The Interaction of α-Thalassaemia and Haemoglobin G Philadelphia

An American Negro woman was found to have HbH disease in association with HbG Philadelphia (α68-asnlys). Starch gel electrophoresis failed to reveal the presence of any HbA or HbA₂ and studies of globin chain synthesis indicated absence of α^A production. The α^G/β synthesis ratio was 0.63. The woman's son and her two half-sibs had α-thalassaemia trait with no HbH and α/β synthesis ratios of 0.84, 0.84 and 0.76. The data indicate that there is no functioning α^A gene linked to the α^G gene. The absence of α^A synthesis by the propositus also indicates that the α-thalassaemia gene trans to the α^G gene completely suppresses α chain production, the first evidence for such a gene in Negroes.     

Atypical HbH disease in a Surinamese patient resulting from a combination of the −SEA and −α3.7 deletions with HbC heterozygosity

The first case of haemoglobin H (HbH) disease in combination with haemoglobin C (HbC) is reported in a man of Surinamese origin. Only haemoglobin A (HbA) and HbC were detected by electrophoresis. The amount of HbC was much less than expected in HbC heterozygotes. The synthesis ratio (β^A +β^C/α) indicated an α-thalassaemia defect with two non-functional α genes, which did not correlate with the degree of haemolysis and anaemia displayed by the patient. The DNA analysis of the α-genes clusters revealed a defect combination −SEA/−α^3.7. The haematological data and the physiopathology of this atypical case are compared with the typical HbH disease found in a first cousin of the propositus. Data on the globin chains expression and on the formation of β^A and β^C homotetramers in HbH/HbC disease are presented.     

A base substitution (T→C) in codon 29 of the α2-globin gene causes α thalassaemia

Summary. We have identified three individuals of Greek or Greek Cypriot origin with an atypical form of HbH disease characterized by a severe hypochromic microcytic anaemia associated with relatively small amounts of HbH in the peripheral blood. Molecular analysis has shown that each is a compound heterozygote for a previously described mutation affecting the poly A addition signal (AATAAA→ÁTAAG) and a previously undescribed mutation involving a T→C transition in codon 29 of the α2 gene causing a leucine→pro-line substitution. Although this mutation would be expected to produce an unstable haemoglobin and hence a haemolytic anaemia, simple heterozygotes for the α^29Leu→Pro mutation have the phenotype of α-thalassaemia trait.     

Severe thalassaemia intermedia caused by interaction of homozygosity for α-globin gene triplication with heterozygosity for β thalassaemia

Summary A 3-year-old child was evaluated for β-thalassaemia intermedia. Molecular characterization including β-globin gene sequence analysis revealed heterozygosity for a single β-thalassaemia mutation, IVSI nt1 (GA). In addition the patient was found to be homozygous for α-globin gene triplication (ααα^anti3,7/ααα^anti3,7). The propositus has a significantly more severe phenotype than has been previously reported with this combination of genetic defects. In contrast, four individuals heterozygous for both triplicated α and for β-thalassaemia had a phenotype of thalassaemia minor, and a fifth had very mild thalassaemia intermedia.     

Rapid analysis of -α3.7 thalassaemia and αααanti 3.7 triplication by enzymatic amplification analysis

Summary In this report we describe a PCR-based method for the diagnosis of the most common form of α thalassaemia, the –α^3.7 deletion which occurs throughout all tropical and subtropical regions of the world. The same procedure also identifies the reciprocal recombinant chromosome (ααα^{anti 3.7}). Restriction mapping of the PCR products has enabled us to distinguish between the type I (–α^3.7I), type II (–α^3.7II) and type III (–α^3.7III) deletions. This strategy will be very useful in screening programmes of α thalassaemia occurring on its own or in association with β thalassaemia and sickle cell disease.     

The interaction of α° thalassaemia with Hb Icaria: three unusual cases of haemoglobinopathy H

The clinical, haematological, biosynthetic and molecular data of three Greek haemoglobin H (HbH) disease patients with a distinctive clinical phenotype are described. During infancy all three patients had unusually severe clinical manifestations for HbH disease, with anaemia necessitating blood transfusions, signs of bone changes, growth impairment, and splenomegaly. Molecular analysis identified a rare α-thalassaemia genotype (− −^Med/α ^Icα) . Splenectomy resulted in marked amelioration of the clinical signs; post splenectomy all three patients preserve adequate haemoglobin levels (9–10 g/dl) with growth restored to normal. Despite the initial severe clinical phenotype in these patients, our experience indicates that splenectomy modifies the clinical course to that of mild thalassaemia intermedia. This observation should be considered carefully when giving genetic counselling to families carrying the rare Hb Icaria mutation and an α° thalassaemia mutation.     

