Alpha-globin gene organisation and prenatal diagnosis of alpha-thalassaemia in Chinese

Screening of Some Indicators for Alpha-Thalassemia in Fujian Province of Southern China

Background

Carrier screening is the most effective means of controlling the prevalence of alpha-thalassemia. However, due to the differences in ethnic populations and genotypes, the distribution of mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and hemoglobin A₂ (HbA₂) varies in different regions. This study aimed to examine screening efficiency of these indicators in different genotypes of alpha-thalassemia in Fujian Province, China.

Methods

The data of 13,294 subjects collected from May 2016 to December 2019 were reviewed. The participants were categorized as alpha-thalassemia group and negative-for-alpha-thalassemia group based on the results of the genetic analysis. The distribution of MCV, MCH, and HbA₂ in different groups was analysed statistically. And the screening efficiency of different indicators and schemes was compared in different genotypes. The positive criteria of MCV < 80fL, MCH < 27pg, and Hb A₂< 2.5% were applied.

Results

Among the 13,294 subjects, 2658 were alpha-thalassemia carriers. The genotypes of –^SEA/αα and -α^3.7/αα are the most prevalent with 63.9% and 21.9% in Fujian Province, China. There were significant differences in the distribution of the three indicators in different groups. The detection rate of the three indicators combined screening was 92.6%.

Conclusion

The distribution of the three indicators overlapped partly between alpha-thalassemia group and negative-for-alpha-thalassemia group. They showed significant differences in the median comparison of seven common genotypes. Combined screening with MCV, MCH and HbA₂ improved the detection rate of alpha-thalassemia. The results of this study provide a data basis for clinical laboratories and a reliable reference for clinical consultation.

Prenatal diagnosis of a rare β-thalassemia gene －90 (C>T) (HBB: c.-140 C>T) mutation associated with deletional Hb H disease (--SEA /-α4.2 )

Background

Hemoglobin H (Hb H) disease can be caused by compound heterozygosity for two different mutations or from homozygotes for mutations, and conventional genetic methods may lead to misdiagnosis when Hb H disease is combined with a rare β‐thalassemia.

Methods

Hematology parameters and hemoglobin electrophoresis analysis, gap‐polymerase chain reaction (gap‐PCR) and reverse dot‐blot hybridization (RDB‐PCR) were employed to identify common α‐thalassemia and Hb H disease. Rare β‐thalassemia mutations were detected by DNA sequencing.

Results

Hematological analysis and hemoglobin electrophoresis revealed a mild anemia α⁰‐thalassemia trait (Hb 90 g/L, MCV 71 fL, and MCH 22.7 pg) compound with β⁺‐thalassemia trait (MCV 71 fL, MCH 22.7 pg, and HbA2 5.51%) for the pregnant woman. DNA sequencing for the β‐globin gene revealed rare a －90 (C>T) (HBB: c.‐140 C>T) mutation for the woman. DNA analysis identified that the fetus inherited the α⁰‐thalassemia mutation [‐‐^SEA (Southeast Asian)] and a rare β⁺‐thalassemia mutation －90 (C>T) (HBB: c.‐140 C>T) from the mother, and the α⁺‐thalassemia mutation [‐α^4.2 (leftward)] from the father.

Conclusion

We reported a rare －90 (C>T) (HBB: c.‐140 C>T) mutation combined with the ‐‐^SEA/‐α^4.2 in a family. This finding enriched the mutation spectrum of thalassemia molecular characteristics in China and emphasized the significance in DNA sequencing in mutation screening for the families with thalassemia.

Analysis of genotype distribution of thalassemia and G6PD deficiency among Hakka population in Meizhou city of Guangdong Province

Objective

The aim of the study was to explore genotype distribution thalassemia and G6PD deficiency in Meizhou city, China.

Methods

A total of 16 158 individuals were involved in thalassemia genetic testing. A total of 605 subjects were screened for common Chinese G6PD mutations by gene chip analysis. Genotypes and allele frequencies were analyzed.

Results

A total of 5463 cases carried thalassemia mutations were identified, including 3585 cases, 1701 cases, and 177 cases with α‐, β‐, and α + β‐thalassemia mutations, respectively. ‐‐^SEA (65.12%), ‐α^3.7 (19.05%), and ‐α^4.2 (8.05%) deletion were the main mutations of α‐thalassemia, while IVS‐II‐654(C → T) (40.39%), CD41‐42(‐TCTT) (32.72%), ‐28(A → G) (10.11%), and CD17(A → T) (9.32%) mutations were the principal mutations of β‐thalassemia in Meizhou. There were significant differences in allele frequencies in some counties. Genetic testing for G6PD deficiency, six mutation sites, and one polymorphism were detected in our study. A total of 198 alleles with the mutation were detected among 805 alleles (24.6%). G6PD Canton (c.1376 G → T) (45.96%), G6PD Kaiping (c.1388 G → A) (39.39%), and G6PD Gaohe (c.95 A → G) (9.09%) account for 94.44% mutations, followed by G6PD Chinese‐5 (c.1024 C → T) (4.04%), G6PD Viangchan (c.871G → A) (1.01%), and G6PD Maewo (c.1360 C → T) (0.51%). There were some differences of the distribution of G6PD mutations among eight counties in Meizhou.

Conclusions

The ‐‐^SEA, ‐α^3.7, and ‐α^4.2 deletion were the main mutations of α‐thalassemia, while IVS‐II‐654(C → T), CD41‐42(‐TCTT), ‐28(A → G), and CD17(A → T) mutations were the principal mutations of β‐thalassemia in Meizhou. G6PD c.1376 G → T, c.1388 G → A, and c.95 A → G were the main mutations of G6PD deficiency. There were some differences of the distribution of thalassemia and G6PD mutations among eight counties in Meizhou.

Recent Progress on Genetic Diagnosis and Therapy for β-Thalassemia in China and Around the World

Thalassemia is a recessive monogenic hematological disease associated with reduced amounts of functional hemoglobin caused by mutations/deletions in at least one of the globin genes. This disease has attracted significant attention throughout the years in terms of genetic diagnosis and developments in gene and cell therapy. Here, recent progress is reviewed in the genetic diagnosis and development of therapeutics for thalassemia, particularly β-thalassemia, in China and around the world.

