A new DNA polymorphism for prenatal diagnosis of beta-thalassaemia in Mediterranean populations

The origin of the sickle mutation in Greece; evidence from beta S globin gene cluster polymorphisms

Study of the Hpa I polymorphism 3' to the beta-globin gene in the Greek population revealed absence of the site in 238 beta S chromosomes, in contrast to a much larger sample of chromosomes carrying the beta A gene, where this site was consistently positive. Subsequent haplotype analysis of the beta-globin gene cluster in 82 beta S chromosomes demonstrated that 79 (96%) belonged to haplotype #19, while the three exceptions (all Hpa I negative) could be explained by a delta-beta recombination event. Haplotype #19 was never encountered in a parallel study of the 83 beta A chromosomes. Comparison of the above results with similar surveys in other parts of the world and consideration of various historical events suggest that the beta S mutation was introduced into Greece over the last few centuries by the Saracen raids and/or by settlements of North African slaves brought in by the Arabs, Franks, Venetians, or Ottoman Turks, who have occupied the country over the last millennium.

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.

Circulating 'trophoblast' cells in pregnancy have maternal genetic markers

A syncytiotrophoblast-associated antigen identified by the monoclonal antibody (McAb) H315 is detectable on the surface of a low proportion of peripheral blood cells in pregnant women, raising the possibility of a new approach to prenatal diagnosis of genetic disorders. We aimed at verifying the trophoblastic origin of H315+ cells and their use for prenatal diagnosis of beta-thalassaemia. H315+ cells were separated from the peripheral blood of pregnant women: the DNA obtained from these cells in two selected cases was shown to have genetic markers indistinguishable from those of the mother and definitely different from the fetus. Our results suggest that H315 antigen is expressed by maternal cells and that prenatal diagnosis on peripheral blood of the mother using H315 McAb is not feasible.

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.

Meiotic recombination in the beta globin gene cluster causing an error in prenatal diagnosis of beta thalassaemia

In the course of a prenatal diagnosis for beta thalassaemia by linkage analysis of restriction fragment length polymorphisms, a homozygous beta thalassaemia fetus was misdiagnosed as beta thalassaemia trait. Extensive studies of the polymorphic sites within the beta globin gene cluster in all the members of the family resulted in the conclusion that the paternal chromosome 11 of the newborn was different from that expected. Paternity was confirmed by HLA typing and blood group studies. The analysis of another polymorphic locus on chromosome 11 within the family was in agreement with the possibility of a crossing over between the two paternal chromosomes in a region 5' to the beta gene, previously indicated to contain a 'hot spot' area for recombination. This report underlines the risk of performing prenatal diagnosis using restriction polymorphisms 5' to the beta gene.

Haplotypes of thalassaemic families from the Po river delta: importance for prenatal diagnosis of beta-thalassaemia

The beta globin haplotypes, corresponding to 50 normal and 50 thalassaemic chromosomes, were determined in 25 families from the Po river delta area who had beta thalassaemia. The haplotypes were obtained by studying the familial segregation of 6 restriction fragment length polymorphisms of the beta globin gene cluster. The results show an almost exclusive presence of 3 haplotypes linked to the beta thalassaemia chromosomes of this area: haplotype I, II and IX according to Orkin's classification. It is therefore possible that only two thalassaemic mutations are present. A wider variety of haplotypes was found to be linked to normal chromosomes. Prenatal diagnosis, by the analysis of polymorphic sites (the 6 plus one other) was possible in 92% of the cases. The probable high homogeneity of the molecular mutations makes the use of specific oligonucleotides practical and applicable to prenatal diagnosis.

