The haemoglobin constitution of infants with the haemoglobin Bart's hydrops foetalis syndrome

Detection of maternal carriers of common α-thalassemia deletions from cell-free DNA

α-Thalassemia is a common inherited blood disorder manifested mainly by the deletions of α-globin genes. In geographical areas with high carrier frequencies, screening of α-thalassemia carrier state is therefore of vital importance. This study presents a novel method for identifying female carriers of common α-thalassemia deletions using samples routinely taken for non-invasive prenatal tests for screening of fetal chromosomal aneuploidies. A total of 68,885 Vietnamese pregnant women were recruited and α-thalassemia statuses were determined by gap-PCR, revealing 5344 women (7.76%) carried deletions including αα/--SEA (4.066%), αα/-α3.7 (2.934%), αα/-α4.2 (0.656%), and rare genotypes (0.102%). A two-stage model was built to predict these α-thalassemia deletions from targeted sequencing of the HBA gene cluster on maternal cfDNA. Our method achieved F1-scores of 97.14-99.55% for detecting the three common genotypes and 94.74% for detecting rare genotypes (-α3.7/-α4.2, αα/--THAI, -α3.7/--SEA, -α4.2/--SEA). Additionally, the positive predictive values were 100.00% for αα/αα, 99.29% for αα/--SEA, 94.87% for αα/-α3.7, and 96.51% for αα/-α4.2; and the negative predictive values were 97.63%, 99.99%, 99.99%, and 100.00%, respectively. As NIPT is increasingly adopted for pregnant women, utilizing cfDNA from NIPT to detect maternal carriers of common α-thalassemia deletions will be cost-effective and expand the benefits of NIPT.

Molecular Detection of Alpha Thalassemia: A Review of Prevalent Techniques

Alpha thalassemia (α-thalassemia) is an autosomal recessive disorder due to the reduction or absence of α globin chain production. Laboratory diagnosis of α-thalassemia requires molecular analysis for the confirmatory diagnosis. A screening test, comprising complete blood count, blood smear and hemoglobin quantification by high performance liquid chromatography and capillary electrophoresis, may not possibly detect all the thalassemia diseases. This review focused on the molecular techniques used to detect α-thalassemia, and the advantages and disadvantages of each technique were highlighted. Multiplex gap-polymerase chain reaction, single-tube multiplex polymerase chain reaction, multiplex ligation-dependent probe amplification, and loop-mediated isothermal amplification were used to detect common deletion of α-thalassemia. Furthermore, the reverse dot blot analysis and a single tube multiplex polymerase chain reaction could detect non-deletion mutation of the α-globin gene. Sanger sequencing is widely used to detect non-deletion mutations of α-thalassemia. Recently, next-generation sequencing was introduced in the diagnosis of both deletion and point mutations of α-thalassemia. Despite the advantages and disadvantages of different techniques, the routine method employed in the laboratory should be based on the facility, expertise, available equipment, and economic conditions.

A Novel Single Gene Deletion (−αMAL3.5) Giving Rise to Silent α Thalassemia Carrier Removing the Entire HBA2 Gene Observed in Two Chinese Patients with Hb H Disease: Case Report of Two Probands

We report a novel deletion at the HBA2 presented with Hb H disease in two Malaysian- Chinese patients. The two unrelated probands were diagnosed with Hb H disease in a primary hematological screening for thalassemia. Results from routine molecular analysis with gap-polymerase chain reaction (PCR) method revealed a genotype asynchrony with the observed clinical presentation. Subsequent DNA analysis using a battery of molecular methods such as gap-PCR, multiplex ligation dependent probe amplification, DNA sequencing, confirmed the presence of a novel deletion in both the index cases removing the entire α2 globin gene. We have designated the deletion as (−αMAL3.5). Hematological indices and clinical findings suggest that the deletion has an α+ phenotype. The molecular process of this deletion is the result from misalignment and unequal crossover event between the duplicated homologous Y-boxes within the α globin gene cluster. Uncharacterized deletions, single nucleotide polymorphism and other nucleotide indels at the primer binding sites may impede the optimum condition for its annealing and extension and therefore may invalidate the gap-PCR obscuring the real genotype.我们报告了两例马来西亚华裔患者中随HbH病表现出的一种HBA2的新型缺失。 这两例不相关的先证者在地中海贫血的初步血液筛查中被诊断出患有HbH病。 采用跨越断裂点聚合酶链反应（PCR）方法进行常规分子分析的结果显示出一种与观察到的临床表现不一致的基因型。 后续采用一系列分子方法（如跨越断裂点PCR、多重连接探针扩增、DNA测序）进行的DNA分析证实了这两个指示病例中的新型缺失的存在消除了整个α2珠蛋白基因。 我们将该缺失命名为（-αMAL3.5）。 血液学指标和临床结果提示该缺失具有α+表型。 这种缺失的分子过程是α珠蛋白基因簇内部重复的同源Y-盒之间之间错配和不等交换事件的结果。 未表征的缺失、单核苷酸多态性和其它核苷酸插入/缺失的引物结合位点可能阻碍其退火和延伸的最佳条件，因此可能使跨越断裂点PCR无效，模糊了真实的基因型。

