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.     

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.     

Homozygous beta+ thalassaemia owing to a mutation in the cleavage-polyadenylation sequence of the human beta globin gene.

A mild, non-transfusion dependent, beta thalassaemia phenotype is described in a Dutch patient homozygous for a mutation in the cleavage-polyadenylation sequence of the beta globin gene. The molecular basis of the mutation, AATAAA greater than AATGAA, was determined using denaturing gradient gel electrophoresis (DGGE) and direct sequencing of genomic DNA amplified by the polymerase chain reaction (PCR). Different fragments of the beta globin gene were amplified and analysed on DGGE for the presence of mutations. The fragment with an abnormal melting behaviour was reamplified and the base substitution in the polyadenylation sequence was identified by direct sequencing.     

Filipino beta zero thalassaemia: a high Hb A2 beta zero thalassaemia resulting from a large deletion of the 5'' beta globin gene region.

A large novel deletional beta zero thalassaemia mutation associated with unusually high levels of haemoglobin (Hb) A2 in heterozygotes is described in two unrelated subjects of Filipino background. The deletion was characterised by DNA mapping including pulsed field gel electrophoresis. Filipino beta zero thalassaemia extends for approximately 45 kb beginning approximately 1.5 kb 3' to the delta globin gene. It is the largest deletion to date which gives rise to the beta zero thalassaemia phenotype. This mutation, similar to previously described deletional beta zero thalassaemias associated with high Hb A2, removes sequences 5' to the beta globin gene promoter and emphasises the functional importance of the 5' beta globin region in eliciting the unusually high level of Hb A2. This example also suggests that it is the 3' sequences which are transposed rather than the actual deletion size which are significant in the raised fetal haemoglobin (Hb F) found with some of the thalassaemias.     

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.     

Bone marrow and peripheral blood globin chain synthesis in sickle cell beta zero thalassaemia.

A similar imbalance of globin chain synthesis, with low non-alpha/alpha ratios, was shown in peripheral blood and in bone marrow of compound heterozygotes for both the Hb S and beta zero thalassaemia genes (S/beta zero thalassaemia). Previous purification of whole cell globin obtained from the bone marrow did not change the non-alpha/alpha ratio. The mean non-alpha/alpha ratios were 0.57 +/- 0.13 (means +/- SD) for the peripheral blood of 12 patients, 0.52 +/- 0.10 for five patients using bone marrow globin purified on Sephadex G100, and 0.55 +/- 0.16 for the unfiltered bone marrow globin of five patients. The data show that patients with S/beta zero thalassaemia have a similar beta chain deficiency in reticulocytes and in bone marrow cells, provided whole cell globin is used which avoids the removal of the free alpha chains. The non-alpha/alpha ratios in the peripheral blood of an S/beta zero thalassaemia patient and a beta thalassaemia heterozygote from the same family were compared in seven families and no significant difference was found.     

Frequency of haplotypes in the beta globin gene cluster in a selected sample of the mexican population

Five polymorphic restriction enzyme sites in the beta globin gene cluster (HindIII Gγ-Hind III Aγ-, Ava II^{INV ?2}β-and Hpa I and Bam HI 3′β-globin gene) were studied in individuals from 13 families: 13 homozygote patients for sickle cell anemia, two double heterozygotes (one SC and one S/β^Thal), 35 AS heterozygotes (23 parents and 12 siblings), one father (A/β^Thal), and three normal siblings. In addition, 17 normal unrelated Mexican subjects were studied. All subjects were from the state of Veracruz on the coast of the Gulf of Mexico. The Southern blot technique was used. Fifteen haplotypes were identified in the 142 chromosomes. Five were the most frequent: two haplotypes, (+?+++) (52.4%) and (??+?+) (19.0%) were associated with β^S chromosomes; two haplotypes, (??+++) (38.2%) and (???++) (19.7%), were linked with β^A chromosomes, and the fifth (??++?) was present in both types of chromosomes. Haplotype (+?+++) corresponded to the Bantu or Senegal type. With Hinc II analysis after PCR amplification in both the 5′ and 3′ regions of the ψβ-globin gene, it was possible to distinguish between these African types, as in the former both restriction sites are absent. This analysis was done in 23 β^S and 10 β^A subjects. All β^S chromosomes disclosed the Bantu type, while β^A were similar to Caucasians. Bantu and Benin haplotypes have been found with high frequency in African populations, indicating the great influence of African genes in the population of the Mexican coasts. In addition, two previously unidentified haplotypes were found: (++??+) and (?++++). These can be explainded by crossing-over events and/or by new mutations. © 1995 Wiley-Liss, Inc.     

Counselling for prenatal diagnosis of sickle cell disease and beta thalassaemia major: a four year experience.