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-thalassaemia in Campania: DNA polymorphism analysis in beta A and beta thal chromosomes and its usefulness in prenatal diagnosis

In order to evaluate the feasibility of first trimester prenatal diagnosis of beta-thalassaemia by restriction fragment length polymorphism (RFLP) in Campania, one of the most affected regions in Southern Italy, DNA polymorphism analysis was performed on 40 unrelated patients, affected with homozygous beta-thalassaemia, and on their parents. Frequency of the presence of the Hinc II epsilon, Hind III G gamma and A gamma, Hinc II psi beta and 3' psi beta, Ava II psi beta, Ava II beta and Bam HI 3' beta sites have been determined in the beta A and beta thal chromosome samples. In 31 families (over 75%), RFLPs enabled tracing the beta-thalassaemia mutations in both father and mother (100% diagnosis). In the remaining nine families, RFLPs enabled tracing only one of the two mutations (50% diagnosis) because the other parent was found to be homozygous in all the analysed polymorphic sites. Restriction haplotypes, assembled on the basis of linkage analysis, were most heterogeneous, hence a wide heterogeneity of mutations is expected.

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%.

A benign form of thalassaemia intermedia may be determined by the interaction of triplicated alpha locus and heterozygous beta-thalassaemia

In this paper we report that the combination of a triplicated alpha globin locus with heterozygous beta-thalassaemia produces a clinical phenotype of thalassaemia intermedia in five Italian subjects from four unrelated families, while in two other cases the phenotype was thalassaemia minor. The haematological findings of the five patients were uniform, producing a benign form of thalassaemia intermedia, transfusion independent, with a long life expectancy. The pattern of inheritance of the two genetic determinants and the more pronounced beta/alpha globin chain imbalance, demonstrates that the genetic combination is indeed the cause of the phenotype. The pattern of restriction enzyme site polymorphisms suggests the presence of the beta IVS I 110 G----A mutation at least in three of these cases.

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.

Feasibility of prenatal diagnosis of beta thalassaemia by DNA polymorphisms in an Italian population

A feasibility study of prenatal diagnosis of beta thalassaemia in a northern Italian population has been carried out. Twenty-five families have been studied, each consisting of two parents and a homozygous beta thalassaemia child, thus enabling linkage analysis of restriction fragment length polymorphisms (RFLPs) to the normal and the thalassaemic chromosomes. Using seven standard RFLPs, 19/25 families could be offered prenatal diagnosis; inclusion of the recently described Ava II psi beta polymorphism increased this figure to 23/25 (92%) of the families.

Meiotic recombination between two polymorphic restriction sites within the beta globin gene cluster

Analysis of beta globin gene haplotypes for prenatal diagnosis of beta thalassaemia has revealed a recombination event within the beta globin gene cluster. Both a change in the AvaII polymorphic site within the beta globin gene and a change in the phenotype of the beta globin gene were observed. Paternity was established by the pedigree analysis of hypervariable 'minisatellite' DNA polymorphisms and the most probable explanation of the recombination event is a crossover between the psi beta globin gene and the beta globin gene. The data provide direct evidence in support of a DNA region 3' to the beta globin gene with a recombination frequency much higher than expected, and have important implications for the prenatal diagnosis of beta thalassaemia by linked restriction fragment length polymorphisms.

Prenatal diagnosis of the common haemoglobin disorders

New techniques of DNA analysis have been applied to the prenatal diagnosis of the common haemoglobin disorders. Currently, it is possible to provide a comprehensive programme for the prevention of these conditions, although this entails the use of several different techniques including globin chain synthesis analysis, direct identification of mutations with restriction enzymes, linkage analysis of restriction fragment length polymorphisms, and the use of oligonucleotide probes. At present, the best combination of these approaches has to be worked out for individual populations, but as the techniques of chorion villus sampling and DNA analysis improve it should be possible to rationalise these prenatal diagnosis programmes and thus make them simpler and less expensive.

Antenatal diagnosis of severe beta thalassemia during the first trimester of pregnancy

Prenatal diagnosis of hemoglobinopathies may be obtained during the first trimester of pregnancy by a combination of chorion biopsy and DNA mapping. This study illustrates 2 DNA approaches which are available for identification of abnormal globin genes. These include restriction fragment length polymorphisms (RFLPs) and direct gene mapping.