Beta thalassaemia mutations in Sardinians: implications for prenatal diagnosis

A review of the main genetic factors influencing the course of COVID-19 in Sardinia: the role of human leukocyte antigen-G

Introduction

A large number of risk and protective factors have been identified during the SARS-CoV-2 pandemic which may influence the outcome of COVID-19. Among these, recent studies have explored the role of HLA-G molecules and their immunomodulatory effects in COVID-19, but there are very few reports exploring the genetic basis of these manifestations. The present study aims to investigate how host genetic factors, including HLA-G gene polymorphisms and sHLA-G, can affect SARS-CoV-2 infection.

Materials and Methods

We compared the immune-genetic and phenotypic characteristics between COVID-19 patients (n = 381) with varying degrees of severity of the disease and 420 healthy controls from Sardinia (Italy).

Results

HLA-G locus analysis showed that the extended haplotype HLA-G*01:01:01:01/UTR-1 was more prevalent in both COVID-19 patients and controls. In particular, this extended haplotype was more common among patients with mild symptoms than those with severe symptoms [22.7% vs 15.7%, OR = 0.634 (95% CI 0.440 - 0.913); P = 0.016]. Furthermore, the most significant HLA-G 3'UTR polymorphism (rs371194629) shows that the HLA-G 3'UTR Del/Del genotype frequency decreases gradually from 27.6% in paucisymptomatic patients to 15.9% in patients with severe symptoms (X² = 7.095, P = 0.029), reaching the lowest frequency (7.0%) in ICU patients (X² = 11.257, P = 0.004). However, no significant differences were observed for the soluble HLA-G levels in patients and controls. Finally, we showed that SARS-CoV-2 infection in the Sardinian population is also influenced by other genetic factors such as β-thalassemia trait (rs11549407C>T in the HBB gene), KIR2DS2/HLA-C C1+ group combination and the HLA-B*58:01, C*07:01, DRB1*03:01 haplotype which exert a protective effect [P = 0.005, P = 0.001 and P = 0.026 respectively]. Conversely, the Neanderthal LZTFL1 gene variant (rs35044562A>G) shows a detrimental consequence on the disease course [P = 0.001]. However, by using a logistic regression model, HLA-G 3'UTR Del/Del genotype was independent from the other significant variables [OR_M = 0.4 (95% CI 0.2 - 0.7), P_M = 6.5 x 10^-4].

Conclusion

Our results reveal novel genetic variants which could potentially serve as biomarkers for disease prognosis and treatment, highlighting the importance of considering genetic factors in the management of COVID-19 patients.

2,000 Year old β-thalassemia case in Sardinia suggests malaria was endemic by the Roman period

OBJECTIVES

The island of Sardinia has one of the highest incidence rates of β-thalassemia in Europe due to its long history of endemic malaria, which, according to historical records, was introduced around 2,600 years ago by the Punics and only became endemic around the Middle Ages. In particular, the cod39 mutation is responsible for more than 95% of all β-thalassemia cases observed on the island. Debates surround the origin of the mutation. Some argue that its presence in the Western Mediterranean reflects the migration of people away from Sardinia, others that it reflects the colonization of the island by the Punics who might have carried the disease allele. The aim of this study was to investigate β-globin mutations, including cod39, using ancient DNA (aDNA) analysis, to better understand the history and origin of β-thalassemia and malaria in Sardinia.

MATERIALS AND METHODS

PCR analysis followed by sequencing were used to investigate the presence of β-thalassemia mutations in 19 individuals from three different Roman and Punic necropolises in Sardinia.

RESULTS

The cod39 mutation was identified in one male individual buried in a necropolis from the Punic/Roman period. Further analyses have shown that his mitochondrial DNA (mtDNA) and Y-chromosome haplogroups were U5a and I2a1a1, respectively, indicating the individual was probably of Sardinian origin.

CONCLUSIONS

This is the earliest documented case of β-thalassemia in Sardinia to date. The presence of such a pathogenic mutation and its persistence until present day indicates that malaria was likely endemic on the island by the Roman period, earlier than the historical sources suggest.