A journey in science: early lessons from the hemoglobin field

Real innovations in medicine and science are historic and singular; the stories behind each occurrence are precious. At Molecular Medicine we have established the Anthony Cerami Award in Translational Medicine to document and preserve these histories. The monographs recount the seminal events as told in the voice of the original investigators who provided the crucial early insight. These essays capture the essence of discovery, chronicling the birth of ideas that created new fields of research; and launched trajectories that persisted and ultimately influenced how disease is prevented, diagnosed, and treated. In this volume, the Cerami Award Monograph is by David J Weatherall, Founder, Weatherall Institute of Molecular Medicine, Oxford University, John Radcliffe Hospital. A visionary in the field of hemoglobin, this is the story of Professor Weatherall's scientific journey.

Alpha-thalassaemia

Alpha-thalassaemia is inherited as an autosomal recessive disorder characterised by a microcytic hypochromic anaemia, and a clinical phenotype varying from almost asymptomatic to a lethal haemolytic anaemia.

It is probably the most common monogenic gene disorder in the world and is especially frequent in Mediterranean countries, South-East Asia, Africa, the Middle East and in the Indian subcontinent. During the last few decades the incidence of alpha thalassaemia in North-European countries and Northern America has increased because of demographic changes. Compound heterozygotes and some homozygotes have a moderate to severe form of alpha thalassaemia called HbH disease. Hb Bart's hydrops foetalis is a lethal form in which no alpha-globin is synthesized. Alpha thalassaemia most frequently results from deletion of one or both alpha genes from the chromosome and can be classified according to its genotype/phenotype correlation. The normal complement of four functional alpha-globin genes may be decreased by 1, 2, 3 or all 4 copies of the genes, explaining the clinical variation and increasing severity of the disease. All affected individuals have a variable degree of anaemia (low Hb), reduced mean corpuscular haemoglobin (MCH/pg), reduced mean corpuscular volume (MCV/fl) and a normal/slightly reduced level of HbA₂. Molecular analysis is usually required to confirm the haematological observations (especially in silent alpha-thalassaemia and alpha-thalassaemia trait). The predominant features in HbH disease are anaemia with variable amounts of HbH (0.8-40%). The type of mutation influences the clinical severity of HbH disease. The distinguishing features of the haemoglobin Bart's hydrops foetalis syndrome are the presence of Hb Bart's and the total absence of HbF. The mode of transmission of alpha thalassaemia is autosomal recessive. Genetic counselling is offered to couples at risk for HbH disease or haemoglobin Bart's Hydrops Foetalis Syndrome. Carriers of alpha⁺- or alpha⁰-thalassaemia alleles generally do not need treatment. HbH patients may require intermittent transfusion therapy especially during intercurrent illness. Most pregnancies in which the foetus is known to have the haemoglobin Bart's hydrops foetalis syndrome are terminated due to the increased risk of both maternal and foetal morbidity.

Ultrasonographic prediction of homozygous alpha0-thalassemia using placental thickness, fetal cardiothoracic ratio and middle cerebral artery Doppler: alone or in combination?

OBJECTIVE

To compare the predictive values of three ultrasonographic parameters: placental thickness (PT), fetal cardiothoracic ratio (CTR) and middle cerebral artery peak systolic velocity (MCA-PSV), alone or in combination, in pregnancies affected by homozygous alpha(0)-thalassemia at 12-20 weeks' gestation.

METHODS

Pregnant women at risk of carrying a fetus affected by homozygous alpha(0)-thalassemia were studied from 1995 to 2006 using serial ultrasonography at 12-15 weeks, 16-20 weeks and 30 weeks' gestation. We measured CTR and PT from 1995, and MCA-PSV as well from 1997. An invasive prenatal test was offered if cardiomegaly with or without placentomegaly was detected but the MCA-PSV results were used only retrospectively for analysis.

