Prenatal diagnosis of beta-thalassaemia with the synthetic-oligomer technique

Professionally responsible management of the ethical and social challenges of antenatal screening and diagnosis of β-thalassemia in a high-risk population

Thalassemias are among the most frequent genetic disorders worldwide. They are an important social and economic strain in high-risk populations. The benefit of β-thalassemia screening programs is growing evident but the capacity to diagnose fetal β-thalassemia exceeds the treatment possibilities and even when treatment before birth becomes feasible, difficult decisions about the relative risks will remain. This paper can be of practical and ethically justified aid when counseling women about screening, diagnosis, and treatment of β-thalassemia. It takes in consideration various social challenges, medical issues such as antenatal screening, preimplantation genetic diagnosis, prenatal diagnosis, non-invasive prenatal testing and prenatal therapy. We also describe the Sardinian experience in applying and promoting high-risk population screening and diagnosis programs and future trends in the management of β-thalassemia.

From Prenatal to Preimplantation Genetic Diagnosis of β-Thalassemia. Prevention Model in 8748 Cases: 40 Years of Single Center Experience

The incidence of β-thalassemia in Sardinia is high and β-39 is the most common mutation. The prevention campaign started in 1977 and was performed in a single center (Microcitemico Hospital, Cagliari, Sardinia, Italy). It was based on educational programs, population screening by hematological and molecular identification of the carriers. Prenatal and pre-implantation diagnosis was offered to couples at risk. 8564 fetal diagnosis procedures using different invasive approaches and analysis techniques were performed in the last 40 years. Trans-abdominal chorionic villous sampling was preferred due to lower complication risks and early diagnosis. Chorionic villous DNA was analyzed by PCR technique. 2138 fetuses affected by β-thalassemia were diagnosed. Women opted for termination of the pregnancy (TOP) in 98.2% of these cases. Pre-implantation genetic diagnosis (PGD) was proposed to couples at risk to avoid TOP. A total of 184 PGD were performed. Initially, the procedure was exclusively offered to infertile couples, according to the law in force. The success rate of pregnancies increased from 11.1% to 30.8% when, crucial law changes were enacted, and PGD was offered to fertile women as well. Forty years of β-thalassemia prevention programs in Sardinia have demonstrated the important decrease of this severe genetic disorder.

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.

Control of beta-thalassaemia by carrier screening, genetic counselling and prenatal diagnosis: the Sardinian experience

Homozygous beta-thalassaemia in a number of at-risk populations (Greek and Turkish Cypriots, Greeks, Continental Italians and Sardinians) has been prevented at the population level by programmes based on carrier screening, genetic counselling and prenatal diagnosis. The Sardinian experience is based on a 20-year programme. Voluntary screening has been offered to prospective parents and, primarily, to women with an ongoing pregnancy. Education of the population at large, training of health personnel, and use of posters and informative booklets have been critical elements for the success of the programme. Genetic counselling has been carried out in a non-directive manner following well-established guidelines. The use of extended family screening magnified the efficacy of the screening programme, allowing the identification of the large majority of parents at risk by screening only 13% of the population at child-bearing age. Following counselling, the large majority of parents accepted prenatal diagnosis. Definition of the parents' mutation and prenatal diagnosis were carried out by a number of PCR-based procedures. The programme was effective, as indicated by the reduction of the birth rate of thalassaemia major from 1:250 live births to 1:4000.

Changes in the Approach for Invasive Prenatal Diagnosis in 35,127 Cases at a Single Center from 1977 to 2004

OBJECTIVES

To evaluate the changes in the approaches used for invasive prenatal diagnosis for beta-thalassemia and karyotyping at a single center from 1977 to 2004.

METHODS

For beta-thalassemia, in 1977 placentacentesis, in 1982 amniocentesis, in 1983 fetoscopy and cordocentesis, in 1983 trancervical chorionic villi sampling (TC-CVS), in 1984 cardiocentesis, in 1986 transabdominal CVS, and in 2002 preimplantation genetic diagnosis (PGD) were introduced. For karyotyping, in 1977 amniocentesis, in 1983 cordocentesis and cardiocentesis and TC-CVS, in 1986 TA-CVS and in 1991 hepatic vein sampling were introduced. Rates of approaches used were retrospectively considered, for 5 different groups (1977-1981; 1982-1985; 1986-1993; 1994-1999; 2000-2004).

