α0-thalassemia in affected fetuses with hemoglobin E-β0-thalassemia disease in a high-risk population in Thailand

OBJECTIVES

A co-inheritance of α⁰-thalassemia can ameliorate the clinical severity of the hemoglobin (Hb) E-β-thalassemia disease. This information should be provided at prenatal diagnosis. Identification of α⁰-thalassemia in an affected fetus is therefore valuable. We have explored this genetic interaction in a large cohort of affected fetuses with hemoglobin (Hb) E-β-thalassemia in northeast Thailand.

METHODS

A study was done retrospectively on 1,592 couples at risk of having fetuses with Hb E-β⁰-thalassemia, encountered from January 2011 to December 2019. A total of 415 left-over DNA specimens of the affected fetuses with Hb E-β⁰-thalassemia disease were further investigated. Examination of α⁰-thalassemia was done using gap-PCR or a multiplex PCR assay for simultaneous detection of Hb E and α⁰-thalassemia mutations.

RESULTS

Of the 415 affected fetuses, the two most common β⁰-thalassemia genes found were the codons 41/42 (-TTCT) (199/415; 48.0%) and codon 17 (A-T) (115/415; 27.7%). α⁰-thalassemia was found unexpectedly in 21 (5.1%) fetuses. Hematologic phenotypes of the parents indicated that it was impossible to differentiate a pure β⁰-thalassemia carrier from a double β⁰-thalassemia/α⁰-thalassemia heterozygote unless DNA analysis is performed. In contrast, a reduced level of Hb E in the Hb E carrier (<25%) is a valuable marker for predicting double heterozygosity for Hb E/α⁰-thalassemia. This could be further confirmed using a multiplex PCR assay.

CONCLUSIONS

There is a high prevalence of co-inheritance of α⁰-thalassemia in fetuses with Hb E-β⁰-thalassemia disease. In a high-risk population such as Thailand, we recommend screening for α⁰-thalassemia in all affected fetuses with Hb E-β⁰-thalassemia disease and providing complete genetic information to the parents to make appropriate decisions at prenatal diagnosis and genetic counseling.

Evaluation of staff performance and interpretation of the screening program for prevention of thalassemia

Introduction

Thalassemia screening program has been implemented for years in Southeast Asia, but no external quality assessment program has been established. We have developed and initiated the proficiency testing (PT) program for the first time in Thailand with the aim to assess the screening performance of laboratory staff and their competency in interpretation of the screening results.

Materials and methods

Three PT cycles per year were organized. From the first to the third cycle of the PT scheme, a total number of participant laboratories increased from 59 to 67. In each cycle, 2 PT items (assigned as blood samples of the couple) were provided. Performance evaluation was based on the accuracy of screening results, i.e. mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and the dichlorophenolindophenol (DCIP) test for haemoglobin E, including the competency in interpretation of screening results and assessment of foetal risk. Performance was assessed by comparing the participants’ result against the assigned value.

Results

Of all 3 cycles, most laboratories reported acceptable MCV and MCH values. From the first to the third cycle, incorrect DCIP test and misinterpretation rates were decreased while incorrect risk assessment varied by cycle to cycle. Combining the accuracy of thalassemia screening and the competency in interpretation and risk assessment, approximately half of participants showed excellent performance.

Conclusion

Improved performance observed in many laboratories reflects the achievement and benefit of the PT program which should be regularly provided.