Haplotype analysis of α-thalassemia chromosomes reveals heterogeneity and multiple founders in Ashkenazi Jews

Support Vector Machine-Based Formula for Detecting Suspected α Thalassemia Carriers: A Path toward Universal Screening

The blood counts of α thalassemia carriers (α-thal) are similar to those of β thalassemia carriers, except for Hemoglobin A2 (Hb A2), which is not elevated. The objective of this study was to determine whether mathematical formulas are effective for detecting suspected α-thal. The data were obtained from the database of the prevention program for detecting couples at risk for having a child with hemoglobinopathy. Red Blood Cells (RBC) indices were analyzed using mathematical formulas, and the sensitivity and negative predictive value (NPV) were calculated. Among 1334 blood counts suspected of α-thal analyzed, only the Shine and Lal and the Support Vector Machine formulas revealed high sensitivity and NPV. Sensitivity was 85.54 and 99.33%, and NPV was 98.93 and 99.93%, respectively. Molecular defects were found in 291, and 81 had normal α genes. Molecular analysis was not performed in 962 of the samples. Based on these results, mathematical formulas incorporating one of these reliable formulas for detecting suspected α or β thalassemia carriers in the program of the automatic analyzers can flag these results, increase the awareness of the primary physicians about the carrier risk, and send an alert with a recommendation for further testing.

The -α3.7III subtype of α+-thalassemia was identified in China

OBJECTIVE

The 3.7 kb deletion (-α^3.7) in the α-globin cluster, which characterizes α⁺-thalassemia, has been reported to have a carrier rate of 4.78% in southern China. Three -α^3.7 subtypes have been identified worldwide. However, the -α^{3.7 III} subtype has not previously been identified in China. Herein, we reported identification of the -α^{3.7 III} subtype in a Chinese patient.

METHODS

We used gap-PCR and a liquid chip system to detect α-thalassemia mutations. Multiple ligation-dependent probe amplification was performed to detect the large deletion. We finally used Sanger sequencing and single molecule real-time sequencing to characterize and confirm the genotype.

RESULTS

The proband, characterized as -α^{3.7 III} heterozygous, showed microcytosis and hypochromic red cells, with a mean corpuscular volume of 78 fL and mean corpuscular hemoglobin of 25.4 pg. The proband's mutation was inherited from her father, who had normal blood parameters.

CONCLUSION

We first identified the -α^{3.7 III} subtype in China. Consequently, all -α^3.7 subtypes have now been identified in the Chinese population. Therefore, attention should be paid to -α^{3.7 III} in clinical prenatal diagnosis, given that commonly used methods such as gap-PCR may lead to misdiagnosis or missed diagnosis.

Molecular characteristics of α+-thalassemia (3.7 kb deletion) in Southeast Asia: Molecular subtypes, haplotypic heterogeneity, multiple founder effects and laboratory diagnostics

OBJECTIVE

The 3.7 kb deletion (-α^3.7) is the most common form of α⁺-thalassemia found in multiple populations which can be classified into three subtypes. In order not to mis-identify it, the molecular information within each population is required. We have addressed this in northeast Thai and Laos populations.

METHODS

Screening for α⁺-thalassemia was initially done on 1192 adult Thai subjects. In addition, 77 chromosomes of Thai newborns and 26 chromosomes of Laos with -α^3.7 α⁺-thalassemia were also examined. All subjects were screened for -α^3.7 α⁺-thalassemia and subtyped by PCR-RFLP assay. Exact deletion breakpoint of each -α^3.7 subtype was determined by DNA sequencing. α-Globin gene haplotypes were determined.

RESULTS

The proportions of -α^3.7 subtypes found in 216 Thai -α^3.7 chromosomes were 94.9% for -α^3.7I, 4.2% for α^3.7II and 0.9% for -α^3.7III. All 26 Laos -α^3.7 chromosomes were of -α^3.7I variety. At least six α-globin gene haplotypes were associated with the -α^3.7I α⁺-thalassemia.

CONCLUSION

All -α^3.7 subtypes were observed among Southeast Asian population. Haplotype analysis indicated a multiple origin of this common disorder in the region. A multiplex PCR assay has been developed for simultaneous detection of all subtypes of -α^3.7 α⁺-thalassemia as well as other α⁺-thalassemia found in the region including -α^4.2 α⁺-thalassemia, Hb Constant Spring and Hb Paksé.