Prevalence of α-thalassaemia genotypes in pregnant women in northern Thailand

Stability of Hemoglobin Constant Spring Identified by Capillary Electrophoresis

Objective

Hemoglobin Constant Spring (HbCS) is often missed by routine hemoglobin analysis. The aim of this research was to study HbCS stability as identified by capillary electrophoresis (CE) to determine the specimen storage time limit.

Methods

The EDTA blood of 29 HbCS samples were kept at 4°C and analyzed every workday until CE could not detect HbCS or until 7 weeks after blood collection. The genotypes were confirmed by multiplex polymerase chain reaction.

Results

The median subject age was 27 years and 10 subjects were male. The HbCS levels were stable during the first 7 days but became undetectable in 5 cases (17.2%) after 1 week. All of them were heterozygous HbCS. Longer detection times were correlated with the higher baseline HbCS levels, with a correlation coefficient of 0.582 (P  ≤ 0.001)

Conclusion

Routine hemoglobin typing and quantitation should be performed within 1 week after blood collection to detect low HbCS levels, especially in heterozygous HbCS.

Prevalence and molecular spectrum of α- and β-globin gene mutations in Hainan, China

This study investigated prenatal diagnosis of α-thalassemia and β-thalassemia in 3049 families in 18 regions of Hainan Province. Molecular diagnosis was performed in 3049 couples with thalassemia in Hainan Province. Genomic DNA was extracted from peripheral blood of the couples and villus, amniotic fluid, or cord blood of fetuses. DNA-based diagnosis was performed using polymerase chain reaction. The most commonly detected mutation for α-thalassemia was- SEA/αα (31.53%), followed by - α4.2/αα (11.15%) and - α3.7/αα (11.02%). The most common mutation for β-thalassemia was CD41/42 (30.27%), followed by - 28 (2.56%). Prevalence was highest in the coastal regions and lowest in the Wenchang, Lingao, and Ding'an regions. We also found that the most common gene mutations in Han people and other minority groups were not homogeneous. Prenatal diagnosis showed 556 normal fetuses, 116 with α-thalassemia hydrops, and 134 with β-thalassemia major. Our findings provide important information for clinical genetic counseling regarding prenatal diagnosis for thalassemia major in Hainan Province.

Telomere shortening correlates with disease severity in hemoglobin H disease patients

Hemoglobin H (Hb H) disease is the most significant health problem of the α-thalassemia syndromes. The Hb disease patients are categorized based on their genotype to deletional and nondeletional, with the latter genotype presents the more severe clinical symptoms. Since telomere length is an indicator of biological aging and health, we hypothesized that telomere length could reflect Hb H disease's severity. In this study, we recruited 48 deletional and 47 nondeletional Hb H disease patients, along with 109 normal controls, for telomere length assessment. The leukocyte telomere length was assessed by monochromatic multiplex real-time PCR and reported as the telomere to single-copy gene (T/S) ratio. When telomere length was adjusted for age, the analysis of covariance between the control and the two Hb H disease groups revealed no significant difference. However, the telomere shortening rate was more rapid in the nondeletional Hb H disease group than those of the control and deletional Hb H disease groups. Gender analysis found that male patients have a significantly lower T/S ratio than females in the nondeletional group but not in the control and deletional groups. In the two disease groups, the T/S ratio was not influenced by ferritin level or transfusion burden but was positively correlated with the absolute reticulocyte count.

Prevalence of Alpha(α)-Thalassemia in Southeast Asia (2010-2020): A Meta-Analysis Involving 83,674 Subjects

Alpha(α)-thalassemia is a blood disorder caused by many types of inheritable α-globin gene mutations which causes no-to-severe clinical symptoms, such as Hb Bart's hydrops fetalis that leads to early foetal death. Therefore, the aim of this meta-analysis was to provide an update from year 2010 to 2020 on the prevalence of α-thalassemia in Southeast Asia. A systematic literature search was performed using PubMed and SCOPUS databases for related studies published from 2010 to 2020, based on specified inclusion and exclusion criteria. Heterogeneity of included studies was examined with the I2 index and Q-test. Funnel plots and Egger's tests were performed in order to determine publication bias in this meta-analysis. Twenty-nine studies with 83,674 subjects were included and pooled prevalence rates in this meta-analysis were calculated using random effect models based on high observed heterogeneity (I2 > 99.5, p-value < 0.1). Overall, the prevalence of α-thalassemia is 22.6%. The highest α-thalassemia prevalence was observed in Vietnam (51.5%) followed by Cambodia (39.5%), Laos (26.8%), Thailand (20.1%), and Malaysia (17.3%). No publication bias was detected. Conclusions: This meta-analysis suggested that a high prevalence of α-thalassemia occurred in selected Southeast Asia countries. This meta-analysis data are useful for designing thalassemia screening programs and improve the disease management.

