Different Forms of Hb H Disease in the Chinese

A marked genetic and clinical variability of the Hb H syndrome occurs because of the molecular heterogeneity of α-thalassemia (thal). The hallmark is the presence of excess β chains forming Hb H (β tetramer). In the Chinese, classical Hb H disease presents as “α-thalassemia intermedia” and is due to a double heterozygosity for two deletional forms of α-thal, α-thal-1 and α-thal-2. The majority of cases with an α-thal-1 defect have a deletion of at least 18.1 kb starting 3′ to the ζ1 gene which includes the ψα and the two a genes; it is similar to that described in Thais. However, two families had a deletion of the entire ζ-α gene cluster, i.e. ζ-α-thal-1. Of 33 α-thal-2 defects studied, 26 were the rightward deletion (α^?3.7 kb, all type I defects) and seven the leftward deletion (α^?4.2 kb); one of the latter was associated with Hb Q. About 10% of the α-thal defects belong to the nondeletion type, the most common form being Hb Constant Spring (CS). This anomaly, when coinherited with α-thal-1, produces Hb H-CS disease which has a most marked anemia and splenomegaly due to the instability of the α-CS chain. Hb Quong Sze produces an α-thal-2 because of the unstable α-Quong Sze chain. One patient who inherited classical Hb H disease and Hb New York (NY) [α113(G15)Val→Glu] had severe anemia, and required frequent blood transfusions due to the deleterious effect of an increased α-NY chain turnover. Unlike usual cases of Hb H disease, two patients with the nondeletional form of Hb H had severe anemia during fetal life resulting in hydropic changes (Hb H Hydrops Fetalis). These cases of severe α-thal pose special problems for prenatal diagnosis.     

Rapid molecular characterization of Hb H disease in Chinese by polymerase chain reaction

Summary We have developed a rapid method to molecularly distinguish different types of Hb H disease. The study depended on (a) most of the Hb H disease in Taiwan having an-thalassemia-1 of the Southeast Asia type (-SEA) in one allele and (b) the differences of X box of-globin gene cluster in the other allele. To detect the -SEA allele, we utilized the primers located on either side of the breakpoint to do PCR, then characterized the amplified products. For the other allele, we sequenced part of the X box, and found that bases –2803 to –2461 of the X box of – ^3.7 belonged to the X box of ₂ globin gene. In – ^4.2, the bases belonged to the X box of ₁ globin gene, whereas in ^cs it contained both X boxes of ₁ and ₂ globin genes. There was anMboII site at this region of the X box of ₂ globin gene. We utilized PCR to amplify this region and digested it with restriction enzymeMboII, then combined it with another PCR of different primer pairs to molecularly diagnose different types of Hb H disease. One hundred and one cases of Hb H disease from different families were studied: all of the cases had one allele of -SEA deletion, while the other allele showed that 52/101 were – ^3.7, 41/101 were ^cs , 7/101 were – ^4.2, and 1/101 was – ^G.Taichung. Of 52 cases of Hb H with – ^3.7, 47 were type-I deletion and five were type-II deletion.     

Hb Icaria–Hb H disease: identification of the Hb Icaria mutation through analysis of amplified DNA

Hb Icaria-Hb H disease was observed in a Yugoslavian teenager who exhibited moderate anaemia with severe microcytosis and hypochromia and 16% Hb H. Four of his relatives were Hb Icaria heterozygotes; their haematological data were comparable to those with a deletional type of alpha-thalassaemia-2. The patient also had an additional alpha-thalassaemia-1 deletion, an approximately 20.5 kb deletion, common among Mediterranean populations. The Hb Icaria mutation, i.e. the TAA----AAA mutation at codon 142, was identified by hybridization of amplified DNA with specific probes. The mutation is located on the alpha 2-globin gene; the one remaining alpha 1-globin gene is apparently able to compensate sufficiently for the loss of the three alpha-globin genes to maintain a haemoglobin level of 8-9 g/dl.     