Haemoglobin Constant Spring has an unstable α chain messenger RNA

Haemoglobin Constant Spring (Hb CS) is a variant with an elongated α-chain associated with an α⁺ thalassaemia phenotype. The amount of α mRNA relative to β mRNA in reticulocytes was reduced in carriers of Hb CS by an amount equivalent to the reduction observed in carriers of α⁺ thalassaemia. In a patient with Hb CS-H disease there was greater α/β mRNA ratio in bone marrow nuclear RNA than in the peripheral blood. Furthermore, all the α mRNA in the patient's peripheral blood was derived from the α1 (α^A) gene. The data suggest that α^CS mRNA is unstable and degraded in the cytoplasm. This instability may be due to destabilization of a specific sequence in the 3'non-coding region during translation.     

Homozygous deletional α+ thalassaemia associated with unequal expression of the two remaining α1 genes (α1A and α1Q)

S ummary . A Cambodian family presenting several haemoglobinopathies, Hb E, Hb Q and α⁺ thalassaemia, has been investigated. DNA analysis showed that the thalassaemia syndrome corresponds to a leftward type (4.2 kb) deletional from of α⁺ thalassaemia. Genotypes found in the family are: propositus -α^A/-α^Q, β^A/β^E, mother and older sister α^Aα^A/ -α^Q, β^A/β^E; father α^Aα^A/-α^A, β^A/β^A. The propositus consistently presents an α^Q/α^A chain ratio of 60/40 although both chains are products of α₁ loci. The relatively higher expression of the α^Q chain is not observed in the mother and therefore makes it unlikely to reflect anything other than differential expression of the maternal -α^Q/ and paternal -α^A/ haplotypes. This observation raises the possibility that both haplotypes are not strictly identical and that the region of the cross-over event is important for α gene expression.     

α-Thalassaemia in the population of Cyprus

We have determined the α-thalassaemia (α-thal) determinants in 78 patients with Hb H disease from Cyprus; 25 were Turkish Cypriots and 53 were Greek Cypriots. Four deletional and three non-deletional α-thal alleles were present; the -α(3.7 kb) α-thal-2 and the —^MED-1α-thal-1 were most frequently seen; —^MED-II and -(α)^20.5 deletions occurred at considerably lower frequencies. About 15% of all chromosomes carried a non-deletional α-thal-2 allele; of these the 5 nucleotide (nt) deletion at the first intervening sequence (IVS-I) donor splice site was present in ˜ 8% of all chromosomes. Two types of polyadenylation signal (poly A) mutations were observed. No striking frequency differences were seen between Greek and Turkish Cypriot patients. Combinations of the various types of α-thal resulted in eight different forms of Hb H disease. The phenotypes were comparable except for great variations in the level of Hb H which was highest (average ˜ 22%) in the 12 patients with the α^5ntα/—^MED-I combination. One patient with the same form of Hb H disease but with an additional β-thal (IVS-I-110, G → A) heterozygosity had a most severe microcytosis and hypochromia with < 1% Hb H. Variations in the level of Hb H might correlate with the severity of the disease, although this was not evident from the haematological data.     

The triplicated α-globin gene locus in β-thalassaemia heterozygotes: clinical, haematological, biosynthetic and molecular studies

Excess α-globin chains play a major role in the pathophysiology of homozygous β-thalassaemia. In β-thalassaemia carriers a minor effect of α-globin chain excess is reflected in a minimal or mild anaemia without clinical symptoms. Factors that increase α-chain excess in heterozygotes are expected to accentuate the severity of the clinical and haematological phenotype.
We report the clinical, haematological, biosynthetic and molecular data in three β-thalassaemia heterozygotes with the rare interaction of homozygosity for α-globin gene triplication, and in 17 heterozygotes with a single additional α-globin gene. The three patients homozygous for the α-globin gene locus (anti 3.7 kb arrangement) had β °-thalassaemia mutations and a diagnosis of thalassaemia intermedia, preserving haemoglobin levels around 7–8 g/dl. Of the 17 β-thalassaemia heterozygotes (six children and 11 adults), 16 had severe β-thalassaemia mutations interacting with an additional α-globin gene (13 with ααα^anti-37 and four with ααα^anti-42). Compared to simple β-thalassaemia heterozygotes, they had lower haemoglobin levels and red cell indices, but higher α/β biosynthesis, HbF levels and reticulocytes.
Our results suggest that homozygous α-gene triplication interacts with a severe β-thalassaemia mutation to cause an α-chain excess equivalent to that observed in homozygous β-thalassaemia intermedia. In heterozygotes for severe β-thalassaemia mutations with one additional α-globin gene, the α-chain excess causes a more pronounced degree of anaemia than is usually seen in simple β-thalassaemia heterozygotes.     