The β‐Thalassemia Mutation/Haplotype Distribution in the Moroccan Population

The present study compiles the results of our own research and of a prior study on beta-thalassemia (thal) in Morocco, comprising a total of 187 beta-thalassemic chromosomes. Six major mutations: (beta0) codon 39 (C --> T), (beta+) IVS-I-6 (T --> C), (beta0) frameshift codon (FSC) 6 (-A), (beta0) FSC 8 (-AA), (beta0) IVS-I-1 (G --> A) and (beta+) -29 (A --> G) account for 75.7% of the independent chromosomes studied. A regional predominance was observed (Gharb and West regions) for the (beta+) IVS-I-6 (T --> C) mutation. Despite an observed heterogeneity of molecular anomalies, a direct method of diagnosis of the prevalent mutations is feasible in this population. The distributions of mutations and haplotypes are in conformity with the geographical location of Morocco and the historical links with both the Mediterranean communities that have successively interspersed with the Berbers, the Phoenicians, the Carthaginians, the Romans, the Arabs, the population of the Iberian Peninsula and, to a lesser degree, the Vandals and the Byzantines and permanently, with the Sub-Saharan Africans. In the adult population, the levels of fetal hemoglobin (Hb) in heterozygotes vary from trace quantities to 2.38 g/dL of total Hb. With the exception of the (beta0) codon 39 (C --> T) nonsense mutation, no statistically significant correlation was found, neither between mutation and Hb F levels, nor gender and Hb F levels in heterozygotes. The genetic markers for Hb F increase, located within cis active sites such as the XmnI site at -158 bp of the Ggamma-globin gene and the AT(X)T(Y) repeat region at -540 bp of the beta-globin gene, were assessed. The polymorphism XmnI shows linkage disequilibrium with haplotypes III, IV and IX, as previously observed in the Algerian, Sicilian and Portuguese beta-thal populations. Contrary to what has previously been reported for a population of beta-thal carriers of European descent, this sample does not show a statistically significant correlation between Hb F levels and the presence of the genetic markers XmnI restriction site at -158 bp of the Ggamma-globin gene and AT(X)T(Y) alleles at 5' of the beta-globin gene.

β-globin cluster haplotypes in normal individuals and β039-thalassemia carriers from Sardinia, Italy

Seven polymorphic sites in the beta-globin cluster in association with specific thalassemia mutations were analyzed in a sample from Sardinia, Italy. In order to verify previous works carried out on normal samples (beta(A)/beta(A)) and family studies on beta-thalassemia homozygotes individuals, the haplotype frequencies in both normal individuals (beta(A)/beta(A)) and beta(0)39-thalassemia carriers (beta(A)/beta0) were studied. In our work chromosomes carrying beta(0)39 mutation are characterized by a prevalence of haplotype II (- + + - + + +) (52%) relative to haplotype I (+- - - - + +) (29%), in contrast, among chromosomes with beta(A) the frequency of haplotype I is much greater than that of haplotype II. These data confirm what was found by other authors. Nevertheless, our results disagree with those of previous studies of Sardinians, both in frequencies values and in the numbers of haplotypes identified. Population analysis performed with samples carrying the beta-thalassemic mutation highlighted the peculiarity of Sardinians with respect to other Mediterranean populations. The Corsican population is most similar to the Sardinian population, confirming previous analyses performed with both classical markers and mitochondrial and genomic DNA.

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.

Molecular characterization of beta-thalassemia in Syria

This study concerns the determination of beta-thalassemia alleles and other hemoglobin variants in 82 patients from Syria. We have characterized 146 chromosomes and found 17 different beta-thalassemia mutations, and one beta-globin chain variant that gives rise to the abnormal Hb S. The eight most common beta-thalassemia mutations were the IVS-I-110 (G-->A), IVS-I-1 (G-->A), codon 5 (-CT), -30 (T-->A), codon 39 (C-->T), IVS-I-6 (T-->C), IVS-II-1 (G-->A), and codon 15 (TGG-->TAG). These mutations accounted for almost 75% of the total beta-thalassemia chromosomes. We identified 34 different genotypes with a high level of homozygosity. The various beta-thalassemia mutations were characterized using gene amplification with specific oligonucleotide primers, restriction enzyme analysis, denaturing gradient gel electrophoresis and direct sequencing. By combining these three approaches we were able to detect mutations in almost 90% of the chromosomes studied. Our findings provide a sound foundation on which to base a preventive program for thalassemia and we believe that the data that we present will facilitate the improvement of medical services such as carrier screening, genetic counseling, and prenatal diagnosis. Furthermore a detailed knowledge of the molecular pathology of beta-thalassemia will strongly improve the prenatal diagnosis services in Syria.