Non-deletional alpha thalassaemia: a review

BACKGROUND

Defective synthesis of the α-globin chain due to mutations in the alpha-globin genes and/or its regulatory elements leads to alpha thalassaemia syndrome. Complete deletion of the 4 alpha-globin genes results in the most severe phenotype known as haemoglobin Bart's, which leads to intrauterine death. The presence of one functional alpha gene is associated with haemoglobin H disease, characterised by non-transfusion-dependent thalassaemia phenotype, while silent and carrier traits are mostly asymptomatic.

MAIN BODY

Clinical manifestations of non-deletional in alpha thalassaemia are varied and have more severe phenotype compared to deletional forms of alpha thalassaemia. Literature for the molecular mechanisms of common non-deletional alpha thalassaemia including therapeutic measures that are necessarily needed for the understanding of these disorders is still in demand. This manuscript would contribute to the better knowledge of how defective production of the α-globin chains due to mutations on the alpha-globin genes and/or the regulatory elements leads to alpha thalassaemia syndrome.

CONCLUSION

Since many molecular markers are associated with the globin gene expression and switching over during the developmental stages, there is a need for increased awareness, new-born and prenatal screening program, especially for countries with high migration impact, and for improving the monitoring of patients with α-thalassaemia.

Molecular characteristics of thalassemia and hemoglobin variants in prenatal diagnosis program in northern Thailand

Molecular analysis of globin genes is an essential process for prenatal diagnosis (PND) of severe thalassemia. This study aimed to describe the molecular characteristics of thalassemia and hemoglobin (Hb) variants in PND program in northern Thailand. The type and frequency of globin gene mutations from 1290 couples at risk of fetal severe thalassemia diseases that were tested at Thalassemia Laboratory at Chiang Mai University from 2012 to 2017 were retrospectively reviewed. The PND program detected 444 (34.4%), 196 (15.2%) and 642 (49.8%) couples at risk of fetal Hb Bart's hydrops fetalis, beta-thalassemia major (BTM) and beta-thalassemia/Hb E disease, respectively. Coinheritance of more than one type of thalassemia was common and eight (0.6%) couples were at risk of two types of severe thalassemia. There were two types of alpha⁰-thalassemia; 893 (99.7%) Southeast Asian and 3 (0.3%) Thai deletions. Twenty beta-globin gene mutations were found with 94.3% of beta⁰-thalassemia. The codon 41/42 (- TTCT), codon 17 (A>T), IVS-I-1 (G>T) and codon 71/72 (+ A) comprised 90% of beta-thalassemia mutations. The study shows a high percentage of couples at risk of fetal Hb Bart's hydrops fetalis and BTM. The percentage of beta⁰-thalassemia is higher than those seen in other regions of Thailand.

Fast-Track Strategy for the Prevention of Hb Bart’s Hydrops Fetalis Syndrome

We propose a fast-track strategy [direct blood DNA analysis using a quantitative real-time polymerase chain reaction (PCR) technique] for the early risk detection and prenatal diagnosis of α(0)-thalassemia (SEA and Thai deletion). Blood DNA samples were obtained from a volunteer group of 1235 ANC couples. They were assessed using quantitative real-time PCR to detect carriers of α(0)-thalassemia (SEA and Thai deletion). At-risk couples were identified, and further prenatal diagnosis by amniocentesis was implemented. Fetal DNA was isolated from the amniotic cells and characterized by quantitative real-time PCR to detect the α(0)-thalassemia mutation, which was reconfirmed using the droplet digital PCR method. Fifteen at-risk couples were identified. The timing of prenatal diagnosis was appropriate for all couples and four of the fetuses were diagnosed with Bart’s hydrops fetalis. The results were compatible with those calculated using the Hardy-Weinberg equation for a recessively inherited single gene disorder. The conclusion was that the fast-track strategy could shorten screening policy timelines, promoting early risk detection for couples and early prenatal diagnosis. The fast-track strategy might be beneficial for the prevention of hemoglobin Bart’s hydrops fetalis syndrome.

[Identification of a new 3.8kb deletional α thalassemia and detection of the deletion fragment]

OBJECTIVE

To report the identification of a novel 3.8-kb deletion that caused α thalassemia and establish the method for detecting the deletion fragment.

METHODS

Peripheral blood samples were collected from the proband and his mother for analysis of the hematological parameters and routine test for thalassemia genes. For the sample with an inconsistency between the genotyping results and phenotypic analysis results, a specific gap-PCR was employed to identify the rare or novel mutations.

RESULTS

A novel 3814-bp deletion causing α thalassemia was found in the proband and his mother, who had genotypes of -α4.2/-α3.8 and αα/-α3.8, respectively.

CONCLUSION

We identified a 3.8-kb deletion in the α-globin gene cluster that caused α thalassemia, and this finding enriches the α thalassemia gene mutation spectrum. Specific gap-PCR offers a convenient and efficient means for for detecting this deletion fragment.