δ-Hemoglobinopathies in Thailand: screening, molecular basis, genotype-phenotype interaction, and implication for prevention and control of thalassemia

Prevalence of thalassaemia among childbearing-age Li and Han populations in Hainan Province

OBJECTIVES

Accurate epidemiological data are crucial for effective disease prevention and treatment. We conducted a large-scale survey to explore the thalassaemia prevalence and spectrum among the two major ethnic groups in Hainan Province.

METHODS

A total of 399,053 childbearing-age individuals of Li (n = 77,563) and Han(n = 321,490) ethnic groups were recruited from 18 cities and counties in Hainan, and their thalassemia genotypes were systematically screened and statistically analysed.

RESULTS

This study revealed a significantly higher thalassaemia carrier rate in the Li (55.39%) than that in the Han (13.13%). Specifically, the carrier rate of α-thalassaemia was 46.39% in the Li and 10.02% in the Han. The predominant α-thalassaemia mutations were - α3.7 and - α42. in Li, whereas the main mutation were - SEA and - α4.2 in Han. For β-thalassaemia, the carrier rates were 1.68% in Li and 2.38% in Han, with CD41-42(-CTTT) the most prevalent mutation in both groups. The carrier rates of β-/α-compound thalassaemia were 7.32% in Li and 0.73% in Han. Additionally, there were regional differences in the distribution of thalassemia among the Li and Han within Hainan Province.

CONCLUSION

Epidemiological characteristics and molecular spectrum of thalassaemia among the Li and Han ethnic groups in Hainan were revealed in this study. These findings can provide a scientific basis to develop and implement prevention strategies for thalassaemia in Hainan.

Hb A2-Guangxi [δ79 (EF3) Asp→Asn, HBD: C.238G > A] and polyA + 70 (HBD: C.*200G > A): Two Novel δ-Globin Gene Mutations Identified in a Chinese Family

We report the molecular and hematological identifications of two novel δ-globin gene mutations found in Guangxi Zhuang Autonomous Region, China. Capillary electrophoresis of the proband showed 1.3% Hb A2, accompanied by a minor unknown peak (0.7%) within the Z1 zone. High-performance liquid chromatography also revealed the presence of 1.5% Hb A2 and a 0.6% unknown peak. Routine genetic testing (Gap-PCR and reverse dot-blot hybridization) for common α-thalassemia was performed, and no mutations were observed. Sanger sequencing identified a heterozygous mutation for GAC > AAC at codon 79 (HBD:c.238G > A) and G > A at polyA + 70 (HBD:c.*200G > A) of the δ-globin gene. This variant was named Hb A2-Guangxi [δ79 (EF3) Asp→Asn, HBD:c.238G > A] after the geographic origin of the proband.

Association of thalassemia, hemoglobinopathies, and vitamin D levels with lipid profile in adults: Community-based research in southern Thai population

This study explored the frequency of lipid-lowering drug use in the thalassemia population and investigated the association of thalassemia, hemoglobinopathies, and serum 25(OH)D levels with lipid profile and red blood cell parameters. A combination of cross-sectional and community-based studies was conducted with 615 participants from the southern Thai population. Thalassemia and hemoglobinopathies were diagnosed using hemoglobin analysis and polymerase chain reaction-based methods to genotype globin genes. Biochemical parameters such as lipid profile, fasting blood sugar (FBS), and serum 25(OH)D levels were assessed using standard enzymatic methods and electrochemiluminescence immunoassays. Differences in the means of hematological and biochemical parameters between the thalassemia and non-thalassemia groups were compared and analyzed. A significantly lower frequency of lipid-lowering drug use was observed in the thalassemia group. Thalassemia, with clearly defined abnormalities in red blood cells, is associated with a 4.72-fold decreased risk of taking lipid-lowering drugs. Among thalassemia participants, the total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels were significantly lower than those in non-thalassemia participants. The prevalence of hypovitaminosis D in carriers of thalassemia and/or hemoglobinopathies in the southern Thai population was 53 % in females and 21 % in males. The highest lipid profile was observed in samples without thalassemia and hypovitaminosis D. The genetics of thalassemia and hemoglobinopathies with obviously abnormal red blood cells could explain the variable lipid levels, in addition to lipid metabolism-related genes and environmental factors. However, the effect of thalassemia on lipid levels in each population may differ according to its prevalence. A larger sample size is required to confirm this association, especially in countries with a high prevalence of thalassemia.

Hemoglobin profile and molecular characteristics of the complex interaction of hemoglobin Doi-Saket [α9(A7) asn > lys, HBA2:c.30C > a], a novel α2α1 hybrid globin variant, with hemoglobin E [β26(B8) Glu > lys, HBB:c.79G > A] and deletional α+-thalassemia in a Thai family

BACKGROUND

An increasing number of α-hemoglobin (Hb) variants is causing various clinical symptoms; therefore, accurate identification of these Hb variants is important.

OBJECTIVE

This study aimed to describe the molecular and hematological characteristics of novel Hb Doi-Saket that gives rise to a typical α+-thalassemia phenotype in carriers with and without other hemoglobinopathies.

MATERIALS AND METHODS

Biological samples from a proband and his family members were analyzed. Hematological profiles were analyzed using a standard automated cell counter. Hb was analyzed by capillary electrophoresis and high-performance liquid chromatography. Mutations and globin haplotype were identified by DNA analysis. Novel diagnostic tools based on allele-specific polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism were developed.