RESULTS

35,127 invasive prenatal diagnoses were considered, and 42 PGD included. For beta-thalassemia 6,547 diagnoses were performed and 42 PGD. Since 1986-1993, TA-CVS was the only approach used except for 42 PGD in the 2000-2004 group. For karyotyping 28,538 diagnoses were performed. Amniocentesis and TA-CVS have been the most frequently used in the last years, while cordocentesis and hepatic vein sampling have shown a decline after their introduction.

CONCLUSION

TA-CVS is now the only technique used for beta-thalassemia. For karyotype, amniocentesis and TA-CVS are the most frequently used procedures. Obstetrical and laboratory experience, the availability of screening, and other individual factors, have influenced the choice, towards an earlier approach in pregnancy.

A 12-year preventive program for beta-thalassemia in Northern Sardinia

From 1980 to 1991, 6.3% of the adult population of the province of Sassari, Northern Sardinia, underwent voluntary beta-thalassemia screening. Of the 28,000 subjects examined, 15.7% proved to be heterozygotes for beta-thalassemia. In addition, the screening of 7500 students in 26 villages in Sassari province fixed the frequency of beta-thalassemia in this part of Sardinia at 10.4%. Of the 539 couples at risk to be expected from this figure, the screening detected 43% (234). The data suggest that inductive screening played a major role in the efficiency of this preventive beta-thalassemia program. Follow up of 221 pregnancies found to be at risk for homozygous beta-thalassemia and referred to the Antenatal Diagnosis Service, Cagliari, Southern Sardinia, showed that antenatal diagnosis was carried out in 80% of them. The overall percentage of couples refusing antenatal diagnosis was 10.8%, but over the years the acceptance rate for the procedure increased from 87% to 96%. Atypical hematological findings in 1.5% of 468 members of the couples at risk required globin chain synthesis and molecular analyses to define the precise beta-thalassemia genotype. Heterogeneous "mild" beta-thalassemia mutations as well as coexisting delta-thalassemia were found in silent type I and type II beta-thalassemia carriers which, without chain synthesis and DNA investigations, would have escaped detection.

BamH1 polymorphism in the Chinese, Malays, and Indians in Singapore and its application in the prenatal diagnosis of beta-thalassemia

The distribution of restriction fragment length polymorphism (RFLP) at the BamH1 site of the beta-globin gene was investigated in the Chinese, Indian, and Malay race in Singapore. The sample comprised of 183 normal individuals and 35 beta-thalassemia carriers in which 13 were couples with at least one beta-major child. The results from this study indicate that BamH1 polymorphism will be informative in 22% of pregnancies at risk for beta-thalassemia major in Chinese, 19% in Malays and 7% in Indians. In prenatal diagnosis using BamH1 polymorphism for one beta-major affected family, the fetus was diagnosed to be normal or beta-carrier. The validity of BamH1 polymorphism in the exclusion of beta-thalassemia major was subsequently confirmed at birth by globin chain biosynthesis.

Screening and prenatal diagnosis of the haemoglobinopathies

In this paper we have reviewed the social and technical aspects of carrier screening and prenatal diagnosis of the inherited haemoglobinopathies. The characteristics of programmes based on carrier screening and prenatal diagnosis ongoing in a number of at-risk Mediterranean populations have been described. The most relevant and common aspects of these programmes are the continuous educational campaign directed to the population at large, the voluntary basis and non-directive counselling. The target population has been most commonly couples before or after marriage. The vast majority of couples counselled accepted prenatal diagnosis. All programmes have encountered a high degree of success as indicated by the marked reduction in the birth rate of infants with thalassaemia major. No significant adverse effects have been reported. A programme with similar characteristics and for which the preliminary results are encouraging, is operating for sickle cell anaemia in the Cuban population. In a population with high frequency of hydrops fetalis, screening for deletion alpha-thalassaemia is recommended to prevent the negative effects on a pregnant woman of the presence of an hydropic fetus. Thalassaemia carrier screening is now carried out by automatic red cell indices and HbA2 determination. Definition of atypical cases may require iron studies, globin chain synthesis determination and/or alpha, beta- and delta-globin gene analysis. Identification of the carrier state is followed by definition of the mutation on enzymatically amplified DNA. Known mutations may be detected by restriction endonuclease analysis, non-denaturing polyacrylamide gel electrophoresis, allele-specific primers or allele-specific probes. The most promising procedures, which are also amenable to complete automation are reverse oligonucleotide hybridization and primer-specific amplification. Unknown mutations are defined by denaturing gradient gel electrophoresis, single-strand conformation polymorphism analysis, and chemical mismatch cleavage analysis followed by direct sequencing. The same methods on enzymatically amplified chorionic villus DNA are used for prenatal diagnosis. The potential pitfall resulting from maternal contamination can be avoided by careful dissection of the maternal decidua from the chorion and by the simultaneous amplification of a suitable polymorphism.