Prenatal diagnosis of beta-thalassemia among Indians using denaturing gradient gel electrophoresis

We have offered first trimester prenatal diagnosis to 55 couples at risk for beta-thalassemia, originating from various parts of India, using polymerase chain reaction and denaturing gradient gel electrophoresis. Apart from the six common mutations, codon 30 (CAG-->CAA), Cap site +1 (A-->C), as well as three uncharacterized mutations were seen among the parents. In the majority of cases, the diagnosis was possible by scanning only one fragment (B) where most of the Indian mutations are situated. In 18 out of 55 cases, framework analysis could also have been used to offer prenatal diagnosis without characterizing the beta-thalassemia mutations. In the two cases where the mutations were uncharacterized, prenatal diagnosis was done only on the basis of the anomalous denaturing gradient gel electrophoresis patterns seen in the parents and in previously affected children. This is the first attempt of prenatal analysis using denaturing gradient gel electrophoresis in the extremely diverse Indian population where the profile of mutations has not yet been fully elucidated.

Beta-thalassemia alleles in Aegean region of Turkey: effect on clinical severity of disease

Beta (beta) globin gene analysis was performed in 54 homozygous beta-thalassemia patients followed up in the Pediatric Hematology Department of Medical School of Ege University. The spectrum of beta-thalassemia alleles and their effect on clinical severity of disease were investigated. Twelve different mutations were determined in our patients. The six most frequent alleles, IVSI-110 (G-A), IVSI-6 (T-C), IVSI-I (G-A), IVSII-745 (C-G), Cd39 (C-T), and FSC8, account for 80.6% of all the disease genes. Eleven percent of the chromosomes could not be identified with the probes used in this study. In 38 patients both of whose beta-thalassemia alleles were identified, the beta-thalassemia alleles were found to be the major determinant of the clinical severity of disease. The clinical progress of disease was also closely related to the degree of iron overload.

Sickle cell anemia, sickle cell beta-thalassemia, and thalassemia major in Albania: characterization of mutations

We have analyzed the hemoglobin abnormalities in nearly 50 Albanian patients with a significant hemoglobinopathy and included 37 relatives in this study. Sickle cell anemia (SS) is a common disorder; all 15 sickle cell anemia patients had the complications expected for this disease. The beta S haplotype was type 19 (Benin); alpha-thalassemia-2 was rare. Three beta-thalassemia alleles (IVS-I-110, G-->A; codon 39, C-->T; IVS-I-6, T-->C) were present in nearly 85% of the beta-thalassemia alleles; their frequencies were intermediate between those observed in the populations of neighboring countries. A few rare mutations were also found, which might have originated in India, Turkey, Macedonia, and Greece. Nearly all patients with Hb S-beta-thalassemia had the IVS-I-110 (G-->A) mutation. The frequencies of 11 beta-thalassemia mutations in 17 mostly Mediterranean countries have been reviewed.

DNA diagnosis for the detection of sickle hemoglobinopathies

At this time, the sole generally accepted use for DNA diagnosis in the hemoglobinopathies is for the prenatal detection of disease, which can be identified by these means early in the first trimester of pregnancy. By ascertaining genotype rather than phenotype, the confusion that results from diagnostic errors should be diminished. DNA diagnostics are the future of all genetic disease detection and this future will soon be upon us.

The population genetics of the haemoglobinopathies

The haemoglobinopathies are the commonest single gene disorders known, and are so common in some regions of the world that the majority of the population carries at least one genetic abnormality affecting the structure or synthesis of the haemoglobin molecule. The prevalence of the common haemoglobinopathies (the alpha- and beta-thalassaemias, HbS, HbC and HbE) is almost certainly a result of the protection they provide against malaria, as the epidemiological evidence reviewed in this chapter shows. World-wide, the distributions of malaria and the common haemoglobinopathies largely overlap, and micro-epidemiological surveys have confirmed the close relationship between the disorders. However, there are complications to this picture which appear to undermine the malaria hypothesis. First, in some areas, malaria and haemoglobinopathies are not coincident. Second, the malaria hypothesis does not easily explain why no two regions of the world have the same haemoglobinopathy or combination of haemoglobinopathies. The majority of mutations have arisen only once and are regionally specific. By using molecular characterization of mutations and the analysis of haplotypes on haemoglobinopathy-bearing chromosomes it is possible to show how a combination of selection by malaria, genetic drift and population movements can explain the first complication. In order to explain the second, we have argued that malaria selection has operated relatively recently on human populations (within the last 5000 years). The present distribution is then seen as the result of selection elevating sporadic mutations in local populations. In the absence of sufficient gene flow to spread all mutations to all populations, the consequence is a patchwork distribution of haemoglobinopathies. Given time, we would expect the mutations that protect and do not compromise the health of their carriers to become widely disseminated, but it is likely that human intervention will alter this process of natural selection.