Molecular basis of Hb H disease in southwest Iran

Although alpha0-thalassemia (thal) defects are not very frequent in the Iranian population, Hb H disease does occur in the country. We have analyzed the alpha gene cluster of 13 patients showing the presence of Hb H to establish the molecular background of this disease in southwest Iran (Shiraz and Hormozgan provinces). Using gap-polymerase chain reaction (gap-PCR) and direct DNA sequencing we have found the --MED-I deletion, the polyadenylation signal (poly A) mutations alphaT-Saudi alpha and alphaT-Turkish alpha and Hb Constant Spring (Hb CS) in association with the common -alpha3.7 deletion. This study has revealed that: 1) at least six genotypes are responsible for Hb H disease in the area: .-alpha3.7/ --MED-I; -alpha3.7/alphaT-Saudi alpha; alphaT-Saudi alpha/alphaT-Saudi alpha; alphaCSalpha/--MED-I; --MED-I/alphaT-Turkish alpha; and the atypical forms of Hb H disease -alpha3.7/alphaCSalpha. 2) The molecular background of Hb H disease in the southwest area of Iran is more similar to the Mediterranean type than to the Southeast Asian. 3) Hb Bart's hydrops fetalis syndrome and mild, intermediate or severe postnatal Hb H disease conditions can be expected, but at a relatively low incidence. 4) The diagnostic flowchart for patients with microcytic hypochromic anemia should include iron deficiency, beta-thal, alpha+- and alpha0-thal analyses.     

Genotype-phenotype correlation in Iranian patients with Hb H disease

Thalassemia is the most common genetic disorder in Iran. Some α-globin genotypes leading to Hb H disease may cause severe anemia and dependence on regular blood transfusions. In this study, 40 patients were analyzed for the molecular basis and the genotype-phenotype correlation of Hb H disease in Iran. α-Globin molecular analysis was performed by polymerase chain reaction (PCR) followed by agarose gel electrophoresis, reverse hybridization test strips or DNA sequencing. The most frequently observed α-globin genotypes were -α(3.7)/- -(MED) in 10 patients (25%), - -(20.5)/α(-5nt)α in six patients (15%) and - -(20.5)/-α(3.7) in four patients (10%). A subset of the identified Hb H genotypes, including - -(MED)/α(CS)α, - -(MED)/α(PolyA2)α and α(CS)α/α(CS)α, was associated with a need for regular or irregular blood transfusions. Our findings provide a basis for predicting phenotype severity by identifying the Hb H genotype and making more selective decisions for prenatal diagnosis.     

The nondeletional types of Hb H disease in Guangxi.

Three primers were designed, one specific for alpha 1-globin DNA, a second for alpha 2-globin DNA, and a third that is common for both alpha 1- and alpha 2-globin DNA. These three primers can be applied for selective amplification of the two globin DNA fragments, which is useful for identification of nondeletional types of Hb H disease. Fifty-nine DNA samples of Hb H patients from Guangxi were studied by selective amplification, and 27 cases (45.8%) were confirmed as nondeletional types. Of these, 22 (81.5%) had the Hb Constant Spring (CS) mutation and one had the Hb Quong Sze (QS) mutation; both were identified by hybridization with synthesized oligonucleotide probes. Nondeletional Hb H disease in Guangxi seems to be more severe than the deletional types. The average hemoglobin level of the nondeletional Hb H/CS (--/alpha alpha) is 6.8 g/dl, which is lower than that of the deletional types (7.9 g/dl), while the levels of Hb H and Hb Bart's were much higher in the patients with Hb H/CS than in those with the deletional types.     

Characterization of a rare single alpha-globin gene deletion in a Chinese woman with Hb H disease

A Chinese patient with Hb H (beta4) disease was found to be a compound heterozygote for a 2.4 kb alpha(+)-thalassemia (thal) deletion and the common Southeast Asian alpha0-thal deletion. The endpoints of the 2.4 kb deletion were identified by sequence analysis of the deletion junction. The deletion removes the entire alpha1-globin gene and leaves the alpha2-globin gene intact.     

Molecular defects in 2 examples of severe Hb H disease

Severe Hb H disease presented in unexpected ways in 2 families of Greek origin. In 1, Hb H disease led to neonatal death. The underlying molecular defect was double-heterozygosity for the --Med/ alpha thalassaemia haplotype and a nondeletional alpha thalassaemia defect (alpha alpha T'Karditsa'/). The 2nd family requested antenatal diagnosis. The husband had mild nondeletional alpha thalassaemia. Initial investigations in the wife demonstrated unexpected gene mapping patterns. These have recently been shown to result from the (-alpha)Med 20.5/ haplotype.     

Genetic and molecular diversity in nondeletion Hb H disease.

Restriction endonuclease mapping of nondeletion alpha-thalassemia determinants from a variety of racial groups showed no detectable abnormalities within a 40-kilobase region of the zeta-alpha globin gene cluster. By using a zeta-specific probe, we defined three different types of interactions that give rise to Hb H disease, each involving a nondeletion alpha-thalassemia haplotype. mRNA analysis showed further diversity within these groups, indicating that there are at least three nondeletion determinations.     

