A large cohort of deletional high hemoglobin F determinants in Thailand: A molecular revisited and identification of a novel mutation

Prenatal diagnostic errors in hemoglobin Bart's hydrops fetalis caused by rare genetic interactions of α-thalassemia

OBJECTIVES

To describe rare genetic interactions of α-thalassemia alleles causing Hb H disease and Hb Bart's hydrops fetalis which could lead to diagnostic errors in a routine practice.

METHODS

Hematological and molecular characterization were carried out in a Thai family with a risk of having fetus with Hb Bart's hydrops fetalis.

RESULTS

Both parents were found to be the thalassemia intermedia patients associated with unusual forms of Hb H disease. DNA analysis of common α-thalassemia mutations in Thailand identified α+-thalassemia (-α3.7 kb del) and unknown α0-thalassemia in the father and α0-thalassemia (--SEA) with unknown α+-thalassemia in the mother. Fetal DNA analysis unlikely identified a homozygosity for α0-thalassemia (--SEA/--SEA). Further analysis identified that the father carried a rare South African α0-thalassemia in combination with α+-thalassemia (--SA/-α), whereas the mother was a patient with Hb H-Queens Park disease (--SEA/ααQP). The fetus was, in fact, a compound heterozygote for (--SA/--SEA).

CONCLUSIONS

As shown in this study, routine screening for α-thalassemia at prenatal diagnosis in the region should include both common and rare α0-thalassemia alleles found in the population to effectively prevent a fatal condition of Hb Bart's hydrops fetalis syndrome.

Rapid and Visual Molecular Detection of High Hb F Determinants; HPFH6, Asian Indian inv-del (Aγδβ)0-Thalassemia, and Thai del-inv-ins (Aγδβ)0-Thalassemia Using LAMP Colorimetric Phenol Red Assays

Hemoglobin (Hb) F, or fetal hemoglobin, is the predominant Hb in fetuses and is converted to adult hemoglobin (Hb A) at the age of 2 years. However, high Hb F levels in adults are typically present in conditions such as β-thalassemia disease and high Hb F determinants including large deletional β-globin gene clusters, and hereditary persistence of fetal hemoglobin (HPFH). The accurate detection of these conditions is crucial for effective disease management and genetic counseling. Several molecular techniques have been used to identify high Hb F determinants but require advanced instrumentation, highly skilled personnel, high cost, long time duration, and post-PCR processing. This study aimed to develop a rapid and cost-effective molecular assay for detecting common high Hb F determinants using colorimetric loop-mediated isothermal amplification (LAMP) with phenol red assays. We focused on the detection of HPFH6, Asian Indian inv-del (Aγδβ)0-thalassemia, and Thai del-inv-ins (Aγδβ)0-thalassemia. A total of 331 DNA samples encompassing 21 genotypes were screened using the developed LAMP assays, which were optimized to detect these determinants within 60-70 min. The assays showed high sensitivity (100%) and specificity (99.6-100%) in each mutation with detection limits of 2.5 ng/reaction. Validation by comparison with conventional methods confirmed the efficacy of the LAMP assays, which is simple, inexpensive, and suitable for use in low-resource settings. Rapid performance, visual detection, and accurate diagnosis may be useful for genetic counseling, particularly in Thailand and Southeast Asia. This innovation is suitable for application in thalassemia screening programs, especially in remote areas.

Rapid Identification of β-Thalassemia, Hb E, and High Hb F Determinants Using a High-Resolution Melting Analysis: Application in Prenatal Diagnosis in Southern Thailand

