α0-thalassemia in affected fetuses with hemoglobin E-ß0-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-ß-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-ß-thalassemia in northeast Thailand. METHODS: A study was done retrospectively on 1,592 couples at risk of having fetuses with Hb E-ß0-thalassemia, encountered from January 2011 to December 2019. A total of 415 left-over DNA specimens of the affected fetuses with Hb E-ß0-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 ß0-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 ß0-thalassemia carrier from a double ß0-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-ß0-thalassemia disease. In a high-risk population such as Thailand, we recommend screening for α0-thalassemia in all affected fetuses with Hb E-ß0-thalassemia disease and providing complete genetic information to the parents to make appropriate decisions at prenatal diagnosis and genetic counseling.

Erythrocyte indices in a large cohort of ß-thalassemia carrier: Implication for population screening in an area with high prevalence and heterogeneity of thalassemia.

INTRODUCTION: Most ß-thalassemia carriers have hypochromic microcytosis with mean corpuscular volume (MCV) < 80 fL and mean corpuscular hemoglobin (MCH) < 27 pg. These can be variable due to ß-thalassemia mutations, genetic interaction between thalassemic genes, and blood cell counters. We have examined whether these indices are effective in screening of ß-thalassemia in Thailand where thalassemia is prevalence and heterogeneous. METHODS: Retrospective data were reviewed on 11 443 Thai subjects encountered from August 2014 to August 2017. Subjects with heterozygous ß-thalassemia based on Hb and DNA analyses were recruited along with MCV and MCH values and analyzed. RESULTS: Among the 11 443 subjects reviewed, 1425 were ß-thalassemia carriers. Data were available on 1214 subjects for MCV and 965 subjects for MCH. DNA analysis identified 20 different ß0 -thalassemia mutations in 874 (72.0%) cases and 6 ß+ -thalassemia mutations in 340 (28.0%) subjects. Of these 1214 carriers, 26 (2.1%) had MCV ≥ 80 fL; 6 (23.1%) carried ß0 -thalassemia, and the remaining 20 (76.9%) had ß+ -thalassemia. In contrast for those having MCH values, only 4 of 965 (0.4%) had MCH ≥ 27 pg. DNA analysis identified both ß0 -thalassemia and ß+ -thalassemia mutations. CONCLUSIONS: Using MCV alone for the screening of ß-thalassemia may pose a significant number of false negative although three-quarter of them are carriers of mild ß+ -thalassemia. MCH with approximately five times more sensitive is a better screening marker. Using a combined MCV and MCH is highly recommended, especially in an area with high prevalence and heterogeneity of thalassemia like Thailand.

A large cohort of ß(+)-thalassemia in Thailand: molecular, hematological and diagnostic considerations.

We report the molecular and hematological characteristics associated with a large cohort of ß(+)-thalassemia in Thailand. Study was done on 21,068 unrelated subjects referred to our center in northeast Thailand for hemoglobinopathies investigation. Among 21,068 subjects, 2637 (12.5%) were found to carry ß-thalassemia. Of these 2637 cases, 705 (26.7%) carried ß(+)-thalassemia with eight different mutations including 6 promoter mutations; NT-28 (A-G), NT-31 (A-G), NT-50 (G-A), NT-86 (C-G), NT-87 (C-A) and NT-90 (C-T) and two missense mutations; Hb Malay (codon 19; AAC-AGC) and Hb Dhonburi (codon 126; GTG-GGG). Hematological features of carriers with these ß(+)-thalassemia (n=528) were compared with those with ß(0)-thalassemia (n=309). Data for Hb E-ß(+)-thalassemia (n=177) were also presented along with Hb E-ß(0)-thalassemia in our series (n=94). All patients with Hb E-ß(+)-thalassemia were associated with mild thalassemia intermedia phenotypes. Most of the ß(+)-thalassemia carriers had elevated Hb A2 and mild hypochromic microcytosis, some demonstrated borderline MCV and MCH values which, could compromise carrier screening. Analysis of α/ß-globin mRNA ratio in representative cases with normal, Hb E trait, ß(+)-thalassemia trait, Hb Dhonburi trait and ß(0)-thalassemia trait demonstrated the average values of 1.1, 1.7, 2.1, 1.7 and 3.1, respectively which is helpful in identification and differentiation of the cases.