Why are some genetic diseases common? Distinguishing selection from other processes by molecular analysis of globin gene variants

Various processes (selection, mutation, migration and genetic drift) are known to determine the frequency of genetic disease in human populations, but so far it has proved almost impossible to decide to what extent each is responsible for the presence of a particular genetic disease. The techniques of gene and haplotype analysis offer new hope in addressing this issue, and we review relevant studies of three haemoglobinopathies: sickle cell anaemia, and alpha and beta thalassaemia. We show how for each disease it is possible to recognize a pattern of regionally specific mutations, found in association with one or a few haplotypes, that is best explained as the result of selection; other patterns are due to population migration and genetic drift. However, we caution that such conclusions can be drawn in special circumstances only. In the case of the haemoglobinopathies it is possible because a selective agent (malaria) was already suspected, and the investigations could be carried out in relatively genetically homogenous populations whose migratory histories are known. Moreover, some data reviewed here suggest that gene conversion and the haplotype composition of a population may affect the frequency of a mutation, making interpretation of gene frequencies difficult on the basis of standard population genetics theory. Hence attempts to use the same approaches with other genetic diseases are likely to be frustrated by a lack of suitably untrammelled populations and by difficulties accounting for poorly understood genetic processes. We conclude that although this combination of molecular and population genetics is successful when applied to the study of haemoglobinopathies, it may not be so easy to apply it to the study of other genetic diseases.

Molecular characterization of beta-thalassemia in Egyptians

We sought to determine the spectrum of mutations producing beta-thalassemia in Egypt using genomic PCR and a variety of mutation-screening procedures. Thirty-four beta-thalassemia and three Hb S/beta-thalassemia patients originating from different regions of Egypt were studied, and the causative mutation was found in 69 of 71 (97%) beta-thalassemia genes. Four mutations accounted for 78% of beta-thalassemia genes in this population; IVS-1, nt 110 (41%), IVS-1 nt 6 (13%), IVS-1, nt 1 (13%), and IVS-2, nt 848 (11%). The latter allele, a C-A mutation at the third nucleotide of an acceptor site consensus sequence, has been described previously only in one Egyptian, one Iranian, one Tunisian, and one Black American patient. Nine other alleles each accounted for 1-3% of beta-thalassemia genes. Among these was one codon 27 allele (Hb Knossos), two frameshift 106/107 alleles previously seen only in a Black American, and a rarely observed mutation in the distal promoter region of the beta-globin gene, -87 (C-A). Our results suggest that from a molecular genetic standpoint a beta-thalassemia prevention program based on carrier screening and prenatal diagnosis can be implemented in Egypt. In couples at risk for beta-thalassemia, the causative mutation should be identifiable in both members in 92% and in one member in the remaining 8%.

Molecular screening and fetal diagnosis of beta-thalassemia in the Italian population

This paper reports our experience of molecular screening and fetal diagnosis of beta-thalassemia in 457 at risk couples of Italian descent. Molecular screening was carried out by dot blot analysis on amplified DNA with oligonucleotide probes complementary to the eight most common mutations in Italians [beta zero 39 (C----T); beta zero 6 (-A); beta+ -87 (C----G); beta+ IVSI nt 110 (G----A); beta zero IVSI nt 1 (G----A); beta+ IVSI nt 6 (T----C); beta zero IVSII nt 1 (G----A); beta+ IVSII nt 745 (C----G)]. By using this approach, we have been able to define the mutation in 92.8% of cases. The rest (all but four) were defined by direct sequencing and this led to the detection of nine rare mutations [beta zero 76 (-C); beta+ IVSI nt 5 (G----A); beta+ IVSI nt 5 (G----C); beta+ IVSI -1 (cod 30) (G----C); beta+ -87 (C----T), beta zero -290 bp del.; beta+ -101 (C----T)], and to the characterization of a novel mutation consisting of the deletion of the G at the invariant AG of the IVSII splice acceptor site of the beta-globin gene (beta IVSII nt 850 -1 bp). In the remaining four cases, the beta-globin gene showed entirely normal sequences and the beta-globin gene cluster was intact, as indicated by Southern blot analysis. Fetal diagnosis was carried out by dot blot analysis with the oligonucleotide probes defined in the parents. The procedure is simple and reliable, and the results can be obtained within 1 week of sampling. No misdiagnosis has so far occurred. The results indicate that fetal diagnosis of beta-thalassemia by DNA analysis may be obtained in practically all cases (even in a population showing marked heterogeneity of beta-thalassemia) by the combination of dot blot analysis for detecting common mutations, and direct sequencing for defining those that are uncommon.