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.

Early transabdominal chorionic villus sampling in couples at high genetic risk

OBJECTIVE

The purpose of the study was to evaluate the feasibility and safety of transabdominal chorionic villus sampling before 9 weeks' gestation.

STUDY DESIGN

Two hundred pregnancies at risk for beta-thalassemia (n = 198) or Duchenne muscular dystrophy (n = 2) underwent transabdominal CVS at 6 through 8 weeks. Sampling success and fetal loss are expressed in percentages.

RESULTS

Sampling was successful in all cases (100%). Forty-eight fetuses were affected by beta-thalassemia and one by Duchenne muscular dystrophy. The percentage of fetal loss, expressed as a proportion of continuing pregnancies, was 4.0%. All women (n = 144) have been delivered, and no misdiagnoses have occurred. We observed one anencephalus and one mild limb defect consisting of absence of distal phalanges of index and little fingers of both hands and distal phalanges of both little toes.

CONCLUSION

Transabdominal CVS before 9 weeks is a reliable and relatively safe method for prenatal diagnosis in patients at high risk for genetic diseases. However, further studies are necessary to assess the risk to the fetus.

Molecular basis of beta thalassemia in the south of Thailand

A total of 103 beta thalassemia genes from 78 children (45 with Hb E/beta thalassemia, 8 with beta thalassemia heterozygotes, and 25 with homozygous beta thalassemia) were analyzed using dot-blot hybridization of the polymerase chain reaction-amplified DNA and direct DNA sequencing. Nine mutations were characterized in 98/103 (95%) of beta thalassemia alleles, of which six (a 4 bp deletion in codons 41-42, a G-C transition at position 5 of IVS-1, A-G transition at codon 19, an A-T transition at codon 17, an A-G transition at position -28 upstream of the beta globin gene, a G-T transition at position 1 of IVS-1), accounted for 92%. The spectrum of beta thalassemia mutations in Chinese Thai is similar to that reported among the Chinese from other parts of the world. The distribution of beta thalassemia mutations in Muslim Thai is similar to that reported among Malaysians. The most common beta thalassemia mutation in Thai and Chinese Thai patients is the frameshift mutation at codons 41-42, in comparison with the Muslim Thai in whom the G-C transition at position 5 of the IVS-1 mutation predominates. The heterogeneity of molecular defects causing beta thalassemia should aid in the planning of a prenatal diagnosis program for beta thalassemia in the South of Thailand.

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.

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.

Prenatal diagnosis of alpha- and beta-thalassaemias in Singapore--current status

Prenatal diagnosis was performed in 31 pregnancies where the fetuses were at risk for either homozygous alpha(0) - or beta-thalassaemia. First-trimester prenatal diagnosis by DNA analysis using chorionic villi was carried out for 17 pregnancies at risk for homozygous alpha (0)-thalassaemia. The alpha-globin genes in fetal DNA were detected by gene mapping using restriction endonuclease mapping and hybridization with cloned alpha-globin probe. Homozygous alpha (0)-thalassaemia was detected in four fetuses and the results were subsequently confirmed by electrophoresis of the cord blood where only Hb Barts was detected. Prenatal diagnosis for beta-thalassaemia was carried out by globin chain biosynthesis using fetal blood at 18-20 weeks' gestation. Using carboxymethyl (CM) sepharose chromatography, homozygous beta-thalassaemia was predicted in six pregnancies, and one fetus carried Hb E-beta thalassaemia. The seven pregnancies were terminated and globin chain analysis using cord blood confirmed the prenatal diagnoses. The remaining seven fetuses were diagnosed as either normal or beta-thalassaemia carriers. Using DNA analysis and globin chain biosynthesis for prenatal diagnosis of homozygous alpha(0)- and beta-thalassaemia, a 100% correlation was achieved with fetuses predicted to possess the homozygous condition.

