Antenatal diagnosis of thalassemia major in Sardinia.

In this report, we summarized our experience, carried out in Sardinia, with antenatal diagnosis in one thousand pregnancies in which the fetus was at risk for homozygous beta-thalassemia. In the majority of these cases, the thalassemia lesion segregating in the family was the nonsense mutation at the codon corresponding to amino-acid 39. At the outset (976 cases) we used globin chain synthesis analysis by column chromatography on fetal blood obtained by placental aspiration, and recently (24 cases) we employed the synthetic oligonucleotide method on amniocyte DNA. Apart from 126 pregnancies still in progress, in all the other cases the diagnosis has been confirmed. In the majority of the cases (99%), we obtained sufficient fetal blood for the analysis. The fetal mortality associated with placental aspiration was 6.1%. The biochemical analysis gave reliable results. We had two misdiagnoses (0.2%): one due to a nonglobin protein comigrating with the beta chains and the other for a misclassification of the type of thalassemia segregating in the family. The oligonucleotide method gave clear-cut results in all the cases tested. The method was sensitive enough to detect the mutation directly in the DNA isolated from 20-25 ml of amniotic fluid in 75% of the pregnancies tested. In one case, we successfully employed this method for the analysis of the DNA isolated from chorionic villi. The oligonucleotide method seems to be the best procedure for monitoring the pregnancies at risk for beta-thalassemia in places where one or a few beta-thalassemia lesions are prevalent.

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.

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.

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.

Developmental pattern of beta-chain production at midtrimester pregnancy in Sardinian beta o-thalassemia heterozygotes.

This study shows a minor, statistically non significant increase, of beta-chain synthesis from 18 to 24 weeks gestation in both normal and beta o-thalassemia heterozygous fetuses with no significant changes in the ratio between the values for the two groups as a function of gestational age. This result indicates that at midtrimester pregnancy the developmental pattern of Hb F to Hb A switching in beta o-thalassemia heterozygotes is similar to that of normal fetuses.

Hematological phenotype of the double heterozygous state for alpha and beta thalassemia.

In this study, we have correlated the hematological phenotype of 56 Sardinian beta o-thalassemia heterozygotes with their alpha-globin genotype as defined by restriction endonuclease mapping. We found that the coinheritance of the deletion of one alpha-globin and, more obviously, two alpha-globin genes tend to normalize the thalassemia-like hematological phenotype commonly associated with the beta o-thalassemia carrier state. On the other hand, the association of the deletion of three alpha-globin genes caused a more severe phenotype. By globin chain synthesis analysis, those beta o-thalassemia heterozygotes with the (-alpha/alpha alpha) alpha-globin genotype had less deficiency of beta-chain synthesis than did those with the normal alpha-globin genotype (alpha alpha/alpha alpha). In heterozygotes with the (-alpha/-alpha) and in those with the (--/-alpha) alpha-globin genotype the imbalance was actually reversed with a mild or marked alpha-chain synthesis excess respectively.

Diagnosis of the beta 0 thalassemia trait at birth.

This study shows the results of in vitro globin chain synthesis analysis in 33 infants who had been previously evaluated for the presence of thalassemia in the second trimester of gestation and were restudied after the stage of hematological maturity. Four children with alpha-thalassemia-1, identified in a newborn screening, were also included. Normals and beta-thalassemia heterozygotes could be distinguished in the neonatal period by beta/alpha or beta/gamma ratios. However, as a considerable overlap of alpha-thalassemia-1 with normals and alpha-thalassemia-2 with beta-thalassemia heterozygotes were found, biosynthetic studies at birth seem to be inappropriate to make reliable diagnosis of hemoglobin chain deficiencies. There were no differences between hematological indices of normal and heterozygous beta-thalassemia newborns, while alpha-thalassemia-1 carriers showed a statistically significant difference from normals in mean MCV and MCH.

Globin chain synthesis analysis in obligate beta 0-thalassemia heterozygotes with isolated increase of hemoglobin A2 levels.

Globin chain synthesis analysis was carried out in 14 obligate beta 0-thalassemia heterozygotes, i.e., parents of children with thalassemia major or intermedia due to homozygous beta 0-thalassemia, with almost normal red blood cell indices and isolated increase of Hb A2 levels. alpha/beta globin chain synthesis ratios were almost balanced or slightly reduced (0.62-1.30). This finding suggests that these heterozygotes carry both alpha- and beta-thalassemia genes. However, alpha-globin structural gene mapping by restriction enzyme analysis must be carried out to confirm this explanation.