The spectrum of β thalassaemia in Burma

The molecular defects causing beta thalassaemia have been analysed in 85 unrelated Burmese patients. The patients included 14 with homozygous beta thalassaemia, 70 with HbE/beta thalassaemia and one with HbS/beta thalassaemia. Using a combination of allele-specific oligoprobe hybridization and direct sequencing of genomic DNA amplified by the polymerase chain reaction, 95/99 of the beta-thalassaemia alleles have been characterized. Six mutations have been identified of which three, the G-T at IVS-1 position 1, the G-C at IVS-1 position 5 and the deletion of TCTT in codons 41/42, accounted for 85% of the alleles. Despite the diversity of ethnic groups in Burma, the number of beta-thalassaemia alleles in Burma is relatively small. Thus, diagnosis of the majority of the beta thalassaemias would be possible using a limited number of oligonucleotide probes.

The molecular basis of β-thalassemia in Turkey

By using oligonucleotide hybridization, restriction endonuclease analysis and direct sequencing of amplified genomic DNA, we have been able to characterize 18 different mutations in the beta-globin genes of 161 beta-thalassemia homozygotes and 107 beta-thalassemia heterozygotes from Turkey (429 beta-thalassemia chromosomes). Previous studies dealing with beta-thalassemia in Mediterranean countries have shown that, in most Mediterranean populations, only a few mutations are prevalent. In contrast, beta-thalassemia in Turkey does not seem to be associated with a few predominant mutations. The six most frequent alleles, IVS-I-110 (G----A), IVS-I-6(T----C), FSC-8 (-AA), IVS-I-1(G----A), -30(T----A) and FSC-5 (-CT), account for only 69.3% of the disease genes; indeed, all 26 mutations assayed represent 85.8% of the disease genes, confirming the considerable molecular heterogeneity of beta-thalassemia among Turks, and indicating the possible presence of rare, previously undefined, mutations in the population. Two mutations observed in this study, IVS-I-116 (T----G) and Cd44(-C), have not been reported in the Turkish population to date. Since preventive medical services, such as genetic counseling and prenatal diagnosis, are greatly improved by detailed knowledge of the molecular pathology of beta-thalassemia, we strongly believe that the presented data will facilitate the intended establishment of a prenatal diagnosis center, based on DNA analysis, in Turkey.

Molecular characterization of beta-thalassemia in the Sardinian population

This study reports the molecular characterization of beta-thalassemia in the Sardinian population. Three thousand beta-thalassemia chromosomes from prospective parents presenting at the genetic service were initially analyzed by dot blot analysis with oligonucleotide probes complementary to the most common beta-thalassemia mutations in the Mediterranean at-risk populations. the mutations which remained uncharacterized by this approach were defined by denaturing gradient gel electrophoresis (DGGE) followed by direct sequence analysis on amplified DNA. We reconfirmed that the predominant mutation in the Sardinian population is the codon 39 nonsense mutation, which accounts for 95.7% of the beta-thalassemia chromosomes. The other two relatively common mutations are frameshifts at codon 6 (2.1%) and at codon 76 (0.7%), relatively uncommon in other Mediterranean-origin populations. In this study we have detected a novel beta-thalassemia mutation, i.e., a frameshift at codon 1, in three beta-thalassemia chromosomes. The DGGE procedure followed by direct sequencing on amplified DNA is a powerful approach for the characterization of unknown mutations in this genetic system. The results herein presented allowed an expansion of the applicability of prenatal diagnosis by DNA analysis, to all couples at risk for beta-thalassemia in our population.

Population-based genetic screening

A preventive genetic programme aimed to control beta-thalassemia in the Sardinian population is based on a combination of increased awareness of the population, carrier screening, genetic counselling and prenatal diagnosis. As a result, the registry of thalassemia major demonstrated a profound decline in the incidence of this disease from 1 per 250 to 1 per 1200 live births, with 90% of cases effectively prevented.

Diminished A gamma T fetal globin levels in Sardinian haplotype II beta 0-thalassaemia patients are associated with a four base pair deletion in the A gamma T promoter

