PCR-based diagnosis of the Filipino (--(FIL)) and Thai (--(THAI)) alpha-thalassemia-1 deletions

Development and clinical validation of a novel detection kit for α-thalassemia in southern Chinese

Objective

This study aimed to develop and assess a novel reverse dot blot assay for the simultaneous detection of 10 types of α-thalassemia alleles in the Chinese population, including six common variants of-SEA, -α3.7, -α4.2, αCS, αQS, and αWS, and four rare variants of αααanti-4.2, αααanti-3.7, --FIL deletion and--THAI deletion.

Methods

The novel thalassemia gene assay utilized a two-tier multiplex polymerase chain reaction amplification system and one round of hybridization. Genomic DNA samples were sourced from three hospitals in southern China. Each clinically validated DNA sample was re-evaluated using the new multiplex polymerase chain reaction/reverse dot blot assay Ⅲ (M-PCR/RDB Ⅲ).

Results

The study analyzed a total of 1,148 unrelated participants, consisting of 810 thalassemia patients and 338 healthy control subjects. Valid hybridization results were obtained for 1,147 samples, with one case (thalassemia carrier) being excluded from the study due to the poor quality of DNA. All 1,147 samples, including those with α heterozygous thalassemia, α homozygous thalassemia, α compound heterozygous thalassemia, and control subjects were accurately genotyped, showing 100% concordance with the reference assays.

Conclusion

The novel M-PCR/RDB Ⅲ assay proved to be simple, rapid, and precise, indicating its potential for genetic screening and clinical diagnosis of both common and rare α-thalassemia variants in Chinese populations.

Single-tube multiplex real-time PCR with EvaGreen and high-resolution melting analysis for diagnosis of α0-thalassemia--SEA,--THAI, and--CR type deletions

Regions with a high prevalence of α-thalassemia (α-thal) require simple, rapid, and accurate tests for carrier screening and prenatal diagnosis. Diagnosis of multiple deletions in a single tube is necessary to clearly identify individuals with α0-thalassemia in the routine setting, especially in at-risk couples. Therefore, we aimed to develop a single-tube multiplex real-time PCR with EvaGreen and high-resolution melting (HRM) analysis for the identification of α0-thalassemia Southeast Asian (SEA), Thai and Chiang Rai (CR) type deletions. The results of the HRM analysis indicated that the amplified fragments from α0-thal--CR,--THAI,--SEA, and the wild-type α-globin gene had specific peak heights at mean melting temperature (Tm) values of 85.40°C, 86.50°C, 87.65°C, and 91.04°C, respectively. The frequencies of α0-thal--SEA,--THAI,--CR obtained from routine testing in 2,135 samples were 17.89%, 0.19% and 0.19%, respectively. This method would be useful for preventing Hb Bart's hydrops fetalis. Detection of multiple deletions in a single run is cost-effective, highly accurate and timesaving. This technique could enable wider α-thalassemia diagnosis in high prevalence areas and served as an example for thalassemia routine setting.

Diagnosis of α-thalassaemia by colorimetric gap loop mediated isothermal amplification

α-Thalassaemia is an inherited haemoglobin disorder that results from the defective synthesis of α-globin protein. Couples whom both carry the α-thalassaemia 1 gene are at risk of having a foetus with the most severe thalassaemia, Hb Bart's hydrops fetalis, with a risk of maternal mortality. However, haematological parameters alone cannot distinguish between a α-thalassaemia 1 carrier and a homozygous α-thalassaemia 2, in which one α-globin gene has been deleted on each chromosome. A rapid and accurate molecular detection assay is essential for prevention of the disease in populations where α-thalassaemia 1 is common. Multiplex Gap-PCR analysis is widely used for diagnosis of α-thalassaemia. However, the technique requires a thermocycler and post-amplification processing, which limits its application in primary care or in rural areas in developing countries. Loop mediated isothermal amplification (LAMP) amplifies target DNA at a constant temperature and does not require a thermocycler. This study developed a colorimetric Gap-LAMP using malachite green to allow naked eye visualization of two deletional α-thalassaemia 1 commonly found in Asian populations, the Southeast Asian type (--^SEA) and the Thai type (--^THAI) deletions. The Gap-LAMP was performed on DNA samples from 410 individuals carrying various α-thalassaemia gene defects with 100% concordance with conventional Gap-PCR analysis. This method eliminates post-amplification processing or the use of expensive sophisticated equipment and allows screening large populations for the prevention and control of α-thalassaemia.