RESULTS

Of a total of 777 at-risk fetuses studied, 138 (17.8%) were affected by homozygous alpha(0)-thalassemia. At 12-15 weeks' gestation, 598 ultrasound examinations were performed. CTR was better than both PT and MCA-PSV in the prediction of affected pregnancies. The highest sensitivity (98.3%) was achieved by the combination of CTR and/or MCA-PSV at a false-positive rate of 15.8%. At 16-20 weeks' gestation, 410 ultrasound examinations were performed, 121 of which were at the patient's first visit and 289 of which were at a follow-up visit. Both CTR and MCA-PSV predicted the affected pregnancies equally well. The sensitivity of CTR was 100.0%, but the false-positive rate was 5.2%. In contrast, the false-positive rate of MCA-PSV alone was 1.4% and that of the combination of CTR and MCA-PSV was 0%, although their sensitivities were less than 65%.

CONCLUSIONS

The data suggest that adding MCA-PSV to CTR in the prediction of homozygous alpha(0)-thalassemia can increase the sensitivity at 12-15 weeks and decrease the false-positive rate at 16-20 weeks' gestation.

The effect of hypoxia in development

There is increasing evidence that the oxygen supply to the human embryo in the first trimester is tightly controlled, suggesting that too much oxygen may interfere with development. The use of hypoxia probes in mammalian embryos during the organogenic period indicates that the embryo is normally in a state of partial hypoxia, and this may be essential to control cardiovascular development, perhaps under the control of hypoxia-inducible factor (HIF). A consequence of this state of partial hypoxia is that disturbances in the oxygen supply can more easily lead to a damaging degree of hypoxia. Experimental mammalian embryos show a surprising degree of resilience to hypoxia, with many organogenic stage embryos able to survive 30-60 min of anoxia. However, in some embryos this degree of hypoxia causes abnormal development, particularly transverse limb reduction defects. These abnormalities are preceded by hemorrhage/edema and tissue necrosis. Other parts of the embryo are also susceptible to this hypoxia-induced damage and include the genital tubercle, the developing nose, the tail, and the central nervous system. Other frequently observed defects in animal models of prenatal hypoxia include cleft lip, maxillary hypoplasia, and heart defects. Animal studies indicate that hypoxic episodes in the first trimester of human pregnancy could occur by temporary constriction of the uterine arteries. This could be a consequence of exposure to cocaine, misoprostol, or severe shock, and there is evidence that these exposures have resulted in hypoxia-related malformations in the human. Exposure to drugs that block the potassium current (IKr) can cause severe slowing and arrhythmia of the mammalian embryonic heart and consequently hypoxia in the embryo. These drugs are highly teratogenic in experimental animals. There is evidence that drugs with IKr blockade as a side effect, for example phenytoin, may cause birth defects in the human by causing periods of embryonic hypoxia. The strongest evidence of hypoxia causing birth defects in the human comes from studies of fetuses lacking hemoglobin (Hb) F. These fetuses are thought to be hypoxic from about the middle of the first trimester and show a range of birth defects, particularly transverse limb reduction defects.

Outcome of intensive care of homozygous alpha-thalassaemia without prior intra-uterine therapy

AIM

To review the outcome of homozygous alpha-thalassaemia without prior intra-uterine therapy treated in neonatal intensive care unit and identify the factors associated with survival.

METHODS

The hospital records of all patients with homozygous alpha-thalassaemia treated in our neonatal intensive care unit in the last 15 years were reviewed. A literature search beginning in the year 1980 was done to identify homozygous alpha-thalassaemia actively treated in neonatal intensive care units. Those receiving prior intra-uterine therapy were excluded. The following information was collected: the severity of hydrops, sizes of liver and spleen, haemoglobin level, Apgar score at 5 min, ventilator settings, timing and forms of red blood cell transfusion and presence of persistent hypoxaemia. The survivors and the non-survivors were compared.

RESULTS

In our centre, in the last 15 years there were six infants born with homozygous alpha-thalassaemia who did not receive intra-uterine therapy; one survived and five succumbed despite aggressive respiratory therapy. In our literature search there were more reports of survivors (10) than non-survivors (six) for these infants, suggesting a reporting bias towards selection of rare cases of survival. Apgar score of four or above occurred in seven of the eight survivors with data available in the reports, whereas this occurred in four of the 11 non-survivors (P = 0.035, Fisher Exact test). Five of the 11 survivors had abnormal neurological outcome including developmental delay and spastic quadriplegia.

CONCLUSION

Without prior intra-uterine therapy, homozygous alpha-thalassaemia has grave outlook in terms of mortality and morbidity despite aggressive respiratory therapy.