β-thalassemia (thal), hemoglobin (Hb) E, and high Hb F determinants, which are caused by mutations in the β-globin gene cluster, are common genetic disorders in Thailand and Southeast Asia. Prenatal diagnosis is essential for couples at risk to identify severe forms, including homozygous β-thal and Hb E/β-thal. Conventional methods, including reverse dot-blot hybridization and gap-polymerase chain reaction (PCR) for genotyping of point and large deletion mutations, require post-PCR steps, which are time-consuming and costly. This study aimed to develop a rapid and efficient method using monoplex high-resolution melting (HRM) analysis for genotyping of Hb E and 11 β-thal mutations; multiplex HRM analysis for identifying six deletional mutations, including two β0-thal mutations (3.5 and 45 kb deletion); and a novel method for detecting four high Hb F determinants, namely, δβ0-thal (12.5 kb deletion), HPFH6, Indian inv-del (Aγδβ)0-thal, and Thai del-inv-ins (Aγδβ)0-thal. The developed assays were validated using 182 blinded fetal DNA samples with 41 β-thal genotypes. Different HRM patterns were observed among wild-type, heterozygote, homozygote, and compound heterozygote genotypes. Six deletional mutations showed specific melt curves. This technique demonstrated 100% concordance with conventional methods. The assay showed 100% sensitivity, specificity, and positive and negative predictive values within the limit of detection at DNA concentrations of 8.0 ng/reaction. Finally, this developed assay was efficient in identifying both point mutations and large deletion, convenient, rapid, and cost-effective and did not require post-PCR steps. Thus, this technique has potential for application in prenatal diagnosis of thal and can inform prevention and control programs.

A large cohort of Hb H disease in northeast Thailand: A molecular revisited, diverse genetic interactions and identification of a novel mutation

BACKGROUND AND AIMS

To update the molecular characteristics of α-thalassemia in northeast Thailand, the molecular basis and genetic interactions of Hb H disease were examined in a large cohort of patients.

MATERIALS AND METHODS

A study was done on 1,170 subjects with Hb H disease and various genetic interactions encountered during 2009-2023. Hb and DNA analyses were carried out.

RESULTS

As many as 40 genotypes with several known, previously undescribed, and novel mutations were observed. These included 698 subjects (59.8 %) of Hb H disease, 357 (30.6 %) with EABart's disease, 63 (5.4 %) with EEBart's disease, 18 (1.7 %) with abnormal Hbs, 17 (1.5 %) with β-thalassemia, and 4 (0.4 %) with EFBart's or EFABart's disease. The molecular basis of 13 subjects (1.1 %) remains unknown. The α0-thalassemia included --SEA (n = 1,139, 97.4 %) and --THAI (n = 21, 1.8 %). Two rare mutations were identified in 3 subjects (0.3 %) with --SA and --CR deletions. For α+-thalassemia, -α3.7 kb del (n = 626, 53.5 %), Hb Constant Spring (n = 415, 35.5 %), -α4.2 kb del (n = 44, 3.8 %), Hb Paksé (n = 36, 3.1 %), and Hb Q-Thailand (n = 19, 1.6 %), were detected. Ten rarer α+-thalassemia were identified, including a novel mutation, namely the Hb Chumphae (HBA2:c.32T>A). The Hb H-Lansing-Ramathibodi, Hb H-Jax, and Hb H-Chumphae are hitherto undescribed in this region. PCR-based diagnostic methods for these α-thalassemia defects were described.

CONCLUSIONS

This study confirms the diverse heterogeneity and genetic interactions causing Hb H disease in northeast Thailand. The results should prove useful for laboratory diagnosis and genetic counseling of this genetic disorder in the region.

Molecular epidemiology and hematological profiles of hemoglobin variants in southern Thailand

Data on hemoglobin (Hb) variants in southern Thailand are lacking. This study aimed to reassess the frequency of Hb variants and the clinical aspects of compound heterozygous Hb variant with other hemoglobinopathies. We enrolled 13,391 participants from ten provinces in southern Thailand during 2015-2022. Hb analysis was performed using capillary electrophoresis, and mutations in the HBA and HBB genes were identified using PCR or DNA sequencing. Hb variants were identified in 337 (2.5%) unrelated subjects. Nine β-chain variants, namely Hb Malay (76.9%), Hb C (10.1%), Hb D-Punjab (2.9%), Hb G-Makassar (2.3%), Hb Dhonburi (2.3%), Hb Tak (1.4%), Hb J-Bangkok (1.4%), Hb New York (0.3%), and Hb Hope (0.3%), and four α-chain variants-Hb G-Georgia (HBA1) (0.9%), Hb G-Georgia (HBA2) (0.3%), Hb Q-Thailand (0.6%), and Hb St. Luke's-Thailand (0.3%)-were identified. The southern population exhibited a distinct spectrum of Hb variants compared to that observed in the populations from other areas. Several compound heterozygous genotypes were also identified. Combining Hb Malay with Hb E or high Hb F determinants did not require a blood transfusion. This study provides essential information for genetic counseling in thalassemia prevention and control programs in this region.