A non-directive programme of prenatal counselling was used during a four year period. Forty-three couples at risk for having a baby with a haemoglobinopathy were identified. Prenatal diagnosis was offered in 19 pregnancies to 14 couples at risk of having a baby with sickle cell anaemia and in two pregnancies in two couples at risk of a baby with beta thalassaemia major, who presented before the 18th week of pregnancy. Six couples at risk for sickle cell anaemia accepted prenatal diagnosis in 10 pregnancies, as did both couples at risk for thalassaemia. Couples who were eligible for prenatal diagnosis but refused it tended not to have been informed about sickle cell disease before counselling, one partner was more frequently absent at the time of the initial counselling session, or they either had no children with sickle cell disease or the children were not severely affected. Other factors influencing their decision included a poor obstetric history and rejection of abortion, mainly on moral grounds. The approximately 50% uptake of prenatal diagnosis in this initial study highlights the complex issues involved. Our experience indicates that with systematic screening and counselling in the antenatal clinic, and with increased awareness of the haemoglobinopathies, couples at risk will be in a better position to make informed decisions.     

Postmortem molecular diagnosis of sickle beta thalassaemia

This report describes a case in which the diagnosis of sickle cell disease (SCD) was established after death. The diagnosis of sickle cell syndrome was made in a 68 year old black patient who was found to have sickled red blood cells in many organs at necropsy although the disease had not been diagnosed during her lifetime. DNA was isolated from a peripheral blood smear obtained on the day of the patient's death. The beta globin gene was polymerase chain reaction amplified and sequenced, revealing that the patient had S-beta(+) thalassaemia. This study shows that blood smears are a suitable source for retrospective DNA analysis studies. This case illustrates that relatively "mild" forms of SCD can be overlooked, despite symptomatology suggestive of a sickle syndrome, and demonstrates the feasibility of the postmortem molecular diagnosis of haemoglobinopathies in such cases.     

Prenatal diagnosis of beta thalassaemia by oligonucleotide analysis in Mediterranean populations.

We have used four oligonucleotide probes and two restriction enzymes to detect the beta thalassaemia mutation in a group of 61 couples of Italian descent who were prospective parents. We have been able to define the beta thalassaemia mutation in both parents in 47 couples and in only one parent in 12 couples. Prenatal diagnosis was accomplished successfully either by amniocyte (two) or trophoblast (26) DNA analysis in 28 couples in which the pregnancy was in progress. These results indicate that direct identification of the mutation by oligonucleotide or restriction endonuclease analysis is a practical and useful method for prenatal diagnosis of beta thalassaemia in childless couples.     

Homozygous beta thalassaemia in Liberia.

The clinical and haematological findings in 19 Liberians probably homozygous for beta thalassaemia are described. The haemoglobin patterns were similar with Hb F levels in the 30-50% range and a raised level of Hb A2 and, although the clinical severity varied widely, over half the cases were symptomless and even the more severely affected ones showed a milder picture than that found in Mediterranean races. Haemoglobin-synthesis studies carried out on three homozygotes and two heterozygotes indicated a variable degree of globin-chain imbalance. The reasons for the mild course of the disease in Liberians and other African races are discussed; it is likely that the beta-thalassaemia genes in these populations are different from those in other racial groups. It is noted that all persons in this study belong to tribes which have a low incidence of the sickle-cell gene.     

A genetic combination of silent beta-thalassaemia, high Hb A2 beta-thalassaemia, and single alpha globin gene deletion causing mild thalassaemia intermedia.

This paper reports a Sardinian patient, who was a compound heterozygote for silent beta-thalassaemia and high Hb A2 beta o-thalassaemia with the clinical phenotype of mild thalassaemia intermedia; alpha globin gene mapping showed a single alpha globin gene deletion. The reduced alpha globin chain output resulted in more balanced globin chain synthesis, which in turn accounted for the mild clinical phenotype.     

Dominantly inherited beta thalassaemia intermedia caused by a new single nucleotide deletion in exon 2 of the beta globin gene: Hb morgantown (beta91 CTG>CG)

Family members in multiple generations of an Irish-American family were investigated for moderate to severe microcytic anaemia, inherited in an autosomal dominant fashion. A novel frameshift mutation of the beta globin gene was discovered. This study highlights the importance of considering dominantly inherited beta thalassemia in the investigation of anaemia, even in patients with ethnic backgrounds not usually associated with beta thalassaemia.     

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.     

Detection of beta and delta globin gene mutations by PCR and direct DNA sequencing in an individual with normal HbA2 beta thalassemia.

Normal HbA2 beta thalassemia in a Greek individual was shown to be due to co-inheritance of beta and delta thalassemias. The genetic defects were characterized by enzymatic amplification of the beta and delta globin genes and direct genomic sequencing. Two children with a typical high HbA2 beta thalassemia trait had inherited the beta thalassemia allele whilst a third child had low-normal HbA2 associated with delta+ thalassemia. Segregation patterns confirmed that the delta+/beta zero thalassemia defects were present in trans.