A new strategy for prenatal diagnosis of homozygous alpha(0)-thalassemia

OBJECTIVES

We have shown previously that ultrasound examination performed by one experienced operator can be useful to exclude homozygous alpha(0)-thalassemia in a tertiary referral center. This study aimed to determine whether the technique was still applicable when performed by several operators and in different centers.

METHODS

At the Maternal and Neonatal Hospital of Guangzhou (MNH) and Tsan Yuk Hospital of Hong Kong (TYH), women at risk of homozygous alpha(0)-thalassemia were given the option of a non-invasive approach (using serial ultrasound examinations at 12-15, 16-20 and 25-30 weeks' gestation) to exclude an affected pregnancy. The fetal cardiothoracic ratio (CTR) was measured at each of these examinations and the placental thickness was measured at 12-15 weeks' gestation. The operators of MNH received training on the ultrasound examination techniques at TYH and the quality of the subsequent ultrasound examinations was checked regularly. The final diagnosis of homozygous alpha(0)-thalassemia was confirmed using an invasive test.

RESULTS

Of 832 at-risk pregnancies studied in the two hospitals, 168 (20.2%) were affected. The overall sensitivity and specificity of the non-invasive approach was 100% and 95.6%, respectively. At MNH, the need for an invasive test was reduced by 80.8%, and all the affected pregnancies were diagnosed before 24 weeks' gestation. The results achieved at MNH were comparable with those at TYH. The at-risk pregnancies including the affected ones presented at a more advanced gestational age at MNH. At each hospital, one affected pregnancy was missed at the 12-week scan but this was subsequently detected at the 15-18-week scan.

CONCLUSIONS

This non-invasive approach to exclude homozygous alpha(0)-thalassemia can be applicable when it is performed by several operators and in different centers.

Biochemistry testing associated with pregnancy and the newborn period -- a lot has changed since you were a baby!

Everyone has been a newborn, and everyone's mother has been pregnant. Despite the commonality of these events, medical care and the clinical chemistry laboratory's role in it have changed remarkably over the last 50 years. This review is a historical overview of clinical chemistry testing that is related to pregnancy and the newborn period.

Heterogeneity in alpha-thalassemia interactions in Malays, Chinese and Indians in Malaysia

AIM

Interactions between different determinants of alpha-thalassemia raises considerable problems, particularly during pregnancies where antenatal diagnosis is necessary. This study aims to determine the different types of deletional alpha-thalassemia and Hemoglobin Constant Spring (HbCS), and their frequency in Malays, Chinese and Indians in Malaysia.

METHODS

DNA from 650 pregnant women from the Antenatal Clinic of the University of Malaya Medical Center in Kuala Lumpur, Malaysia who showed mean cell volume < or =89 fL and/or mean cell hemoglobin < or =28 pg were analyzed for the double alpha-globin gene South-East Asian deletion (--SEA), the -alpha3.7 and -alpha4.2 single alpha-globin gene deletions and HbCS.

RESULTS

One hundred and three (15.8%) of the pregnant women were confirmed as alpha-thalassemia carriers: 25 (3.8%) were alpha-thalassemia-1 carriers with the --SEA/alphaalpha genotype, 64 (9.8%) were heterozygous for the -alpha3.7 rightward deletion (-alpha3.7/alphaalpha), four (0.6%) were heterozygous for the -alpha4.2 leftward deletion (-alpha4.2/alphaalpha), nine (1.4%) were heterozygous for HbCS (alphaCSalpha/alphaalpha) and one (0.2%) was compound heterozygous with the -alpha3.7/alphaCSalpha genotype. The double alpha-globin gene --SEA deletion was significantly higher in the Chinese (15%) compared to the Malays (2.5%) and not detected in the Indians studied. The -alpha3.7 deletion was distributed equally in the three races. HbCS and -alpha4.2 was observed only in the Malays.

CONCLUSION

The data obtained gives a better understanding of the interactions of the different alpha-thalassemia determinants in the different ethnic groups, thus enabling more rapid and specific confirmation of alpha-thalassemia in affected pregnancies where antenatal diagnosis is necessary.

Alpha-thalassemia major presenting in a term neonate without hydrops

We describe the clinical and pathologic features of an unusual case of alpha-thalassemia major in a patient who survived to term and lived for 9 days. The neonate was nonhydropic and the clinical picture was dominated by severe hypoxia with pulmonary hypertension. The diagnosis was not suspected until postnatal examination of the blood smear, which prompted the performance of hemoglobin electrophoresis and subsequent molecular confirmation. This case illustrates that alpha-thalassemia major should be in the differential diagnosis of hypoxic neonates even in the absence of hydrops.

