Genotype-Phenotype Relationship of the δ-Thalassemia and Hb A₂Variants: Observation of 52 Genotypes

Abstract

The increase of Hb A(2) (α2δ2) beyond the upper limit [2.0-2.2/3.3-3.4% of the total hemoglobin (Hb)] is an invaluable tool in the hematological screening of β-thalassemia (β-thal) carriers. Factors decreasing Hb A(2) percentages can hinder correct diagnosis. In order to analyze the genotype-phenotype relationship, we characterized δ-, β- and α-globin genotypes in 190 families where the probands had Hb A(2) values of ≤2.0% or were β-thal heterozygotes with normal Hb A(2) levels. Hb A(2) was measured with cation exchange high performance liquid chromatography (HPLC). Mutations were detected with allele-specific methods or DNA sequencing; two multiplex-ARMS (amplification refractory mutation system) assays were set up. The molecular basis underlying the decrease in Hb A(2) was extremely heterogeneous. Nineteen δ-globin alleles (Hb A(2)-S.N. Garganico was new) were detected; their interaction with α- or β-globin alleles (10 and eight, respectively) led us to observe 52 genotypes in 261 carriers. The type of δ-globin mutations, the relative genotypes, the interaction with α(0)-thal traits, are the most important factors in decreasing the Hb A(2) percentage. These results are extremely useful in addressing the molecular diagnosis of hemoglobinopathies and thalassemias.

Hemoglobinopathy testing: the significance of accuracy and pitfalls in HbA2 determination

“…Normal HbA 2 reference ranges between HPLC and CE are similar but not identical, and they are slightly lower using CE (2.25-3.05%) than using HPLC (2.34-3.2%) [7]. Although these differences may seem trivial, they could be of clinical significance as the upper limit of a normal HbA 2 percentage is critical for defining borderline and thalassemia ranges.…”

Effect of Mutations on mRNA and Globin Stability: The Cases of Hb Bernalda/Groene Hart and Hb Southern Italy

“…All data regarding the families under study and the experimental results were collected in an anonymous form in a database developed on the Microsoft Visual Fox 6.0 platform and interfaced with an external software such as Microsoft Excel and Microsoft Word (Microsoft, Redmond, WA, USA) [ 25 ].…”

A Novel Deletion/Insertion Caused by a Replication Error in the β-Globin Gene Locus Control Region

“…Then it is important to perform complete molecular studies including MLPA analysis (11) or more sophisticated techniques such as comparative genomic hybridization (CGH) array (18). A typical β-thal hematological phenotype with normal Hb A 2 and Hb F levels results mainly from an interaction with a δ + -or δ 0 -thal mutation in cis or in trans to the β-thal mutation (19,20). However, more complex associations such as (εγδβ) 0 -thal or the Corfu type of (δβ)-thal can result in such a such phenotype (21).…”