Characterization of two novel Alu element-mediated alpha-globin gene cluster deletions causing alpha(0)-thalassemia by targeted next-generation sequencing

摘要

alpha-thalassemia is an inherited blood disorder commonly caused by deletions or point mutations involving one or both alpha-globin genes. Recent studies shed new light on the critical role of upstream enhancers multi-species conserved sequences (MCSs) in the ordered regulation of alpha-globin gene expression. Herein, we reported two unrelated probands with deletions in alpha-globin genes and MCSs, respectively. The proband from Family A is a compound heterozygote carrying a known alpha(+) mutation (-alpha(3.7)) and a novel 60.2 kb deletion causing the absence of both alpha-globin genes. The proband from Family B, on the other hand, is a compound heterozygote with a known alpha(0) mutation (--(SEA)) and a novel deletion involving only upstream regulatory elements MCS-R1, R2 and R3, while the alpha-globin genes remain intact. Notably, both these two patients suffered varied extent of anemia, indicating that the loss of enhancer elements could equally lead to reduced synthesis of alpha-globin. Upon these observations, we then confirmed the exact breakpoints of these two novel deletions using a targeted next-generation sequencing (NGS) previously established by our group, which may enable further elucidation of the rearrangement mechanisms on these deletions and functional dissection of MCSs. Taken together, our study reports a reliable NGS-based molecular screening approach for accurate identification of copy number variations (CNVs) in the alpha-globin cluster and the genetic diagnosis of these two probands may help to extend the spectrum of alpha-thalassemia mutations in Chinese population.