Deletional alpha-thalassemia and hematological phenotype: predictive parameters of different deletions

Abstract

Introduction: Thalassemias are characterized by a quantitative imbalance of the globin chains due to the reduction or suppression of the synthesis of one of the globin chains.The hematological tests usually used as indicative for the investigation of α-thalassemia are the blood count with MCV (Mean Cell Volume) < 80 fL and/or MCH (Mean Cell Hemoglobin) < 27 pg and normal Hb A2 (< 3.5%). Aim: This study aimed to correlate the different deletional α-thalassemia genetic alterations with the corresponding hematological phenotype, based on casuistry from 2015 to 2019. Methodology: Was evaluated retrospectively 496 cases suspected of deletional α-thalassemia from 2015 to 2019 and correlated them with the hematological data available. We searched for α-thalassemia deletions by Gap-PCR and Multiplex Gap-PCR. Haematological evaluation was carried out by the erythrogram, Hb isoelectric focusing and quantification of Hb A2 and Hb F (Ion exchange high performance liquid chromatography). The statistical analysis of the results was carried out through calculating the mean, standard deviation, median, and t-Student test, with a significance level of 0.05. Results and discussion: Most patients (n=190) had a normal genotype (αα/αα), followed by heterozygosity (-α3.7/αα) (n=148) and homozygosity (-α3.7/α3.7) (n=141) for the 3.7kb deletion. We also detected 5 cases of heterozygosity for the 4.2Kb deletion (-α4.2/αα), 4 of double heterozygosity (α3.7/α4.2), 7 heterozygosity α0 (--SEA /αα) and 1 of HbH (--SEA/-α3.7). The results showed that the MCV and the MCH are excellent hematological indices for screening and selection of patients for molecular testing (their value being the lower the greater the number of deleted genes). Our results are in line with those described in the literature and reinforce that the cut-off value of 25 pg (MCH) is sensitive enough to infer the presence of α0 -thalassemia deletion. The detection of the α0 deletion is very important in preventing the occurrence of Hb Bart's in the offspring of a carrier couple. The diagnosis of deletional α-thalassemia is realised by genetic testing, however hematological indices are relevant predictive markers of the number of deleted alpha genes and the phenotype /genotype correlation.N/