In Sardinia, the beta-39 nonsense mutation is the primary cause of beta 0-thalassaemia. This mutation is found mainly on beta-globin gene cluster haplotypes I and II, which differ in their A gamma globin types (A gamma I and A gamma T, respectively). This report presents data on G gamma, A gamma I and A gamma T levels, and the presence or absence of a 4 base pair (bp) deletion at -225 to -222 of the A gamma globin promoter, in 55 poly-transfused beta 0-thalassaemia major patients. Six patients were homozygotes for the normal (N) A gamma promoter lacking the 4 bp deletion, had no A gamma T globin, and their mean G gamma:A gamma I: A gamma T ratio was 52.9:47.1:0. Twenty-five patients were homozygotes for the mutant (M) A gamma promoter with the 4 bp deletion, had no A gamma I globin, and the mean G gamma:A gamma I: A gamma T ratio was 62.1:0:37.9. For M/M compared to N/N, the lower A gamma T than A gamma I was significant by the t-test (P less than 0.001). Twenty-four N/M cases had mean G gamma:A gamma I:A gamma T of 56:24.4:19.6, and the lower A gamma T than A gamma I was also significant (P less than 0.001). Partial haplotype analysis on these and 17 other beta 0-thalassaemia patients suggested that the 4 bp deletion was strongly associated with haplotype II. Of 33 M/M, 32 were haplotype II/II and one was II/5a; of 31 N/M, 29 were I/II and two were II/IX; of eight N/N, seven were haplotype I/I and one was I/IX. These data show a strong association of the 4 bp promoter deletion with decreased expression of the A gamma T globin gene on haplotype II.

Antenatal diagnosis of beta-thalassemia in Sardinia

This paper reviews the characteristics and the results of 15 years of experience with a preventive program, based on carrier screening and prenatal diagnosis, designed to control thalassemia major in the Sardinian population. The education of the population about thalassemia and the modalities for its prevention was accomplished via the mass media. Carrier screening was carried out voluntarily on couples of child-bearing age. Prenatal diagnosis was initially carried out by fetal blood analysis; since 1983, it has been done by DNA analysis on non-amplified or amplified DNA. Different chorionic villous sampling procedures have been used. Nowadays, we have adopted the transabdominal approach because, in our experience, it seems to be associated with a low risk (2%) of fetal mortality. At the present time, the beta-thalassemia mutations are detected directly by dot-blot analysis of amplified DNA with 32P- or horseradish peroxidase-labeled allele-specific oligonucleotide probes. Two oligonucleotide probes, one complementary to the codon-39 nonsense mutation, which accounts for 95.7% of the beta-thalassemia chromosomes in the Sardinian population, and the other complementary to the frameshift at codon 6, which is the second most common mutation in our population (2.1%), allow us to make prenatal diagnosis in the large majority of cases. Notwithstanding a careful dissection of maternal decidua from chorionic villi, co-amplification of maternal sequence was detected in 4 out of 425 cases tested by this procedure. In order to avoid this pitfall, the simultaneous amplification of highly polymorphic VNTR (variable number of tandem repeats) segments could be used. On the whole we have so far carried out 2711 prenatal tests: 1130 by fetal blood analysis, 1156 by oligonucleotide hybridization on electrophoretically separated DNA fragments, and 425 by dot-blot analysis on amplified DNA with allele-specific oligonucleotide probes. Two errors occurred by fetal blood analysis and none by DNA analysis. The incidence of thalassemia major declined from 1:250 live births in the absence of prevention to 1:1000 after the establishment of this program, indicating that carrier screening and prenatal diagnosis are effective means for preventing thalassemia major at the population level.

Molecular characterization of beta-thalassaemia in 174 Greek patients with thalassaemia major

The mutations producing beta-thalassaemia in 174 Greek patients with thalassaemia major were investigated by dot-blot hybridization of oligonucleotide probes to genomic DNA amplified by the polymerase chain reaction procedure, by direct sequencing of amplified DNA, and by gene mapping. beta-thalassaemia in Greeks was found to be very heterogeneous at the molecular level as 17 different mutations were observed: 86.6% of the beta-thalassaemic genes, however, could be identified with five probes: IVS-I-110 (G----A) (42.5%), codon 39 (C----T) (17%), IVS-I-1 (G----A) (13.2%), IVS-I-6 (T----C) (7.2%) and IVS-II-745 (C----G) (6.9%). Several mutations which had not previously been reported in the Greek population and which occurred at an incidence of 2% or lower were observed in this study. The information obtained will facilitate the prenatal diagnosis of beta-thalassaemia in Greece.

Molecular basis of beta-thalassemia in Turkey: detection of rare mutations by direct sequencing

Using restriction endonuclease analysis, oligonucleotide hybridization, and direct sequencing of amplified genomic DNA, we characterized 11 different mutations in the DNA of 26 patients from Turkey homozygous for beta-thalassemia. We found that mutations IVS-1 nt110, IVS-1 nt6, and the frameshift at codon 8 were the most frequent. By direct sequencing we characterized two very rare mutations not previously reported in the Turkish population: a frameshift +1 at codons 9/10 and a nonsense mutation at codon 15.

