Haemoglobin Miyada, a beta-delta fusion peptide (anti-Lepore) type discovered in a Japanese family

Abnormal hemoglobin anti-Lepore Hong Kong compound with β0-thalassemia ameliorate thalassemia severity when co-inherited with α-thalassemia

Abnormal hemoglobin anti-Lepore Hong Kong is a rare βδ fusion variants resulting from non-homologous crossover during meiosis. Anti-Lepore Hong Kong is known to consistently exhibit significantly increased level of HbA2. In this study, we used multiplex ligation-dependent probe amplification (MLPA) and single molecular real-time (SMRT) sequencing, as well as Sanger sequencing, to identify variants in five unrelated families with abnormal elevated HbA2 level. All probands in these five families were found to be heterozygous for anti-Lepore Hong Kong. Among them, two families showed co-occurrence of β0-thalassemia and α-thalassemia (-SEA/ or αCSα/). Heterozygotes for anti-Lepore Hong Kong displayed an average HbA2 level of 17.7% and behaved normal. However, when combined with β0-thalassemia and α-thalassemia, the probands exhibited higher HbA2 level (30.2-40.8%) and behaved with β-thalassemia trait. Furthermore, determination of the α/β-mRNA ratio revealed a slight downregulation of β-globin, similar to that of β-thalassemia minor. Our study is the first to identify compound heterozygotes for anti-Lepore Hong Kong, β0-thalassemia and α-thalassemia, provide valuable information for prenatal counseling.

Detection of a novel βδ-globin fusion gene, anti-lepore Hb CHORI (β(through IVS-I-57)/δ(from IVS-I-101)), by multiplex ligation-dependent probe amplification

Anti-Lepore hemoglobins (Hbs) are rare βδ fusion variants that arise from non homologous crossover during meiosis. Using multiplex ligation-dependent probe amplification (MLPA), we identified a novel anti-Lepore Hb in an individual with an ambiguous Hb variant detected on routine screening by electrophoresis and high performance liquid chromatography (HPLC). The results of MLPA revealed duplication of β and δ gene segments. Resolution of the rearrangement by DNA sequencing confirmed a novel anti-Lepore Hb, molecularly distinct from Hb P-Nilotic, which we have named anti-Lepore Hb CHORI (Children's Hospital Oakland Research Institute) (β(through IVS-I-57)/δ(from IVS-I-101)).

Beta-thalassemia intermedia with exceptionally high hemoglobin A2: relationship to mutations in the beta-gene promoter

Small deletions of the 5' portion of the beta-globin gene that remove the promoters but stop 3' to the delta-globin gene are recognized as the sole cause of beta-thalassemia with exceptionally high hemoglobin A2 (HbA2) levels. Two patients with beta-thalassemia intermedia and exceptionally high levels of HbA2 (10.4 and 12.0%) were examined. One patient was a combined heterozygote for the -88 C----T and a novel -87 C----A mutation, while the other was homozygous for the -29 A----G beta(+)-thalassemia mutation. The remainder of the beta genes were normal. There was no evidence for deletions involving the 5' portion of the beta gene or the region between the beta and delta genes. Gene mapping studies excluded the possibility of a beta delta-anti-Lepore hemoglobin gene with beta promoters and delta coding sequences. There were no mutations in the promoters of the G gamma or A gamma-globin genes that have been associated with the hereditary persistence of HbF phenotype. The delta-globin gene promoters were normal from codon 17 to position -145 relative to the mRNA capping site. There appears to be considerable heterogeneity of HbA2 and HbF levels in patients who are homozygous or mixed heterozygotes for mutations in the TATA box and other promoter elements of the beta-globin gene. The capacity for proteolysis within the erythrocyte may vary among individuals. The authors hypothesize that in the exceptionally high HbA2 beta-thalassemia intermedia phenotype, proteolysis of superfluous alpha-globin chains is less efficient than in patients with customary levels of HbA2.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemoglobin Miyada: DNA analysis of the anti-Lepore beta delta fusion gene

Hemoglobin Miyada, an anti-Lepore hemoglobin, represents the protein product of a nonhomologous crossover between beta and delta genes. The mutant globin is beta-like from the N terminus to amino acid 12, and delta-like from amino acid 22 through the C terminus, thus predicting a crossover site in the first coding region of the gene. DNA analysis, using multiple restriction endonucleases and hybridization to delta and beta globin gene-specific probes, confirms that the beta delta hybrid gene 1) is located on a single chromosomal fragment between normal delta and beta genes, and 2) has 5' beta promoter sequences, delta IVS 1 and 2, and 3' coding and flanking sequences.