Neurodevelopmental outcome and haematological course of a long-time survivor with homozygous alpha-thalassaemia: case report and review of the literature

AIM

Homozygous alpha-thalassaemia, also called haemoglobin (Hb) Bart's hydrops fetalis, has been thought to be a lethal condition. Due to prenatal diagnosis and intrauterine blood transfusions, a few patients with Hb Bart's hydrops fetalis have survived. This fact raises the urgent questions of clinical management and appropriate follow-up of these patients, both of which are addressed in this article.

METHODS

We report on a 6.5-y-old patient with homozygous alpha-thalassaemia and review the literature of 13 other survivors published to date. Transfusion requirements were evaluated and the rate of liver iron accumulation was assessed by biomagnetic liver susceptometry before and after institution of iron-chelating therapy. Psychometric evaluation was carried out using Munich's Functional Development Test, the Columbia Mental Maturity Scale, the Kaufman Assessment Battery for Children, and the Peabody Picture Vocabulary Test.

RESULTS

Our patient had significant delay of psychomotor development. Psychometric evaluation at the age of 5 y revealed an IQ of 85 and an intellectual level of a 4-y-old child. Early tissue iron overload was seen, but a negative iron balance was achieved after institution of desferrioxamine treatment at dosages used for beta-thalassaemia.

CONCLUSION

Homozygous alpha-thalassaemia should no longer be regarded as a lethal condition. Early intervention during pregnancy and careful haematological as well as neuropsychological follow-up was able to provide long-term survival and good life quality in our patient.

Vascular-type disruptive defects in fetuses with homozygous α-thalassemia: report of two cases and review of the literature

BACKGROUND

The thalassemias are an inherited group of heterogeneous anemias in which one or more of the globin chains in the hemoglobin tetramer are absent. Fetuses with homozygous alpha-thalassemia, which is particularly prevalent in people of Southeast Asian extraction, experience deficient alpha-globin chain synthesis and cannot produce hemoglobin F (the primary fetal hemoglobin after 8 weeks' gestation). Instead, they produce an anomalous hemoglobin, hemoglobin Bart's, with an unusually high affinity for oxygen, leading to profound anemia and tissue hypoxia.

METHODS AND RESULTS

Here we report on two fetuses with homozygous alpha-thalassemia who displayed structural defects of a vascular disruptive type. Both fetuses demonstrated limb anomalies, including terminal transverse limb deficiencies, and one fetus was found to have a brain malformation consisting of a neuronal migrational defect. The limb anomalies and suspected brain malformation were detected on prenatal ultrasound prior to confirmation of the diagnosis of alpha-thalassemia in one case; in the other case prenatal records were not available. While microcephaly, hydrocephalus, and retarded brain growth have been rarely reported in association with homozygous alpha-thalassemia, this is the first report of a true brain malformation in an affected fetus. Limb anomalies, on the other hand, appear to be more frequent. Recently, aggressive in utero and postnatal therapies for homozygous alpha-thalassemia have been attempted with some success.

CONCLUSIONS

Our cases and those from the medical literature suggest that couples need to be counseled about the risks of congenital anomalies of a vascular disruptive type in affected fetuses. Furthermore, data from the literature suggests that in utero therapy may not significantly decrease these risks as such anomalies may be present prior to the institution of therapy. In addition, in hydropic infants with vascular disruptive defects, especially in those of Southeast Asian origin, homozygous alpha-thalassemia should be suspected as a likely etiology.

Changing outcome of homozygous alpha-thalassemia: cautious optimism

Only a few long-term survivors of homozygous alpha-thalassemia, a usually fatal condition, have been reported. The authors present a surviving infant with this disorder and discuss the complications, treatments, and implications of this genetic hemoglobinopathy. The child had no antenatal intervention and has been treated with regular transfusions. She has had normal growth and development and is currently 2.5-years-old. A literature review of survivors with Bart hemoglobinopathy reveals an intense perinatal course and a great prevalence of congenital urogenital and limb defects. Advances in antenatal diagnosis, intrauterine intervention, and postnatal treatments have resulted in extended survival of children with congenital defects that until recently were considered invariably fatal. Transfusion and chelation therapy and bone marrow transplantation provide long-term treatment and potential curative options.