Investigation of the mechanism of copy number variations involving the α-globin gene cluster on chromosome 16: two case reports and literature review

Thalassemia is one of the most common single-gene disorder worldwide. An important genetic cause of thalassemia is copy number variations (CNVs) in the α-globin gene cluster. However, there is no unified summary and discussion on the detailed information and mechanisms of these CNVs. In this study, two novel CNVs, a tandem duplication (αααα¹⁵⁹) and deletion (--²⁵⁹), were identified in two Chinese families with thalassemia patients, according to the results of hematologic analysis, routine genetic testing for thalassemia, multiplex ligation-dependent probe amplification (MLPA), next-generation sequencing (NGS) and other molecular methods. Co-inherited with β^CD41-42 mutation and --^SEA deletion separately, αααα¹⁵⁹ and --²⁵⁹ resulted in a patient with β-thalassemia intermedia and a lethal fetus with Hb Bart's hydrops fetalis syndrome, respectively. Next, a literature review was performed to summarize all known CNVs involving the α-globin gene cluster. The molecular structure characteristics of these CNVs were analyzed and the possible mechanism was explored. It is the first time to analyze the generation mechanism of genome arrangements in the α-globin gene cluster systematically.

Prevalence and Genetic Analysis of Thalassemia and Hemoglobinopathy in Different Ethnic Groups and Regions in Hainan Island, Southeast China

Background: There are limited studies on the molecular profile of thalassemia in Hainan, the free trade island in China. Our aim was to reveal the prevalence and molecular mutation spectrum of thalassemia in different ethnic groups and regions of Hainan through a large sample study for the first time.

Methods: A total of 231,596 individuals from 19 cities and counties in Hainan were screened by hematological parameter analysis, and further genetic analysis was performed on individuals with MCV less than 82 fL.

Results: Totally, 31,780 (13.72%) subjects were diagnosed as thalassemia carriers. The overall prevalence of α-thalassemia, β-thalassemia, and α+β-thalassemia were 11.04%, 1.48%, and 1.20%, respectively. We further analyzed the molecular profiles of thalassemia in various ethnic groups and mainly compared the difference between Han and Li. The results showed that the frequency of thalassemia in the Li population (47.03%) was much higher than that in Han (9.37%). Except for β-thalassemia (1.31% of Li vs. 1.47% of Han), the frequencies of α-thalassemia (39.59% of Li vs. 7.35% of Han) and α+β-thalassemia (6.13% of Li vs. 0.56% of Han) in the Li were obviously higher than those in Han. The high-frequent genotypes of α-thalassemia in Han were αα/--SEA (25.55%), -α3.7/αα (22.17%), -α4.2/αα (21.59%), αWSα/αα (8.93%), and -α3.7/-α4.2 (4.17%) and those of Li were -α4.2/αα (17.24%), -α3.7/αα (17.16%), -α3.7/-α4.2 (15.09%), αWSα/αα (9.69%), and αWSα/-α3.7 (8.06%), respectively. The αα/--SEA was the highest genotype of α-thalassemia in Han but only accounted for 1.87% in Li. For β-thalassemia, the top three high-frequent genotypes in both Han and Li were βCD41/42(-TTCT)/βN, β-28(A>G)/βN, and βIVS-Ⅱ-654(C>T)/βN, but the frequency of βCD41/42(-TTCT)/βN in Li (90.96%) was much higher than that in Han (56.32%) and the data reported in other provinces of China. Additionally, the prevalence of thalassemia ranged from 8.16% to 34.35% in Hainan, Wuzhishan, Baoting, Qiongzhong, and Baisha have a higher prevalence than other areas.