Molecular analysis of hemoglobinopathies in a large ethnic Hakka population in southern China

Thalassemia is an inherited autosomal recessive disorder with microcytic hypochromic anemia resulting from reduced or absent synthesis of 1 or more of the globin chains of hemoglobin. This study provided the insight into prevalence and molecular characterization of thalassemia in Hakka population. 14,524 unrelated subjects were included in our study from January 2015 to November 2017. All the subjects were detected by hematological analysis, hemoglobin electrophoresis analysis, and molecular diagnosis (gap-polymerase chain reaction and flow-through hybridization technology). Data analysis was used to compare allele frequencies between the Hakka populations. Seven thousand four hundred twenty-two cases of microcytosis were found. The percentage of microcytosis in Meizhou, Ganzhou, and Heyuan was 50.91% (6738/13,236), 51.27% (445/868), and 56.90% (239/420), respectively. A total of 5516 mutant chromosomes were identified, including 3775 α-thalassemia and 1741 β-thalassemia. --/αα was the most common α-thalassemia genotype, followed by -α/αα and -α/αα, accounted for 84.92% of α-thalassemia genotypes. Twelve kinds of mutations and 26 genotypes in β-thalassemia were found. IVS-II-654(C→T), CD41-42(-TCTT), -28(A→G), and CD17(A→T) alleles accounted for 92.65% of these mutations. IVS-II-654/N, CD41-42/N, -28/N, CD17/N genotypes accounted for 91.53% of β-thalassemia genotypes. 27 fetuses with at-risk pregnancies were subjected to prenatal diagnosis. Five fetuses were Bart's hydrops syndrome and 2 fetuses with β-thalassemia major. There were some differences in molecular characterization of thalassemia among Hakka people in different areas of southern China. Our results enriched the related information of thalassemia in the region, which provided valuable references for the prevention and control of thalassemia.

Molecular prenatal diagnosis of alpha and beta thalassemia in pregnant Hakka women in southern China

BACKGROUND

To date, there has been no systematic study of DNA-based prenatal diagnosis of thalassemia in pregnant Hakka women in southern China.

METHODS

A total of 279 pregnant Hakka women with confirmed cases of thalassemia who had been treated at the Meizhou People's Hospital in China's Guangdong Province from January 2014 to December 2016 were here enrolled. Genomic DNA was extracted from peripheral blood of couples and villus, amniotic fluid, or fetal cord blood. DNA-based diagnosis was performed on the tissues of fetuses whose parents had tested positive for α- and β-globin gene mutations were found using polymerase chain reaction (PCR) and flow-through hybridization technique. Follow-up visits were performed 6 months after the fetuses were born. Prenatal diagnosis was performed on 279 fetuses in at-risk pregnancies.

RESULTS

Here, 211 α-thalassemia fetuses were confirmed, including 41 (19.43%) that tested positive for Bart's hydrops syndrome and 15 (7.11%) for Hb H disease. There were 103 (48.81%) heterozygotes. β-thalassemia was confirmed in 68 fetuses, including 23 (33.82%) with severe thalassemia and 27 (39.71%) heterozygotes. Another 12 cases were confirmed with α+β-thalassemia, including three cases of severe β-thalassemia. DNA-based testing prenatal diagnosis of thalassemia was found to be highly reliable.

CONCLUSIONS

Our findings provide key information for clinical genetic counseling of prenatal diagnosis for major thalassemia in pregnant Hakka women in southern China.

The prevalence and molecular characterization of (δβ)0 -thalassemia and hereditary persistence of fetal hemoglobin in the Chinese Zhuang population

Objective

To reveal the prevalence and molecular characterization of (δβ)⁰‐thalassemia [(δβ)⁰‐thal] and hereditary persistence of fetal hemoglobin (HPFH) in the Chinese Zhuang population.

Methods

A total of 105 subjects with fetal hemoglobin (Hb F) level ≥5% from 14 204 unrelated ones were selected for the study. Multiplex ligation dependent probe amplification was firstly used to analyze dosage changes of the β‐globin gene cluster for associated with (δβ)⁰‐thal and HPFH mutations. The gap polymerase chain reaction was then performed to identify the deletions using the respective flanking primers. Hematologic data were recorded and correlated with the molecular findings.

Results

Twenty‐one (0.15%) subjects were diagnosed with Chinese ^Gγ(^Aγδβ)⁰‐thal. Nine (0.06%) were diagnosed with Southeast Asia HPFH (SEA‐HPFH) deletion. Seventy‐five (0.53%) cases remained uncharacterized. Three genotypes for Chinese ^Gγ(^Aγδβ)⁰‐thal and SEA‐HPFH deletion were identified, respectively. The genotype‐phenotype relationships were discussed.

Conclusion

Our study for the first time demonstrated that (δβ)⁰ and HPFH were not rare events, and molecular characterized ^Gγ(^Aγδβ)⁰‐thal and HFPH mutations in the Chinese Zhuang population. The findings in our study will be useful in genetic counseling and prenatal diagnostic service of β‐thalassemia in this populations.

The prevalence and molecular spectrum of α- and β-globin gene mutations in 14,332 families of Guangdong Province, China

OBJECTIVE

To reveal the familial prevalence and molecular variation of α- and β-globin gene mutations in Guangdong Province.

METHODS

A total of 40,808 blood samples from 14,332 families were obtained and analyzed for both hematological and molecular parameters.

RESULTS

A high prevalence of α- and β-globin gene mutations was found. Overall, 17.70% of pregnant women, 15.94% of their husbands, 16.03% of neonates, and 16.83% of couples (pregnant women and their husbands) were heterozygous carriers of α- or β-thalassemia. The regions with the highest prevalence were the mountainous and western regions, followed by the Pearl River Delta; the region with the lowest prevalence was Chaoshan. The total familial carrier rate (both spouses were α- or β-thalassemia carriers) was 1.87%, and the individual carrier rates of α- and β-thalassemia were 1.68% and 0.20%, respectively. The total rate of moderate-to-severe fetal thalassemia was 12.78% among couples in which both parents were carriers.