Fetal erythropoiesis and the diagnosis and treatment of hemoglobin disorders in the fetus and child

Although synthesis of adult hemoglobin (alpha 2 beta 2) is reduced or absent in both alpha and beta thalassemias, these disorders differ in their clinical significance to the fetus and neonate. alpha-Globin synthesis is observed in the yolk sac by 3 weeks of gestation and, by 9 weeks of gestation, alpha-globin represents the main alpha-like hemoglobin in the fetus. By contrast, the switch to beta-globin chain synthesis usually remains incomplete until 1 year after birth. Therefore, the clinical manifestations of homozygous beta-thalassemia may be ameliorated by sustained synthesis of fetal hemoglobin during the first 6 months of life, whereas up until 10 years ago, homozygous alpha-thalassemia was invariably associated with death in utero. More recently, reports of infants with homozygous alpha-thalassemia surviving the neonatal period have emerged, observations particularly relevant to large numbers of immigrants to North America from Southeast Asia, where alpha-thalassemia is common. Studies of patients with the beta-globin disorders thalassemia and sickle cell disease showed that the severity of both disorders is ameliorated by sustained synthesis of fetal hemoglobin into adult life. Hence, treatment for both these disorders has focused on the pharmacological manipulation of fetal hemoglobin. Studies in vitro, in animal models, and in affected patients have shown that several compounds stimulate gamma-globin synthesis and fetal hemoglobin production through a variety of proposed mechanisms. Some of the successes in human trials are outlined herein.

Ultrasound measurement of placental thickness to detect pregnancies affected by homozygous alpha-thalassaemia-1

Homozygous alpha-thalassaemia-1, a common cause of hydrops fetalis, is usually diagnosed invasively. We measured placental thickness by ultrasound at 10-21 weeks' gestation in 231 at-risk pregnancies. 60 were affected (by DNA analysis). The sensitivity and specificity in detecting affected pregnancies at cut-off of mean placental thickness plus 2 SD before 12 weeks' gestation were 0.72 (95% CI 0.52-0.93) and 0.97 (0.9-1.0). After 12 weeks sensitivity increased to 0.95 (0.89-1.0) and by 18 weeks reached 1.0 (0.60-0.99) without change in specificity. Selection of pregnancies at risk by measurement of placental thickness will reduce the number of invasive diagnostic procedures.

The structure and function of normal and abnormal haemoglobins

This chapter reviews general aspects of the normal human haemoglobins which include those predominantly present in the embryo, the fetus and newborn baby, and in the normal adult. Special emphasis is given to factors which affect the levels of fetal haemoglobin in the adult because increased percentages of Hb F can be of great benefit to adults with certain haemoglobinopathies such as sickle cell anaemia and beta-thalassaemia. A review of the numerous Hb variants published since the discovery of Hb S in 1959 reveals a steady stream of newly detected abnormalities; most of these are the result of single-point mutations in the alpha-, beta-, gamma-, or delta-globin genes. Of the more than 600 variants listed in a repository, some 200 have clinical significance because of a decreased stability, a change in functional properties, among others. Methodology developed for the detection and quantitation of normal and abnormal Hb components has been greatly modified during the past 30 years; isoelectrofocusing and different fast developing micro chromatographic procedures are the methods of choice. Analyses of DNA isolated from the white cells has become most useful for the final characterization of the variants; this methodology consists of amplification of a desired segment of DNA and identification of a mutation with labelled oligonucleotide probes. Additional methods include sequence determination of this amplified DNA and identification of known mutations with an allele specific amplification procedure.

alpha-Thalassaemia

The large number of naturally occurring mutants of this well-characterized locus provides an excellent opportunity for elucidating the relationship between its structure and function. Comparisons of what has been learned about the alpha-globin locus with complementary observations on the beta-globin locus, provide a strategy for understanding the co-ordinate regulation of eukaryotic gene expression. From a practical point of view it is important to remember that millions of individuals throughout the world are carriers of alpha-thalassaemia and every year many thousands of pregnancies are at risk of producing children with the severe alpha-thalassaemia syndromes. The data summarized here provide the basis for accurately predicting the genotype in such cases and thus enabling appropriate prenatal testing. However, because this is a genetic disease that predominantly affects individuals from countries with limited health resources, simpler and cheaper methods of screening and diagnosis will have to be developed before this information has a significant impact on the attendant morbidity and mortality (see Chapter 9, this volume).

Identification of an extensive zeta-alpha globin gene deletion in a Chinese individual

We describe a novel alpha-thalassaemia-1 deletion that removes the entire zeta-alpha globin gene cluster. A Chinese couple were referred for counselling after two consecutive pregnancies ended with fetal hydrops. Gene mapping was used to demonstrate that the mother is heterozygous for the South-east Asia alpha-thalassaemia-1 deletion (zeta zeta zeta alpha alpha/zeta zeta--SEA), while the father carries an alpha-thalassaemia-1 deletion of more than 100 kilobases (zeta zeta alpha alpha/----). This newly discovered deletion extends for unknown distances 3' and 5' of the zeta-alpha globin gene cluster and has been designated (--HW).

