin was determined; electrophoresis of hemoglobin in the cellulose-acetate films was made as well as a lack or presence of the interplay between the studied parameters was established through estimating the correlation factor. The results showed significant changes in many parameters both in homo- and hetero-thalassemia versus such parameters in healthy subjects. Blood tests by hematology analyzers in cases of carrier-state of the thalassemia gene were acknowledged to be extra valuable since no clinical signs are available in such disease variation. MCV and MCH are most useful parameters in the diagnosis of heterozygous thalassemia for a reliably direct correlation was found between them.

The prevalence and spectrum of alpha and beta thalassaemia in Guangdong Province: implications for the future health burden and population screening

AIM

Thalassaemia is a good candidate disease for control by preventive genetic programmes in developing countries. Accurate population frequency data are needed for planning the control of thalassaemia in the high risk Guangdong Province of southern China.

METHODS

In total, 13397 consecutive samples from five geographical areas of Guangdong Province were analysed for both haematological and molecular parameters.

RESULTS

There was a high prevalence of carriers of alpha thalassaemia (8.53%), beta thalassaemia (2.54%), and both alpha and beta thalassaemia (0.26%). Overall, 11.07% of the population in this area were heterozygous carriers of alpha and beta thalassaemia. The mutation spectrum of alpha and beta thalassaemia and its constitution were fully described in this area. This study reports the true prevalence of silent alpha thalassaemia in the southern China population for the first time. In addition, two novel mutations that give rise to alpha thalassaemia, one deletion resulting in beta thalassaemia, and a rare deletion (--(THAI) allele) previously unreported in mainland China were detected. The frequency of the most common mutation, the Southeast Asian type of deletion (--(SEA), accounting for 48.54% of all alpha thalassaemias) was similar to the total of two alpha(+) thalassaemia deletions (-alpha(3.7) and -alpha(4.2), accounting for 47.49% of alpha thalassaemia).

CONCLUSION

Both alpha and beta thalassaemia are widely distributed in Guangdong Province of China. The knowledge gained in this study will enable the projected number of pregnancies at risk to be estimated and a screening strategy for control of thalassaemia to be designed in this area.