CONCLUSIONS

There was a high prevalence of α- and β-thalassemia in Guangdong Province. This study will contribute to the development of thalassemia prevention and control strategies in Guangdong Province.

Hematopoietic stem cell engraftment by early-stage in utero transplantation in a mouse model

A novel intrauterine transplantation (IUT) approach was developed to improve the efficiency of engraftment of hematopoietic stem cells (HSCs). HSCs with a green fluorescent protein (GFP) reporter gene were transplanted in utero on days 12.5, 13.5 and 14.5 post coitum (p.c.). The degree of chimerism of donor cells in recipient newborn mice was examined using fluorescent microscopy, polymerase chain reaction (PCR), fluorescence-activated cell sorting (FACS), and fluorescence in situ hybridization (FISH) analyses. Microscopic examination revealed the presence of green fluorescent signal in the peripheral blood of the chimeric mice. The highest survival rate (47%) as well as the highest chimerism rate (73%) were achieved by our new approach in the newborn mice that were subjected to in utero transplantation (IUT) on day 12.5 p.c. (E12.5) compared to the conventional IUT method. FACS analysis indicated that 1.55+/-1.10% of peripheral blood cells from the newborn mice were GFP-positive donor cells. FISH showed that cells containing the donor-specific GFP sequence were present in the bone marrow (BM) of the chimeric mice. Thus, the efficiency of chimera production with this new method of IUT was significantly improved over the existing IUT techniques and instruments.

Carrier screening for alpha- and beta-thalassemia in pregnancy: the results of an 11-year prospective program in Guangzhou Maternal and Neonatal hospital

OBJECTIVES

To evaluate the first prospective screening program in China for control of alpha and beta-thalassemia in the population of pregnant couples.

METHODS

During the period between January 1993 and December 2003, a hospital-based preventive program was conducted at the biggest birth center in Guangzhou, with 1/17 of all deliveries in this city referred annually by use of conventional heterozygote screening strategy in combination with the system of regular healthcare examination in pregnancy.

RESULTS

The screened records included 49 221 pregnant women, and 4503 husbands of the pregnant women showed positive on the screening test. Of the at-risk couples, there were 198 for alpha-thal (4.4%) and 83 for beta-thal (1.8%), respectively. Genetic counseling was offered to all at-risk couples and a successful prenatal diagnosis was performed for 269 out of 281 (95.7%) for alpha- or beta-thal major, with the remaining 12 couples refusing to accept prenatal diagnosis. Out of 187 pregnancies at risk for homozygous alpha0-thal and 82 at risk for beta-thal major, 51 hydrops fetalis with Hb Bart's and 18 beta-thal major were identified. All pregnancies with affected fetuses were voluntarily terminated, leading to a marked reduction of severe alpha- and beta-thal births at this hospital since the program has been launched.

CONCLUSIONS

Our hospital-based program proved to be highly effective in reducing severe thals in pregnant populations.

In utero transplantation of human hematopoetic stem cells into fetal goats under B-type ultrasonographic scan: an experimental model for the study of potential prenatal therapy

OBJECTIVE

Using fetal goats as animal models, to establish the methodology of in utero transplantation of human hematopoeitic stem cell (HSC) under B-scan ultrasonographic guidance for prenatal therapy.

STUDY DESIGN

Human HSC were directly injected into the peritoneal cavities of the recipient fetal goats at 45-55 days of gestation (term: 145 days) under the guidance of B-type ultrasound scan. After birth, the peripheral blood was collected for fluorescence assisted cell sorting (FACS), quantitative real-time PCR and fluorescence in situ hybridization (FISH) to detect and analyze the presence of human cells in the recipients.

RESULTS

The 32 recipients were born alive except one miscarriage. To test for the presence of human-goat chimeras, cells from 13 randomly selected transplanted goats were collected. FACS analyses showed the presence of human cells in all the transplanted goats tested. The average proportion of CD34+ cells and GPA+(glycophorin A) cells in the peripheral blood were 1.34 +/- 1.10% and 2.80 +/- 2.10%, respectively. No CD34+ or GPA+ cells were found in the non-transplanted goats tested. The results of the quantitative real-time PCR in three engraftment goats were 1.2 x 10(4), 2.9 x 10(4), and 3.2 x 10(4) copies of human GPA DNA per mug of genomic DNA. FISH experiments showed that cells containing human specific alpha-satellite DNA sequence were present in the peripheral blood of the transplanted goats.

CONCLUSIONS

The method described herein is safe and reliable, with low miscarriage risk and high chimerism rate. This approach may provide a promising animal model for potential prenatal treatment.

The prevalence and spectrum of alpha and beta thalassaemia in Guangdong Province: implications for the future health burden and population screening

AIM

Thalassaemia is a good candidate disease for control by preventive genetic programmes in developing countries. Accurate population frequency data are needed for planning the control of thalassaemia in the high risk Guangdong Province of southern China.

METHODS

In total, 13397 consecutive samples from five geographical areas of Guangdong Province were analysed for both haematological and molecular parameters.

RESULTS

There was a high prevalence of carriers of alpha thalassaemia (8.53%), beta thalassaemia (2.54%), and both alpha and beta thalassaemia (0.26%). Overall, 11.07% of the population in this area were heterozygous carriers of alpha and beta thalassaemia. The mutation spectrum of alpha and beta thalassaemia and its constitution were fully described in this area. This study reports the true prevalence of silent alpha thalassaemia in the southern China population for the first time. In addition, two novel mutations that give rise to alpha thalassaemia, one deletion resulting in beta thalassaemia, and a rare deletion (--(THAI) allele) previously unreported in mainland China were detected. The frequency of the most common mutation, the Southeast Asian type of deletion (--(SEA), accounting for 48.54% of all alpha thalassaemias) was similar to the total of two alpha(+) thalassaemia deletions (-alpha(3.7) and -alpha(4.2), accounting for 47.49% of alpha thalassaemia).

