Hemoglobin H disease induced by the common SEA deletion and the rare hemoglobin Quong Sze in a Thai female: longitudinal clinical course, molecular characterization, and development of a PCR/RFLP-based detection method

The First Thai Case of Nondeletional HbH Disease Caused by Compound Heterozygosity for α-Thalassemia-1 Chiang Rai (--CR) Type Deletion with Hb Constant Spring

Hemoglobin (Hb) H disease presents a wide range of clinical phenotypes, from asymptomatic to severe forms, depending on significant genetic heterogeneity. This is the first report of clinical and hematological features of the nondeletional HbH disease caused by --CR/αCSα. A baby was born to a father and a mother with --CR and αCSα carriers, respectively. She had severe symptomatic hypochromic microcytic anemia at 2 months of age with Hb 7.8 g/dL, packed cell volume (PCV) 0.27 L/L, mean corpuscular volume (MCV) 64.3 fL, and mean corpuscular Hb (MCH) 18.3 pg. The Hb analysis using capillary electrophoresis (CE) showed Hb Bart's, HbH, and Hb CS peaks at 17.1%, 2.2%, and 1.6%, respectively. A better understanding of a patient's clinical and hematological features with --CR/αCSα is useful for hemoglobinopathy counseling for the national thalassemia controlling program.

The Clinical Phenotypes of Alpha Thalassemia

Clinical manifestations of α-thalassemia range from no symptoms to severe transfusion-dependent anemia. Alpha thalassemia trait is deletion of 1 to 2 α-globin genes, whereas α-thalassemia major (ATM; Barts hydrops fetalis) is the deletion all 4 α genes. All other genotypes of intermediate severity are categorized as HbH disease, a vastly heterogenous group. Clinical spectrum is classified as mild, moderate, and severe by symptoms and need for intervention. Anemia in prenatal period may be fatal without intrauterine transfusions. New therapies to modify HbH disease or provide cure for ATM are under development.

Association of Hb Shenyang [α26(B7)Ala→Glu, GCG>GAG, HBA2: c.80C>A (or HBA1)] with Several Types of α-Thalassemia in Thailand

Hb Shenyang [α26(B7)Ala→Glu, HBA2: c.80C>A (or HBA1)] is a rare α chain variant. Its genotype-phenotype relationship and origin have not been described in Thailand before. Three Thai subjects (P1-P3) carrying this variant were studied. Hemoglobin (Hb) analysis was performed by capillary electrophoresis (CE) and high performance liquid chromatography (HPLC) as well as molecular characterization using appropriate polymerase chain reaction (PCR) techniques and DNA sequencing. Hemoglobin analysis by HPLC revealed fast-moving abnormal peaks at a retention time (RT) of 1.59-1.62 min., while CE revealed a fast-moving abnormal Hb at zone 12 and ahead of Hb A₂ in three subjects. DNA analysis revealed a C>A transition at codon 26 of the α2-globin gene glutamic acid to replace alanine, corresponding to Hb Shenyang. The Southeast Asian [- -^SEA α-thalassemia-1 (α-thal-1)] deletion was also identified in P1 and his mother, while Hb Constant Spring (Hb CS, HBA2: c.427T > C) was identified in P2. The Hb Shenyang concentration measured by CE revealed 5.1-17.2% heterozygosity with normal red blood cell (RBC) parameters. The α haplotype [+ - S + - + -] [S signifies the inter ζ hypervariable region (HVR)] was associated with the Thai Hb Shenyang. The genotype-phenotype relationship indicates Hb Shenyang is likely a non pathological Hb variant that has neither dramatic clinical symptoms nor hematological anomalies. A simple multiplex allele-specific PCR for rapid diagnosis of Hb Shenyang has been developed.

Rapid detection of non-deletional mutations causing α-thalassemia by multicolor melting curve analysis

BACKGROUND

α-Thalassemia, caused by mutations in the α-globin genes, is one of the most common monogenic inherited disorders in the world. However, non-deletional α-thalassemia mutations remain undetected in routine clinical testing due to the lack of a suitable method. In this study, a closed- and single-tube assay for the detection of six common non-deletional α-thalassemia mutations in the HBA2 gene was developed based on multicolor melting curve analysis.

METHODS

The assay consisted of one pair of primers specific for the HBA2 gene and four dual-labeled, self-quenched probes targeting six non-deletional α-thalassemia mutations. The sensitivity, reproducibility, and accuracy of the method were validated via 700 genomic DNA samples.