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

103 couples attending the antenatal clinic in Sardinia were screened for the beta o-39 (nonsense) mutation, which codes for beta-thalassaemia, with the oligonucleotide method. In 94 couples both members had the beta o-39 mutant and thus were eligible for antenatal testing with this method. These pregnancies were monitored with amniocentesis (61) or trophoblast biopsy (33). Prenatal diagnosis in those monitored with amniocentesis was carried out with DNA analysis of uncultivated amniocytes (19) or cultivated cells (38). In 4 pregnancies results were unsatisfactory, and prenatal diagnosis was repeated with fetal-blood analysis. Trophoblast biopsy was unsuccessful in 1 pregnancy and gave a misdiagnosis in another because of maternal contamination. In the latter case the genotype of the fetus was established with amniocyte DNA analysis and globin-chain-synthesis studies.

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.

Heterozygous beta-thalassemia: relationship between the hematological phenotype and the type of beta-thalassemia mutation.

In this study we have correlated the severity of the hematological features to the type of the beta-thalassemia mutation [codon 39 (C----T), IVS-I nt 110 (G----A), IVS-I nt 1 (G----A), IVS-I nt 6 (T----C), IVS-II nt 745 (C----G), -87 (C----G) and beta 6 (-1 bp)], in a group of beta-thalassemia heterozygotes of Italian descent in whom we excluded the presence of iron deficiency or deletion alpha-thalassemia. The beta-thalassemia mutation was defined by dot blot analysis on amplified DNA with allelic specific oligonucleotide probes. We found that a) heterozygotes for beta+ IVS-I nt 6 and beta+ -87 mutations produce larger and better hemoglobinized red blood cells, and b) heterozygotes for beta+ IVS-I nt 6 and beta+ IVS-I nt 110 mutations have a less marked increase of Hb A2 levels as compared to heterozygotes for the other mutations investigated. These findings indicate that milder beta-thalassemia mutations such as the beta+ IVS-I nt 6 and beta+ -87, express also in the heterozygous state a milder phenotype as compared to beta o-thalassemia or severe beta+ thalassemia (beta+ IVS-I, nt 110). The Hb A2 levels, on the other hand, were not related to the severity of the mutation because of less marked increase was found in a mild (beta+ IVS-I nt 6) as well in a severe (beta+ IVS-I nt 110) mutation. From the practical point of view these findings should be adequately considered in carrier screening and genetic counselling.

Thalassaemia types and their incidence in Sardinia.

The frequency of thalassaemia syndromes in Sardinia was examined by a population survey. The data indicate that about 12.6% of the Sardinian subjects are carriers of beta-thalassaemia, while 6.9% of the population carries an alpha-thalassaemia gene, with a slight difference between the various provinces. These are among the highest frequencies of thalassaemia genes found in a Caucasian population today. A survey of hospital inpatients and outpatients showed a newborn incidence of homozygous beta-thalassaemia of 1 in 300. The reasons for the difference between the expected and observed incidence figures are discussed. Moreover, 3 subjects with deltabeta0-thalassaemia trait, 6 carriers of heterocellular persistence of fetal haemoglobin (HPFH), 1 sickle cell trait, and 3 subjects with Hb J Sardegna were found. Genetic heterogeneity of beta-thalassaemia syndromes in this population may generally result from interaction of alpha- and beta-thalassaemia genes.

Prenatal diagnosis of beta thalassaemia by fetal red cell enrichment with NH4-Cl-NH4HCO3 differential lysis of maternal cells.

Prenatal diagnosis with globin chain synthesis analysis on fetal red blood cells concentrated by NH4Cl-NH4HCO3 differential lysis of maternal cells (Orskov lysis) was carried out in 27 pregnancies at risk for beta thalassaemia and one at risk for sickle cell beta0 thalassaemia. The beta/gamma globin chain synthesis ratio was also determined after anti-i-differential agglutination (12 cases), in almost pure fetal samples (sic cases) and by extrapolation (one case). Differential lysis permitted the study of samples drawn by placental aspiration containing as little as 3.2% fetal red blood cells. There was no consistent difference between the beta/gamma ratios observed after differentail lysis and those determined after the use of the other approaches. A presumptive diagnosis of homozygous beta thalassaemia was made in nine cases. All but one of these pregnancies was terminated. The absence of beta chain synthesis was confirmed by the study of fetal blood after abortion in four cases with suitable samples. Of the remaining pregnancies, six proceeded to term and non-homozygous infants were delivered. The others are still in progress. No fetal loss occurred. Orskov lysis seems to be a very reliable method for prenatal diagnosis of beta chain abnormalities. Moreover it can minimize the number and duration of placental aspirations required and thus the risk to the fetus.

Beta 0 thalassemia trait in Sardinia.

The red cell indices and results of globin chain synthesis in peripheral blood of obligate beta 0 thalassemia (beta 0 thal) carriers (parents of homozygous beta 0 thal children) and beta thalassemia (beta thal) carriers identified during mass screening are reported. Red cell indices were similar in obligate beta 0 carriers and in carriers diagnosed during mass screening. However there was a higher incidence of anemia in female obligate beta 0 thal carriers. In Sardinia the beta 0 thal carrier showed the usual hematological characteristics of the high Hb A2 beta thal carrier with microcytosis, hypochromia, reduced osmotic fragility; Hb F greater than 1% was found in 30% of the carriers. With MCV, MCH, osmotic fragility test (OFT) and Shine and Lal discriminant function we found 3.5%, 1.5%, 3.5% and 4.0% respectively false negatives in carrier identification. A part from one subject, all obligate carriers had elevated Hb A2 levels. The alpha/beta ratio in obligate carriers (mean +/- SD) was 1.83 +/- 0.26 (N = 30).

