BackgroundHemoglobin (Hb) variants are structurally inherited changes of globin chains. Accurate diagnoses of these variants are important for planning of appropriate management and genetic counseling. Since no epidemiological study has been conducted before, we have investigated frequencies, molecular and hematological features of Hb variants found in a large cohort of Thai subjects.Materials and MethodsStudy was conducted on 26,013 unrelated subjects, inhabiting in all geographical parts of Thailand over a period of 11 years from January 2002-December 2012. Hb analysis was done on high performance liquid chromatography (HPLC) or capillary electrophoresis (CE). Mutations causing Hb variants were identified using PCR and related techniques.ResultsAmong 26,013 subjects investigated, 636 (2.4%) were found to carry Hb variants. Of these 636 subjects, 142 (22.4%) carried α-chain variants with 13 different mutations. The remaining included 451 (70.9%) cases with 16 β-chain variants, 37 (5.8%) cases with Hb Lepore (δβ-hybrid Hb) and 6 (0.9%) cases with a single δ-chain variant. The most common α-globin chain variant was the Hb Q-Thailand (α74GAC-CAC, Asp-His) which was found in 101 cases (15.8%). For β-globin chain variants, Hb Hope (β136GGT-GAT, Gly-Asp) and Hb Tak (β146+AC, Ter-Thr) are the two most common ones, found in 121 (19.0%) and 90 (14.2%) cases, respectively. Seven Hb variants have never been found in Thai population. Hb analysis profiles on HPLC or CE of these variants were illustrated to guide presumptive diagnostics.ConclusionsHb variants are common and heterogeneous in Thai population. With varieties of thalassemias and hemoglobinopathies in the population, interactions between them leading to complex syndromes are common and render their diagnoses difficult in routine practices. Knowledge of the spectrum, molecular basis, genotype-phenotype correlation and diagnostic features should prove useful for prevention and control of the diseases in the region.

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Introduction Most β‐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 β‐thalassemia mutations, genetic interaction between thalassemic genes, and blood cell counters. We have examined whether these indices are effective in screening of β‐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 β‐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 β‐thalassemia carriers. Data were available on 1214 subjects for MCV and 965 subjects for MCH. DNA analysis identified 20 different β0‐thalassemia mutations in 874 (72.0%) cases and 6 β+‐thalassemia mutations in 340 (28.0%) subjects. Of these 1214 carriers, 26 (2.1%) had MCV ≥ 80 fL; 6 (23.1%) carried β0‐thalassemia, and the remaining 20 (76.9%) had β+‐thalassemia. In contrast for those having MCH values, only 4 of 965 (0.4%) had MCH ≥ 27 pg. DNA analysis identified both β0‐thalassemia and β+‐thalassemia mutations. Conclusions Using MCV alone for the screening of β‐thalassemia may pose a significant number of false negative although three‐quarter of them are carriers of mild β+‐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.

We report the molecular and hematological characteristics of two rare hemoglobin (Hb) variants found in associations with a common α(0)-thalassemia (α(0)-thal) in Thai patients. The first case (P1) was a generally healthy 27-year-old man discovered during our ongoing thalassemia screening program. Hemoglobin and DNA analyses identified a previously undescribed condition of compound heterozygosity for Hb Thailand [α56(E5)Lys→Thr] and α(0)-thal (SEA deletion). The second case (P2) was a 4-year-old boy with hypochromic microcytic anemia. Hemoglobin and DNA analyses also identified a compound heterozygosity for Hb Phnom Penh [α117(GH5)-Ile-α118(H1)] in association with α(0)-thal (SEA deletion). Although Hb H (β(4)) inclusion bodies were observed in both cases, Hb analysis using both high performance liquid chromatography (HPLC) and capillary electrophoresis (CE) did not show Hb H. While the two Hb variants could be recognized on Hb HPLC analysis, their corresponding Hb A(2) derivatives: the Hb A(2)-Thailand and Hb A(2)-Phnom Penh, were clearly observed on CE. Apparently, combination of these two Hb variants with α(0)-thal are not expressed as Hb H disease. The two Hb variants could be confirmed by polymerase chain restriction-restriction fragment length polymorphism (PCR-RFLP) and allele-specific PCR assays.

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