CONCLUSION

Both alpha and beta thalassaemia are widely distributed in Guangdong Province of China. The knowledge gained in this study will enable the projected number of pregnancies at risk to be estimated and a screening strategy for control of thalassaemia to be designed in this area.

Alpha0 thalassaemia as a result of a novel 11.1 kb deletion eliminating both of the duplicated alpha globin genes

AIMS

To characterise a novel 11.1 kb deletion that eliminated both of the duplicated alpha globin genes, giving rise to a typical alpha0 thalassaemia phenotype in four carriers from a Chinese family.

METHODS

Haematological investigations were carried out on all family members. The seven common forms of alpha thalassaemia were screened for by the polymerase chain reaction (PCR) and Southern blotting was used to analyse the alpha globin gene cluster. DNA sequence analysis of the entire alpha1 and alpha1 globin gene region was carried out and reverse transcription (RT)-PCR was used to investigate the transcription levels of the alpha and beta globin genes.

RESULTS

The breakpoints were found to lie between coordinates 31695-31724 and 42846-42867 of the alpha globin gene cluster (NG_000006), with a total of about 11,135 nucleotides deleted. These sequences are involved in (CA)n repeats, suggesting a homologous recombination event. RT-PCR analysis gave a transcription level of the alpha globin gene in heterozygotes comparable with that of SEA deletion heterozygotes, confirming no output of alpha globin from the linked pair of alpha globin genes. The heterozygosity for this novel deletion was confirmed by PCR diagnosis in all four carriers from this family.

CONCLUSIONS

This rare mutation constitutes an additional heterogeneous defect causing alpha thalassaemia in the Chinese population.

PCR-based analysis of alpha-thalassemia in Southern Taiwan

The Southeast Asia type deletion of alpha-thalassemia-1 (--SEA) is the most common type of alpha-thalassemia-1 in Taiwan. There are 2 less common types, Filipino type (--FIL) and Thai type (--THAI). In the current study, we screened 754 cases of alpha-thalassemia-1 in Southern Taiwan using a polymerase chain reaction (PCR)-based method. Our results show that the prevalence of the (--SEA) type is 90.6%, followed by the (--FIL) type (8.6%), the (--THAI) type (0.5%), and the (-alpha(3.7/-alpha(3.7)) type (0.3%). We also analyzed the genotypes of 96 patients with hemoglobin (Hb) H disease and 48 cases of hydrops fetalis with Hb Bart's. The frequencies of the genotypes of the alpha-thalassemia-1 allele in Hb H disease are in accordance with the results of analyses of alpha-thalassemia-1 cases. The alpha-thalassemia-2 allele includes alpha(4.2), alpha(G), alpha(CS), and alpha(QS)alpha. Forty-one cases, 6 cases, and 1 case of hydrops fetalis with Hb Bart's were caused by --SEA/--SEA, --SEA/--FIL and --SEA/--THAI respectively. The genotypes and frequencies of alpha-thalassemia in this study are different from those in previous studies in Taiwan and Hong Kong. These differences may be attributed to the diverse genetic origin among different ethnic groups and the extensive inclusion of the (--FIL) and (--THAI) alpha-thalassemia-1 types.

The studies of hemoglobinopathies and thalassemia in China--the experiences in Shanghai Institute of Medical Genetics

BACKGROUND

In the past two decades, a large-scale survey of hemoglobinopathies and thalassemia was carried out in mainland China, involving nearly one million people in 28 provinces. The incidences of hemoglobin (Hb) variants, alpha-thalassemia and beta-thalassemia were 0.33%, 2.64% and 0.66%, respectively. The chemical structural analysis identified 67 Hb variants. Among them, 20 are new variants. The analysis of the alpha-globin gene organization in 111 HbH patients showed 76 cases (68.5%) were of the deletion type, 8 had Hb Constant Spring and the other cases were of non-deletion type. The results of the molecular characterization of more than 200 beta-thalassemia alleles showed that the most common types of beta-thalassemia mutations in China are CD 41/42 (-4 bp), IVS-II-nt.654 C-->T, CD 17 A-->T, CD 71/72 (+A) and -28 A-->G.

METHODS

To explore the simple method for molecular diagnosis of beta-thalassemia, multiplex allele-specific amplification (MAS-PCR) was used that could simultaneously detect the above five common types of beta-thalassemia mutations.

RESULTS

Based on the molecular analysis of beta-thalassemia intermedia, beta-thalassemia homozygotes or compound heterozygotes combined with alpha-thalassemia, as well as the conjunctive abnormalities of beta-thalassemia heterozygote with triplicated haplotype of alpha-globin genes, were the most common cause of thalassemia intermedia in China. We also used the RT-PCR quantitation method to show that the most common beta-thalassemia allele, IVS-II-nt.654 C-->T, still produced a small amount (about 15%) of normally spliced beta-globin mRNA, therefore, causing beta+-thalassemia. In clinical trials of hydroxyurea (HU) treatment for beta-thalassemia patients, we found that HU may enhance the expression of the beta-globin gene in some patients, leading to an alleviation of clinical symptoms. In the studies of the reversal of aberrant splicing of IVS-II-nt.654 C-->T allele by the antisense approach, we constructed a mammalian expression vector that can produce an antisense RNA targeting against the aberrant splice sites of IVS-II-nt.654 C-->T pre-mRNA.

CONCLUSIONS

The results indicated that the antisense RNA produced from the vector could efficiently suppress the aberrant splicing pattern and restore the correct splicing pathway in vitro and in vivo, leading to the improvement of globin chain biosynthesis in thalassemia cells.