Globin Biosynthesis in Erythroid Bursts of Heterozygous α or β Thalassaemia

S ummary . We examined globin chain synthesis in erythroid bursts (BFU-E) of patients with heterozygous α or β thalassaemia. BFU-E were cloned from circulating mononuclear cells, labelled with [H]leucine and globin chains purified by gel filtration and column chromatography. In six patients heterozygous for β thalassaemia, globin synthesis in BFU-E was nearly balanced, with an α/non α ratio of 1.05 0α12. These BFU-E produced 33.8 12.7%γ globin chain, an amount similar ( P >1 0.05) to that found in 10 controls with sickle cell anaemia (25.6 6.7) but greater ( P <0.05) than that of five normal controls (17.2 2.2). The balanced globin synthesis appeared due to the large amounts of γ chain made by BFU-E. In two α thalassaemia carriers, who also had sickle cell trait, the BFU-E α/non-α ratio was 0.67 and 0.79. These BFU-E produced 15% and 20%γ chain and 39% and 45%β^S globin. The synthesis of β^S globin in BFU-E exceeded the erythrocyte levels of 20% and 29% HbS and indicated nearly equal expression of β^A and β^B globin genes in these proliferating erythroid precursors. This provides further evidence that the low levels of HbS in sickle cell carriers with α thalassaemia are due to post-translational events resulting from the differing affinity of β^S and β^A globin for α chain and the destruction of excessive β^S chain.     

Red blood cell phenotypes in the α+ thalassaemias from early childhood to maturity

The α⁺ thalassaemias are the most common single gene disorders of humans, yet little is known about their haematological characteristics in childhood. Blood samples have been collected randomly from more than 2000 individuals in village communities in Vanuatu in the South West Pacific and analysed for α thalassaemia and associated haematological changes. Here we describe the haematological effects of the α⁺ thalassaemias from early childhood through to maturity in this population. Mean cell volume (MCV) and mean cell haemoglobin (MCH) levels in individuals of normal, heterozygous and homozygous genotype differed significantly from one another throughout the entire age range (2 P  < 0.05). In contrast, haemoglobin levels in heterozygous and homozygous individuals were well maintained throughout development. Adults of normal genotype attain Hb levels which are indistinguishable from Caucasian reference values, a finding made all the more remarkable given the high frequency of clinical malaria in this population. It is clear from these findings that haematological data are valuable in screening for carriers of α⁺ thalassaemia in this population. MCH is clearly the most sensitive discriminator. None of the homozygous adults tested had an MCH of >27 pg, whereas <10% of normals had a value of <27 pg. These data provide reference values for areas in which the α⁺ thalassaemias are common and often confused with iron-deficiency anaemia.     

A variant of spectrin low-expression allele αLELY carrying a hereditary elliptocytosis mutation in codon 28

Summary. Allele α^LELY is a low-expression allele of the erythroid spectrin α-gene. It carries mutations in exon 40 (α^V/41 polymorphism) and intron 45, respectively, and is associated with partial skipping of exon 46. The latter phenomenon is thought to impair the recruitment of α-chains by β-chains, and would eventually account for the low-expression character. When it occurs in trans to an α-allele responsible for hereditary elliptocytosis (α^HE allele; α^HE/α^LELY diplotype), allele α^LELY enhances the severity of elliptocytosis. Because allele α^LELY is widespread, we anticipated that it would occasionally carry HE determinants. These variants of allele α^LELY will be designated α^HE-LELY alleles. We report two families with the same α^HE-LELY allele. The HE component was the known α28 Arg → His mutation. This α^HE-LELY allele was investigated within the α^HE-LELY/α^LELY diplotype, a diplotye not described before. Except for the neonatal period, the presentation was mild. In a consistent manner, the α^LELY component in cis of the α^HE mutation counteracted the like component in trans .     