Reliability of prenatal diagnosis of genetic diseases by analysis of amplified trophoblast DNA

Dot blot analysis on enzymatically amplified trophoblast DNA with allele specific oligonucleotide probes is currently used for the prenatal diagnosis of single gene disorders characterised at the molecular level, such as the beta thalassaemias, phenylketonuria, sickle cell anaemia, and alpha 1-anti-trypsin deficiency. A potential problem with the use of this procedure is the co-amplification of maternal sequences, which may obscure the diagnosis in the fetus. To address this question, we carried out prenatal diagnosis of beta thalassaemia in 300 couples at risk by dot blot analysis on enzymatically amplified DNA with 32P or horseradish peroxidase labelled allele specific oligonucleotide probes. We verified the diagnosis obtained by this procedure with oligonucleotide hybridisation on electrophoretically separated non-amplified trophoblast DNA fragments. We detected no co-amplified maternal sequences, even with a faint signal, in the dot blot of trophoblast DNA from those fetuses diagnosed as normal or homozygotes, nor in those diagnosed as heterozygotes, who were born to parents carrying different mutations and had inherited the paternal mutation. These results indicate that, when careful dissection of trophoblast tissue from maternal decidua is carried out, amplification of chorionic villi DNA is not associated with amplification of maternal DNA sequences. We may thus conclude that dot blot analysis of trophoblast DNA is a very reliable procedure for prenatal diagnosis.

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.

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.

Diagnosis of sickle cell anemia and beta-thalassemia with enzymatically amplified DNA and nonradioactive allele-specific oligonucleotide probes

We have developed a simple and rapid nonradioactive method for detecting genetic variation and have applied it to the diagnosis of sickle cell anemia and beta-thalassemia. The procedure involves the selective amplification of a segment of the human beta-globin gene with oligonucleotide primers and a thermostable DNA polymerase, followed by hybridization of the amplified DNA with allele-specific oligonucleotide probes covalently labeled with horseradish peroxidase. The hybridized probes were detected with a simple colorimetric assay. We demonstrated the usefulness of this method in a retrospective analysis of two pregnancies at risk for beta-thalassemia and one at risk for sickle cell anemia, as well as in an analysis of nine DNA samples simulating three family sets.

Prenatal diagnosis of beta-thalassaemia by second-trimester chorionic villus sampling

In this study we evaluated the feasibility of second-trimester transabdominal chorionic villus sampling for prenatal diagnosis of beta-thalassaemia in 80 pregnancies at risk presenting in the second trimester at the Antenatal Service. Sampling was carried out from 13 to 20 weeks and was successful in all cases. The amount of chorionic villi obtained varied from 10 to 40 mg, which was sufficient to make fetal diagnosis by oligonucleotide analysis within 10 days from sampling in all cases. No fetal losses occurred. From these results we conclude that transabdominal chorionic villus sampling is a useful procedure for prenatal diagnosis of beta-thalassaemia in those couples presenting after the first trimester.

The spectrum of beta-thalassaemia mutations in Sicily

To characterize beta-thalassaemia genes among the Sicilian population we have previously determined the DNA haplotypes in the beta-globin gene cluster of 99 beta-thal chromosomes. We found seven haplotypes, although 95 of 99 beta-thal chromosomes contained framework 1 and framework 3 beta genes. We have now determined the mutation in all 99 of these beta-thal genes by the use of oligonucleotide hybridization. PCR-amplification and direct genomic sequencing, and direct restriction analysis. Our results indicate that (1) the beta (0)-39 mutation is most frequent (35%); (2) beta(0)-39, IVS-1 nt 110 and IVS-1 nt 6 mutations account for 90% of beta-thal genes: (3) the IVS-1 nt 6 mutation is more frequent in thalassaemia intermedia (77%) than in Cooley's disease (34%): (4) the association between haplotypes and specific mutations is imperfect, but mutation spread has occurred within haplotypes containing the same beta-gene framework: (5) the beta(0)-39 and the IVS-1 nt 6 mutations, with a mutation spread to two major haplotypes, may be older than the IVS-1 nt 110 mutation: (6) these data make possible first-trimester prenatal diagnosis in many families (85%) in Sicily using only three pairs of oligonucleotides. In addition, a new mutation, a frameshift at codon 76 due to loss of a C residue, was found in a single beta-thal chromosome.

