Distinct Distribution of HBB Variants in Two Cohorts of Beta Thalassemia Patients, and a Novel Variant from Turkey

Introduction: Beta thalassemia is a serious disease for which mutation-based diagnostic and screening tests are readily available. These tests are based on specific variant profile in the regions of the testing centers. De novo mutations and migration change the distribution of these variants. We aim to update the variant spectrum in the HBB gene in our region. In addition, we present a variant, which not been detected before in Turkey, and also a changed classification of another variant. Methods: This study includes 142 patients (46 of Turkish, 96 of Syrian) who were investigated for defects in their beta-globin gene with Sanger sequencing. Clinically, 52 of these patients had thalassemia major, and 90 had thalassemia minor. Results: Twenty three types of pathogenic variants were identified causing beta thalassemia and abnormal hemoglobins. Variant distribution has differed considerably between Turkish and Syrian patients. While the IVSI-110G>A was the most prevalent variant (41.1%) in Turkish patients, the IVSII-1G>A and Codon 39 (C>T) variants were found in 22% and 21.3%, respectively, in Syrian patients. We detected the novel c.31_32insT variant in 3 Syrian patients. Conclusion: The detection of updated regional HBB variant spectrum will contribute to future prenatal and/or postnatal molecular diagnostic tests. Also, our study presents a novel variant that was not previously reported.