RESULTS

Hb analysis showed a major abnormal Hb fraction, moving slower than HbA, and a minor Hb fraction alongside HbA2 in the proband, his father, and son. DNA analysis of the α-globin gene identified the -α3.7 deletion and in cis the C > A mutation on codon 9 of the α2α1 gene, corresponding to Hb Doi-Saket [α9(A7) Asn > Lys]. This mutation could be identified using newly developed allele-specific PCR-based assays. The Hb Doi-Saket al.lele was significantly associated with haplotype [- + M + + 0 -]. Interaction of αDoi-Saket with βE globin chains led to a new Hb variant (HbE Doi-Saket). Phenotypic expression was clinically silent in heterozygotes and might present slight microcytosis.

CONCLUSIONS

Hb Doi-Saket emphasizes a great diversity present in α-globin gene. The mutation in this family from Thailand was linked to -α3.7 and caused mild microcytosis in the carriers. The combination of this variant with deletions in α genes might cause a severe clinical phenotype. Different methods of separation can provide useful information in diagnosis, and a complete molecular approach is needed for confirmation before considering patient management.

Prospective screening for δ-hemoglobinopathies associated with decreased hemoglobin A2 levels or hemoglobin A2 variants: A single center experience

BACKGROUND

δ-hemoglobinopathies may lead to misdiagnosis of several thalassemia syndromes especially β-thalassaemia carrier, it is important to evaluate the δ-globin gene defects in areas with high prevalence of globin gene disorders. We describe a prospective screening for δ-hemoglobinopathies in a routine setting in Thailand.

METHODS

Study was done on a cohort of 8,471 subjects referred for thalassemia screening, 317 (3.7%) were suspected of having δ-globin gene defects due to reduced hemoglobin (Hb) A₂ levels and/or appearance of Hb A₂-variants on hemoglobin analysis. Hematologic and DNA analysis by PCR and related assays were carried out.

RESULTS

DNA analysis of δ-globin gene identified seven different δ-globin mutations in 24 of 317 subjects (7.6%). Both known mutations; δ^-77(T>C) (n=3), δ^-68(C>T) (n=1), δ^-44(G>A) (n=8), Hb A₂-Melbourne (n=5), δ^{IVSII-897(A>C)} (n=5), and Hb A₂-Troodos (n=1) and a novel mutation; the Hb A₂-Roi-Et (n=1) were identified. This Hb A₂-Roi-Et, results from a double mutations in-cis, δ^{CD82(AAG>AAT)} and δ^{CD133(GTG>ATG)}, was interestingly found in combination with an in trans, 12.6 kb deletional δβ⁰-thalassemia in an adult Thai woman who had no Hb A₂ and elevated Hb F. A multiplex-allele-specific PCR was developed to detect these novel δ-globin gene defects.

CONCLUSIONS

The result confirms a diverse heterogeneity of δ-hemoglobinopathies in Thailand which should prove useful in a prevention and control program of thalassemia in the region.

Phenotypic Expression of Known and Novel Hemoglobin A2-Variants, Hemoglobin A2-Mae Phrik [Delta 52(D3) Asp > Gly, HBD:c.158A > G], Associated with Hemoglobin E [Beta 26(B8) Glu > Lys, HBB:c.79G > A] in Thailand

The interactions of δ-globin variants with α- and β-thalassemia or other hemoglobinopathies cause complex thalassemic syndromes and potential diagnostic problems. Understanding the molecular basis and phenotypic expression is crucial. Four unrelated Thai subjects with second hemoglobin (Hb) A2 fractions were studied. A standard automated cell counter was used to acquire initial hematological data. Hb analysis was carried out by capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) assays. Globin gene mutations and haplotype were identified by appropriate DNA analysis. An allele-specific polymerase chain reaction method was developed to provide a simple molecular diagnostic test. Hb analysis revealed a Hb A2 variant in all cases. DNA analysis of the δ-globin gene identified the Hb A2-Melbourne [δ43(CD2)Glu > Lys] variant in combination with Hb E in three cases. Analysis of the remaining case identified a novel δ-Hb variant, namely Hb A2-Mae Phrik [δ52(D3)GAT > GGT; Asp > Gly], found in association with Hb E and α+-thalassemia, indicative of the as yet undescribed combination of triple heterozygosity of globin gene defects. An allele-specific PCR-based assay was successfully developed to identify this variant. The β-haplotype of the Hb A2 Mae-Phrik allele was strongly associated with haplotype [+ − − − − ± +]. This study advanced our understanding of the phenotypic expression of known and novel δ-Hb variants coinherited with other globin gene defects, routinely causing problems with diagnosis. Therefore, knowledge and recognition of this Hb variant and molecular assessments are crucial to improving diagnosis.

Investigating the reasons for marriage among couples with thalassemia minor, in Iran

Thalassemia is one of the most prevalent genetic disorders in Iran. The birth of a child with thalassemia major is associated with many problems for the family, and society. In the present study, the reasons for marriage among people with thalassemia minor in Iran, in spite of receiving medical advice against it, have been investigated. The present study was a qualitative content analysis conducted in 2019 with the participation of 12 couples (24 participants) with thalassemia minor living in Rafsanjan, Iran; and 2 counselors working with thalassemia patients. Data collection was conducted through in-depth interviews. All interviews were recorded and transcribed. The text was read several times, categorized and main themes were extracted according to content analysis methods. The present study shows that giving inadequate or inaccurate information to people, strong emotional attachment between couples, taking the test at the wrong time, family interference and family insistence on marriage, having seen cases with no problems, and specific thoughts and beliefs are the most important reasons for marriage among couples with thalassemia minor in Iran. According to the results of the present study, the importance of providing thorough and accurate information to the public, setting an appropriate time for counseling and screening which is not immediately before the marriage ceremony, and briefing more efficiently at the time of counseling can help prevent marriage among couples with thalassemia minor in Iran.