The role of cloned genes in the prevention of genetic disease

The application of recombinant DNA technology to the study of human genetic disease promises to increase the scope for carrier detection and prenatal diagnosis. Here we summarize current experience with prenatal diagnosis of single-gene disorders by DNA analysis and highlight some of the technical and organizational problems that remain to be solved.

Termination of pregnancy by a dilatation-evacuation technique to obtain placental tissue for DNA analysis

In 57 patients, following prenatal diagnosis of a fetus affected by beta-thalassaemia major, we terminated the pregnancy by dilatation and evacuation. In 19, we have already performed DNA analysis to evaluate the feasibility of prenatal diagnosis in a subsequent pregnancy.

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.

Fetal diagnosis of inborn errors of metabolism

Nearly 4000 different human disorders are supposed or known to be due to a single gene mutation. In about 10%, an early diagnosis is possible by the demonstration of specific abnormalities of metabolites in blood and/or urine, an abnormal structure/function of a particular (enzyme) protein or by the (in)direct demonstration of the gene mutation using DNA analysis. These methods of molecular analysis can often also be used for carrier detection. Early identification of couples at risk of handicapped offspring followed by genetic counselling forms the basis for prevention. Follow-up studies have shown that more than half of the couples at risk of a child with a genetic disease refrain from pregnancy. An important alternative for couples at risk is prenatal monitoring and selective abortion. During the last 10-15 years, the technology of fetal diagnosis of genetic diseases has improved and the number of Mendelian disorders that can be diagnosed in utero has increased to more than 100. In the second-trimester of pregnancy, about two dozen inborn errors of metabolism have been diagnosed by metabolite analysis of amniotic fluid supernatant using gas chromatography-mass spectrometry or electrophoretic methods. About 5000 pregnancies at risk of different types of haemoglobinopathy, haemophilia, alpha-1-antitrypsin deficiency and a few other diseases not expressed in amniotic fluid cells have been investigated by biochemical analysis after fetal blood sampling. The most common approach towards fetal diagnosis of inborn errors of metabolism has been the demonstration of a specific enzyme deficiency in cultured amniotic fluid cells. In this way some 60 different diseases have been diagnosed, usually after 2-4 weeks of cultivation after amniocentesis at 16 weeks gestation. In addition, some 20 other Mendelian disorders have been diagnosed in utero by ultrasonography and non-biochemical analysis of amniotic fluid cells or fetal skin biopsies. The introduction of chorionic villus sampling has offered the possibility of first-trimester fetal diagnosis of a large number of Mendelian disorders. The overall diagnostic experience until mid-1986 amounts to about 1500 pregnancies at risk. Some 45 different inborn errors have been diagnosed by enzyme assays directly on chorionic villus homogenate or after incubation with radiolabelled precursors of intact villi followed by chromatography or other types of analysis. In a few instances, cell cultivation for a period of 2-3 weeks is required to establish a reliable biochemical diagnosis.

The impact of DNA analysis on fetal diagnosis

There has been rapid progress in mapping disease-specific gene loci to particular chromosomal regions and in cloning the relevant genes or DNA sequences that can act as genetic markers. These advances will have an impact on fetal diagnosis of monogenic disorders for a number of reasons, the most important being the ability to use chorionic villus DNA taken in the first trimester to make a fetal diagnosis, no matter how tissue-specific the gene defect. Diagnosis based on analysis of the protein gene product requires a tissue that is expressing that gene. In a few disorders the mutation within the gene can be detected directly, but more often an approach, termed gene tracking, will be required to predict the genotype of the fetus. This requires blood samples from a few family members and the analysis must be carried out prior to the chorion sampling and ideally before the pregnancy. This initial family study is required to determine whether gene tracking is possible in that particular family. A number of potential problems, both technical and in clinical management, highlight the need for close collaboration between clinical geneticists, molecular geneticists and obstetricians.