Prenatal diagnosis of inherited hemoglobinopathies

This paper reviews the methodology available to make prenatal diagnosis of inherited hemoglobinopathies by DNA analysis and the strategy to be used for the large scale application of this procedure to high-risk populations. The most straightforward approach for prenatal diagnosis is nowadays based on the analysis of DNA enzymatically amplified by the polymerase chain reaction (PCR). The mutations, produced by gross structural rearrangement of the DNA and those affecting a restriction recognition site, are directly detected by visualization following ethidium bromide staining of the electrophoretic pattern resulting from enzymatic digestion of amplified DNA. The remaining ones are detected by dot blot analysis with allelic specific oligonucleotide probes. Because in each population a limited number of specific beta-thalassemia mutations are prevalent, prenatal diagnosis by DNA analysis may be carried out by a population-specific strategy based on the amplification of those regions of the beta-globin genes containing the mutations most frequently occurring in each population followed by dot blot analysis with allelic specific oligonucleotide probes. This approach has the great advantage of being very simple, because radioactive probes are not necessary, very rapid, the results being obtained within 24 hours from sampling and very sensitive, only a limited amount of DNA in the order of 50 ng being necessary.

The molecular basis of beta thalassaemia in Bulgaria

Bulgaria is in a geographical area where beta thalassaemia is relatively common. The frequency of carriers is 2 to 3% of the population. Data on the molecular characteristics of the disorder were obtained from the study of 33 homozygous patients and 57 beta thalassaemia carriers. As in other Mediterranean ethnic groups, haplotype I and the splicing mutation in IVS-1 nt 110 are the most common. Haplotype V is second in frequency and is associated with three different mutations. The second most common mutation, beta null 39, is found in association with haplotype II in 80% of cases. A rare haplotype, possibly resulting from a crossover between a haplotype II and a haplotype V chromosome, was found in two thalassaemia carriers in association with frameshift 6. Altogether four mutations (IVS-1 nt 110, beta null 39, frameshift 6, and IVS-1 nt 6) account for 67% of the thalassaemia chromosomes. Their detection would permit direct fetal DNA analysis in 84% of the families studied (45% fully informative). RFLP analysis (haplotype plus AvaII psi beta) is 100% informative in 79% of the high risk families.

Prenatal diagnosis of beta-thalassaemia in Mediterranean populations by dot blot analysis with DNA amplification and allele specific oligonucleotide probes

In this study, we describe a simple strategy to detect beta-thalassaemia mutations in prospective parents and to make prenatal diagnosis in pregnancies at risk in the Mediterranean population. Screening of prospective parents is carried out by dot blot analysis on enzymatically amplified DNA with a set of oligonucleotide probes complementary to the most common mutations in this population. Prenatal diagnosis is accomplished by the same procedure on enzymatically amplified amniocyte or trophoblast DNA. The main advantages of this procedure are the simplicity, sensitivity (0.05 micrograms of DNA), and rapidity (12-24 h). Further simplification is obtained by amplification of the DNA from crude amniotic cell lysate. The very low amount of fetal material necessary for this analysis eliminates the need to culture amniotic fluid cells and may decrease the fetal loss rate associated with trophoblast sampling. The number of specific DNA sequences obtained by the amplification procedure allowed us to use non-radioactive labelled oligonucleotide probes, which have several advantages compared to radioactive probes.

Direct mutation analysis of beta-thalassemia genes in families of various ethnic origins residing in Germany

DNA from Mediterranean and Asian beta-thalassemia patients, now residing in Germany, has been characterized by oligonucleotide hybridization and direct restriction analysis. Using five oligonucleotide pairs complementary to the most frequent beta-thalassemia mutations, and three different restriction enzymes, we were able to detect 33 of 36 mutations directly.

Prenatal diagnosis of beta thalassaemia based on restriction endonuclease analysis of amplified fetal DNA

In the Mediterranean area, 50% of the beta thalassaemia mutations abolish or create a restriction endonuclease site in the beta globin gene. This study describes a new procedure for prenatal detection of these beta thalassaemia defects based on the direct visualisation, on an ethidium bromide stained polyacrylamide gel, of the discrete DNA fragments produced by restriction endonuclease digestion of fetal DNA, enzymatically amplified using the DNA polymerase from the thermophilus bacterium Thermus aquaticus. We applied this procedure to the Sardinian population to detect the nonsense mutation at codon 39 and the frameshift at codon 6 of the beta globin gene; these are the most frequent beta thalassaemia mutations in this population, accounting for 95% and 2.2% of the beta thalassaemia chromosomes. The main advantages of this procedure are simplicity (no radioactivity), sensitivity (0.2 microgram of DNA), and rapidity (12 hours). The very small amount of fetal material required makes amniotic fluid cell culture unnecessary and may decrease the fetal loss rate associated with trophoblast sampling. By circumventing the use of radioactive and non-radioactive probes, the spread of this technology to the high risk areas will be facilitated.