Detection of zeta-globin chains in the cord blood by ELISA (enzyme-linked immunosorbent assay): rapid screening for alpha-thalassemia 1 (Southeast Asian type)

Fetuses with homozygous alpha-thalassemia 1, in which the deletion of all four alpha-globin genes results in the absence of any alpha-globin chains, are severely anemic with clinical features of hydrops fetalis. Definitive diagnosis of alpha-thalassemia 1 carriers is difficult since there are few red cell abnormalities. Recently Chui et al. found that minute amounts of embryonic zeta-globin chains are present in adult hemoglobin of the Southeast Asian type of alpha-thalassemia 1 carriers. In this study, we screened 521 cord bloods for alpha-thalassemia 1. Hemoglobin analysis, including quantitation of Hb Bart's, was performed using the automated HPLC, alpha-thalassemia short program (VARIANT, Bio-Rad, Hercules, CA). Of these, 200 cord blood samples in which Hb Bart's was demonstrated were tested for the presence of zeta-globin chains by ELISA using labeled anti-zeta monoclonal antibody. Zeta-globin ranged between 0.21 and 0.83% in 19 specimens carrying alpha-thalassemia 1 gene. In the remaining 90 out of 109 specimens in which Hb Bart's was greater than 1.2%, zeta-globin was less than 0.17%. DNA analysis revealed the presence of normal alpha-genotype and other types of alpha-thalassemia including alpha-thalassemia 2 and Hb Constant Spring. One false positive was found in which the zeta-globin was 0.25% by ELISA but in which PCR indicated an alpha-thalassemia 2 heterozygote. Ninety-one samples with Hb Bart's of less than 1.2% by HPLC are most likely normal with a zeta-globin range between 0 and 0.14%. This study also showed that the frequency of alpha-thalassemia 1 in Bangkok is 3.65%.

Hematologic disorders and nonimmune hydrops fetalis

Hematologic disorders are implicated in approximately 10% to 27% of cases of nonimmune hydrops fetalis. In almost all of these disorders, anemia leading to heart failure, edema, ascites, and anasarca is the final common denominator. The etiology of the anemia in these cases can be conveniently divided into two categories: (1) excessive erythrocyte loss by hemolysis or hemorrhage, and (2) erythrocyte underproduction. The former include intrinsic erythrocyte abnormalities such as alpha-thalassemia and glucose-6-phosphate dehydrogenase deficiency, and conditions with excessive fetal blood loss such as fetomaternal hemorrhage and twin-twin transfusion. The latter include bone marrow replacement syndromes and conditions associated with failure of erythrocyte production. The presentation, diagnosis, and management of hematologic disorders associated with nonimmune hydrops fetalis are reviewed.

Rapid detection of -alpha 4.2 deletion of alpha-thalassemia-2 by polymerase chain reaction

We sequenced part of the X boxes of alpha-thalassemia-1 of Southeast Asia type (- -SEA) with -alpha 4.2, -alpha 3.7, -alpha G-Taichung, and alpha CS alpha. We found the X box of -alpha 3.7 belonged to the X box of alpha 2 globin gene and the X box of alpha CS alpha contained X boxes of both alpha 1 and alpha 2 globin gene, whereas the X box of -alpha 4.2 and -alpha G-Taichung was a hybrid of X boxes of alpha 2 and alpha 1 globin gene. We also found there are two types of -alpha 4.2 deletion; type 1 is a common type of -alpha 4.2 deletion and type 2 is linkage to -alpha G-Taichung. We used a combination of two methods, the amplification refractory mutation system (ARMS) and the amplified created restriction sites (ACRS), to amplify the hybrids of X boxes specifically. The upstream primer for X box of alpha 2 globin gene was designed following the standard ARMS procedure to amplify the X segment of the alpha-globin gene. The downstream primer was designed according to the ACRS method to check the specificity of PCR products. Using this approach, we can diagnose the different types of -alpha 4.2 deletion. This kind of approach can also be used to amplify the specific region from the cluster of highly homologous genes.

Diagnosis of thalassaemia by non-isotope detection of alpha/beta and zeta/alpha mRNA ratios

The alpha/beta and zeta/alpha messenger RNA (mRNA) ratios in the thalassaemia syndromes were investigated by polymerase chain reaction (PCR) with silver staining of the PCR products. In this study we used the PCR to amplify cDNA copies of circulating erythroid cell mRNA in order to measure the relative amounts of alpha-, beta- and zeta-globin contained within. Quantitation was performed by scanning the silver stain of specific globin cDNA bands. We found that there were significant differences of alpha/beta-mRNA and zeta/alpha-mRNA in patients with Hb H disease and alpha-thalassaemia-1 compared to normal subjects. There was a marked increase in the alpha/beta-mRNA ratio but not in the zeta/alpha-mRNA ratio in patients with beta-thalassaemia. In two beta-thalassaemia cases abnormal increases of zeta-globin bands were noted and they were confirmed through DNA analysis to be combined with alpha-thalassaemia-1. This method provides a simple, rapid and non-radioactive approach to detect thalassaemia syndromes, and can help to screen cases of beta-thalassaemia with alpha-thalassaemia-1.

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 alpha-thalassemia-1 (alpha-thal-1) gene by primers flanking the breakpoint and sequence differences of the 3' end of the alpha-globin gene and the nonhomologous elements I, II, and III among different types of alpha-thala-2. In the 67 cases studied, all involved alpha-thal-1 of the Southeast Asia type (SEA) in combination with deletional or nondeletional alpha-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 (-alpha 3.7), and three cases were leftward deletion (-alpha 4.2). We found that all of the nondeletion forms were alpha-thal-1 of SEA type with Hb CS. After the subtyping of Hb H with -alpha 3.7, 26 out of 29 were type I deletion and 3 out of 29 were type II deletion. Comparisons 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).

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

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 alpha-thalassemia-1 of the Southeast Asia type (--SEA) in one allele and (b) the differences of X box of alpha-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 -alpha 3.7 belonged to the X box of alpha 2 globin gene. In -alpha 4.2, the bases belonged to the X box of alpha 1 globin gene, whereas in alpha CS alpha it contained both X boxes of alpha 1 and alpha 2 globin genes. There was an MboII site at this region of the X box of alpha 2 globin gene. We utilized PCR to amplify this region and digested it with restriction enzyme MboII, then combined it with another PCR of 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 -alpha 3.7, 41/101 were alpha CS alpha, 7/101 were -alpha 4.2, and 1/101 was -alpha G. Taichung. Of 52 cases of Hb H with -alpha 3.7, 47 were type-I deletion and five were type-II deletion.