Results of programmes for antenatal detection of thalassemia in reducing the incidence of the disorder

The characteristics and the effectiveness of programmes designed to prevent beta-thalassemia major present in high frequency in several areas of the world such as Cyprus, Greece and Sardinia are reviewed. All these programmes are based on heterozygote detection, counselling and foetal diagnosis. The target population for screening have been couples at marriage, conception or early pregnancy. Awareness of the problem and involvement of the population was achieved via mass-media or personal approaches through lectures or discussions. Parent's Association were consulted and have been actively involved. Information leaflets have been made available to prospective couples at several critical areas. Education on thalassemias was introduced into the school curriculum. Counselling was based on a private interview at which the several options available were discussed with the individual carrier or the couple. Prenatal diagnosis was chosen by the large majority of couples counselled. All these programmes resulted in a decline of thalassemia major births by 50-97%. The reasons for residual cases were mostly lack of information and, less frequently, misdiagnoses or refusal of fetal diagnoses.

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.

DNA haplotype heterogeneity of beta-thalassaemia in Greece: feasibility of prenatal diagnosis

We have carried out DNA haplotype analysis of 69 beta-thalassaemia patients in Greece and 42 of the parents using seven standard polymorphic sites. Our data show a high degree of heterogeneity of the chromosomal background in which beta-thalassaemia occurs in Greece, suggesting a high degree of heterogeneity in the beta-thalassaemia mutations involved. Haplotype I is found here to represent 45% of total beta-thalassaemia mutations detected, a proportion well below the 67% reported in earlier studies with Greek-American patients. Nine different haplotypes are detected and the ones carrying beta(+) mutations are the majority, including those which are linked to beta(+) mutations associated with a thalassaemia intermedia phenotype, and which constitute 11% of all haplotypes. One of these haplotypes (---- ) has never before been reported to occur in non-Africans, whether in beta thal or beta A chromosomes, and it is found here to be of African origin rather than the product of recombination. In 21 families haplotype analysis showed that prenatal diagnosis for a second child was feasible in 81% of the cases. Use of the AvaII-psi beta polymorphic site as well as the seven standard ones brought this proportion up to 90%.

DNA analysis for antenatal diagnosis of thalassaemia and haemophilia

Two years' experience with DNA analysis for the antenatal diagnosis of thalassaemia and haemophilia is described. The advantages of DNA testing, including a first-trimester diagnosis and greater availability, must be considered in relation to the problems that are associated with this procedure. In particular, the risk of recombination in DNA polymorphism studies should be understood and explained fully to the patient.

Chorionic villus sampling by rigid forceps: experience with 300 cases at risk for thalassemia major

In this article we report the results of chorionic villus sampling by a biopsy forceps inserted via the cervix under ultrasonic guidance in 300 pregnancies at risk for thalassemia major. A sufficient amount of chorionic villi for deoxyribonucleic acid analysis by oligonucleotide hybridization was obtained in all cases tested but one, with a success rate of 99.7%. The percentage of fetal loss, expressed as proportion of continuing pregnancies, was 4.8%. To verify the results, we carried out amniocyte deoxyribonucleic acid analysis in all the continuing pregnancies for the first 100 cases and in those in which trophoblast deoxyribonucleic acid analysis showed the heterozygous state for beta-thalassemia for the second 200 cases. At the beginning we had two cases of decidual contamination in such an amount to cause misdiagnosis. Successively more careful elimination of decidual tissue from villi avoided avoided this pitfall. These results indicate that chorionic villus sampling by a rigid forceps is a reliable and relatively safe method for fetal diagnosis of genetic diseases by deoxyribonucleic acid analysis.