Potential application of a new screening test for alpha-thalassemia-1 carriers

A murine hybridoma cell line secreting monoclonal anti-human embryonic zeta-globin chain antibody has been established. Using this monoclonal antibody, a slot blot immunobinding assay for the detection of zeta-globin chains in adult hemolysates has been developed. This simple test can identify individuals who are alpha-thalassemia-1 carriers due to the (-SEA/) deletion. It is proposed that this test should be made generally available in Southeast Asia and Southern China, in order to identify couples who are at risk of begetting fetuses afflicted with homozygous alpha-thalassemia.

Ultrasound evaluation of pregnancies at risk for homozygous alpha-thalassaemia-1

Twenty-six pregnant Chinese women who were at risk of giving birth to a fetus affected with homozygous alpha-thalassaemia-1 were examined serially by ultrasound. Six of these 26 pregnancies were affected. In one third of the affected pregnancies progressive fetal ascites appeared before 24 weeks gestation and these pregnancies were terminated. In the remaining two thirds abnormal estimated fetal weight-placental volume (EFW-PV) ratio and fetal growth retardation as evidenced by a falling biparietal diameter (BPD), femur length (FL) but a normal abdominal circumference (AC) was apparent by 28 weeks gestation. Increased transverse cardiac (TC) diameter was another consistent finding but appeared late. All these features appeared before the onset of fetal ascites. A normal EFW-PV ratio and fetal growth until 28 weeks gestation was a reassuring sign of normality. Abnormal EFW-PV ratio was the earliest sign to appear in affected pregnancies and a normal ratio until 28 weeks gestation had a 100 per cent predictive value.

Embryonic zeta-globin chains in adults: a marker for alpha-thalassemia-1 haplotype due to a greater than 17.5-kb deletion

Hemolysates from adults with the alpha-thalassemia-1 haplotype due to the greater than 17.5-kb deletion of both alpha-globin genes from the same chromosome were found to contain embryonic zeta (zeta)-globin chains (alpha-globin-like chains), as determined by a specific and sensitive radioimmunoassay and an electrophoretic technique. zeta-Globin chains were not present in hemolysates from adults with deletion of a single alpha-globin gene from one or both chromosomes. These results indicate that zeta-globin chains, which can be assayed by immunologic techniques, can serve as markers for the alpha-thalassemia-1 haplotype due to the greater than 17.5-kb deletion. The ability to detect zeta-globin chains may be useful in populations in which the gene frequency of the greater than 17.5-kb deletion is high, for screening couples at risk of having offspring with homozygous alpha-thalassemia.

Human embryonic zeta-globin chains in adult patients with alpha-thalassemias

Human embryonic zeta-globin chains are alpha-globin-like chains that are normally present during the first three months of gestation. In this investigation, zeta-globin chains measured by a specific and sensitive radioimmunoassay and by an electrophoretic technique were found to be present in all 7 patients studied with hereditary Hb H disease, and in 8 out of 24 patients with alpha-thalassemia trait. zeta-Globin chains were not detected in 20 other patients with beta-thalassemia trait. These results suggest that the deletion of two alpha-globin genes on the same chromosome is accompanied by the continued expression of embryonic zeta-globin genes in adult individuals.

Differential diagnosis of hydrops fetalis

Apart from isoimmunization, a number of conditions may present as hydrops fetalis and now account for a large proportion of hydropic infants. A large differential diagnosis must be considered when investigating the hydropic fetus and placenta while in utero, in the neonatal period, and at autopsy. An investigative protocol is proposed.

A new genetic basis for hemoglobin-H disease

We studied 11 families with alpha-thalassemia from the Qatif population of eastern Saudi Arabia to determine the genetic and molecular basis of hemoglobin-H disease, which is being encountered in this area with increasing frequency. The results show that there are two common alpha-thalassemia haplotypes, a deletion (-alpha/) determinant and a nondeletion (alpha alpha T/) determinant, which interact to produce a series of overlapping phenotypes. The most severe, hemoglobin-H disease, results from the homozygous state for the nondeletion determinant--a pattern of inheritance not previously recognized for this condition. Its molecular and genetic properties are thus different from those that produce the condition in Oriental or Mediterranean populations.