Immunocytological test to detect adult carriers of (--SEA/) deletional alpha-thalassaemia

The gene frequency for (--SEA/) deletional alpha-thalassaemia is high in Southeast Asian populations. We report a simple immunocytological test that is highly sensitive and specific for the detection of adult carriers of the (--SEA/) deletion. We prospectively studied 206 consecutive adult blood samples. All 41 with the (--SEA/) deletion had a positive test; all but 1 of the 165 non-carriers were negative. This test, whose major requirement is a fluorescence microscope, should be useful to identify couples at risk of conceiving fetuses with homozygous alpha-thalassaemia.

Detection of the (--SEA) double alpha-globin gene deletion by a simple immunologic assay for embryonic zeta-globin chains

Homozygous alpha-thalassemia [alpha-thal-1], with loss of all four alpha-globin genes, causes lethal hydrops fetalis. The most common mutation producing this syndrome is the Southeast Asian (--SEA) double alpha-globin gene deletion. Erythrocytes from adults heterozygous for the (--SEA) deletion have minute amounts of embryonic zeta-globin chains detectable by anti-zeta-globin monoclonal antibodies. Among 225 peripheral blood samples tested by a simple anti-zeta-immunobinding tetrazolium dye test, 81 were positive and 144 were negative. The majority of subjects were of Filipino, Chinese, or Laotian ancestry. All 81 positive samples were confirmed by Bam HI digests and a zeta-cDNA probe to have the (--SEA) mutation. The (--SEA) double alpha-deletion was the only abnormality in 58. In the others, it was combined with alpha-globin or beta-globin mutations, or coincidental iron deficiency. Four other samples from (--SEA) heterozygotes were negative by this immunologic assay. Anti-zeta negative samples included 78 deletions of the total alpha-globin region, (--Tot), 23 single alpha-globin deletions, and a variety of beta-globin mutations; 16 normocytic samples with normal alpha-genes were also negative. Ten anti-zeta positive and 25 anti-zeta negative samples had benign triplicated zeta-globin genes. In this population, the sensitivity of this test was 95%; and specificity for the (--SEA) mutation was 100%. Anti-zeta immunobinding testing provides rapid, simple, and reliable screening for the (--SEA) double alpha-globin deletion, although it does not detect the (--Tot) total alpha-deletions.

The population genetics of the haemoglobinopathies

The haemoglobinopathies are the commonest single gene disorders known, and are so common in some regions of the world that the majority of the population carries at least one genetic abnormality affecting the structure or synthesis of the haemoglobin molecule. The prevalence of the common haemoglobinopathies (the alpha- and beta-thalassaemias, HbS, HbC and HbE) is almost certainly a result of the protection they provide against malaria, as the epidemiological evidence reviewed in this chapter shows. World-wide, the distributions of malaria and the common haemoglobinopathies largely overlap, and micro-epidemiological surveys have confirmed the close relationship between the disorders. However, there are complications to this picture which appear to undermine the malaria hypothesis. First, in some areas, malaria and haemoglobinopathies are not coincident. Second, the malaria hypothesis does not easily explain why no two regions of the world have the same haemoglobinopathy or combination of haemoglobinopathies. The majority of mutations have arisen only once and are regionally specific. By using molecular characterization of mutations and the analysis of haplotypes on haemoglobinopathy-bearing chromosomes it is possible to show how a combination of selection by malaria, genetic drift and population movements can explain the first complication. In order to explain the second, we have argued that malaria selection has operated relatively recently on human populations (within the last 5000 years). The present distribution is then seen as the result of selection elevating sporadic mutations in local populations. In the absence of sufficient gene flow to spread all mutations to all populations, the consequence is a patchwork distribution of haemoglobinopathies. Given time, we would expect the mutations that protect and do not compromise the health of their carriers to become widely disseminated, but it is likely that human intervention will alter this process of natural selection.

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).

A PCR-based strategy to detect the common severe determinants of alpha thalassaemia

A rapid and inexpensive polymerase chain reaction (PCR) based strategy is described which detects the three common, severe alpha thalassaemia determinants observed in southeast Asia (--SEA) and the Mediterranean (--MED and -(alpha)20.5). Oligonucleotide primers have been chosen which allow specific identification of both normal (alpha alpha) and abnormal (--) chromosomes using identical conditions in either the same or parallel PCR reactions. This strategy should be useful in the development of screening programmes to identify carriers of alpha thalassaemia (--/alpha alpha) and prenatal diagnosis of the Hb Bart's hydrops fetalis syndrome (--/--) for those populations in which this represents a major cause of perinatal death.

Hb Q-Thailand [alpha 74(EF3)Asp-->His]: gene organization, molecular structure, and DNA diagnosis

Hb Q-Thailand [alpha 74(EF3)Asp-->His] is often found in Thailand, China, and other Southeast Asian countries. The alpha-Q-Thailand gene is strongly linked to an alpha gene deletion and has important implications in the identification and diagnosis of hemoglobinopathies and thalassemias. The alpha-Q-Thailand mutation was previously mapped to the alpha 1 gene in a study of Chinese patients. In this paper, a Thai patient with Hb Q-Thailand/Hb H disease and his mother were studied at the DNA level, and the gene organization of Hb Q-Thailand in the Thai patient was found to be the same as that of Chinese patients (i.e. the Hb Q-Thailand gene is located on the alpha 1 gene of chromosome #16, while the -4.2 kb or leftward deletion involves the alpha 2 gene). Also, the GAC-->CAC mutation proposed at codon 74, has been confirmed by DNA sequencing and a simple and accurate method for diagnosis of the Hb Q-Thailand variant has been developed based on restriction enzyme analysis. Since the GAC-->CAC mutation generates new cutting sites for both restriction enzymes Apa LI and Hgi AI, polymerase chain reaction amplification of a specific region around codon 74, followed by digestion with these enzymes and agarose gel electrophoresis of the digested products, permits rapid and accurate identification of Hb Q-Thailand.