Conclusion: Our study revealed the characteristics of ethnic and regional differences in the prevalence of thalassemia in the childbearing age population of Hainan for the first time, indicating that the prevalence of thalassemia among Li nationality is the highest in China. Those findings will be useful for genetic counseling and the prevention of thalassemia.

Prenatal diagnosis of thalassemia in 695 pedigrees from southeastern China: a 10-year follow-up study

Thalassaemia is highly prevalent in southeastern China. This 10-year follow-up study aimed to characterize the genotype and karyotype of thalassaemia in fetal samples derived from thalassemia carriers in Fujian province, southeastern China. A total of 476 prenatal samples from 472 couples carrying α-thalassaemia traits and 224 samples from 223 couples carrying β-thalassaemia traits were collected for STR analysis, detection of thalassemia genotypes and karyotyping. The common deletional α-thalassemias and rare thalassemia genotypes were detected using Gap-PCR assay, and the common β-globin gene mutations were detected using PCR-RDB assay. We detected 43.49% prevalence of α-thalassaemia minor, 26.05% prevalence of α-thalassaemia intermediate and major and 1.89% prevalence of rare form among the 476 prenatal samples from couples with α-thalassaemia, and 85 fetuses with β-thalassemia heterozygote, 16 with homozygote and 21 with double heterozygote, and a rare β^{IVS-2-654(C→T)} /Chinese G_γ (^A γδβ)⁰  genotype among the 224 prenatal samples from couples with β-thalassemia. Karyotyping showed 7 fetuses with abnormal karyotypes. Totally 153 pregnancies were terminated, and genetic diagnosis of thalassemia using fetal umbilical cord blood following induction of labor showed consistent results with prenatal diagnosis. No thalassemia phenotypes were identified in normal infants half a year after birth, and the infants with α-thalassemia and β-thalassemia minor had no or mild anemia symptoms, but normal development, while 15 babies with hemoglobin H disease presented moderate anemia symptoms. Our data suggest the pregestational screening of thalassemia, notably compound and rare forms of thalassemia, for couples carrying thalassemia traits.

Coinheritance of High Oxygen Affinity Hb Helsinki [HBB: c.248A>T; β82(EF6)Lys→Met] with Hb H Disease

Hb Helsinki [HBB: c.248A>T; β82(EF6)Lys→Met] is a high oxygen affinity hemoglobin (Hb) causing polycythemia, whereas Hb H (β4) disease causes mild to severe chronic hemolytic anemia. The clinical characteristics, gel electrophoresis, capillary electrophoresis (CE) and molecular genotyping of a case of Hb Helsinki coinherited with Hb H disease in an ethnic Malay is described, illustrating the interaction between the β-globin variant and coinheritance of three α gene deletions. The proband was asymptomatic, exhibited microcytosis and a normal with Hb value.

Invasive prenatal diagnosis of fetal thalassemia

Thalassemia is the most common monogenic inherited disease worldwide, affecting individuals originating from many countries to various extents. As the disease requires long-term care, prevention of the homozygous state presents a substantial global disease burden. The comprehensively preventive programs involve carrier detections, molecular diagnostics, genetic counseling, and prenatal diagnosis. Invasive prenatal diagnosis refers to obtaining fetal material by chorionic villus sampling (CVS) at the first trimester, and by amniocentesis or cordocentesis at the second trimester. Molecular diagnosis, which includes multiple techniques that are aimed at the detection of mutations in the α- or β-globin genes, facilitates prenatal diagnosis and definitive diagnosis of the fetus. These are valuable procedures for couples at risk, so that they can be offered options to have healthy offspring. According to local practices and legislation, genetic counseling should accompany the invasive diagnostic procedures, DNA testing, and disclosure of the results. The most critical issue in any type of prenatal molecular testing is maternal cell contamination (MCC), especially when a fetus is found to inherit a particular mutation from the mother. The best practice is to perform MCC studies on all prenatal samples. The recent successful studies of fetal DNA in maternal plasma may allow future prenatal testing that is non-invasive for the fetus and result in significant reduction of invasive diagnostic procedures.

