Screening and Diagnosis of Rare Thalassemia Variants: Is Third-Generation Sequencing Enough?

ABSTRACT

CONTEXT.­ Rare thalassemia subtypes are often undiagnosed because conventional testing methods can only identify 23 common types of α- and ß-thalassemia. OBJECTIVE.­ To assess a comprehensive approach for the screening and diagnosis of rare thalassemia. DESIGN.­ The study cohort included 72 individuals with suspected rare thalassemia variants. Screening was conducted by next-generation sequencing (NGS) combined with third-generation sequencing (TGS) and chromosomal microarray analysis (CMA)/copy number variation sequencing. RESULTS.­ Of the 72 individuals with suspected rare thalassemia, 49 had rare α- or ß-gene variants. NGS combined with gap polymerase chain reaction detected a total of 42 cases, resulting in a positive detection rate of 58.3%. Additionally, 4 α-globin genetic deletions were identified by TGS, which increased the variant detection rate by 5.6%. Two samples with a microdeletion of chromosome 16 or 11 were detected by CMA, which increased the detection rate by 2.8%. For one sample, reanalysis of the NGS and TGS data confirmed the presence of the ß41-42/ßN and ßN/ßN mosaic. The HBBc.315 + 2delT mutation was initially reported in Guangdong Province, China. Two HBB gene mutations (HBBc.315 + 5G>C and HBBc.295G>A) and 4 rare HBA gene deletions (-11.1, -α27.6, -α2.4, and -α21.9) were initially identified in the Zhonshan region. The hematologic phenotypes of all rare cases in this study were clarified. CONCLUSIONS.­ Rare thalassemia variants are more common than previously thought. Despite advancements in TGS, there is still no foolproof method for detection of all types of thalassemia. Thus, a comprehensive approach is necessary for accurate screening and diagnosis of rare thalassemia variants.