Analysis of RFLPs and DNA deletions in the Chinese Duchenne muscular dystrophy gene

Sixty-nine unrelated Chinese DMD patients were studied with a series of genomic and cDNA probes. Analysis of 13 polymorphic sites showed that pERT87-1, 87-8, 87-15, and XJ probes gave favourable allele frequencies in the Chinese population, and nearly 90% of the DMD families in this study were informative for prenatal diagnosis and carrier detection using these four polymorphic markers. Nine out of 69 (13%) were also found to have gene deletions using a panel of genomic probes. However, when using cDNA probes, deletions were found in 56.5% of the patients. The deletions were concentrated in the areas of probes 7 and 8, giving a proportion of about 80% of all deleted patients in this study. All these results provide valuable information for planning prenatal diagnosis programmes for DMD in China.

Prenatal diagnosis of Chinese homozygous alpha-thalassaemia 1 and haemoglobin H disease by analysis of alpha- and phi zeta-globin genes in chorionic villi and amniocytes

Eighty-eight high-risk pregnancies, 81 for homozygous alpha-thalassaemia 1 and 7 for haemoglobin (Hb) H disease, were collected in this study. Chorionic villus sampling (CVS) was done in 63 cases and amniocentesis in 25 cases to obtain fetal cells. Southern blotting and DNA hybridization with alpha- and phi zeta-globin gene probes were used to determine the alpha-globin gene status. In two non-informative families with non-deletional mutations, DNA analysis failed to rule out the affected condition, and fetal blood sampling (FBS) and Hb electrophoresis were used for the final diagnosis. In the 81 fetuses at risk for homozygous alpha-thalassaemia 1, 17 (13 by CVS and 4 by amniocentesis) were affected, 30 were alpha-thalassaemia 1 heterozygotes, 19 were normal, and the remaining 15 were either normal or heterozygous. In the seven fetuses at risk for Hb H disease, one was normal, three were alpha-thalassaemia 1 heterozygotes, two were alpha-thalassaemia 2 heterozygotes, and one was affected with Hb H disease and developed hydrops fetalis. DNA analysis on fetal cells enabled us to diagnose prenatally severe alpha-thalassaemias, to prevent the birth of infants with Hb H disease, and to minimize maternal obstetrical complications from harbouring a fetus with Hb Bart's hydrops fetalis.

Molecular screening for haemoglobin constant spring

Haemoglobin H/Constant Spring is an important cause of severe haemoglobin H disease, but the Constant Spring protein is difficult to detect by electrophoresis. A technique for allele specific polymerase chain amplification of the 3'-end of the alpha 2 globin gene improved detection of the alpha cs alpha haemoglobin variant in DNA samples by slot-blot hybridisation. The alpha cs alpha mutation was confirmed in subjects that had been previously diagnosed by haemoglobin electrophoresis, and it was also detected in patients who were negative by protein electrophoresis. 10 of 103 unrelated Laotians with HbE were alpha cs alpha heterozygotes. Of these, 3 were negative to the normal probe because they had -alpha 3.7/alpha cs alpha with a single alpha globin deletion. 5 samples did not amplify or hybridise to either probe because they had deletions of both alpha 2 globin regions. The gene frequency for alpha cs alpha is about 0.05 for Laotians. This technique, which is highly specific and sensitive for rapid detection of the alpha cs alpha mutation, is suitable for clinical diagnoses and population studies. The true incidence of alpha cs alpha may prove to be greater than previously suspected from protein electrophoresis.

Protection of kidney function and decrease in albuminuria by captopril in insulin dependent diabetics with nephropathy

STUDY OBJECTIVE

To assess whether long term inhibition of angiotensin converting enzyme with captopril and frusemide or bendrofluazide protects kidney function in diabetic nephropathy.

DESIGN

Non-randomised controlled before-after trial of matched hypertensive insulin dependent diabetics with nephropathy treated with captopril and frusemide or bendrofluazide.

SETTING

Outpatient diabetic clinic in tertiary referral centre.

PATIENTS

Treatment group of 18 hypertensive insulin dependent diabetics with nephropathy (mean age 33), who had not been treated previously. Control group of 13 patients (mean age 32) fulfilling the same entry criteria from a prospective study.

INTERVENTIONS

Treatment group was given daily captopril 37.5-100.0 mg and frusemide (mean) 98 mg (10 patients) or bendrofluazide (mean) 4 mg (seven). Treatment was continued for about two and a half years. Controls were not treated.

END POINT

Measurement of arterial blood pressure, albuminuria, and glomerular filtration.

MEASUREMENTS AND MAIN RESULTS

Baseline values were identical in treated and untreated groups respectively: mean blood pressure 146/93 (SE 3/1) mm Hg v 137/95 (2/1) mm Hg; geometric mean albuminuria 982 (antilog SE 1.2) micrograms/min v 936 (1.2) micrograms/min; and mean glomerular filtration rate 98 (SE 5) ml/min/1.73 m2 v 96 (6) ml/min/1.73 m2. Mean arterial blood pressure fell by 8.7 (1.3) mm Hg with captopril and rose by 6.6 (1.5) mm Hg in controls, (p less than 0.001); Albumin excretion decreased to 390 (1.1) micrograms/min with captopril and rose to 1367 (1.3) micrograms/min in controls (p less than 0.001). The rate of decrease in glomerular filtration rate was lower with captopril (5.8 (0.7) ml/year v 10.0 (1.3) ml/year) (p less than 0.01). Rate of fall in glomerular filtration rate and mean arterial blood pressure were significantly correlated (n = 31, r = 0.37, p less than 0.05).

CONCLUSIONS

Captopril is a valuable new drug for treating hypertension in insulin dependent diabetics with nephropathy.

The molecular basis of HbH disease in Taiwan

We have determined the molecular characteristics of alpha-thalassemia in 12 HbH subjects from Taiwan by restriction endonuclease mapping with alpha- and zeta-specific probes. We have found four types of defects in the alpha-thalassemia-2 genetic determinant: -alpha 3.7 type I; -alpha 4.2; alpha CS alpha; and alpha alpha T. All HbH subjects carried the --SEA genotype in the alpha-thalassemia-1 determinant. At least two different subtypes of --SEA genotype were observed in this study.