Beta thalassaemia mutations in Turkish Cypriots

Using oligonucleotide hybridisation or restriction endonuclease analysis, we have characterised the molecular defect in 94 patients with thalassaemia major and four with thalassaemia intermedia of Turkish Cypriot descent. We found that four mutations, namely beta+ IVS-1 nt 110, beta zero IVS-1 nt, beta+ IVS-1 nt 6, and beta+ IVS-2 nt 745 were prevalent, accounting for 69.9%, 11.7%, 8.7%, and 5.6% respectively of the beta thalassaemia chromosomes. This information may help in the organisation of a large scale prevention programme based on fetal diagnosis of beta thalassaemia by DNA analysis in the Turkish population.

The molecular basis of thalassaemia major and thalassaemia intermedia in Asian Indians: application to prenatal diagnosis

A study of the molecular pathology of beta thalassaemia in the Asian Indian immigrant population in the U.K. included 37 patients with thalassaemia major and 14 with thalassaemia intermedia. Using a combination of oligonucleotide probe hybridization and restriction endonuclease analysis the mutations in 100/102 (98%) of the beta thalassaemia genes were characterized. Nine different types were found, of which six are associated with beta zero, one with severe beta+ and two with mild beta+ thalassaemia. Comparison of the beta-globin gene cluster haplotypes, alpha globin genotypes and beta gene mutations of the thalassaemia major group with the thalassaemia intermedia group suggests that the co-inheritance of a high Hb F determinant associated with the - + - + + 5' beta haplotype and the inheritance of a mild beta-thalassaemia mutation are the major ameliorating factors of disease severity in Asian Indians. In comparison with other population groups. beta thalassaemia in Asian Indians is not associated with one or two predominant mutations. Despite this, prenatal diagnosis by direct detection is possible in the majority of families by restriction analysis and a limited number of oligonucleotide probes since the majority of severely affected individuals are homozygous for a single mutation. The characterization of these mutations should be useful for the planning of prenatal diagnosis programmes for beta thalassaemia in other Asian Indian communities.

Molecular basis of beta thalassemia in south China. Strategy for DNA analysis

The phenotype of beta thalassemia can be caused by over 40 different mutations. To set up a prenatal diagnosis program using DNA analysis, it is important to determine the type and frequency of mutation in a particular geographic area. We have delineated the molecular lesions that cause beta thalassemia in the Guangdong province of China, and found six mutations in four different haplotypes. The surprising finding that five of these mutations each occur in two different haplotypes suggests the occurrence of crossing over or gene conversion events at the beta-globin locus. The delineation of the haplotypes and mutations will permit the choice of the appropriate probes for prenatal detection of beta thalassemia in this part of China.

Beta-thalassemia mutations in the Portuguese population

In this study we have carried out haplotype analysis on the beta-globin gene cluster and characterized the beta-thalassemia mutation by oligonucleotide hybridization in 14 patients with thalassemia major and 5 with sickle cell/beta-thalassemia originating from southern Portugal. We found that three mutations, namely the beta(0)-39, beta(0) IVS-1 nt 1 and beta(+) IVS-1 nt 110 are prevalent accounting for 53%, 32% and 10% of the beta-thalassemia chromosomes respectively. In general each mutation was associated with a specific chromosomal haplotype; the beta(0)-39 mutation, however, was linked to three different haplotypes. These results indicate that three oligo-probes complementary to the most common mutations allow prenatal diagnosis by oligonucleotide analysis in 96% of the couples at risk of having offspring with thalassemia major in southern Portugal.

Chorionic villus sampling and acceptance rate of prenatal diagnosis

In this paper, we compared the acceptance rate of fetal diagnosis for beta-thalassemia in three group of couples of Sardinian descent; the first counselled before DNA analysis was available, the second presenting after DNA analysis was introduced but too late for chorionic villus sampling and thus monitored by amniocyte DNA analysis and the third presenting within the first trimester after DNA analysis was introduced and thus in time for trophoblast DNA analysis. A higher proportion of couples from the latter group opted for fetal testing as compared to the 1st and 2nd group. These results indicate that in this population, introduction of 1st trimester diagnosis made prenatal testing acceptable to practically all counselled couples at risk.