Detection of α-thalassemia-1 Southeast Asian and Thai type deletions and β-thalassemia 3.5-kb deletion by single-tube multiplex real-time PCR with SYBR Green1 and high-resolution melting analysis

Background

Prevention and control of thalassemia requires simple, rapid, and accurate screening tests for carrier couples who are at risk of conceiving fetuses with severe thalassemia.

Methods

Single-tube multiplex real-time PCR with SYBR Green1 and high-resolution melting (HRM) analysis were used for the identification of α-thalassemia-1 Southeast Asian (SEA) and Thai type deletions and β-thalassemia 3.5-kb gene deletion. The results were compared with those obtained using conventional gap-PCR. DNA samples were derived from 28 normal individuals, 11 individuals with α-thalassemia-1 SEA type deletion, 2 with α-thalassemia-1 Thai type deletion, and 2 with heterozygous β-thalassemia 3.5-kb gene deletion.

Results

HRM analysis indicated that the amplified fragments from α-thalassemia-1 SEA type deletion, α-thalassemia-1 Thai type deletion, β-thalassemia 3.5-kb gene deletion, and the wild-type β-globin gene had specific peak heights at mean melting temperature (T_m) values of 86.89℃, 85.66℃, 77.24℃, and 74.92℃, respectively. The results obtained using single-tube multiplex real-time PCR with SYBR Green1 and HRM analysis showed 100% consistency with those obtained using conventional gap-PCR.

Conclusions

Single-tube multiplex real-time PCR with SYBR Green1 and HRM analysis is a potential alternative for routine clinical screening of the common types of α- and β-thalassemia large gene deletions, since it is simple, cost-effective, and highly accurate.

High prevalence of alpha- and beta-thalassemia in the Kadazandusuns in East Malaysia: challenges in providing effective health care for an indigenous group

Thalassemia can lead to severe transfusion-dependent anemia, and it is the most common genetic disorder in Malaysia. This paper aims to determine the prevalence of thalassemia in the Kadazandusuns, the largest indigenous group in Sabah, East Malaysia. α- and β-thalassemia were confirmed in 33.6% and 12.8%, of the individuals studied respectively. The high prevalence of α- and β-thalassemia in the Kadazandusuns indicates that thalassemia screening, genetic counseling, and prenatal diagnosis should be included as part of their healthcare system. This preliminary paper serves as a baseline for further investigations into the health and genetic defects of the major indigenous population in Sabah, East Malaysia.

Newborn screening for hemoglobinopathies in California

BACKGROUND

Newborn screening (NBS) for hemoglobinopathies facilitates early identification of affected individuals to ensure the prompt institution of comprehensive medical care for affected newborns in California. When linked to extensive follow-up and education, NBS has been shown to significantly reduce mortality in children with sickle cell disease. Due to changing immigration patterns from Asia and Latin America, the State of California has witnessed an increased prevalence of clinically significant hemoglobin (Hb) disorders, including those resulting from novel genotypes. In 1999, newborn screening for Hb H disorders was incorporated in the statewide hemoglobinopathy screening program.

PROCEDURE

Primary screening for hemoglobin variants was performed using high performance liquid chromatography. Confirmatory testing on hemoglobinopathy mutations was performed by electropheresis techniques and genotyping methods.