Thalassemia heterozygotes in Hawaii: ethnic attitudes toward screening and prenatal diagnosis

The attitudes toward screening and prenatal diagnosis for the hemoglobinopathies Hb E and alpha-thalassemia, prevalent in Southeast Asia, it were studied in Southeast Asians living in Hawaii. Since May 1985, one Laotian and two Filipino Outreach Workers were trained to make home visits to educate and recruit prospective subjects for a federally-funded thalassemia screening project. Volunteers over age 18 were interviewed to assess their comprehension about thalassemia and their attitudes toward screening, family planning, and prenatal diagnosis using structured questionnaires to measure subjective responses. Prenatal diagnosis was explained to all subjects using simple brochures in Laotian and in three Filipino dialects. Culturally oriented genetic counceling was offered to all heterozygotes, emphasizing that their status was common and benign. By July 1987, 597 adult participants had been interviewed; 262 were male, 335 female (65 pregnant); 250 were Laotian, 221 Filipino, 90 Chinese, and 36 of other races. Among female interviewees, 268 said they would want prenatal diagnosis and 196 said they would abort an affected fetus. Most interviewees, especially those who were pregnant, were in favor of: 1) public education about screening, 2) having relatives tested, and 3) prenatal diagnosis when indicated. These attitudes seemed to be influenced by Western culture and religious constraints. Comprehension of genetic concepts correlated closely with education. Ten pregnancies occurred in 16 couples where both partners were heterozygous for a thalassemia (thal) (at least two non-referred couples had homozygous alpha-thal-1 fetuses during this time). Five had amniocentesis for risk of alpha-thal homozygosity, two for risk of beta-thal homozygosity, two miscarried, and one was referred too late for fetal testing. After amniocentesis, one couple declined termination for a fetus with Hb E/beta-thal, and was sceptical of the results when their infant seemed normal at birth; one couple kept a homozygous beta-thal fetus, possibly modified by alpha-gene deletions.

Prenatal diagnosis of thalassemia: experiences at the Shanghai Children's Hospital

Using DNA dot-blot hybridization, restriction endonuclease gene mapping with oligonucleotide probes, restriction fragment length polymorphism linkage analysis, and hybridization, prenatal diagnosis was performed for 32 pregnancies at risk for alpha-thalassemia and for 10 pregnancies at risk for beta-thalassemia. The DNA samples were prepared from chorion villi or amniotic fluid cells.

The different types of alpha-thalassemia: practical and genetic aspects

From May 1985 to October 1987, 1,564 Southeast Asians living in Hawaii were screened for hereditary anemias. Microcytosis was determined by electronic red cell indices and morphology; iron deficiency was ruled out by normal red cell distribution width and normal protoporphyrin levels; Hb E was determined by electrophoresis; beta-thalassemia (thal) heterozygotes were identified by raised Hb A2 on column chromatography. alpha-Thalassemia heterozygotes were diagnosed by exclusion. Family studies helped identify or confirm diagnoses, especially for the alpha-thal-2 heterozygotes (-alpha/alpha alpha) and homozygotes (-alpha/-alpha). Provisional diagnoses are being checked by DNA analyses. Iron deficiency prevented detection of possibly coexisting alpha-thalassemias in 97 individuals. Technical problems included the obscuring of standard criteria for recognizing the alpha-thal variants by the presence of Hb E or beta-thal. In such cases, alpha-thal could only be detected by family studies or DNA analyses. Problems with hemoglobin (Hb) electrophoresis included Hb H migrating beyond the edge of the strip if incubation was not closely monitored, and difficulty in detecting the small amounts of unstable Hb Constant Spring. DNA analyses also had limitations, since the nondeletion alpha-thalassemias would not be detected by routine Southern blotting. DNA analyses suggested that about 50% of presumed alpha-thalassemias were alpha-thal-2 (-alpha/alpha alpha) variants, and a corresponding number of alpha-thal-2 variants were among the apparent normals. Gene frequencies in the unselected Lao subjects were approximately 0.2 for Hb E, at least 0.1 for (-alpha), usually a rightward (alpha -3.7) type, 0.04 for (-), and 0.01 for a beta-thal. Multistep screening for the alpha- and beta-thalassemias was an effective and efficient strategy.

Disorders of haemoglobin in China

A large scale survey of haemoglobinopathies and thalassaemia has been carried out in China, involving 900,000 people in 28 provinces. It has resulted in the finding of many new variants and some interesting cases of thalassaemia, and in a study on the chemical structure of abnormal haemoglobins and DNA analysis of thalassaemia. We report here data on haemoglobin disorders in the Chinese, mainly the characterisation of the geographical distribution of haemoglobin variants, the analysis of globin genes of alpha, beta, gamma, or delta beta thalassaemia, and the progress in prenatal diagnosis of alpha and beta thalassaemia conducted in the authors' laboratory.

Organization of the zeta-alpha genes in Chinese

Analysis of alpha and zeta genes in 101 healthy normals and hospitalized patients with non-haematological diseases revealed a 3% incidence of alpha thalassaemia in the local Chinese population of Hong Kong. Triple alpha genes were found in only one person while triple zeta genes were more prevalent, occurring in 13 subjects. Studies of 28 unselected patients with Hb H disease indicated a predominance of the rightward alpha gene deletion. The extent of alpha gene deletion in homozygous alpha thalassaemia 1 was at least 18.1 kb, beginning from the BamH I site 3' to the zeta 1 gene and includes the psi alpha, alpha 2 and alpha 1 genes. Nineteen of the 20 chromosomes bearing the alpha thalassaemia 1 deletion had identical zeta-intergenic hypervariable region suggesting a common origin of this mutation. The co-inheritance of alpha thalassaemia in beta thalassaemia subjects was 8%, but did not ameliorate the clinical features of those with homozygous beta thalassaemia.

Molecular characterization of HbH disease in the Cuban population

Molecular characterization of the alpha-thalassemia mutations present in nine HbH subjects from Cuba was achieved by digestion with Bam HI, Bgl II, and Apa I and hybridization with alpha- and zeta-specific probes. The results show that the molecular basis of the genetic defect is quite homogeneous, all the subjects carrying the - alpha 3.7 type I/--SEA genotype. Variations are observed in the size of the zeta polymorphic fragments.

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.