Beta thalassaemia mutations in Sardinians: implications for prenatal diagnosis

In this study we have characterised by oligonucleotide hybridisation and direct restriction endonuclease analysis the beta thalassaemia mutation in 494 Sardinian beta thalassaemia heterozygotes. The most prevalent mutation, accounting for 95.4% of the cases, was the nonsense mutation at codon 39. The remainder, in decreasing order of frequency, were a frameshift at codon 6 (2.2%), beta + IVS-1, nt 110 (0.4%), and beta + IVS-2, nt 745 (0.4%). This information allows prenatal diagnosis by DNA analysis to be made in the great majority of Sardinian couples at risk for beta thalassaemia.

Pitfalls in prenatal diagnosis of beta thalassaemia

In this paper, we report a pregnancy at risk for beta thalassaemia in which the fetal red blood cell volume was reduced while that of the mother was relatively great, so that the presence of a fetal red blood cell population in a mixed maternal-fetal sample was difficult to recognise. The molecular basis for these haematological phenotypes was clarified by follow up examination and alpha globin gene mapping. These indicated that the fetus was heterozygous for beta thalassaemia and had deletion of three alpha globin structural genes, while the mother, heterozygous for beta thalassaemia, also had deletion of two alpha globin structural genes. When the coinheritance of alpha thalassaemia is suspected, it is necessary to examine carefully the red blood cell distribution of a placental sample, so that the presence of a population of fetal red blood cells is not missed.

The evolution of the alpha- and beta-globin gene clusters in human populations

DNA analysis of the alpha- and beta-globin gene clusters has revealed substantial variability between individuals and populations. As well as restriction enzyme site and length polymorphisms, variation in gene copy number and type is observed. Because of this extensive polymorphism DNA analysis offers a highly informative method of studying genetic affinities between human populations. Haplotypes, consisting of a set of restriction enzyme polymorphisms distributed along the cluster, have been developed for both loci. Analysis of the molecular basis of numerous beta-thalassaemia alleles has revealed, in general, different sets of mutations in different populations, indicating that these postdate the racial divergence. Recent microepidemiological studies on the distribution of alpha-thalassaemia support the hypothesis that this condition, like the beta s-mutation, has been selected because it confers protection against malaria. Population-specific DNA polymorphisms at these and other loci promise to be of considerable value to genetic anthropology.

Clinical applications of gene probes in human genetic disease, malignancy, and infectious disease

Recent developments in recombinant DNA technology have made possible the production of gene probes consisting of cloned gene segments, cloned segments of DNA linked to genes, and synthetic gene fragments. Several methods have been developed by which these probes may be used for the diagnosis of human disease. This technology has been outstandingly successful for prenatal diagnosis and carrier detection in many genetic diseases. These methods have also been successfully applied to the analysis of human malignancies, by providing for the determination of cell lineage and clonality in lymphoid neoplasms. Finally, these methods have shown potential for rapid and sensitive diagnosis of some infectious diseases.

Prenatal diagnosis of thalassemia major by fetal blood analysis: experience with 1000 cases

In this report we have summarized our experience with the prenatal diagnosis of beta-thalassemia in 1000 pregnancies followed at least until 12 months after birth. In the majority of these cases, the thalassemia lesion was the nonsense mutation at the codon corresponding to amino acid 39, which produces the hematological phenotype of beta o-thalassemia. Fetal blood sampling was carried out by placental aspiration, by which a sufficient amount of fetal blood for analysis was obtained in the majority of cases (99 per cent). The fetal mortality associated with fetal blood sampling was 6.3 per cent. Those placental samples contaminated by maternal cells were successfully purified by Orskov lysis. Fetal blood was analysed by globin chain synthesis on CM-52 columns, which gave reliable results. Two misdiagnoses (0.2 per cent) have been made of which one was due to a non-globin protein co-migrating with the beta-chains while the other resulted from a misclassification of the type of thalassemia segregating in the family.

Diagnosis of genetic disease using recombinant DNA

Recombinant DNA technology promises to make an important contribution to the analysis and diagnosis of inherited human disease. Direct detection and analysis of various genetic defects at the DNA level are now possible using cloned gene or oligonucleotide probes. In addition, the use of restriction fragment length polymorphisms associated with linked DNA segments should permit not only the diagnosis of hitherto undetectable disease states but also the chromosomal localization of the loci responsible. The eventual isolation of disease loci should lead to a better understanding of the molecular basis of inherited disease.