RESULTS

Of 530,000 newborn samples screened annually in California, 2,118 samples were referred to the Hemoglobin Reference Laboratory (HRL) for confirmatory testing between January 1, 1998 and June 30, 2006 (0.05%). Sickle cell disease was most frequently observed (1 in 6,600 births) followed by alpha-thalassemia (1 in 9,000 births) and beta-thalassemia disease (1 in 55,000 births). The confirmatory analysis modified the initial screening in 5% of cases and revealed 25 rare or new genotypes. Diverse ethnicities were associated with hemoglobin mutations including Southeast Asian, Black, Indian/Asian, Middle Eastern, and Hispanic.

CONCLUSIONS

The California hemoglobinopathy screening program provides accurate diagnosis of hemoglobinopathies. Increasing incidence of diverse mutations require new strategies of laboratory screening, counseling, and patient management.

Molecular assay of −α3.7 and −α4.2 deletions causing α-thalassemia by denaturing high-performance liquid chromatography

OBJECTIVES

alpha-Thalassemia, the most common single gene disorder in humans, is due to the absence of one (-alpha/alphaalpha) or both (--/alphaalpha) of the two functional alpha-globin genes (alpha1 and alpha2). The -alpha(3.7) and -alpha(4.2) single gene deletions are common in Southeast Asian populations. Southern blotting analysis and gap PCR assay are commonly used for the detection of such alpha-thalassemia genotypes. The two genes are located on chromosome 16, with high homology (>96%).

DESIGN AND METHODS

Based on the sequence variation within the two Z boxes, a denaturing high-performance liquid chromatography (DHPLC)-based assay was developed for rapid genotyping of the -alpha(3.7) and -alpha(4.2) alleles. To demonstrate the utility of this approach, 40 DNA samples with known genotypes were analyzed, including -alpha(3.7)/alphaalpha (7 cases), -alpha(4.2)/alphaalpha (4 cases), -alpha(3.7)/--(SEA) (6 cases), -alpha(4.2)/--(SEA) (3 cases), and 20 unaffected subjects (alphaalpha/alphaalpha).

RESULTS

We successfully distinguished all of the alpha-thalassemia genotypes through their characteristic chromatograms of alpha1 and alpha2 genes. The accuracy of this technique for our sample was 100% sensitivity and specificity.

CONCLUSION

This novel and alternative DHPLC-based alpha-thalassemia genotype assay is easy, rapid, and highly accurate. This technique enables the diagnosis of silent alpha+ thalassemia and hemoglobin H disease for large scale population screening.

Alpha(0)-thalassemia and related disorders in northeast Thailand: a molecular and hematological characterization

Alpha(0)-thalassemia is the most severe form of alpha-thalassemia commonly encountered in Asians. To provide relevant information for effective prevention and control of this disorder, we have examined the molecular basis and hematological features of alpha(0)-thalassemia-related disorders in northeast Thailand. A multiplex polymerase chain reaction for simultaneous detection of the southeast Asian (SEA) and the THAI alpha(0)-thalassemia determinants was developed and used for screening of 1,541 Thai individuals who were positive at the preliminary screening in an ongoing thalassemia control program. Alpha(0)-thalassemia deletions were detected in 397 (25.8%) cases, 396 with the SEA deletion and 1 with the THAI deletion. While the latter was found in association with the Hb Constant Spring in a patient with severe Hb H disease, the former was encountered in as many as 12 thalassemia genotypes whose hematological features were comparatively presented. The results obtained should prove useful in carrier screening and prenatal diagnosis programs of this common genetic disorder in the region.

Rapid diagnosis of alpha(o)-thalassemia using the relative quantitative PCR and the dissociation curve analysis

A method for diagnosis of alpha(o)-thalassemia was developed based on detection of accumulated PCR product using SYBR Green I, a double-stranded DNA binding dye, and a fluorescence-detecting thermocycler. Primers were designed to specifically amplify - -SEA and - -Thai deletions of alpha(o)-thalassemia. Albumin was selected as the reference gene. The comparative CT method was used to quantitate the target gene relative to the albumin gene. Dissociation curve analysis was used as a qualitative tool to distinguish different types of alpha(o)-thalassemia. In this study, the melting temperatures of the - -Thai and - -SEA deletions were 83 and 86 degrees C, respectively. Application of the assay for the diagnosis of alpha(o)-thalassemia heterozygotes and homozygotes is reported. The assay is highly robust and amenable to high throughput. It is thus a useful tool for the rapid detection of alpha(o)-thalassemia in populations with a high frequency of alpha(o)-thalassemia, - -SEA and - -Thai deletions.