RESULTS

The assay had a reproducibility of 100%, could detect gDNA of different genotype as low as 1 ng per reaction, and had an overall accuracy of 100% when compared with RDB analysis and Sanger sequencing.

CONCLUSIONS

The developed assay is rapid, robust, and cost-effective while maintaining high sensitivity, specificity, and throughput.

Identification of nondeletional α-thalassemia in a prenatal screening program by reverse dot-blot in southern China

The aim of this study was to demonstrate the performance of nondeletional α-thalassemia (α-thal) prevention using a reverse dot-blot method at a Mainland Chinese hospital. A prenatal control program for nondeletional Hb H disease was performed between January 2009 and December 2013. All couples were screened for α-thal trait, and for couples in which one partner tested positive for α(0)-thal, the other was subjected to screening for Hb Constant Spring (Hb CS, HBA2: c.427T > C) and Hb Quong Sze (Hb QS, HBA2: c.377T > C) mutations by reverse dot-blot assay. Prenatal diagnoses were offered in at-risk pregnancies. During the study period, 51,105 couples were found to be carrying α-thal; among these, 35 (0.07%) couples were found to be at-risk of conceiving an offspring with nondeletional Hb H disease, including 25 couples for Hb H-CS and 10 cases for Hb H-QS. Nine fetuses were diagnosed with nondeletional Hb H disease, and eight of the affected pregnancies were terminated. Detection of nondeletional α-thal is necessary for any prenatal diagnosis (PND) programs in Southeast Asian countries. Reverse dot-blot is a relatively simple method for simultaneous typing of common nondeletional α-thal mutations.

Low cost biosensor-based molecular differential diagnosis of α-thalassemia (Southeast Asia deletion)

Thalassemias are genetic hematologic diseases which the homozygous form of α-thalassemia can cause either death in utero or shortly after birth. It is necessary to accurately identify high-risk heterozygous couples. We developed a quartz crystal microbalance (QCM) to identify the abnormal gene causing the commonly found α-thalassemia1, [Southeast Asia (SEA) deletion]. This work is an improved method of our previous study by reducing both production cost and analysis time.

A silver electrode on the QCM surface was immobilized with a biotinylated probe. The α-globin gene fragment was amplified and hybridized with the probe. Hybridization was indicated by changes of quartz oscillation. Each drying step was improved by using an air pump for 30 min instead of the overnight air dry. The diagnostic potency of the silver QCM was evaluated using 70 suspected samples with microcytic hypochromic erythrocytes.

The silver QCM could clearly identify samples with abnormal α-globin genes, either homozygous or heterozygous, from normal samples. Thirteen out of 70 blood samples were identified as carrier of α-thalassemia1 (SEA deletion). Results were consistent with the standard agarose gel electrophoresis. Using silver instead of gold QCM could reduce the production expense 10-fold. An air pump drying the QCM surface could reduce the analysis time from 3 days to 4 h.

The silver thalassemic QCM was specific, sensitive, rapid, cheap and field applicable. It could be used as a one-step definite diagnosis of α-thalassemia1 (SEA deletion) with no need for the preliminary screening test.

Nondeletional Hb Queens Park [α32(B13)Met→Lys]/Hb H (β4) disease

A rare nondeletional α-thalassemia-2 (α-thal-2) allele was identified in a Thai boy with Hb H (β4) disease. The proband has α-thal-1 (- -(SEA) type) together with a non productive Hb Queens Park (HBA1:c.98T>A) [α32(B13)Met→Lys] α1-globin variant. No abnormal hemoglobin (Hb) fraction was detected by high performance liquid chromatography (HPLC). The clinical effect of this mutation in the proband was comparable to that of deletional α-thal-2 present in Hb H disease.

Screening for mutations in the α-globin genes leading to abnormal hemoglobin variants with high resolution melting analysis

α-Thalassemia is one of the most commonly inherited single-gene disorders in southern China. It is important to identify non-deletional α-thalassemia in areas where α-thalassemia is prevalent, since non-deletional HbH disease (

An approach based on high-resolution melting (HRM) analysis was used. A total of 74 samples, including 54 abnormal α-chain samples and 20 control samples, were tested.

All of the 54 samples with point mutations at the exons 1, 2 or 3 of the α-globin genes, including 33 non-deletional α-thalassemia, were successfully detected.

HRM has the potential to become an efficient, rapid screening method for non-deletional α-thalassemia.