A fusion gene in man: DNA sequence analysis of the abnormal globin gene of hemoglobin Miyada

An abnormal globin gene from a patient heterozygous for Hemoglobin Miyada was cloned and sequenced. The results indicated that the 5' flanking region and the 5' side of the gene were identical to those of a beta-globin gene and that the 3' side was identical to that of a delta-globin gene. The part of the gene identical to a beta-globin gene shifted to the part identical to the delta-globin gene somewhere in a homologous sequence region between the third nucleotide of the 17th codon and the second nucleotide of the 22nd codon of these two genes. Thus, results of analysis of the nucleotide sequence support the idea that the abnormal globin gene of Hemoglobin Miyada was generated as a fusion gene by unequal crossing over between a beta- and a delta-globin gene.

Unexpected relationships between four large deletions in the human beta-globin gene cluster

Two independent gamma delta beta-thalassemias are each associated with large deletions. We show, by comparing DNA sequences, that the deletions are due to non-homologous DNA exchanges. The 5' breakpoints are located approximately the same distance apart and in the same order along the DNA as their 3' breakpoints. Two independent cases of hereditary persistence of fetal hemoglobin, also involving large deletions, show the same unexpected relationship between their 5' and 3' breakpoints. This relationship is most simply explained if, within each pair, the deletions are of approximately the same length. The results suggest that the four deletions were generated by a common mechanism. Perhaps their 5' and 3' breakpoints are physically close in the nucleus, although far apart on the linear DNA.

An unusual phenotypic expression of Hb-Leiden

After a boy of Mexican-American descent became jaundiced during treatment of a serious urinary tract infection with an oxidant drug, an extensive hematological examination was made. The important finding was the presence of Hb-Leiden to the extent of less than 3% or about a tenth of the usual percentage. Although inclusion bodies are present in the erythrocytes at all times, his hematological parameters have remained normal. The genetic basis for the unusually small amount of Hb-Leiden in the propositus may be due to the Hb-Leiden gene in an anti-Lepore configuration, that is, and Hb-Leiden gene in cis to the normal beta and delta genes.

Triplicated alpha-globin loci in humans

We have identified 12 individuals who are heterozygous for a chromosome with three alpha-globin genes. We determined the presence of the third alpha-globin locus by restriction endonuclease digestion and hybridization with alpha-globin cDNA probes. The three alpha-globin loci resided in an elongated fragment on digestion with EcoRI, BamHI, and Xba I, and the third locus was present in an additional 3.7-kilobase fragment on digestion with Hpa I, Sac I, and Bgl II. The locations of the restriction sites are compatible with a nonhomologous crossover mechanism producing the triple alpha loci. The frequency of the triple alpha loci was 0.0036 in American blacks and less than 0.004 in Sardinians, but was higher in Greek Crypriots (0.05). Individuals with five alpha-globin genes (alpha alpha/alpha alpha alpha) apparently showed no clinical or hematologic abnormalities.

Variation in hemoglobin A2

The structure, properties and function of, and some biosynthetic and genetic aspects of, Hb A2 are described. The structural variants of Hb A2 are reviewed and their geographical distribution presented. Hb A2, Hb A2-Flatbush and Hb A2-Babinga are characteristic of negro populations and may have originated in Western or Central Africa. Hb A2-Sphakia is characteristic of Canadian Amerindian and Hb A2-Indonesia of Indonesian/Malay populations. Hb A2-NYU has only been found sporadically and most frequently in persons of Eastern European origin. The other three variants of Hb A2 have only been reported in a single person or in single families. Some conditions which are associated with changes in Hb A2 levels are reviewed.

Haemoglobin LeporeBoston in a Turkish family

Haemoglobin Lepore was demonstrated in four members of a Turkish family. It was found in the heterozygote state and was associated with erythrocyte morphology similar to that observed in the beta thalassaemia trait. The average concentration of haemoglobin Lepore was 8.1% of the total haemoglobin. Structural analysis showed that the Lepore haemoglobin was the LeporeBoston type. This is the first reported instance of the occurrence of haemoglobin Lepore in Turkey.