Simple fluorescent PCR method for detection of large deletions in the beta-globin gene cluster

We developed a semi-automated approach to detect large deletions in the beta-globin gene cluster, based on the quantitative differences in the amplifications of samples by a fluorescent PCR. With this strategy, we were able to detect the presence of HPFH-2 in an African-Brazilian subject, confirmed by sequencing analysis. Differently from other PCR strategies, GAP-PCR for example, it has the potential to identify new deletions.

Detection of severe nondeletional alpha-thalassemia mutations using a single-tube multiplex ARMS assay

Alpha-thalassemia is a common hereditary anemia due to decreased or absent synthesis of alpha-globin chains. The most common causes of alpha-thalassemia are deletions that remove one or both functional alpha-globin genes, with a small proportion of cases involving nondeletional mutations of the alpha2- or alpha1-globin genes. Herein, we describe a single-tube multiplex amplification refractory mutation system (ARMS) assay for rapid detection of six of the most common and severe nondeletional alpha-thalassemia mutations. These alleles are found predominantly among southeast Asian populations, and are associated with the most severe forms of hemoglobin (Hb) H disease or Hb H hydrops fetalis.

Compound heterozygosity for alpha0-thalassemia (- -THAI) and Hb constant spring causes severe Hb H disease

We report two unrelated cases of Hb H-Constant Spring (Hb H-CS) disease caused by a compound heterozygosity for alpha0-thalassemia (--THAI deletion) and Hb CS (alpha142, TAA-->CAA) in Thai patients. Hematological and clinical observations in the probands are more severe than those of deletional type of Hb H disease (- -/-alpha), owing to an early onset of anemia and recurrent episode of anemic crises. These cases also address the importance of the - - THAI deletion which causes a severe clinical phenotype, and that could be missed by routine screening. We suggest that testing for this mutation should be included in the screening program for the prevention and control of thalassemia in Thailand, and possibly in other countries in Southeast Asia, where alpha0-thalassemias are highly prevalent.

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.

Universal newborn screening for Hb H disease in California

Newborn screening is an accepted public health measure to ensure that appropriate health care is provided in a timely manner to infants with hereditary/metabolic disorders. Alpha-thalassemia is a common hemoglobin (Hb) disorder, and causes Hb H (beta4) disease, and usually fatal homozygous alpha(0)-thalassemia, also known as Hb Bart's (gamma4) hydrops fetalis syndrome. In 1996, the State of California began to investigate the feasibility of universal newborn screening for Hb H disease. Initial screening was done on blood samples obtained by heel pricks from newborns, and stored as dried blood spots on filter paper. Hb Bart's levels were measured as fast-moving Hb by automated high-performance liquid chromatography (HPLC) identical to that currently used in newborn screening for sickle cell disease. Subsequent confirmation of Hb H disease was done by DNA-based diagnostics for alpha-globin genotyping. A criterion of 25% or more Hb Bart's as determined by HPLC detects most, if not all cases of Hb H disease, and few cases of alpha-thalassemia trait. From January, 1998, through June, 2000, 89 newborns were found to have Hb H disease. The overall prevalence for Hb H disease among all newborns in California is approximately 1 per 15,000. Implementation of this program to existing newborn hemoglobinopathy screening in populations with significant proportions of southeast Asians is recommended. The correct diagnosis would allow affected infants to be properly cared for, and would also raise awareness for the prevention of homozygous alpha(0)-thalassemia or Hb Bart's hydrops fetalis syndrome.

