Utility and importance of accurate Hb A2 measurements for defining a strategy for β-thalassemia screening: experience in the Balearic Islands, Spain

The first validated criteria for effective screening and a new simplified method for α-globin gene sequencing for diagnosis of uncommon α-globin mutations

No well-defined phenotypes that distinguish between unknown α- and β-globin mutations have been reported to date. Direct DNA sequencing of α-globin genes can be technically challenging, as α1- and α2-globin genes are nearly indistinguishable. To detect hemoglobin variants (HbXs) on Hb analysis, the entire β- and α-globin genes were directly sequenced using a newly developed sequencing protocol for α-globin genes. An algorithm to distinguish between α- and β-HbXs was constructed and subsequently validated in the independent validation group. Distinctive characteristics that can distinguish 39 α-HbXs from 24 β-HbXs were the presence of unidentifiable variants of HbA₂ and/or HbX of <37% on isoelectric focusing and <31% on high-performance liquid chromatography. Another set of 67 HbXs was employed to validate our algorithm. This accurately predicted 33 α-HbXs with 100% sensitivity and 97.1% specificity. Our sequencing protocol for α-globin genes was able to identify 11 rare mutations among all exons of both α-globin genes from 72 subjects. Six of these variants were first discovered in Thais. This is the first well-characterized algorithm for distinguishing unknown Hb variants in a large cohort. Our validated criteria and DNA sequencing procedure are highly efficient for molecular characterization of rare Hb mutations.

Molecular characterization and phenotypical study of β-thalassemia in Tucumán, Argentina

The main hereditary hemoglobin (Hb) disorder in Argentina is β-thalassemia (β-thal). Molecular studies performed in the center of the country exhibited a marked prevalence of the codon 39 (C > T) and IVS-I-110 (G > A) mutations. The northwest region of Argentina has a different demographic history characterized by an important Spanish influx. Seventy-one β-thal carriers attending the Instituto de Bioquímica Aplicada, Tucumán, Argentina, were investigated for β-globin gene mutations by real-time polymerase chain reaction (RT-PCR). To examine the genotype-phenotype relationship, mean corpuscular volume (MCV), mean corpuscular Hb (MCH) and Hb A2 were measured. In order to recognize β-thal, Mentzer Index, Shine & Lal and Red Cell Distribution Width Index (RDWI), were calculated. The ethnic background of subjects revealed that 82.0% of the population was of Italian, Spanish and Arab origin. Seven mutations were detected: codon 39 (45.0%), IVS-I-1 (G > A) (22.5%), IVS-I-110 (16.3%), IVS-II-1 (G > A) (4.1%), IVS-I-1 (G > T) (2.0%), IVS-I-6 (T > C) (2.0%) and IVS-II-745 (G > C) (2.0%). In three families (6.1%), β-thal mutations were not determined. These results differed from other Argentinian studies because at present codon 39 and IVS-I-1 are the most prevalent; MCV, MCH and Hb A2 did not correlate with the type of mutation (β(0)/β(+)). Values of MCV (67.0 fL) and Hb A2 (4.85%) were unable to discriminate between them. Significant differences (p < 0.05) in MCV, MCH and Shine & Lal were observed between the undetermined group and the three most common mutations. These data show different patterns of β-thal mutations in the center and northwest regions of Argentina. Differences might represent the influence of Spanish immigration.