The α-Galactose Specificity of Anti-Pk

Abstract. These studies indicate that α-galactose is the terminal and immunodominant sugar of the P^k determinant. Human anti-P^k and the 'anti-P^k' activity of salmon and trout protectins are strongly inhibited by α-galactosyl groups of galactose, disaccharides and macromolecules, e.g. P₁ substance. Removal of a-galactose from P₁ substance abolishes its ability to inhibit anti-P^k antibody activity.
Anti-P^k antibody has a narrow spectrum for terminal a-galactosyl groups of cell surface antigens defining those of P^k but not those of B, P₁ or P₂ cells, while all these cells are agglutinated by the fish roe protectins. We suggest that anti-P^k antibody selects a larger determinant than the terminal α-galactosyl group and the full determinant is structurally different from those of B, P₁ and P₂ antigens. By contrast, fish roe agglutinins bind to a part only of the α-galactosyl group, present in all these antigens.     

The Abnormal Haemoglobins in Homozygous α-Thalassaemia

S ummary The red cells from Chinese stillborn infants with erythroblastosis foetalis due to homozygous α-thalassaemia contain about 80% Hb-_γ4, the second haemoglobin always present does not contain α-chains and has the structure Hb_γ2X₂ identical to Hb-Portland 1. Hb-A, Hb-F, or Hb-A₂ were not detected.     

REVIEW: α1-Antitrypsin deficiency associated liver disease

α₁-Antitrypsin (α₁-AT) deficiency is the most common genetic cause of liver disease in children and genetic disease for which children undergo liver transplantation. It also causes cirrhosis and hepatocellular carcinoma in adults. Studies by Sveger in Sweden have shown that only a subgroup of the population with homozygous PiZZ α₁-AT deficiency develop clinically significant liver injury. Other studies have shown that the mutant α₁-AT Z molecule undergoes polymerization in the endoplasmic reticulum and that a subpopulation of α₁-AT-deficient individuals may be susceptible to liver injury because they also have a trait that reduces the efficiency by which the mutant α₁-AT Z molecule is degraded in the endoplasmic reticulum.     

Haemoglobin Manukau β67[E11] Val→Gly: transfusion-dependent haemolytic anaemia ameliorated by coexisting alpha thalassaemia

Summary Haemoglobin Manukau (β67 Val→Gly) is a novel haemoglobin variant presenting in two brothers as non-spherocytic haemolytic anaemia which became transfusion dependent by 6 months of age. The severity of clinical expression seems to be modulated by coexisting alpha thalassaemia: the severely affected children have a normal complement of alpha globin genes with an unusual genotype (-α^3,7/ααα^3,7), while their father, who carries the abnormal gene with minimal symptoms, has homozygous α⁺ thalassaemia (-α^3,7/ -α^3,7) Another unusual feature of this case is the association of the β67 Val→Gly mutation with modification of β141 Leu to a residue (believed to be hydroxyleucine) that is not detected by standard amino acid analysis. This finding offers an explanation for the previous report of an association of another mutation at this site (Hb Sydney β67 Val→Ala) with Hb Coventry (deletion of β141 Leu).     

FIRST DESCRIPTION OF A FRAMESHIFT MUTATION IN THE α1-GLOBIN GENE ASSOCIATED WITH α-THALASSAEMIA

A frameshift mutation in the α₁-globin gene, responsible for a clinically mild α-thalassaemia phenotype, has been characterized in a Spanish woman. After excluding the most common forms of α-thalassaemia found in the Mediterranean area, both α-globin genes (α₁ and α₂) were amplified and analysed selectively by non-radioactive single-strand conformation polymorphism (SSCP). An abnormal SSCP mobility was present in the second exon of the α₁-globin gene and direct sequence analysis revealed a 13 bp deletion (between codons 51 and 55) affecting a single allele. The consequence of this mutation is a reading frameshift leading to a novel amino acid coding sequence from codons 51–61 and a premature stop signal at new position 62, which results in a net reduction of the affected α-globin chain output. The presence of this new mutation was confirmed by restriction enzyme analysis of the specific PCR product.     

Hb Utrecht [α2 129(H12)Leu → Pro], a new unstable α2-chain variant associated with a mild α-thalassaemic phenotype

We describe a new α₂-globin gene point mutation found in six individuals of a three-generation Dutch family. The mutant, which is associated with a mild α-thalassaemic phenotype, is not detectable at the protein level. The α₂ cd129 (CTG → CCG) transition was found by molecular analysis using denaturing gradient gel electrophoresis (DGGE) and single-strand conformation analysis (SSCA) followed by direct sequencing of the α₂-globin gene. Southern analysis revealed a triplication of the ζ-gene in cis with the mutant α-globin gene.