Hb H hydrops foetalis syndrome: a case report and review of literature

Haemoglobin H (Hb H) disease is caused by deletion or inactivation of three alpha-globin genes, leaving only one intact and active alpha-globin gene. People with Hb H disease usually have moderate anaemia, but are generally thought to be asymptomatic. Some Hb H disease patients require transfusions, and there are reports of fetuses with Hb H disease who have severe anaemia in utero resulting in fatal hydrops foetalis syndrome. We now report a case of Hb H hydrops foetalis syndrome, caused by the inheritance of a hitherto novel alpha-globin gene point mutation (codon 35 TCC-->CCC or Serine-->Proline) and an alpha-thalassaemia deletion of the Filipino type removing all zeta-alpha-globin genes on the other chromosome 16. The infant was delivered prematurely because of pericardial effusion and fetal distress, and was found to have severe anaemia and congenital anomalies. A review of the relevant literature on this syndrome is presented, and serves to underscore the phenotypic variations of Hb H disease and the need for surveillance for this condition among newborns and genetic counselling in communities with a high proportion of at-risk populations.

Hemoglobin H (Hb H) disease in Canada: molecular diagnosis and review of 116 cases

Over the past decade, we have characterized at the DNA level a total of 116 hemoglobin H (Hb H) disease patients living in Canada. The majority of patients were of southeast Asian descent (Chinese, Filipino, Laotian, Vietnamese), with a small number being of Mediterranean, Middle Eastern or East Indian background. A total of 15 distinct genotypes were detected, all but one being compound heterozygotes for a two-gene cis deletion and a single-gene deletion (-alpha/-) or a non-deletion mutation of the alpha2-globin gene (alpha(T) alpha/-). Seven different two-gene cis deletions were encountered, along with nine single-gene deletions and point mutations. The wide range of mutations associated with Hb H disease in Canada is a reflection of the population heterogeneity. The diagnosis of Hb H disease at the molecular level is important with respect to genetic counseling and the identification of families at risk for having pregnancies affected with Hb Bart's hydrops fetalis syndrome and/or Hb H disease. Six of the Hb H disease patients in our cohort had spouses who carried single-gene deletions, making these couples at risk for having children with Hb H disease. More important, seven patients had partners who carried two-gene cis deletions. These couples are at reproductive risk for both Hb Bart's hydrops fetalis syndrome and Hb H disease.

A reliable screening test to identify adult carriers of the (--SEA) alpha zero-thalassemia deletion. Detection of embryonic zeta-globin chains by enzyme-linked immunosorbent assay

Homozygous (--SEA) alpha zero-thalassemia deletion, the cause of up to 80% of fetal hydrops in Southeast Asia, is encountered in many other countries. Heterozygous carrier rates of the deletion in Southeast Asian populations range from 4% to 14%. The laboratory screening for adult carriers of (--SEA) and other alpha zero-thalassemia deletions currently rests primarily with microscopic detection of hemoglobin H inclusion bodies within erythrocytes (Hb H screen). This test is laborious and observer dependent and has poor sensitivity. We assessed a colorimetric enzyme-linked immunosorbent assay (ELISA) to detect embryonic zeta-globin chains in adult hemolysates as an alternative to detect (--SEA) alpha zero-thalassemia deletion carriers. Blood samples from 221 adults with a mean corpuscular volume less than 80 micron 3 (80 fL) were studied prospectively by currently accepted hemoglobin screening tests and ELISA. Suspected cases of alpha-thalassemia were confirmed by DNA-based diagnostics. ELISA was highly sensitive (1.0) and specific (0.94) for the detection of adult carriers of (--SEA) alpha zero-thalassemia deletion. The hemoglobin H screen had a sensitivity of 0.47 and specificity of 0.99. The zeta-globin ELISA proved simple to perform, rapid, and applicable to high volume or population-based screening programs.