Molecular and clinical features of Hb H disease in northern Thailand

Clinical assessment, hematological studies and molecular analyses were performed in 102 pediatric patients with Hb H disease in northern Thailand. A total of six mutations of the alpha-globin gene, which produced five genotypes, were detected. All patients had an alpha(0)-thalassemia (thal) deletion on one chromosome 16. All but one of these were of the South East Asian type (--SEA); one patient had the THAI deletion (--THAI). The deletional alpha(+)-thal mutations comprised 3.7 kb (-alpha(3.70) and 4.2 kb (-alpha(4.2)) deletions which were found in 34 (33.3%) and 10 (9.8%) alleles, respectively. The nondeletional alpha(+)-thal mutations comprised 55 (53.9%) alleles of Hb Constant Spring (CS) (alpha142, TAA --> CAA) and three (2.9%) alleles of Hb Pakse (alpha142, TAA --> TAT). Six patients with Hb H-CS disease also carried Hb E (AEBart's CS disease). The clinical features were diverse and the nondeletional genotypes were associated with more severe clinical and hematological features, including younger age at presentation, larger size of liver and spleen, lower hemoglobin (Hb) level, and higher transfusion requirements. The high proportion of nondeletional Hb H disease observed in this study was inconsistent with the previously reported gene frequencies of alpha-thal in the region, suggesting that many deletional Hb H patients with milder symptoms may have escaped recognition.     

Unusual molecular basis of Hb H disease in the Azores Islands, Portugal

An Azorean family with Hb H disease (10% Hb H) was studied in order to elucidate its molecular basis. DNA studies on the patient only revealed a 4.2 kb "leftward" deletion of paternal origin which implies the co-inheritance of a nondeletional alpha-thalassemia determinant. Restriction endonuclease and oligonucleotide analysis allowed the exclusion of five point mutations: initiation codon (at both alpha 1- and alpha 2-globin genes), IVS-I donor splice junction pentanucleotide deletion, codon 125 CTG----CCG substitution, and Saudi Arabian polyadenylation signal mutation. These findings suggest that the molecular basis of this form of Hb H disease is probably different from those described previously.     

Molecular basis and hematological characterization of Hb H disease in Southeast Asia

We molecularly characterized sixty-seven cases of Hb H disease by the polymerase chain reaction. The strategy depends on amplifying the α-thalassemia-1 (α-thal-1) gene by prlmers flanking the breakpoint and sequence differences of the 3′ end of the α-globin gene and the nonhomologous elements I, II, and III among different types of α-thala-2. In the 67 cases studied, all involved α-thal-1 of the Southeast Asia type (SEA) In combination with deletional or nondeletional α-thal-2. Thirty-two cases were of the deletion form and 35 cases were of the nondeletion form. In 32 cases of the deletion form, 29 cases were rightward deletion (-α^3.7), and three cases were leftward deletion (-α^4.2). We found that all of the nondeletion forms were α-thal-1 of SEA type with Hb CS. After the subtyping of Hb H with -α^3.7, 26 out of 29 were type I deletion and 3 out of 29 were type II deletion. Comparlsons of clinical data of deletion forms and the nondeletion form showed that there were earlier occurrence of anemic symptoms and a larger erythrocyte volume in the nondeletion form group (P < 0.005). © 1994 Wiley-Liss, Inc.     

A novel alpha-thalassemia-2 (-2.7-kb) observed in a Chinese patient with Hb H disease

We describe a newly detected alpha-thalassemia-2 (alpha-thal-2) deletion characterized by a small -2.7-kb deletion involving the alpha 1 globin gene. This deletion has thus far been observed in only one Chinese subject with Hb H disease.     

Hydrops fetalis due to an unusual form of Hb H disease

The occurrence of Hb H hydrops fetalis is reported for the first time. The mother has zeta-alpha thalassemia 1 (zeta zeta alpha alpha/----) and the father has non-deletion alpha thalassemia [zeta zeta alpha alpha/zeta zeta (alpha alpha)T]. The complete deletion of the zeta alpha cluster on one chromosome was confirmed by quantitation of alpha and zeta gene numbers, the normal alpha and zeta gene patterns arising from the remaining normal chromosome, and the decreased alpha/beta globin chain ratio of 0.57. The non-deletion alpha thalassemia defect could only be identified by the imbalanced alpha/beta globin chain ratio of 0.65 in the presence of normal gene numbers and patterns. The newborn was markedly anemic, unlike those with classical Hb H disease, because the non-deletion alpha thalassemia defect is more severe than alpha thalassemia 2. The decreased zeta genes during fetal life might have additional deleterious effects. In this family, the distinct BamHI restriction fragment length polymorphism in the hypervariable region of the zeta genes may be used for future prenatal diagnosis.