Gene deletions in alpha thalassemia prove that the 5' zeta locus is functional

The deletions in the zeta-alpha globin gene cluster in two infants with the hemoglobin Bart's hydrops fetalis syndrome (homozygous alpha thalassemia 1) have been mapped by restriction endonuclease analysis using a zeta-specific probe. DNA from a Thai infant lacked the psi alpha 1 gene and both alpha genes, but the zeta genes were present. A Greek infant's DNA had also lost the 3' zeta 1 gene. Because zeta globin was synthesized in the infant's cord blood, this indicates that the 5' zeta 2 gene recently identified by Lauer et al. [Lauer, J., Shen, C. J. & Maniatis, T. (1980) Cell, in press] must be functional.

The chromosomal arrangement of human alpha-like globin genes: sequence homology and alpha-globin gene deletions

We report the isolation of a cluster of four alpha-like globin genes from a bacteriophage lambda library of human DNA (Lawn et al., 1978). Analysis of the cloned DNA confirms the linkage arrangement of the two adult alpha-globin genes (alpha 1 and alpha 2) previously derived from genomic blotting experiments (Orkin, 1978) and identifies two additional closely linked alpha-like genes. The nucleotide sequence of a portion of each of these alpha-like genes was determined. One of these sequences is tentatively identified as an embryonic zeta-globin gene (zeta 1) by comparison with structural data derived from purified zeta-globin protein (J. Clegg, personal communication), while the other sequence cannot be matched with any known alpha-like polypeptide sequence (we designate this sequence phi alpha 1). Localization of the four alpha-like sequences on a restriction map of the gene cluster indicates that the genes have the same transcriptional orientation and are arranged in the order 5'-zeta 1-phi alpha 1-alpha 2-alpha 1-3'. Genomic blotting experiments identified a second, nonallelic zeta-like globin gene (phi 2) located 10-12 kb 5' to the cloned zeta-globin gene. Comparison of the locations of restriction sites within alpha 1 and alpha 2 and heteroduplex studies reveal extensive sequence homology within and flanking the two genes. The homologous sequences, which are interrupted by two blocks of nonhomology, span a region of approximately 4 kb. This extensive sequence homology between two genes which are thought to be the products of an ancient duplication event suggests the existence of a mechanism for sequence matching during evolution. One consequence of this arrangement of homologous sequences is the occurrence of two types of deletions in recombinant phage DNA during propagation in E. coli. The locations and sizes of the two types of deletions are indistinguishable from those of the two types of deletions associated with alpha-thalassemia 2 (Embury et al., 1979; Orkin et al., 1979; S. Embury et al., manuscript submitted). This information strongly suggests that the genetic disease is a consequence of unequal crossing over between homologous sequences within and/or surrounding the two adult alpha-globin genes.

Alpha thalassaemia in Sicily: haematological and biosynthetic studies

Eight Sicilian patients with Hb H disease and their families have been studied. The standard haematological tests and the alpha/beta chain synthesis ratios showed significantly different results in the patients with Hb H disease as compared with alpha thalassaemia carriers, except for Hb A2 values. There was no significant difference in the mean RBC, MCV, Hb A2, Hb A1 and Hb F of alpha thalassaemia carriers compared with normal controls. On the contrary significant difference was found between the mean alpha/beta chain synthesis ratio of alpha thalassaemia carriers and that of the normal controls; however, the extensive overlapping of alpha/beta values between these two conditions make this parameter insufficiently discriminant. No correlation was found between MCV, MCH, RBC and alpha/beta chain synthesis ratio in patients with alpha thalassaemia trait, suggesting that the ratio cannot be used to distinguish between carriers of a mild gene ('silent' carrier) and carriers of the more severe alpha thalassaemia gene. A possible genetic model for alpha thalassaemia in Sicily is presented.

Thalassemia and pregnancy: results of an antenatal screening program

A thalassemia screening program was implemented at our institution using the finding of a mean corpuscular volume less than 80 fl as the index of abnormality. Further evaluation using hemoglobin (Hb) electrophoresis and serum iron studies was carried out according to the scheme detailed below. A diagnosis of thalassemia was made in 33 women (42 pregnancies). Eight patients had alpha-thalassemia trait, 23 beta-thalassemia trait, and two Hb H disease. Thalassemia trait did not have any adverse effect on pregnancy outcome. In two couples the fetuses were at risk for homozygous disease and in one couple the fetus was at risk for sickle cell beta-thalassemia. The screening program described is an effective and inexpensive means of detecting thalassemia in an antenatal population and is applicable to most every clinic or office setting.