Beta-Thalassaemia types in southern Sardinia.

In this study the prevalence of the different beta-thalassaemia types in southern Sardinia was investigated by cellulose acetate and agar gel electrophoresis or globin chain synthesis analysis on column chromatography or both in (1) all the patients (347) presenting with thalassaemia major or intermedia at our haematology service from 1976 to 1979, and (2) a group of 82 patients with transfusion-dependent thalassaemia major randomly chosen from 236 under our care. Apart from six subjects with delta(beta)0/beta+-thalassaemia genotype and eight with beta0/beta+ or less probably beta+/beta/-thalassaemia, all thalassaemia major and intermedia patients studied were beta0-thalassaemia homozygotes. Globin chain synthesis on peripheral blood cells from these patients, performed at different intervals from blood transfusion, showed no incorporation of radioactive leucine into beta-globin peak, the same as before the transfusion. No correlation between kappa/gamma ratios and clinical severity or hypersplenism was found. Globin chain synthesis analysis carried out at birth in three infants later found to have homozygous beta0-thalassaemia demonstrated imbalanced or borderline kappa/gamma ratios.

Haematological and obstetric aspects of antenatal diagnosis of beta-thalassaemia: experience with 200 cases.

The results of 200 antenatal diagnoses in pregnancies at risk for homozygous beta-thalassaemia, carried out on fetal blood samples obtained by placental aspiration in the second trimester, are described. Globin chain synthesis in the fetuses was measured by means of 3H-leucine incorporation and separation of the chains on carboxy-methyl-cellulose columns. Fetal red cell enrichment was performed by NH4Cl-NH4HCO3 differential lysis of maternal cells or anti-i differential agglutination. Sufficient fetal blood for analysis was obtained in 97.5% of the cases. The overall fetal loss rate was 6.5%, but it declined from 10% in the first consecutive 100 cases to 3% in the last 100 cases. Fetal loss was the result of early or late intrauterine death or spontaneous abortion. Forty-two homozygous fetuses had no beta-chain synthesis and one had a very low beta/gamma ratio (0.005). Of the pregnancies, 37 were terminated at parental request and four aborted spontaneously. Absence of beta-chain radioactivity was confirmed in 12 abortuses with suitable cord blood samples for analysis. Two pregnancies with homozygous fetuses were not terminated, as one member of each couple was a devout Catholic. As expected, both infants developed Cooley's anaemia. Follow-up of the 146 infants, diagnosed in utero as non-homozygotes, showed cerebral palsy in one and a small cutaneous needle injury in three. None of these developed homozygous beta-thalassaemia. Even beta-thalassaemia trait with a beta/gamma ratio of 0.046 +/- 0.012 can be distinguished from normal, showing a beta/gamma ratio of 0.086 +/- 0.019 with a high degree of certainty.

First trimester diagnosis of beta-thalassaemia in a twin pregnancy.

This paper reports the results of first trimester prenatal diagnosis in a twin pregnancy at risk for homozygous beta 0-thalassaemia (beta 0-39 mutant). Trophoblast samples from both twins were obtained at 10 weeks gestation with a forceps guided by ultrasound. Trophoblast DNA analysis, carried out with the oligonucleotide technique, revealed that one fetus was homozygous and the other heterozygous for the beta-39 mutant. This diagnosis was confirmed at 17 weeks gestation by amniocyte DNA analysis. DNA polymorphism analysis within the alpha-globin gene provided useful genetic markers for twin differentiation.

Problems in prenatal diagnosis of beta-thalassaemia by fetal blood analysis: beta-chain variant comigrating with gamma chains.

This report describes a couple at risk for beta-thalassaemia in which one spouse was heterozygous for classical high Hb A2 beta-thalassaemia while the other had the compound heterozygous state for beta+-thalassaemia and a beta-chain variant. This variant comigrates on carboxymethyl-cellulose columns (CMC) with gamma-chains, indicating that globin separation on CMC columns could not have been used for fetal diagnosis. The beta-chain variant migrates separately from the other globin chains on HPLC and the respective abnormal haemoglobin can be separated by isoelectrofocusing. Oligonucleotide hybridization showed that both parents were carriers of the beta+ IVS-1, nt 6 mutation. Prenatal diagnosis was successfully accomplished by oligonucleotide analysis on trophoblast DNA. This case indicates that an Antenatal Service should have alternative methods to CMC columns so as to carry out prenatal diagnosis of beta-thalassaemia in uncommon cases.

Thalassemia intermedia resulting from a mild beta-thalassemia mutation.

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